Vfr848Rr Anyone ?

Hi All,

I've been toying with the idea of a bigbore VFR800 to carry on where Honda could have gone. I've updated all the cycle parts on my Viffer & now looking toward next winters project. So to that end I've bought a few bits to check the possibilities.

First thought was CBR929 pistons @ 74mm bore verses the VFR's 72mm. That would give 825cc, the other option was the CBR954, but I thought that would be one to big & two to heavy, until I found a site by accident listing the 929 to 954 changes, one of which was the pistons are lighter than the 929's !

So I acquired a piston to test the theory & removed a standard one from my spare engine. So here are the findings;-

All pistons use 17mm wrist pins,

Deck heights & piston crown heights are the same.

As are the valve pocket dimension (but would need to check valve to pocket clearances).

VFR Std Piston 72mm = 238grams (inc wrist pin)

CBR929 Piston 74mm = 246grams (inc wrist pin)

CBR954 Piston 75mm = 227grams (inc wrist pin)

So the 954 piston is lighter than both the standard VFR & 929 one, this means the rod loads would NOT exceed standard specs & the rev range could be maintained :) Deck heights & piston crown heights are the same, as are the valve pocket dimension, but would need to check valve to pocket clearances.

The next consideration is cylinder wall strength & compression ratios. The cylinders have 8mm walls & Honda supplies .25 & .5mm oversize pistons for the VFR, so max overbore leaves 7.75mm walls.

929 pistons takes that to 7mm walls & is probably OK & gives 12.2/1 compression ratio, which would restore the dynamic compression ratio to the same as standard with my cams (std=10.86, my cams/929 bore=10.91). Which is perfect for standard unleaded (UK=95RON).

954 pistons takes that to 6.5mm walls & may be OK & gives 12.5/1 compression ratio, which would increase the dynamic compression ratio to 11.16. Which is too much for standard unleaded (UK=95RON) & maybe a bit much for Super unleaded (UK=97RON).

Options ?

1. Risk the wall thickness being sufficient. CBR's have thinner walls between the cylinders & use the same MMC liners !

2. Use containment rings to reinforce the cylinders, only need to reinforce the top 15mm to stop flex at peak pressure, which can cause D-chunk failure of the liner.

3. Machine the 954 pistons to lower the compression ratio, to acceptable levels & match the VFR valve spacing.

4. Have made or modify standard head gasket to fit pistons.

So what would this give us ? Well VFR750's taken to 837cc have shown 133rwhp & they used heavier JE pistons ! So a VFR848 should pump out around 135-140rwhp :) I'd expect around 62-64 ft/lbs torque with the additional compression etc.

Worth the effort ? Well if you do the spannering yourself & use second-hand pistons (they are silly expensive new) Then you should be able to get it all done for less than 1000UKpds (<$1500).

Your views as always are appreciated :)

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Weren't the bigbore VFR800's 870cc's?

If so, then 848cc's should not be a problem.

As for the lighter 954 pistons, one could always lighten the crank to suit the pistons, which would have further benefit beyond ensuring proper balance and lack of vibration.

Also if you did all the necessary work to your spare engine, then fit it to your bike, you would not waste any riding time, and have your standard engine in reserve in case (god forbid) anything happened to the modified engine.

Yeah the racing ones were 870cc but I don't know if they used steel liners, but I know they regularly went off like hand grenages. 870cc would be a 76mm bore & 12.82/1 compression ! I don't want to push to the outer limits :)

I seem to remember the old Dynamo Humm kits being 870, not sure what you are referring to as being a "racing" kit though. With the VFR being a big soft couch, I don't think anyone ever raced them.

www3.sympatico.ca/dyno/wolf.htm

Well I've never seen an 870 VFR, I assumed you were referring to the RC45 870's they built for the TT, same basic engine, all of them went bang !

They obviously didn't do much work to that 870, approx 120rwhp (unless that was a factory pro dyno, which would equate to 138 dynojet hp !) But the torque is where I'd expect it to be :)

I realize I am just a babe in the woods . . . the skirts on the OEM pistons seems to be a lot bigger. I assume this is because of the V4, with the other two being I4's. Do you think that would cause a problem running pistons with such small skirts?

Now to address your question. My vote is as follows:

3. Machine the 954 pistons to lower the compression ratio, to acceptable levels & match the VFR valve spacing.

I don't think you'd have to reduce the compression ratio too much, and you get the lightest pistons. This of course assuming you don't mind dealing with a peakier powerplant.

Veefer800Canuck

I seem to remember the old Dynamo Humm kits being 870, not sure what you are referring to as being a "racing" kit though. With the VFR being a big soft couch, I don't think anyone ever raced them.

www3.sympatico.ca/dyno/wolf.htm

Sure they raced VFRs, especially before the RC30 days when great racers like Bubba Shobert raced them in the Superbike series with much success. Although the engines had a lot of tech infusion from HRC, they still had enough VFR DNA in them. Another instance when the VFRs got a lot of racing cred was when Ron Haslam took a bone stok VFR from a dealer showroom and race it into the top places in Atlantic 200 race in England. A British motorcycling magazine also entered a mostly stock 4th gen into a 24 hour endurance race in the 90's and place at something like 7th place out of at least 200 entrants. Never heard of any sort of racing done with 5th to present gen VFRs though...... So there is something to it when older VFR owners say that VFRs had lost a lot of the "sport" it had......

Beck

Sure they raced VFRs, especially before the RC30 days when great racers like Bubba Shobert raced them in the Superbike series with much success. Although the engines had a lot of tech infusion from HRC, they still had enough VFR DNA in them. Another instance when the VFRs got a lot of racing cred was when Ron Haslam took a bone stok VFR from a dealer showroom and race it into the top places in Atlantic 200 race in England. A British motorcycling magazine also entered a mostly stock 4th gen into a 24 hour endurance race in the 90's and place at something like 7th place out of at least 200 entrants. Never heard of any sort of racing done with 5th to present gen VFRs though...... So there is something to it when older VFR owners say that VFRs had lost a lot of the "sport" it had......

I don't think it's so much that the VFR lost it's "sport", because I see no advantage of a 3rd or 4th gen over a 6th gen in terms of performance......but I feel it's more of the "sport" lost the VFR. There was a time when supersport and superbikes were using the same technology as the VFR, then they got newer technology while the VFR didn't.

Beck

Veefer800Canuck

I seem to remember the old Dynamo Humm kits being 870, not sure what you are referring to as being a "racing" kit though. With the VFR being a big soft couch, I don't think anyone ever raced them.

www3.sympatico.ca/dyno/wolf.htm

Sure they raced VFRs, especially before the RC30 days when great racers like Bubba Shobert raced them in the Superbike series with much success. Although the engines had a lot of tech infusion from HRC, they still had enough VFR DNA in them. Another instance when the VFRs got a lot of racing cred was when Ron Haslam took a bone stok VFR from a dealer showroom and race it into the top places in Atlantic 200 race in England. A British motorcycling magazine also entered a mostly stock 4th gen into a 24 hour endurance race in the 90's and place at something like 7th place out of at least 200 entrants. Never heard of any sort of racing done with 5th to present gen VFRs though...... So there is something to it when older VFR owners say that VFRs had lost a lot of the "sport" it had......

Well aware of the VFR's racing credentials in the hands of Shobert, Rainey Et al. I owned a 1986 VFR750 after all.

Was referring to the VFR800's specifically. Never saw DuHamel flog one on the track in anger, with numberplates, etc.

There's also this food for thought, but it's in a 750 engine:

http://www.vfrdiscussion.com/forum/index.php/topic/68268-96-vfr750-cbr929-pistons/page-10

If you watch this clip from 1:20 onwards, you can tell that the HRC RC45 was NOT a 750. They were reportedly 870 or thereabouts and it obviously has some power , because it is pulling past a race prepared R1. (note the dual exhaust on the RC45)

I love the approach you are taking. I have a set of CBR929 pistons in my garage for the same type project... only I haven't picked up a "spare" 5th gen engine yet.

I would be concerned about two things... the first you already are considering (#1 & #2) and #4 would have to be done regardless of which oversized bore you choose. I would recommend evaluating the stroke to con-rod length con rod to stoke ratio to ensure the short skirt 954 piston will not lead to excessive piston rock at TDC & BDC leading to cylinder wall scoring and possible catastrophic failure (especially at TDC with the thinner wall and increased pressure load). As the connecting rod length gets shorter when compared to stroke the piston rocks more at the top and bottom of it's stroke. On a lot of used 929 pistons you can see scoring where the skirts contacted the cylinder walls. That may be why Honda went with the shorter skirt in the 954.

Looking at the 929 & 954 they have the same stroke (54 mm) just different bores; Ron Ayers list them as the same connecting rod so the stroke/con-rod rod/stroke ratio is the same. What is the length of the VFR con-rod? If it leads to a higher stroke/con-rod length lower rod/stroke ratio then the 929/954 you may suffer excessive piston rock and decreased engine life.

PS: Just ran in the garage and measured the 929/954 con-rod and it is 105mm C-C

PPS: I just googled it and I have the terminology backwards.. the concepts the same. It is the Rod/Stroke ratio.

929/954 R/S ratio = 1.94

The 5th gen R/S ratio may be good for our stock pistons but may be too low for wider pistons that could exaggerate the piston rock. If the 5th gen R/S is greater than 1.94 the 929/954 pistons will be more stable with less rock in your project engine than in their original engines; if it is less they will rock more.

Riding my VFR back to back with my Tuono I can't help but to think the perfection a 1000 cc version of my 98 VFR would be. I'd buy one in a heart beat. Good luck with this project. Hope it works out.

Well I've been trying to locate the JE piston numbers for the dynamo humm 870 cc big bore kit on the VFR800's.

So finding this post has me thinking a little bit differently.

And it has me wondering about few things.

first, what do you do about the Nikasil coatings on the VFR800 bores, If you cut the cylinders more than the 3mm aren't you going to have to replate or reline the cylinders?

But then if you are relining the cylinders, why not re-sleeve and go big!. Why go from 72mm bores to only 75mm? compression goes up less than a full point. Cbr1000rr slugs are 76 stock, with 77mm and 78mm available, that would yield the magic 871, 894 and 917 respectively, Rough calculation says the 917 would have CR of just under 13.6, that is assuming you do nothing with the combustion chamber in the head.

R/S ratio has to with the rod length verses the stroke, It is independent of the bore.

Changing the cylinder bore on the VFR will not affect the R/S ratios, so if the piston has the same size or short length skirt, it has roughly the same or less chance of rocking in the bore and scuffing the liners.

JES_VFR

R/S ratio has to with the rod length verses the stroke, It is independent of the bore.

Changing the cylinder bore on the VFR will not affect the R/S ratios, so if the piston has the same size or short length skirt, it has roughly the same or less chance of rocking in the bore and scuffing the liners.

I agree the R/S ratio has nothing to do with the bore. My points are that the larger the piston diameter the more it will exaggerate the rock by moving a greater distance at the edge of the piston for the same degree of piston rock when compared to a smaller diameter piston; second, when the Honda engineers designed these pistons they know way more than I do about piston rock and they specifically design the skirts, rings & landings, and piston geometry for specific applications and using them for alternative applications may have unforeseen complications. If anyone knows the con-rod length of the 5th gen VFR a quick calculation will tell if these pistons will be more or less stable in the cylinder bore than their originally designed application. I'm hoping more stable... that will open up more opportunities!

I believe the whole 8mm cylinder thick sleeve is made of aluminum Powder/Metal composite so boring it out won't remove any coating. It is a mixture of argil, aluminum oxide and graphite. The manual states that as long as heat is controlled they can be "re-bored in the same manner as conventional sleeves".

PS: A quick calculation based on our 48mm stroke shows that as long as the 5th gen VFR con-rods are longer than 93.4mm C-C than these 929/954 pistons will be more stable in the new cylinder bore than in their engineered application... does anyone have a 5th gen con-rod measurement? Seb... Veefer... Bueller?

Rush2112

I love the approach you are taking. I have a set of CBR929 pistons in my garage for the same type project... only I haven't picked up a "spare" 5th gen engine yet.

I would be concerned about two things... the first you already are considering (#1 & #2) and #4 would have to be done regardless of which oversized bore you choose. I would recommend evaluating the stroke to con-rod length con rod to stoke ratio to ensure the short skirt 954 piston will not lead to excessive piston rock at TDC & BDC leading to cylinder wall scoring and possible catastrophic failure (especially at TDC with the thinner wall and increased pressure load). As the connecting rod length gets shorter when compared to stroke the piston rocks more at the top and bottom of it's stroke. On a lot of used 929 pistons you can see scoring where the skirts contacted the cylinder walls. That may be why Honda went with the shorter skirt in the 954.

Looking at the 929 & 954 they have the same stroke (54 mm) just different bores; Ron Ayers list them as the same connecting rod so the stroke/con-rod rod/stroke ratio is the same. What is the length of the VFR con-rod? If it leads to a higher stroke/con-rod length lower rod/stroke ratio then the 929/954 you may suffer excessive piston rock and decreased engine life.

PS: Just ran in the garage and measured the 929/954 con-rod and it is 105mm C-C

PPS: I just googled it and I have the terminology backwards.. the concepts the same. It is the Rod/Stroke ratio.

929/954 R/S ratio = 1.94

The 5th gen R/S ratio may be good for our stock pistons but may be too low for wider pistons that could exaggerate the piston rock. If the 5th gen R/S is greater than 1.94 the 929/954 pistons will be more stable with less rock in your project engine than in their original engines; if it is less they will rock more.

The piston rock is what I was initially concerned with., although apparently for the wrong reason. I didn't think the rod/stroke ratio had anything to do with it but I guess I'm wrong. It's happened before.

Mohawk

Options ?

1. Risk the wall thickness being sufficient. CBR's have thinner walls between the cylinders & use the same MMC liners !

2. Use containment rings to reinforce the cylinders, only need to reinforce the top 15mm to stop flex at peak pressure, which can cause D-chunk failure of the liner.

3. Machine the 954 pistons to lower the compression ratio, to acceptable levels & match the VFR valve spacing.

4. Have made or modify standard head gasket to fit pistons.

Remember that the gear-driven cams don't leave a lot of room to move with different thickness head gaskets.

timmythecop

If you watch this clip from 1:20 onwards, you can tell that the HRC RC45 was NOT a 750. They were reportedly 870 or thereabouts and it obviously has some power , because it is pulling past a race prepared R1. (note the dual exhaust on the RC45)

that RC45 with the twin pipes is awesome, thanks for the vid !!

RC45s raced with twin or single pipes depending on the year/team/track.

And those were WSB legal so they had to be 750s. I don't know about the IOM bikes displacement though. Maybe Crazy Larry does.

/threadjack

And the VFR800 has MMC bores (metal matrix composite) not nikasil.

Don't know how thick it is though

https://www.google.ca/url?sa=t&source=web&cd=1&ved=0CC8QFjAA&url=http%3A%2F%2Fen.m.wikipedia.org%2Fwiki%2FMetal_matrix_composite&ei=cR_UUcuEEYjJyAHc0ICIDA&usg=AFQjCNF2IKluXV0SI3kSyTJf6aKvCXSjuA

Being an inveterate tinkerer, I love threads like this. Please keep us informed.

Rob, thanks for the vid.

Cylinder Sleeve Info

http://www.vfrdiscussion.com/forum/index.php/gallery/image/64997-vfr800-cylinder-sleeve-info/

Veefer800Canuck

RC45s raced with twin or single pipes depending on the year/team/track.

And those were WSB legal so they had to be 750s. I don't know about the IOM bikes displacement though. Maybe Crazy Larry does.

/threadjack

And the VFR800 has MMC bores (metal matrix composite) not nikasil.

Don't know how thick it is though

https://www.google.ca/url?sa=t&source=web&cd=1&ved=0CC8QFjAA&url=http%3A%2F%2Fen.m.wikipedia.org%2Fwiki%2FMetal_matrix_composite&ei=cR_UUcuEEYjJyAHc0ICIDA&usg=AFQjCNF2IKluXV0SI3kSyTJf6aKvCXSjuA

joey was racing against R1's. a bump up to 870cc seems more than fair.

by the way mohawk, this is awesome! keep up the hard work!!!

a lil research yields:

792cc was the engine size of at least one RC45 raced at the IOM TT. I cant find the article with the alleged 870cc. And I dont know if these numbers help anyway, because it isnt really apples to apples anyway. But interesting nonetheless.

Since the RC45 and RC46 (non-Vtec) pretty much share engines, it's sorta relevant, but I don't know what trickery Honda employed to increase displacement on IOM bikes.

Was it bore only (easier) or bore + stroke, if they could not go too far with the overbore. And what exactly IS "too far" anyhow?

In general, I'm not a fan of seeking moar powah out of a bike that isn't first-and-foremost designed for the track. That said, I'm a huge fan of hobbies that aren't 100% logical. I like the amount of research and testing you've done so far. Good luck with the project!

I have an extra motor that needs to be rebuilt, I'm very interested in this. Maybe the thing to do would be to have a custom copper headgasket made by somebody like these guys : http://www.coppergaskets.us/MCG.html

That is brilliant! Love the idea of a custom copper head gasket!

Rush2112

I agree the R/S ratio has nothing to do with the bore. My points are that the larger the piston diameter the more it will exaggerate the rock by moving a greater distance at the edge of the piston for the same degree of piston rock when compared to a smaller diameter piston; second, when the Honda engineers designed these pistons they know way more than I do about piston rock and they specifically design the skirts, rings & landings, and piston geometry for specific applications and using them for alternative applications may have unforeseen complications.

Rush2112

If anyone knows the con-rod length of the 5th gen VFR a quick calculation will tell if these pistons will be more or less stable in the cylinder bore than their originally designed application. I'm hoping more stable... that will open up more opportunities!

Where are you finding all the dimensions for the honda pistons, I keep just finding bore, rings and pin measurements.

Rush2112

I believe the whole 8mm cylinder thick sleeve is made of aluminum Powder/Metal composite so boring it out won't remove any coating. It is a mixture of argil, aluminum oxide and graphite. The manual states that as long as heat is controlled they can be "re-bored in the same manner as conventional sleeves".

Rush2112

PS: A quick calculation based on our 48mm stroke shows that as long as the 5th gen VFR con-rods are longer than 93.4mm C-C than these 929/954 pistons will be more stable in the new cylinder bore than in their engineered application... does anyone have a 5th gen con-rod measurement? Seb... Veefer... Bueller?

FYI: VFR400R NC30 redlines at 12,500rpm. CBR400RR redlines at 13,000rpm. Both are listed as having 55x42 bore/stroke (or stroke/bore?), and make the same horesepower. Interestingly, they use the same piston part number.

Ciao,

timmythecop

If you watch this clip from 1:20 onwards, you can tell that the HRC RC45 was NOT a 750. They were reportedly 870 or thereabouts and it obviously has some power , because it is pulling past a race prepared R1. (note the dual exhaust on the RC45)

[video: https://www.youtube.com/embed/6wamdJQXI9w?feature=oembed]

Poor Joey but he had a great life yeah R's1 paid the price that day for sure , Timmy right it obvious what you can do with the 870cc

JES_VFR

Where are you finding all the dimensions for the honda pistons, I keep just finding bore, rings and pin measurements.

Can you show us your calculation please, because in my mind that would be a very long rod...

I found the service manuals online somewhere along the way. I have the VFR manuals and the CBR929 manual I downloaded. The parts numbers are from RonAyers.com,

http://www.ronayers.com/

The bike model info I get from BikeZ.com. It has specs for most bikes from 1970 on

http://www.bikez.com/brands/index.php

CBR 929/954 have a 105 mm connecting rod (I measured center to center (C-C) the one in my garage) and a 54 mm stroke. This gives a Rod length to Stroke ratio (R/S) of 1.94.

The 5th gen VFR has a 48mm stroke and it needs a R/S > 1.94 for the pistons to be more stable in the new bore. Therefore,

R/48 mm > 1.94

= R>(48mm*1.94)

= R>93.12 mm, (or 93.4 mm if all the decimal points are left in the calculator and my actual CBR929 con rod measurement was 105.025 mm).

That's a little longer than 3.6" con rod length measured C-C. I don't consider that to be a very long rod...

...YRMV

Rush2112

The bike model info I get from BikeZ.com. It has specs for most bikes from 1970 on

CBR 929/954 have a 105 mm connecting rod (I measured center to center (C-C) the one in my garage) and a 54 mm stroke. This gives a Rod length to Stroke ratio (R/S) of 1.94.

The 5th gen VFR has a 48mm stroke and it needs a R/S > 1.94 for the pistons to be more stable in the new bore. Therefore,

R/48 mm > 1.94

= R>(48mm*1.94)

= R>93.12 mm, (or 93.4 mm if all the decimal points are left in the calculator and my actual CBR929 con rod measurement was 105.025 mm).

That's a little longer than 3.6" con rod length measured C-C. I don't consider that to be a very long rod...

...YRMV

I was thinking that was a long rod based on the compactness of the VFR block and the deck height limit. My last couple of bore and stroke engine upgrade were car engines where a R/s ratio of better than 1.6:1 was considered good.

I remember having to choose a very short piston with the pin bore literally up into the oil ring groove, just to be able to run a long enough rod to hold a 1.67:1 ratio.

FWIW, I can't find a C-to-C length for the VFR800 rod.

IIRC the 870cc Big bores done by TTS and Dynamohumm all worked fine on the stock VFR800 rods. Now going beyond that might increase the chances of piston rocking, but your not going there.

I look forward to finding out the vfr800 rod length, but unless it is really close to 1.6:1 I'm not going to panic.

Heck I still don't have the info on how big a sleeve I can put in the VFR800 cases.

That video wasn't the IOM TT, it was the Ulster GP.

OK, so to summarize:

1. what is the displacement of the 5th gen engine when fitted with 954 pistons?

2. what is the displacement of the 5th gen engine when fitted with CBR 1000 pistons?

3. Do the 1000 and the VFR share wrist pin heights as the VFR and 954 do?

4. What was the displacement of the Dynammo Humm kit, 870cc? If so what bore diameter did they employ and did they bore the MMC liners or replace them?

5. Anyone known to have played with the stroke of the 5th gen engine?

CornerCarver

OK, so to summarize:

1. what is the displacement of the 5th gen engine when fitted with 954 pistons?

848 cc

2. what is the displacement of the 5th gen engine when fitted with CBR 1000 pistons?

pre-2008 = 848cc

2008 - 2012 = 871cc

3. Do the 1000 and the VFR share wrist pin heights as the VFR and 954 do?

Don't know

4. What was the displacement of the Dynammo Humm kit, 870cc? If so what bore diameter did they employ and did they bore the MMC liners or replace them?

I think it was 870cc, IDK but boring out the 8mm MMC liner by 4mm would be seriously reducing it's strength.

5. Anyone known to have played with the stroke of the 5th gen engine?

I contacted A.P.E. and they could stroke the crank but their equipment was only set-up to balance I-4 cranks and wouldn't work on a V configuration. Balancing would have to be done elsewhere, I tried to see if someone doing Ducati cranks could do it with no luck. That was last year and they may have updated equipment since then.

Not sure if any of the people here are involved in the thread over at bikers oracle in the UK:

http://www.bikersoracle.com/vfr/forum/showthread.php?t=123379

Also here is the internet snapshot of Dynamo Humm from 10 years ago, look at the shop rates!!! They are 310% higher now locally!

[image: post-72-0-85775600-1375382205.png]

Here is a 94-97 750 big bore on the dyno, he had a staintune high mount, Ducati rear wheel, and likely a jet kit:

[image: post-72-0-81664800-1375382964.png]

Different bike, 1995 750 torque curves:

[image: post-72-0-94804800-1375383075.png]

Sorry for the distractions, I find these things fun to dig up.

[image: post-72-0-29608200-1375383273.png]

Thanks for the link but not much more info there, unless you are looking for Kawasaki dyno chart...

spinalator

Here is a 94-97 750 big bore on the dyno, he had a staintune high mount, Ducati rear wheel, and likely a jet kit:

[image: attachicon.gif]Screen Shot 2013-08-01 at 12.48.23 PM.png

Different bike, 1995 750 torque curves:

[image: attachicon.gif]Screen Shot 2013-08-01 at 12.51.04 PM.png

Sorry for the distractions, I find these things fun to dig up.

[image: attachicon.gif]Screen Shot 2013-08-01 at 12.54.13 PM.png

Now these are interesting...if I could get 120hp at the wheel by dropping CBR1000 pistons into my spare 5th gen engine I would be very pleased with my track bike...

Rush2112

Cylinder Sleeve Info

http://www.vfrdiscussion.com/forum/index.php/gallery/image/64997-vfr800-cylinder-sleeve-info/

Cheers

Vfr800 5th gen conrod length is 102mm or 4" as near as damn it ! Measured by yours truly ! So R/S ratio of 2.125.

Thanks for the 750 dyno info. Running those torque numbers shows that that is a Factory Pro dyno, so a DJ figure would be 133hp.

So assuming the same dyno for VFR870 that showed 120hp, then a DJ figure would be 138hp, due to the lower rev max torque figure & the fact that the engine probably had no other tuning.

From what I gather that 870 used 76mm pistons & had the MMC completely bored out & 2mm SS liners inserted. So the physical maths is as follows. STD bore = 72mm, cylinder wall thickness = 8mm, so 72+16mm=88mm. So an 870 would be 88- (76+4=80)=8mm or 4mm cylinder wall left !

Now I've seen those MMC cutaways, I can workout the thickness on my spare engine, I'll report back after the weekend.

Don't use copper gaskets, when Cometic in the US can make MLS like the originals, just supply an old one as a template & ask for a larger bore !

The Phantom

Mohawk

Options ?

4. Have made or modify standard head gasket to fit pistons.

Remember that the gear-driven cams don't leave a lot of room to move with different thickness head gaskets.

The Gaskets Need a Bigger hole in the middle for the pistons, nothing else, same thickness as stock ! :) A cold 929 piston just fits in the stock gasket, but those forged slipper pistons expand a lot so it won't fit when hot. If you have to bore through the MMC liner, then it will become a Nikasil coated bore, the other concern is if the MMC is not thick enough, then you would have to go to a bigger bore to remove all the MMC, then the question is does that leave enough meat in the unsupported liner ?

In a week or so we will tear down the spare 5th gen engine. If anyone wants any pics or measurements please let us know...

I know I'm late to this but has the st xx00 or vfr1200 piston or crank specs been checked? It would seem natural to stick with the v engine family.

Couldn't say where she's coming from,

but I just met a lady named Dynamo Humm.

She strolled on over, said look here bum,

I gotta $40 bill says you can't make this thing run.

Ya just can't do it. :laugh:

Suggest you whip off its bloomers and stiffen your thumb and apply rotation as needed.

With apologies to FZ. :goofy:

What? Does it work?

We need more HP from the best engine and not a hand grenade.

Can this be done????.

CornerCarver

In a week or so we will tear down the spare 5th gen engine. If anyone wants any pics or measurements please let us know...

as well as the total depth to the cylinder liner.

Mohawk

Hey Rush thanks very much for that it's the one bit of info I had not managed to find ! So the 929 74mm bore looks like the max without serious work.

Cheers

Vfr800 5th gen conrod length is 102mm or 4" as near as damn it ! Measured by yours truly ! So R/S ratio of 2.125.

I would think that either Brian worked out that 6mm MMC sleeve walls were still thick enough or He replaced them with them with tougher steel sleeves 6mm thick.

What I'm thinking is what if someone was willing to bore the cases for sleeve larger than 88mm in diameter, say 92 mm?

Even if you stay with 7mm walls (the allowed overbore thickness of the mmc liners) your talking about being able to fit 78mm pistons.

That puts you over 917cc's.

That's getting into a very over square engine. In fact it is so far oversquare, that I'm starting to think about the rods and a stroke increase again.

Now with the information about length of the rods, and total length of the cylinders, a stroker kit could be put together with a crank and alternate length rods.

JES, the cylinder wall thickness is 8mm, so a 72mm bore + 16mm walls, means 88mm to remove the cylinder. The spacing between cylinder walls is 5mm, or 93mm piston centre to piston centre. The problem with the VFR cylinders are mainly that the cylinders are NOT full depth, the bearing supports intrude in to the bottom of the bore, so unlike a straight 4 you can't just bore straight through & fit a steel liner. I'm sure a step fit could be made to allow a steel liner to work, but the CBR pistons are NOT designed to work in a steel liner, plus the engine & cooling systems are NOT designed to work with a steel sleeve !

JES_VFR

CornerCarver

In a week or so we will tear down the spare 5th gen engine. If anyone wants any pics or measurements please let us know...

Yeah I want to know the cylinder to cylinder measurement,

as well as the total depth to the cylinder liner.

Mohawk

Hey Rush thanks very much for that it's the one bit of info I had not managed to find ! So the 929 74mm bore looks like the max without serious work.

Cheers

Vfr800 5th gen conrod length is 102mm or 4" as near as damn it ! Measured by yours truly ! So R/S ratio of 2.125.

870cc big bores have been done, I just don't know how to get in touch with the true source Brian Law..

I would think that either Brian worked out that 6mm MMC sleeve walls were still thick enough or He replaced them with them with tougher steel sleeves 6mm thick.

What I'm thinking is what if someone was willing to bore the cases for sleeve larger than 88mm in diameter, say 92 mm?

Even if you stay with 7mm walls (the allowed overbore thickness of the mmc liners) your talking about being able to fit 78mm pistons.

That puts you over 917cc's.

That's getting into a very over square engine. In fact it is so far oversquare, that I'm starting to think about the rods and a stroke increase again.

Now with the information about length of the rods, and total length of the cylinders, a stroker kit could be put together with a crank and alternate length rods.

well John your in luck. I know Brian, grew up with his boys. he lives about ten minutes from my house. I also know Bruce Allnut the mechanic that worked with Brian when he had dynamohumm. I've brought up a few of these threads to him in the past, explaining there is still interest in the projects they we were working on. But that whole endeavor ended kind of bad. there seemed to be little interest on his part. But I will give it another shot and see what he says. I'll try and get him to read some of the threads. Who knows I might be able to convince him to join for some Q&A (don't hold your breath) .

Jess

sub'd :)

well John your in luck. I know Brian, grew up with his boys. he lives about ten minutes from my house. I also know Bruce Allnut the mechanic that worked with Brian when he had dynamohumm. I've brought up a few of these threads to him in the past, explaining there is still interest in the projects they we were working on. But that whole endeavor ended kind of bad. there seemed to be little interest on his part. But I will give it another shot and see what he says. I'll try and get him to read some of the threads. Who knows I might be able to convince him to join for some Q&A (don't hold your breath) .

Jess

Hi Jess, even if you can extract from him how they got the 76mm bore & what was the max possible staying within the MMC liner, that would save me destroying a crankcase to find out !

Thanks

thanks Jess, hope you are successful. beer's in it for you. :beer:

CornerCarver

thanks Jess, hope you are successful. beer's in it for you. :beer:

Right on, Man!

I've been pondering this for two years...

Next round is on me!

:beer: :beer:

Ok, so I texted Brian. He got back to me and said I could pass along his email address to those who wish to get in touch with him. So anyone interested can pm me for the details.

Jess

Whoever does, please share.

This is a little OT, but this fellow has a lot of info on boring out CB750's, one of my friends used his info and bought a kit for some big bore projects. Web Nanny filters may not allow you to access his domain, lol.

http://www.satanicmechanic.org/bigbore.shtml

belovian

Ok, so I texted Brian. He got back to me and said I could pass along his email address to those who wish to get in touch with him. So anyone interested can pm me for the details.

Jess

I don't want to swamp him with the same questions six times 'til Sunday... I suggest one person contact him and share the info.

Mohawk, you want to take the lead since you have an engine in the works? CornerCarver? Bueller?

Well if we put together some specific questions then we can get Jess to send him one email ! And hopefully leave the man in peace :)

So with that in mind, I need to know the following.

1. Do you know how thick the MMC liners are ?

2. What is the maximum overbore you used keeping the MMC, if you did this ?

3. What did you go to achieve the 870cc big bore ? For example Steel liners / Nikasil etc ?

4. What did you do for head gaskets ?

That's all I need to know. If anyone else, has any SPECIFIC questions, then add to my list.

Thanks Jess.

For the head gaskets, someone posted a link earlier for a place that makes custom copper head gaskets.

With the gear drive cams, Im gonna say that the gasket thickness will have to exactly match the OEM gasket.

If you gave them the upper crankcase, the cylinder heads, and a sample OEM gasket, I'm sure they could bang a couple out.

Mohawk

Well if we put together some specific questions then we can get Jess to send him one email ! And hopefully leave the man in peace :)

So with that in mind, I need to know the following.

1. Do you know how thick the MMC liners are ?

2. What is the maximum overbore you used keeping the MMC, if you did this ?

3. What did you go to achieve the 870cc big bore ? For example Steel liners / Nikasil etc ?

4. What did you do for head gaskets ?

5. What pistons and rods did they use? Were they Honda parts bin stuff (i.e. CBR 929, 954, 1000 parts) or after market?

6. Any stroker cranks involved? If yes, what rod length and pistons used and where to get the crank stroked & balanced? Any recommended machine shops?

That's all I need to know. If anyone else, has any SPECIFIC questions, then add to my list.

Thanks Jess.

I would like to add 5 & 6.

Also, on #4 head gaskets, I think someone posted up that Cometic will make MLS custom gaskets just send them a set of originals and they will use it as a template and increase the cylinder bore diameter to fit the application.

I've sent Brians email address to rush and mohawk. that should get the dialog going.

Jess

I bought Brian's Corbin seat for my 95 sometime in the early 2000's. I was considering the big bore and then moved to Ireland for a year and blew all my savings. Hopefully you guys can get this figured out, I am watching the developments!

Been out of town for business...Rush added the only two additional questions I could think of re: stroking the RC46 engine.

So, have Rush or Mohawk contacted Brian yet?

OK, I've complied the questions in a polite email just sent them to Brian. Watch this space for updates.

Cometic should be able to make a custom gasket out of copper and possibly out of their MLS stuff. I like the composite stuff a bit better, as it's that little bit soft to make sure you have a good seal, whereas the MLS stuff you have to have your block and your heads flat within 0.001". On the GT, my block was perfect, but my head was out 0.004" (which is still within OEM spec), and the MLS gasket leaked like a sieve.

As a serial VFR big bore kit owner (see sig...), I am always interested in ways to throw money I don't have at problems that don't exist. Count me in! I think my supercharged 5th-gen really needs an 870cc engine...or maybe a 900? :goofy:

Say "hi" to Brian for me...I think I still owe him a beer! :beer:

Ciao,

OK, so here's my email to Brian, followed by his reply;-

Hi Brian,

I hope you are well, please excuse this intrusion.

Jesse off the VFRD forum gave me your email address, so that hopefully you can answer some questions about the VFR800 Big Bores that Dynamo Hum used to do.

Myself & another forum member have a couple of spare engines & have been working on a big bore VFR plan.

I have info from TTS in the UK, that the VFR800's MMC liners can be safely bored to 74mm & nikasil coated. Although according to Honda they can be bored & honed as normal provided the temperature is kept low ! You may have experience in this area, please feel free to elaborate.

The basic options I have investigated are either a 74mm bore using CBR929 pistons giving 825cc, or a 75mm bore using CBR954 pistons giving 848cc. I assume the dynamo hum 870cc was a 76mm bore, so this has lead to the following questions.

1. Do you know how thick the MMC liners are ? (std bore=72mm + 8mm cylinder wall thickness)

2. What is the maximum overbore you used keeping the MMC, if you did this ?

3. What did you do to achieve the 870cc big bore ? For example Steel liners / Nikasil etc ?

4. What did you do for head gaskets ?

5. What pistons did you use? Were they Honda (i.e. CBR 929, 954, 1000 parts) or after market?

6. What rods did you use? Were they Standard or after market?

I assume that question 7 is self evident as a NO, due to the gear cams, but the other builder has asked, so here it is.

7. Any stroker cranks involved? If yes, what rod length and pistons used and did you have to get the crank rebalanced?

Many thanks for taking the time to answer these questions from us crazy fools :)

Regards

Chris Walker

============================================================================================

Hi Chris

Sorry for the slow reply.

I will try to answer your questions as best I can. I think I destroyed all the technical information in a drunken purge.

I developed the 800 big bore kit with the help of a talented mechanic and JE Pistons (now called Sportsman I think).

At the time we were trying to figure things out Honda was no help whatsoever. The liners were new and Honda didn't want to provide any information.

No stroker for the 800.

We thought about nikasil but rejected this approach. JE helped us design new pistons and we went with steel liners pressed in. When I gave up Dynamo Humm I gave up my rights to the vfr750, 800, and vtr1000 pistons. You should be able to buy just one set at a time. They come with rings and wristpins. Lighter and stronger than stock. Slight raise in the compression ratio. Ran fine on super gas.

The stock rods and crank were lightened, balanced, and polished by Falicon. Because the pistons were a custom order for us we were obliged to buy a minimum of 24 at a time. This allowed us to further balance everything by weighing the pistons, rings, wristpins, and rods.

The head gaskets are stock Honda carefully and meticuosly hand made using a dremel tool. A couple of hours for each set.

The first motor had a design flaw in the pistons and one was hitting the head and eventually cracked it.

The second motor had a badly pressed in liner that caused that motor to go BANG !

The third one blew a head gasket and overheated.

Fourth and subsequent motors were trouble free. I put about 50,000kms on mine.

Hope this helps .... crazy fools rule

Brian

Crazy fools rule. :lol:

Steel liners, interesting.

thank you so much Jesse, Chris and especially Brian for the information!

I hope I am not reading too much into his response but the line about Honda being no help with answers (especially on the MMC liners) would point to not knowing at the time that they liners could be re-honed and re-used provided that they were bored (as we now know 10 years later) slowly to control heat...maybe they would have selected steel liners regardless....

The engine I am building is going into a V7 heavyweight club racing bike and anything 750 and over get lumped together so the more CC's the better for us (as long as it holds up for a season of endurance racing).

So 76mm bore and a probably steel liner for us, I may still inquire about stroking the engine and see if any stock CBR rods match the necessary shorter length for a stroker engine.

I am hoping my biggest problem is how to build a 7.5 gallon fuel tank from a spare 6th gen tank. :goofy: probably not though...

Glad I could help!

I spoke this week to that very talented mechanic Brian was referring to, Bruce Allnut. I stopped by his recently opened shop to chat about all things two wheeled and plied him with a few questions about the big bore kit as well. He essentially mirrored what Brian said, but added a few details. Like on a couple of the engines he remembers removing a set of gears. I believe he was talking about the gears the keep tension on the cam drive gears to quiet them down. said it added some noise but really helped "wake em up". He remembers with quite a bit of detail a lot of the processes involved. If you guys have any other Q's fire away and I'll ask him too!!

Jesse

belovianLike on a couple of the engines he remembers removing a set of gears. I believe he was talking about the gears the keep tension on the cam drive gears to quiet them down. said it added some noise but really helped "wake em up".

Yes the guys racing VFR400s in the Clubman class over here have been doing that for years, sounds like someone has emptied a bag of nails into the valvegear at idle but the reduced rotating mass certainly helps them to rev.

I took them off the cams in my 750 for the same reason, but it's not a simple job as the scissor gear assembly is pressed/riveted into place.

CornerCarver

I may still inquire about stroking the engine and see if any stock CBR rods match the necessary shorter length for a stroker engine.

You can't stroke the 800fi, the gear cams preclude this, it was already stroked 2mm by Honda taking the RC45 750 to 781cc in the 800fi. Every stroker I've seen has seperate barrels so that you can add stroke at the base gasket. The VFR's don't have a base gasket, as the bores are cast into the upper crankcase & the bearing webs intrude into the base of the bore, so you can't make the psitons travel further. That said the 954 piston is about 6mm shorter than the 800's so you could play with the crank & rods within that limit, but I don't know if there would be enough deflection angle to accomodate the extra stroke &/or enough crank web to relocate the bigends with enough meat left to deal with the forces.

A quick calc shows a 75 x 54mm stroke engine would give 953cc, if you could get a 76mm bore then it would give 979cc with the potential for 140+rwhp. Good luck with the huge dollar expense of that one.

Got a write up or other info on that mod?

what about stroking the vtec engine?

belovian

Glad I could help!

I spoke this week to that very talented mechanic Brian was referring to, Bruce Allnut. I stopped by his recently opened shop to chat about all things two wheeled and plied him with a few questions about the big bore kit as well. He essentially mirrored what Brian said, but added a few details. Like on a couple of the engines he remembers removing a set of gears. I believe he was talking about the gears the keep tension on the cam drive gears to quiet them down. said it added some noise but really helped "wake em up". He remembers with quite a bit of detail a lot of the processes involved. If you guys have any other Q's fire away and I'll ask him too!!

Oh, Oh I know this one....

As a former RC51 owner I know this trick. The gears Bruce is referring to are called quieting gears (or silenceing gears) and maintain what is called a zero backlash drive in the cam gear drive. What they are is a spring loaded second gear that keeps pressure on the back side of the gear faces. That keep them quiet and relatively rattle free as well, but adds a bit more friction to cam gear drive. Removing it frees up the gears and they all spin much easier as well as removing a bit of weight ( 15 ounces of rotating weight on each cylinder of the RC51). Sure it allows a tiny bit of backlash (.015 degrees of play at the camshaft on the RC51) to occur any time you violently decelerate the engine, but how often does that really happen???

About the only downside on a Street bike is that the gear driven cams will now clatter quite a bit. On the already loud RC51, it sounds a lot like you somehow added a vented dry clutch. I don't now how much louder it would make the VFR sound, but I'm not rushing to remove them on my street bikes. But those that are thinking of racing, might want to do this "free" mod.

Cool stuff. Makes me wish I had gear driven cams.

Mohawk

You can't stroke the 800fi, the gear cams preclude this, it was already stroked 2mm by Honda taking the RC45 750 to 781cc in the 800fi. Every stroker I've seen has separate barrels so that you can add stroke at the base gasket. The VFR's don't have a base gasket, as the bores are cast into the upper crankcase & the bearing webs intrude into the base of the bore, so you can't make the pistons travel further. That said the 954 piston is about 6mm shorter than the 800's so you could play with the crank & rods within that limit, but I don't know if there would be enough deflection angle to accommodate the extra stroke &/or enough crank web to relocate the big ends with enough meat left to deal with the forces.

A quick calc shows a 75 x 54mm stroke engine would give 953cc, if you could get a 76mm bore then it would give 979cc with the potential for 140+rwhp. Good luck with the huge dollar expense of that one.

First Mohawk thanks for sending the Email to Brian.

I thought I remembered him saying it would need sleeves, but it was so long ago and many hard drives in the past.

So, I was right, bore out the MMC liners to their bottoms and install a steel sleeves. That along with the Cam gear drive means that there is a hard limit to the total range of piston travel, and any stroker will have to be created using shorter pistons.

Now as you pointed out the 954 pistons are approximately 6mm shorter than the VFR pistons.

1mm oversize 954 pistons are out there so the 76mm is not impossible to come up with.

Still adding 6mm of stroke?? That would be a lot of material to take off the rod journals of the crank in offset grinding, far too much in my opinion.

But,... What about adding a little more stroke? Say 1.5mm more... That bumps your 848, to an 875 and the 870 to 898, heck even the stock 781 finally checks into the 800cc range at 806.

2mm more stroke the numbers are great, 848 to 884, 870 to 907.

or better yet push it to 3mm. Now the 848 goes over the 900 mark and the 870 jumps to 925.

Still you've got almost 3mm more clearance up from the bearing webs than you did with the stock VFR piston.

Sure then the piston has to be dished to keep the compression ratio under control, but I'm sure between a bit a dish in the piston and bit of very light porting (basically just matching the perimeter of the chamber to new bore size) the CR can be kept street gas friendly..

So I guess the big question(s) for the folks at Falicon are

What is the smallest you can 'safely' offest grind VFR rod journals and still use a standard VFR rod with an undersize bearing?

What is the limit for welding on new new metal on the outside of the journals to offset grind the crank and use standard honda bearing sizes?

CandyRedRC46

what about stroking the vtec engine?

You could run a thick head gasket to help a smidge with compression, but you would still have to use shorter pistons and you still have to deal with the stroking the crank.

Jes, I thought about stroking the VFR from a design perspective only & the simple answer IMO is this. Rather than gring anything, just seperate the outer cam webs & big end from the inner cam webs, just press fitted AFAIK. Then this is the new thinking bit, have new big ends made that have an offset centre so a bit like a cam lobe, but round. Hard to describe, but this would allow you to offset the rod as much as you like. Press back together & weld up to avoid slippage in future.

_|--|_

_|--|_

Silly attempt at picture, but the left and right sides are the original big ends that fit into the webs & the middle -- (ignore the top extensions) are the new offset big ends where the rods sit. Obviously depending on clearance in the engine case (it's tight in there) & piston depth you may need new rods to keep the piston skirt from clouting the crank webs ! I'll try to measure the bigend to crank web depth over the weekend & see if I can find a way to measure the rod clearances in the crank cases.

Just realised that this idea would require lower decked pistons to allow for both ends of the stroke :( Doh !

:lurk:

Keep at it boys!

Hoping that one day the Honda engineers at HQ that are maybe following this thread will one day step into the light and reveal all........................ :goofy:

Dutchy, one can only hope!!!

so if the stars and planets aligned and the sleeves were fine after being bored the 2 or 3mm. Because the pistons share the same sleeve size then the 929/954 pistons will fit properly on a VFR rod. If we maintain the same head gasket thickness (and don't deck the head) then is the new piston going to be in the proper location at TDC? Is the piston top compared to pin depth the same across all pistons or will we require a longer rod to get the piston to the same height as before? It appears that the crown on the 929/954 pistons are different. I am a newb compared to y'all but I do have a basic understanding of engines.

I believe the wrist pin to piston top is the same for the 5th gen VFR and CBR929... I don't know about the 954. VFR rods will work; but IIRC either the outer edge of the piston needs to be chamfered or the combustion chamber outer edge needs to be machined out 2 mm for the 929 pistons... someone machined the pistons on this forum...

Rush2112

I believe the wrist pin to piston top is the same for the 5th gen VFR and CBR929... I don't know about the 954. VFR rods will work; but IIRC either the outer edge of the piston needs to be chamfered or the combustion chamber outer edge needs to be machined out 2 mm for the 929 pistons... someone machined the pistons on this forum...

then the 954 should be fine also. If i remember correctly all honda did from the 929 to the 954 is lighten the internals and add displacement. And wouldn't shaving down the 954 piston reduce that compression that we are trying to achieve? I really feel like someone needs to bore a block out and find out by just going for it.

Then report here haha

I did a lot of homework on this idea a few years ago and IIRC the 929 pistons would work but the 954 pistons would not... but I lost my notes, so take that with a grain of salt...

This is something I want to do to my bike.

But like for realsies.

Not just talk.

Like, I want to throw down benjamins that I would of spent on a newer/different bike on getting a big bore kit on the bike I have and love.

Why do we have such crap info and unreliable sources about this seemingly 'unpopular' mod?

:cool:

Be my (our) guest... let us know how it works out!

I have a full Vesrah gasket kit in the workshop, waiting for its opportunity...

I have a set of 929 pistons & rods in my garage...

@ G-Rob:

Dude, I know it has been done with 2mm overbore and 929 pistons on a 5th gen... but that only gets you 826cc and a 5.6% bump in displacement.

I'm not sure where the unreliable sources comment comes from... we contacted the guy who pioneered and sold the big bore kit!

This mod has been done... for realsies!

daword2011

Rush2112

I believe the wrist pin to piston top is the same for the 5th gen VFR and CBR929... I don't know about the 954. VFR rods will work; but IIRC either the outer edge of the piston needs to be chamfered or the combustion chamber outer edge needs to be machined out 2 mm for the 929 pistons... someone machined the pistons on this forum...

... wouldn't shaving down the 954 piston reduce that compression that we are trying to achieve?

The machining of the pistons was to chamfer the circumference to keep it from contacting the cylinder head because of the 1mm overhang left from the boring of the cylinder... the other option is to expand the combustion chamber by 1mm around the circumference (2mm total) and smooth the transition into the existing dome. The compression is already increased by the increased sweep of the larger bore and chamfering the pistons or slightly enlarging the edge of the combustion chamber won't drop it much at all...

Rush2112

I have a set of 929 pistons & rods in my garage...

@ G-Rob:

Dude, I know it has been done with 2mm overbore and 929 pistons on a 5th gen... but that only gets you 826cc and a 5.6% bump in displacement.

I'm not sure where the unreliable sources comment comes from... we contacted the guy who pioneered and sold the big bore kit!

This mod has been done... for realsies!

daword2011

Rush2112

I believe the wrist pin to piston top is the same for the 5th gen VFR and CBR929... I don't know about the 954. VFR rods will work; but IIRC either the outer edge of the piston needs to be chamfered or the combustion chamber outer edge needs to be machined out 2 mm for the 929 pistons... someone machined the pistons on this forum...

... wouldn't shaving down the 954 piston reduce that compression that we are trying to achieve?

The machining of the pistons was to chamfer the circumference to keep it from contacting the cylinder head because of the 1mm overhang left from the boring of the cylinder... the other option is to expand the combustion chamber by 1mm around the circumference (2mm total) and smooth the transition into the existing dome. The compression is already increased by the increased sweep of the larger bore and chamfering the pistons or slightly enlarging the edge of the combustion chamber won't drop it much at all...

I see your point. So after the 3mm overbore we are now getting past the point at which the combustion chamber fits the cylinder. So tapering the piston would probably be more cost effective. Expanding the combustion chamber can become expensive quickly I imaging. Plus i wouldn't like the idea of affecting the shape of the chamber. Maybe if my bike starts eating coolant or burning oil this will be something to consider haha. Really the used pistons would be cheap but the machine work might cost you :P

Rush2112

@ G-Rob:

Dude, I know it has been done with 2mm overbore and 929 pistons on a 5th gen... but that only gets you 826cc and a 5.6% bump in displacement.

I'm not sure where the unreliable sources comment comes from... we contacted the guy who pioneered and sold the big bore kit!

This mod has been done... for realsies!

Well I've seen the contact info about past guys that did it, but its like "I destroyed the info in a drunken purge", or "I did all the homework but lost the info", or "Dat one guy went out uh bizness".

That's why.

2mm overbore and 929 pistons. Can't be that easy.

I'm saying the info should be collected and made a sticky if its something that isn't too difficult.

Relatively speaking.

GadiantonRob

Rush2112

@ G-Rob:

Dude, I know it has been done with 2mm overbore and 929 pistons on a 5th gen... but that only gets you 826cc and a 5.6% bump in displacement.

I'm not sure where the unreliable sources comment comes from... we contacted the guy who pioneered and sold the big bore kit!

This mod has been done... for realsies!

2mm overbore and 929 pistons. Can't be that easy.

On a 5th gen... it's that easy. You do have to modify the head gaskets or have them custom made.

Well, full disclosure... I haven't done the mod myself so take my input with a grain of salt, it's all heresay... but I've been researching it for 2 years.

I don't know on your bike though. I think yours is 70mm stock so you would be going 4mm over to use the 929 pistons. That's a lot of material to remove from the cylinder walls without compromising strength. IT would get you to 836cc and 11.8% increase in displacement

GadiantonRob

This is something I want to do to my bike.

But like for realsies.

Not just talk.

Like, I want to throw down benjamins that I would of spent on a newer/different bike on getting a big bore kit on the bike I have and love.

Why do we have such crap info and unreliable sources about this seemingly 'unpopular' mod?

The second issue is the boring itself, the main bearing webs intrude into the lower bore, thus you can't use a straight through bore as done on most engine blocks, if you damage the main bearing webs, then the engine is scrap !!!!!

Still keen ? The bores use Honda's MMC liners, so you can rebore them to 74mm & leave enough strength to work, but 75mm is to much. But due to the MMC having locator lugs to hold them in the bore you have to bore out to 80mm to remove the remnants of the MMC to allow a steel liner to be pressed in, but they would have to be custom made, so more expense. A 2mm liner would give you a 76mm bore, that would either require custom pistons or possibly pistons from another bike might work, but that would require more research & testing !

So in a nut shell, 74mm is the least cost largest rebore you can do, giving 825cc which many people consider to be to little to be worth the effort. I may do this as I have a spare engine, otherwise I agree it would not be worth the effort !

So what were they doing to get 870? Bigass bore and thin sleeves, customs pistons?

spinalator

So what were they doing to get 870? Bigass bore and thin sleeves, customs pistons?

Post #65, JE Pistons, resleeved with steel liners pressed in, etc...

So who's gonna transplant the 1200 in their 5th/6th?

Well, I finally have some progress to report. Having had problems finding somewhere to rebore my block, I spoke to TTS who informed me that they have never destruction tested a block to find out the MMC liner limits, but they are prepared to test bore a cylinder for me to test Honda's claims that they can be bored as per normal steel if kept cool.

To that end I acquired a spare upper crankcase block today & have sectioned cylinder #1 as per the attached pics. The upshot is this.
The total cylinder wall is 8mm thick, the MMC liner is 2.5mm thick on its narrowest section. It does NOT amalgamate with the cast alloy as per Honda's claims. This was evident as I hack-sawed through the section & should have had 1 piece of outer water jacket & 1 piece of cylinder wall, but got 3 pieces ! 1 x MMC piece, 1 x cast Cylinder wall & 1 x outer water jacket !

So assuming the MMC can be bored as per Honda's manual, then a 2mm over bore (74mm giving 825cc) would reduce the MMC thickness to 1.5mm, I believe this is doable. A 3mm overbore (75mm giving 848cc) may be possible, as it would reduce the MMC to 1mm thickness, I would expect this to require Nikasil plating to reinforce the MMC.

The other pictures show the bore offsets & the inside of the upper crankcase/block.


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Interesting.....

Oh hell yes!

Any idea on the mileage of the block you cut ? Looks low .

That won't buff out! ;)

No idea of the mileage on this block, was just happy to find half a crankcase for sale at a reasonable price, so I could gut it. I need to cut deeper to find the horizontal locking lugs to see how deep they are. TTS do a 76mm big bore (870cc) but that removes all of the liner & they then Nikasil the bore. I spoke to them & they send the block to the USA for boring & Nikasil plating !

Just for interest I tried to weigh the upper crankcase & it was more than 6Kg, the limit of my scales, I'l get the bigger set out & get an actual weight. I guess they built this engine for 200HP & 15,000rpm in RC45 guise, so the alloy webs & outer cases are 5mm thick, with the main jpurnal webs being pretty hefty too ! I think with some drilling grinding & titanium & alloy bolts, you could get the weight down by a few Kg. The complete engine is circa 74Kg if memory serves from the service manual ! That's a third of the weight of the bike ! so worth considering ! If I could erase 5Kg of weight whilst boosting power that would be great !

Did TTS say who they send the block to in the U.S.?

I was not referring to the guys who know what they are talking about. Phil is probably right about better flow with the wider bore.

That site is great forthe base info, but yu have to check the valve lift for degree measurements, as they vary a lot, so some valves with long duration are much shorter, when measured at 1mm lift rather than 0.3mm etc.

So our Vfr has steel 29mm intake and 24.5mm exhaust valves. The 2010 zx10r has 24.5mm exhaust valves, and the 2008 gsxr750 has 29mm intake valves, both of which are of the correct 4.5mm valve stem and are made titanium. Hmmmmmm anyone have a clue what the correct valve lengths are?? I believe you can have the valve seats coated and run titanium valves. This would allow us to run big cams and high RPMs while needing less valve spring to do so. I want to look into this.

CandyRedRC46

So our Vfr has steel 29mm intake and 24.5mm exhaust valves. The 2010 zx10r has 24.5mm exhaust valves, and the 2008 gsxr750 has 29mm intake valves, both of which are of the correct 4.5mm valve stem and are made titanium. Hmmmmmm anyone have a clue what the correct valve lengths are?? I believe you can have the valve seats coated and run titanium valves. This would allow us to run big cams and high RPMs while needing less valve spring to do so. I want to look into this.

Oh nice. That might be even better.

As far as I am aware, you only need to change the valve seat for Ti valves to add to the cooling effect on the valve itself.

It has nothing to do with wear and Beryllium copper was the material of choice in racing engines with Ti valves.

If the motor is not being raced, then I'd have to ask the questions

1. Are Ti valves really necessary?

2. If Ti valves are used, what is the expected operational cycle for the engine? Is it going to be revved flat out for extended periods of time.

If the answer to 2 above is no, then you may as well not worry about the seat situation.

when I built my VF750 based superbike in the 80's, I ran Ti valves on the standard seats to 13k RPM with out issue.

These guys here specialise in Ti components for WSBK and other forms of motorsport.

http://www.titanium-valve.com/

They will make valves and seats/guide to whatever you want.

Speaking of guides.

Ti valves should be run in bronze guides to help dissipate the heat.

HighSideNZ

Hi Guys

The following shot is of my Gen5 head and the enlarged head gasket (74mm dia) to suit my 929 bore.

The standard valve head diameters are:

Inlet 29mm

Exhaust 24.5mm

Even with the 2mm bigger bore the valves are pretty close to being shrouded by the bores.

I think it will flow more with the 74mm bores than the 72mm as there is less interference.

[image: attachicon.gif]20140831_162643.jpg

Cheers

Phil

That's a great shot.

It does beg the question. Since the heads are off the cases, so that they cylinders can be enlarged, why not have the edges of the combustion chamber "laid back" to meet the new cylinder bore?

It would help the head's flow characteristics and add a few cc's to the chambers volume to help with the compression ratio...

Just some rough calculations.. Using the stock bore & stroke, the stock CR and calculating the compression volume.

Removing 1cc worth of metal from the chamber would drop the CR to 11.1

Does anyone know how the head gasket is??

Another thought,

While the heads are off, has anyone considered o-ringing the cylinders? Or are we all thinking of using the MLS gaskets from Cometic?

Yes, I did open the chambers up to match the new bores. Best not to shroud the valves if at all possible.

The opened up head gasket is 3.44cc in volume. (per cylinder)

My measured chamber volumes etc. have given a CR of 12.36 and with my cams a dynamic Cr of 11.04

Cheers

Phil

There's no more room for bigger valves , a little room for lift .

Good lookin combustion camber !

HighSideNZ

Yes, I did open the chambers up to match the new bores. Best not to shroud the valves if at all possible.

The opened up head gasket is 3.44cc in volume. (per cylinder)

My measured chamber volumes etc. have given a CR of 12.36 and with my cams a dynamic Cr of 11.04

Cheers

Phil

Phil, I'm try to vet my calculations, how thick was the head gasket after compression??

I'm coming up with .799 mm and a negligible cc gain in the Head's chamber...

I would say your calculation on thickness is correct.

The volume difference is based on going from 72mm to 74mm

Standard it is about 3.26cc with 3.44cc for the 74mm bore

I do not believe there is a need to go with bigger valves as even the HRC RC45's ran 29mm inlets and 24.5mm exhausts, same as stock VFR800

My calcs show that these sizes can pass enough gas to be able to support 170-180 HP

Phil

HighSideNZ

I would say your calculation on thickness is correct.

The volume difference is based on going from 72mm to 74mm

Standard it is about 3.26cc with 3.44cc for the 74mm bore

I do not believe there is a need to go with bigger valves as even the HRC RC45's ran 29mm inlets and 24.5mm exhausts, same as stock VFR800

My calcs show that these sizes can pass enough gas to be able to support 170-180 HP

Phil

Okay,

Did you cc the head to see how much your blending back the chamber periphery might have added?

It wouldn't take much to add a couple of cc's and they will drop the CR pretty fast.

I'd even bet a good de-shrouding and matching to the new bore would keep some of the bigger bore jobs from breaking 12:1.

You would be suprised as to how little the blending added to the chambers as the radius in the chamber is quite shallow.

I volumed all the chambers and piston crowns and ended up with the following.

Chamber = 14.4cc

Piston crown @ 3mm = 13.2cc

Gasket = 3.44cc

This ended up with a Working chamber volume of 18.14cc to 18.20cc across all 4 chambers

Check this out. While this would be totally unnecessary over kill on a stock vfr800, it would be a great idea for those wanting to do major over bores like 74 or 75mm. You could support the cylinders and then bore to 75mm, then oring the deck. This would allow for a huge overbore, while not compromising cylinder strength or head gasket sealing.

http://www.cylindersupportsystem.com/

http://www.b20vtec.com/forums/threads/808207-Proven-alternative-to-sleeves-CSS(cylinder-support-system)!!!

This is why you need more than one bike.....vfr does what it is made to do....get a used rc51

F6bguy

This is why you need more than one bike.....vfr does what it is made to do....get a used rc51

No

CandyRedRC46

Check this out. While this would be totally unnecessary over kill on a stock vfr800, it would be a great idea for those wanting to do major over bores like 74 or 75mm. You could support the cylinders and then bore to 75mm, then oring the deck. This would allow for a huge overbore, while not compromising cylinder strength or head gasket sealing.

http://www.cylindersupportsystem.com/

http://www.b20vtec.com/forums/threads/808207-Proven-alternative-to-sleeves-CSS(cylinder-support-system)!!!

Interesting... looks like he is familiar with Honda cars; someone would need to work with them to develop a VFR800 CNC file for our block. I think MrCarver was thinking big bore...

CandyRedRC46

F6bguy

This is why you need more than one bike.....vfr does what it is made to do....get a used rc51

No

Ditto :tongue: