Anyone Ever Rebored/overbored A 5/6Th Gen

As per title, not interested in comments unless you have actually done this & can tell me what the results were & what's required to get a suitable finish !

Thanks

your not going to find too many ppl have done this mod, the best place to start would be to talk to TTS performance over in the UK they could answer your questions far fast then the forum since they where doing them just a few years ago

Thanks Reaper, Managed to get a sensible answer from the CBR forums, they rebore the Honda MMC (Aluminium Ceramic) liners & Nikasil coat them with no problems ! Winter Big Bore project looming if I can afford it ! :)

Some VFR -V- CBR929 pistons, from 72 to 74mm = 825cc, 12.5/1 comp, more stomp everywhere !

[image: yg1j.jpg]

[image: 53rv.jpg]

[image: 84jo.jpg]

[image: k94a.jpg]

I talked to Superbike Mike down in south florida about doing this. His planned route involed going through a company called Millenium Technologies, He said they would strip the block down and submerge in a nitric acid solution that would remove the metal matrix liners. He said that would get you a 3mm over bore and then they would coat the cylinders with an aluminum-nickel-sil coating (that you mentioned already) that is so hard that it will literally break the tip off of a carbon steel knife if you tried scratching the coating. After the cylinders were done he would have JE pistons make a custom set of vfr800 75mm pistons for a resultant 848 cc displacement. He said this was all basic stuff and would not be a problem. He also strongly discouraged using strock pistons out of the cbrs as the valve reliefs on the top of the pistons would not be in an optimun location. He also advised against boring through the metal matrix liners.

Mohawk I recommend that you call these guys up and pick at their brains a little before making any big desicions.

Superbike Mike Engineering

2928 NW 17th Ter, Oakland Park, FL

Millenium Technologies

1 888 779 6885

http://www.mt-llc.com/

I believe Flyguyeddy was (past tense) working on the CBR929 pistons for the 4th gens. He had to do some machining to them and some work on the dome. So swapping pistons is not a straight forward job.

i believe the 929 piston is a lot closer to the vfr800 design tho.

CandyRedRC46

I talked to Superbike Mike down in south florida about doing this. His planned route involed going through a company called Millenium Technologies, He said they would strip the block down and submerge in a nitric acid solution that would remove the metal matrix liners. He said that would get you a 3mm over bore and then they would coat the cylinders with an aluminum-nickel-sil coating (that you mentioned already) that is so hard that it will literally break the tip off of a carbon steel knife if you tried scratching the coating. After the cylinders were done he would have JE pistons make a custom set of vfr800 75mm pistons for a resultant 848 cc displacement. He said this was all basic stuff and would not be a problem. He also strongly discouraged using strock pistons out of the cbrs as the valve reliefs on the top of the pistons would not be in an optimun location. He also advised against boring through the metal matrix liners.

Mohawk I recommend that you call these guys up and pick at their brains a little before making any big desicions. <snip>

Wow that is a ton of work for a 50cc bump. I love to tinker, but less than a 10% boost in displacement for all that? Yikes!

spinalator

Wow that is a ton of work for a 50cc bump. I love to tinker, but less than a 10% boost in displacement for all that? Yikes!

took the words right outta my mouth. and dont forget to add after it is all done and your wallet is smaller that a singularity, you are completely in the unknown.

There's not a lot of room in the VFR800s engine to hog it out.

You're not gonna get 1000cc's nope.

spinalator

Wow that is a ton of work for a 50cc bump. I love to tinker, but less than a 10% boost in displacement for all that? Yikes!

Not sure which book is really correct (I didn't go through the math to figure it out), but the 5th gen book says the engine is technically a 781cc and the 6th gen book says it is a 782cc, so you would get a little more than just 50cc's. Still less than 10% though as you pointed out.

Hi CandyRed, thanks for the info, but the guys in lala land. The MMC is made from the same grade alloy as the upper crankcase, so immersing it in acid, would erode the whole crankcase ! So no thanks to that one. I have it on good authority from an RC45 tuner that the MMC can be bored like any iron liner, but needs a diamond hone like Nikasil.

Regarding the cc to bang ratio, the whole is worth more than the sum of its parts. VFR750 4th gens make an average 90rwhp, but bored to 837cc (+87cc) they put out 133rwhp (+43hp or 47%) . If we look at the percentage ratios for this, it's a 11.6% cc increase, so 750/90=8.33cc per hp, so 87/8.33=10.4 extra HP, but the 837cc makes 47% more power ! This is achieved with NO other tuning !

So taking the 800 (actual is 782cc) to 74mm bore = 825cc is +43cc (5.5%), or to 75mm bore = 848cc is +66cc (8.44%). So if we assume that similar gains to the 750 would be seen on a bigger 800, then using the same 47% power increase for the 750 & extrapolating it to the 800 with a base 95hp, would be as follows;-

750+87cc=837cc=+47% hp =133rwhp

782+43cc=825cc (87/43)= +23% hp = 117hp

782+66cc=848cc (87/66)= +35% hp = 128hp

Or based on my existing tune of 107rwhp & using the same percentages above, then I'd expect to see 825cc=130hp or 848cc=140hp. Now that would be impressive :)

I have a few tweeks planned for the existing tune to bring it up towards 120hp. If I could pull that off then those tuned figures should certainly be attainable.

All hypothetical until I actually cut metal, roll on the winter :)

I say do it and be sure to include dyno graphs and costs once your project is complete. :fing02:

I always love seeing someone boldly going where all the nay sayers have never gone before. Your bike. Your rules. :biggrin:

according to the factory service manual oversize pistons are available it lists two sizes 0.25mm over and 0.50 over I wonder what the 0.50 would bring the 800 up to oh this is in the 800 6th gen manual

Mohawk

<snip>

Or based on my existing tune of 107rwhp & using the same percentages above, then I'd expect to see 825cc=130hp or 848cc=140hp. Now that would be impressive :)

I have a few tweeks planned for the existing tune to bring it up towards 120hp. If I could pull that off then those tuned figures should certainly be attainable.

All hypothetical until I actually cut metal, roll on the winter :)

That would be impressive and makes more sense. Keep us posted!

What happened with this?.

Has anyone tried this?

Can the heads on a 5th gen have larger valves. If so off what?.

I know you can"t shave the heads so how did honda get 160 odd hp out of the rc45?.

I am pretty sure that the valve sizes on the vfr's are way beyond more than adequate.

From everything that I have read so far, the vfr800's have the same size valves as the rc45, the 929 and the 954.

I would put big money on all the power being held back by the tiny 36mm throttle-bodies/(and even smaller velocity stacks), the mild camshaft specs and the puny exhaust header primaries.

These are the main differences in the rc46 versus rc45. (besides redline and 360 degree crank)

snake

according to the factory service manual oversize pistons are available it lists two sizes 0.25mm over and 0.50 over I wonder what the 0.50 would bring the 800 up to oh this is in the 800 6th gen manual

792cc with .5mm overbore.

Adammac

What happened with this?.

Has anyone tried this?

Can the heads on a 5th gen have larger valves. If so off what?.

I know you can"t shave the heads so how did honda get 160 odd hp out of the rc45?.

Still in the tech discussion phase, as I'm working away from home permanently at the moment, so can't actually do any work, but I did just get another 3 x 75mm CBR954 pistons to go with the 4 x CBR929 ones I have :) That gives me options. I'll probably get another set of crank cases to experiment with on the boring/honing side !

No need for larger valves, the RC45 used these sizes & never ran into breathing problems. Even HRC's head porting only takes a tiny amount out of the ports.

They got 160+hp by revving the engine to 14,500rpm+, They used larger throttle bodies & longer duration cams & high comp pistons to boost the power in the high RPM's, my VFR makes more torque/power than a lightly tuned RC45 everywhere up to 10K/rpm, when the 45 steals ahead & revs out to 13,500rpm !

242 revolutions per second is really quite fast. I have difficulty counting that fast in one second. :goofy:

Right who will do the re-boring?

I have made some inquires here in Australia and they say it can't be done?.

I would also like to know as what to do about the throttle bodies.

Can you bore them out?.

Cbr 600 2010 have 40ml . Can you cut them? do they fit?

Bigger bore more air /fuel more power.

Quiet interested as i wish to create more hp for the bike Honda wont make!!!.

I've just found a workshop that will take on the boring of my 5th Gen case to 74mm dia for fitting CBR929 pistons.

They are quite happy in doing this, just the set up cost will be higher due to the unequal angles from the crankcase faces to the cylinder bores.

Just waiting on my pistons to arrive and it will all be off to the boring bar.

I'll keep everyone posted as to progress.

Cheers

Phil

HighSideNZ

I've just found a workshop that will take on the boring of my 5th Gen case to 74mm dia for fitting CBR929 pistons.

They are quite happy in doing this, just the set up cost will be higher due to the unequal angles from the crankcase faces to the cylinder bores.

Just waiting on my pistons to arrive and it will all be off to the boring bar.

I'll keep everyone posted as to progress.

Cheers

Phil

Sweet!!! Honda manual states the liner can be machined as long as temperature is controlled...

:cheerleader: :cheerleader:

:lurk:

When I contacted APE in the US they stated they could bore it out also...

Wasn't there a kit from Dynamo Hum or something?

Not to say there still is one being made. :unsure:

Got a spot that gets me hot, but you ain't been to it. :goofy:

-Yes there was.

-No there isn't.

-I don't wanna know.

But, the spot... That's my scantily clad backup singers line.

In case that changes your mind. :sleep:

Dynamo Humm is defunct and there's - so far - been no sharing of the ip that Brian Law had/has regarding big bore VFRs. However, people are still chasing this elsewhere and some good leads are emerging.

I did get the info from Brian, posted in another thread. No rocket science involved. They bored out the MMC & inserted a 2mm steel liner & fitted 76mm JE pistons for a nominal 870cc, more torque everywhere but the HP figures we're let down by lack of other tuning to increase the breathing at speed & the fact that the JE pistons were heavier than stock, so could not benefit from high revs.

I contacted TTS in the UK re the big bore kits that they used to offer and this is what I got backup.

Hi, we can still supply the VFR800 bore kit, these are made for us by JE & take the capacity out to 837cc with a comp ratio of 13:1, cost for the pistons £500, the cylinder will need to be bored & re-plated cost for this process £600, plus shipping back to NZ ?? cost for the shipping £100, we have aproxx a 4 week turn round on these kits & plating.

regards

Paul

Paul Bembridge
TTS Performance
Unit 3 West End Farm
Silverstone
Northamptonshire
NN12 8UY
ENGLAND

TEL: +44 (0)1327 858212
FAX: +44 (0)1327 858099

www.TTS-Performance.co.uk
www.RotrexSuperchargers.co.uk

Was a bit pricey for me as 1200 UK pound is close to $2400 NZD

Hence why I'm going with the CBR929 and a local borer.

Phil

I spoke to them too. They send the top case to the USA, to be bored & nikasil plated. No way they have a 4 week turn around, be lucky to get it in 4 months !

The crankcase is currently being bored and I should have it back by the end of the week.

Had to supply the machine shop with the crankcase main bearing bolts so as they could fit the case to their jig, These bolts are M9 thread, yep that is right M9

In all my years I've never seen a M9 bolt.

I'll update the thread once I've got the cases back.

pics when you can?

Yes, pics please... and are you having the bore plated with Nikasil? If not, what kind of a finish are they putting on the MMC?

My understanding is that there is no need to plate the MMC as once honed it works just like cast iron liners.

Hence why they offer 0.25 and 0.5mm oversize pistons as spares.

I'll post pics once ive got all the bits back.

HighSideNZ

My understanding is that there is no need to plate the MMC as once honed it works just like cast iron liners.

Hence why they offer 0.25 and 0.5mm oversize pistons as spares.

I'll post pics once ive got all the bits back.

Does the MMC liner need a cross-hatched finish for the rings to seat like a steel bore does?

Yep, the bore needs to be honed to the required size and finish just like a cast iron liner.

The standard bores had a good 45 deg cross hatching and were in really good shape.

I felt quite bad about boring them out. LOL

The only time I think you need to Nikasil plate the bores is if you go the whole hog and bore the complete MMC liner out as what happened with the big big bore kits.

Looks like we got another Burt Munro here............ :goofy:

Or John Britten? :wink:

Ciao,

Not in either of those gents league and I'm an Ozzie living in NZ.

I've had some experience with V4's in the past building a 880cc Superbike back in the '80's. See below.

[image: post-25941-0-79947800-1407366189.jpg]

[image: post-25941-0-44017000-1407366214.jpg]

[image: post-25941-0-38451900-1407366230.jpg]

^ Awesome!

You 'Da Man!!!!

Nicely done HighSide!

Now I know who to call ;)

GREAT article, thanks so much for posting. I love reading all the stuff that has been done to these bikes.

BTW Burt Munro is still breaking records!

http://www.motorcycle-usa.com/321/18966/Motorcycle-Article/Burt-Munro-Breaks-Record-36-Years-After-Death.aspx

Cool story about Burt.

Glad to see he is still in the head lines.

Just been talking to the machine shop that is doing the bore and hone.

Bore all completed and no issues but they have just checked with the honing equipment suppliers and it seems that the MMC used by Honda is different to what Porsche/BMW etc. use and that is what the shop thought it would be.

There may be a different process to hone the sleeves for our stuff as the liners are not the normal aluminium/silica so they probably cannot use the standard lapping process that removes the aluminium and exposes the silica.

Being sintered, it might be a diamond hone.

Should know tomorrow what the progress/process is.

Very sweet project, were you the rider or mechanic ? And did it ultimately produce any success ? First I've heard of that bike.

Are you boring the MMC to 74mm for the 929 pistons ? Looks like I got beat to it ;) Good man.

No, I'm the mechanic.

Ran 2 strokes before this with TZ350's, TZ500's and RG500's.

Success was an issue. Ran out of money, no sponsors, and then had a cam gear failure that destroyed one head.

That pretty much put paid to it as we couldn't afford to repair it.

Yep boring the MMC to 74mm

Using the 929 pistons same as you were looking at doing.

I need to say that this thread is becoming fucking awesome.

My Vfr has about 160,000 ks on it, when it goes, hopefully I'll be able to ride your coat tails and go big bore.

Guys

I've finished the balancing of my rods and pistons and they are soooo close it doesn't matter.

See shots below:

I've also included a couple of shots outlining the difference in mass of the original 800 piston and what I've been able to get the 929 ones down to without too much issue. I'm still about 0.5g heavier but that is well within the realms of balance factor on the crank and with forged pistons, can't see they are going to break any time soon, when compared to the cast VFR pistons.

One thing I did find interesting was the 929 rods that came with the pistons were majorly different in balance than the VFR stuff. I find this amusing seeing the 929 revs higher than the VFR and was designed as a "sports" bike.

[image: post-25941-0-60203500-1408064881.jpg]

[image: post-25941-0-92823000-1408064889.jpg]

[image: post-25941-0-94394400-1408064897.jpg]

[image: post-25941-0-71531000-1408064905.jpg]

[image: post-25941-0-53448000-1408064913.jpg]

[image: post-25941-0-82205100-1408064920.jpg]

[image: post-25941-0-51243800-1408064928.jpg]

[image: post-25941-0-27225400-1408064936.jpg]

These are the piston shots

[image: post-25941-0-34054300-1408064944.jpg]

Stock VFR piston

[image: post-25941-0-64193600-1408064952.jpg]

Modified 929 piston

Bored crankcases

[image: post-25941-0-66494200-1408065159.jpg]

[image: post-25941-0-48859400-1408065169.jpg]

I'll keep you posted on progress.

Just doing the head gasket mods at present and going to check valve reliefs in the pistons.

Cheers

Phil

Nice!

Excellent!!!

Where did you take the weight off on the 929 pistons?

Shortened the skirts to the same length as the VFR ones and then took weight out under the crowns, above the gudgeon bosses and the gudgeon webs across to the skirts.

I'll see if I can get a photo or two of the pistons and post.

Great job Phil!

Thanks for posting up the info.

Looking very good :) Did you check the piston valve/head clearances before removing the stock pistons ? Something I need to do, the 929 piston crown is .2mm higher than the VFR's. How long do you think it will take you to reassemble the motor ?

One thing, where did you get the cases bored, engine or engineering shop as I'm having trouble finding somewhere to do mine :(

Here are some shots of the underside of the 929 pistons after I attacked them.

[image: post-25941-0-37808800-1408088970.jpg]

[image: post-25941-0-47553300-1408088979.jpg]

[image: post-25941-0-35946300-1408088988.jpg]

[image: post-25941-0-22255500-1408088997.jpg]

When I removed metal from under the crown, it was more from the radius behind the oil ring and also to add a large radius above the gudgeon pin bosses. Basically undercutting the web similar to how a cast piston is cored, or a wiseco is machined. The bottom of the gudgeon bosses have a machined boss that stands proud and is used for balancing. I ground those down and blended them in to the rest of the boss.

I didn't check the valve pockets before I had the cases bored I'm going to do it now with plasticine as I need to check anyway. Looking for 2mm clearances all round.

I had the boring done by an automotive reconditioners who do a lot of race car engine building and had a good reputation.

Sorry, I missed one question. The 0.2mm difference in deck height shouldn't be a problem. When I dissembled the motor, I did notice that the existing crown was pretty much flush with the top of the liner. The gasket is reasonably thick, haven't measured it at present, but as I've opened the new gaskets up to suit the 74mm bore any increase will fit within that space.

I'll know more in a day or so as I'm going to trial assemble with plasticine on the crowns so I'll see how much clearance I have all over.

I'm still waiting on some parts, rings, bearings, pins etc. before I can do the final build.

I'll use the old bearings to do the trial build.

Cheers

Phil

Excellent work Phil & thanks for the info. I started modding the 929 pistons by removing the thin bottom of the skirts making them level with the flats on the bosses & was thinking of using 954 gudgeon pins, as they are shorter & have a wider inside diameter & are thus are 9grams lighter than 929 ones. I was going to use alloy rings to center the pin in the piston. It doesn't lose much piston support.

I just went & measured these parts distances & weights as follows;

Item------------929-----------954

Pin Weight, 52 --- 43 grams

Distance between Piston bearing bosses, 21mm --- 20mm

Piston Boss bearing length, 14mm --- 12mm (this is how much pin is in each boss bearing)

So the 954 pin will give 11.5mm of bearing surface in the boss each side of the piston. Strangely, this pin in a standard 929 piston is almost exactly the same weight as a standard VFR piston ! for obvious reasons you need to keep these centered hence the alloy rings mentioned above !

Bit late for you, but should help others if they follow along !

How are you modifying the head gaskets to fit ? as in what tools ?

Phil, any idea on how much money you have spent so far ?

Switchblade

Phil, any idea on how much money you have spent so far ?

Boo....Hisss...Party Pooper... :tongue:

Not sure about Phil, but this is not expensive if you spanner yourself. That said I've spent the following (UK pounds) so far in my research;-

£75 Spare engine (was cheaper than a set of cams, was from a heavily crashed bike, so lost right side case & a few bits)

£30 4 x 929 pistons complete (secondhand)

£22 4 x 954 pistons complete (secondhand ex race bike, bit worn)

£25 1 x VFR800Fi Top Crankcase (to research the MMC liners)

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

Total £152, plus many hours reading. And I haven't even started yet. But by sharing the info, it has I hope helped Phil get on with it.

So if you just bought the 929 pistons & a full gasket set (circa £200 here) & do the spannering yourself, with a known good engine, so no need to replace bearing unless your found wear. then its more time & space to do it, plus paying for the boring of the cylinders. Total less than £500 (US$800ish)

Lets see how Phil's turns out on the dyno. Shall we start a sweepstake for the HP & Torque figures ????

So what will a VFR825 put out ?

Standard they put out around 95rwhp & about 54ft/lb torque, don't know what other mods Phil has in his, maybe he'll let us know before the guessing starts.

A basic CC/HP calc gives 8.22cc per HP, so in simple theory that should add 5HP, but that excludes torque. A simple torque calc says the CC increase should add 3ft/lb so 54 becomes 57, well my 57.5ft/lb motor kicks out 107HP. So increased compression will increase the torque more than the base calculation, I'd expect circa 59ft/lb, so at peak rpm (~10,500rpm) that should kick out around 110HP ! With some tuning & other parts could be higher :)

I used a trusty old die grinder with 25mm pferd drum sander sleeves to enlarge the head gaskets.

Did my old ones first, just to make sure it would work, and then laid the old over the new and scribed the circles to grind to.

Fitted them onto the case with the dowels and worked from there.

At this point in time I haven't costed it all up/out as I don't want to scare myself.

So far the most expensive part is getting the cams built up and profiled. Going to be close to $2k NZD to do this by itself.

Again, I'm using second hand 929 pistons so they were $75 USD but I'm doing new bearings/rings/gudgeon pins and a full gasket kit whilst it is all down.

All the main expensive bits are second hand and the motor complete, in really good condition was $900 NZD.

I'm aiming for 120/125 rwhp when completed and I feel that is achievable.

Time will tell.

The 929 gudgeon pins are about 1g heavier than the VFR pins.

With some grinding inside the taper, I'm hoping to remove about 3-4g and that should offset the difference in ring set mass.

Bugger, wish I had of known about the 954 pins.

Would have saved a but of work.

Cheers

Phil

cast iron liners wear fast, I used to run cr250's naksil bore, no cylinder wear for years, cr500 (cast iron) would require rebore every 2 years, a very significant difference in bore wear.

These aren't cast iron they are MMC (Metal Matrix Composite) and believe me they don't wear.

Just hard to find someone to bore and hone them.

Women and family... Don't they understand a guys bike and the shed project come well up the priority list than moving a daughter out of home to her own place... LOL

Just got back on to subject.

Mohawk, well you are right regarding the piston deck height.

Wrapped an old VFR piston with insulation tape to fit the new bore and re-assembled No1 and No3 side by side.

Did some measuring and I need to do some machining on the piston crowns.

I'll post some marked up photos later but the guts of it is.

VFR piston

Between the pair of inlet valves the piston deck is 0.2mm below the liner top at TDC.

This is the same for the exhaust side as well.

Across the piston, inline with the pin, the deck is 0.7mm above the liner top at TDC and has a 2x45deg chamfer on the edge.

929 piston

The full area of the crown is 0.9mm above the liner top at TDC.

I will need to get 0.2mm taken off all over and then reduce the front and rear sections between the valves to the liner top or slightly lower.

As I said, I'll post some marked up photos as it is hard to explain in just words.

It's brought proceedings to a stop as I'll need to find someone to do the machining.

Damn, I wish I had a lathe and mill.

Phil

The daughter's bedroom can now be upgraded to bike spare part storeroom no? ;-)

Wife has dibs on it first so looks like I'm still relegated to the garage. LOL

OK, as promised, here are the marked up photos of the pistons with the relevant measurements.

VFR piston

[image: post-25941-0-49818700-1408171775.jpg]

929 piston

[image: post-25941-0-71405100-1408171762.jpg]

Sorry, you will probably need to download the images to easily read the comments.

Cheers

Phil

I've just drawn up the mods for the 929 pistons and the attached PDF file outlines them.

Shouldn't be too hard to get done but it is turning the overall crown, putting a 2 x 45 deg chamfer all over, and then milling the pads 1mm lower.

929 piston mods.pdf

Now to find someone to do the work.

Phil, have you tried it with an old head gasket & the head with some plasticene or plastigage, to check the old piston clearances ? Without bolting it down first, if the head lifts, then you know its too tight, if not then the gauge will tell what clearances are there.

I see you have had cams done. I had a set reprofiled for more duration which added 5HP. They are standard lift, which measured by the cam co was 8.2mm inlet & 8mm exhaust. I didn't get round to checking the piston valve clearance properly, but I did put one piece of electrical tape on a piston & put a head on with NO head gasket & the motor turned over. Then at TDC I turned both cams manually & they just contacted the tape, so I estimate about 1mm clearance at TDC.

Get with the grinder man to skim those piston, Bert Munro style ;)

Keep up the good work.

The old head gasket measures 0.96mm so I'd say a nominal 1mm is what they were designed at.

Can't see the piston clearing at that thickness and when you take rod stretch/bearing float in to account she is going to hit.

Nothing for it I think, but I'll plasticine it and see what is there now.

OK

Took to the pistons with my linisher and have pretty much got the clearances needed without much work.

Just going to plastigage the squish area now and make sure there is enough there.

One side benefit is that it's pulled another 2g off the piston mass and I now have a much better finished piston crown.

Here are some shots of the roughed out piston crowns after linishing then down and stepping the areas between the valve pockets.

I still need to finalise each of them individually as the "eye-micrometer" let me down a bit in the areas between the valve pockets.

It is time consuming as there is no way of measuring them than to assemble them back in to the block.

[image: post-25941-0-34458100-1408260399.jpg]

[image: post-25941-0-71136800-1408260408.jpg]

[image: post-25941-0-29005200-1408260419.jpg]

I'll add more shots once I've finished them off but I can't checks the final valve pocket clearances until I get the reprofiled cams back from the grinders, which looks like it may be a couple more weeks.

Cheers

Phil

Wow, looking good, Bert would be proud :)

Couple of Q's did you take a pressure reading off the cylinders before the strip down ? Just so you can compare the compression ratio ?

I take it from the cams comment that you don't have a spare set ? So can't check the standard clearances.

What spec have you gone to on the cams ? I did the following;-

VFR800 98-01 5th Gen cam timings all at 1mm lift are as follows;-

VFR800 STD

IN open 10BTDC Close 35ABDC Lift 8.2mm measured, Duration 225.

EX open 35BBDC Close 10ATDC Lift 8mm measured, Duration 225.

RC45 STD for comparison

IN open 15BTDC Close 40ABDC Lift 8mm claimed, Duration 235.

EX open 45BBDC Close 10ATDC Lift 8mm claimed, Duration 235.

RC45 HRC Race cams

IN open 23BTDC Close 52ABDC Lift 9.5mm claimed, Duration 255.

EX open 50BBDC Close 20ATDC Lift 8.3mm claimed, Duration 250.

See here. http://www.vfrdiscussion.com/forum/index.php/topic/53905-rc45-vs-5th-gen-vfr-engine/

My Modified VFR800 ones

IN open 15BTDC Close 45ABDC Lift 8.2mm measured, Duration 240.

EX open 45BBDC Close 10ATDC Lift 8mm measured, Duration 235.

Looking good ;)

Awesome info!!!

I can't wait for all this stuff to start coming together.

Mohawk I think the duration on the rc45 race cams is supposed to be 255 in and 250 ex.

Thanks , just curious

Mohawk

Not sure about Phil, but this is not expensive if you spanner yourself. That said I've spent the following (UK pounds) so far in my research;-

£75 Spare engine (was cheaper than a set of cams, was from a heavily crashed bike, so lost right side case & a few bits)

£30 4 x 929 pistons complete (secondhand)

£22 4 x 954 pistons complete (secondhand ex race bike, bit worn)

£25 1 x VFR800Fi Top Crankcase (to research the MMC liners)

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

Total £152, plus many hours reading. And I haven't even started yet. But by sharing the info, it has I hope helped Phil get on with it.

So if you just bought the 929 pistons & a full gasket set (circa £200 here) & do the spannering yourself, with a known good engine, so no need to replace bearing unless your found wear. then its more time & space to do it, plus paying for the boring of the cylinders. Total less than £500 (US$800ish)

Lets see how Phil's turns out on the dyno. Shall we start a sweepstake for the HP & Torque figures ????

So what will a VFR825 put out ?

Standard they put out around 95rwhp & about 54ft/lb torque, don't know what other mods Phil has in his, maybe he'll let us know before the guessing starts.

A basic CC/HP calc gives 8.22cc per HP, so in simple theory that should add 5HP, but that excludes torque. A simple torque calc says the CC increase should add 3ft/lb so 54 becomes 57, well my 57.5ft/lb motor kicks out 107HP. So increased compression will increase the torque more than the base calculation, I'd expect circa 59ft/lb, so at peak rpm (~10,500rpm) that should kick out around 110HP ! With some tuning & other parts could be higher :)

HighSideNZ

I used a trusty old die grinder with 25mm pferd drum sander sleeves to enlarge the head gaskets.

Did my old ones first, just to make sure it would work, and then laid the old over the new and scribed the circles to grind to.

Fitted them onto the case with the dowels and worked from there.

At this point in time I haven't costed it all up/out as I don't want to scare myself.

So far the most expensive part is getting the cams built up and profiled. Going to be close to $2k NZD to do this by itself.

Again, I'm using second hand 929 pistons so they were $75 USD but I'm doing new bearings/rings/gudgeon pins and a full gasket kit whilst it is all down.

All the main expensive bits are second hand and the motor complete, in really good condition was $900 NZD.

I'm aiming for 120/125 rwhp when completed and I feel that is achievable.

Time will tell.

The 929 gudgeon pins are about 1g heavier than the VFR pins.

With some grinding inside the taper, I'm hoping to remove about 3-4g and that should offset the difference in ring set mass.

Bugger, wish I had of known about the 954 pins.

Would have saved a but of work.

Cheers

Phil

Also I don't know if you guys are aware or not, but I have read that metal matrix liners are not compatible with forged pistons, the pistons will have to be coated with a compatible coating for example nikasil etc before use.

CR don't know where you got that info, but it's bogus, ALL Hondas since The RC45 have used mostly MMC liners, including the CBR9929/953 & the VFR800 (all models). It's NOT the means of manufacture, which are CAST =VFR800 or FORGED =CBR's, but the material the piston is made from, as in what alloy composition. The Honda Forged pistons for use in MMC liners are solid lube coated on the piston skirts to reduce friction during break in. As both VFR & CBR use MMC liners, then the pistons are compatible.

PS corrected the HRC cam durations, sorry pasted that in a hurry :(

I got that info from Honda automotive research. The Honda k series block is aluminum with iron sleeves, forged aftermarket pistons are manufactured with no additional coatings needed. On the other hand, the Honda f22 from the s2000 has the mmc liners like our bikes, forged aftermarket pistons for those engines are supplied by fewer companies and more costly, as they require a secondary manufacturing process of the coating.

Now with that being said, if the 929 has mmc liners then it's pistons should be safe with our engines as well, but this would lead me to believe that the 929 pistons are coated to allow them to be forged with out damaging the liners.

If you look on the Honda prelude and s2000 forums there is tons of info on frm and mmc liners with regard to forged pistons.

http://www.preludezone.com/naturally-aspirated/25642-honda-tuning-lets-talk-frm.html

But yeah maybe you're right and it's more about material make up than the coating. I'm not sure. I just wanted to make sure that you had looked into it first :)

Yeah but you re talking about "after market" which are NORMALLY raw alloy finish for use in Iron/Steel liners. The real issue is that Iron/Steel liner expand at a slower rate & not as much as an MMC or Alloy with Nikasil, so the clearances between the fresh bore & piston are critical. Thus the piston has to be designed to work with an MMC or Alloy-Nikasil liner, this means its cold edge clearances will be at perfect tolerance when the engine reaches normal operating temp.

If designed for MMC then they only require the skirts coating with solid lube compounds to protect them during run in. I have a few 954ex race bike pistons & 929 road bike ones that have the lube compound worn off & NO sign of pickup on the skirts. None had any compound between the ring lands & if the piston is matched to the bore correctly, they will not pickup or seize.

That is the basic problem, plus a bunch of idiots on car forums that don't do any research & then spout rubbish as fact :) But that's car modders the world over.

Also, just to add 2 cents worth, the early Preludes used the first gen MMC liners and they had lots of issue with them.

As far as I understand, what we are playing with is the later gen MMC and all the bugs have been ironed out.

I agree with Mohawk, as far as I can see the CBR range ALL use MMC with the forged pistons.

The VFR uses cast pistons just for a cost saving situauion.

Mohawk, I couldn't get cranking pressures on the motor before I stripped it as it was in no state to be turned over so it will be a surprise when i fire it up I suppose.

I'm running the same cam timing as yours. I was going to go with the standard RC45, but after you posted your specs and outlined what you had achieved, I thought yours would be the way to go.

Time will tell, once I've got the cams back.

I'm hoping to strip the pistons out tonight and finish the squish areas off with 1mm clearance from the top of the crowns. This will bring them inline with the standard pistons.

When I linished the pistons down I ended up putting a pin in an old piston and measuring from the underside of the pin to the crown and then doing the same on the 929 pistons.

All of them now measure the same as standard. 31.77mm

If I can get all the squish areas the same I can then burette the combustion chambers and match them all up.

That should be the end of the piston work until I can check valve to piston clearances.

Phil

Question for you Mohawk

The shop doing my cams has had to remove the welsh plugs from the ends of the cams.

I take it your guys had to do the same thing?

What did you use to replace the plugs?

Cheers

Phil

Hi Phil, They were removed and new ones fitted I believe, I had mine done a a bike cam center, Piper Cams, so they have spares for this, they are a tight friction press fit, the oil pressure in the cams is not high.

Thanks for that.

Don't have the options down here in NZ.

I was thinking of getting some aluminium bungs turned up and press fit & loctite them in.

Did that with my VF750 back in the 80's

Yeah that should work, alloy will expand quicker with heat so should stay the course.

Did you strip the anti-lash gears off before sending the cams to be ground ? I did, just as well as they would collect grind, pain in the butt to put back on.

That is what I was thinking with aluminium. higher CoE so should stay in place, especially with some loctitie bearing mount on them.

No I left mine on but I will need to strip them off to clean.

How much of a pain in the butt are you talking?

Also, are the actual drive gears splined on to the cams?

I take it you are pretty much fixed as far as degreeing the cams goes.

What they grind is what you get!

Got the piston crowns completed last night. It removed another 1g in mass so the bare piston is down to 175.5/176.0 type mass now.

With the 929 pins being 1g heavier and the ring set being about 1g heavier as well, the total mass is now pretty much exactly what the standard VFR assemblies were.

Balance factor should not be altered at all, and with me getting the rods as close as I have it should be nice and smooth.

They are a pain to re-assemble because the pin the locates the spring keeps shooting out just as it's about to snick home. Make sure you do it somewhere tidy so you can find the pin.

The gears are standard press fit, so you can adjust them, but it's a real pain & true accuracy is very hard to get, but it can be done. You are obviously limited in the number of attempts !

Thanks for that.

Shame they didn't spline them with say 1 more tooth in the spline compared to the number of teeth on the gear.

You could then use it like a vernier. May not be degree by degree, but a lot easier than pressing them off and back on

Well progress is still happening.

Just sent all the cases off to be vapour blasted so they should come back looking like new.

Still waiting on the cams so can't do anything else until I've got them and the cases, plus bearing and new rod bolts etc.

Next job is to clean up the throttle bodies and fit the R6 trumpets to the air box bottom.

I'll post again once I've got some bits and start the assembly process.

Cheers

Phil

Keep at it Phil, we are all rooting for this ;)

^^^^^ + 1/0

Well just heard from the cam grinders.

They are now going to have to build up and regrind the centre journals on the cams as they have distorted during the refacing process.

Another cost I didn't want or expect!

It probably would have been cheaper and quicker to send the cams to Pipers in the UK than for these people to stuff around with them.

To say I'm annoyed is an understatement.

HighSideNZ

Well just heard from the cam grinders.

They are now going to have to build up and regrind the centre journals on the cams as they have distorted during the refacing process.

Another cost I didn't want or expect!

It probably would have been cheaper and quicker to send the cams to Pipers in the UK than for these people to stuff around with them.

To say I'm annoyed is an understatement.

why are YOU paying more to fix their mistake??? they screwed up.. THEY fix it end of story!!

if they dont.. remind them the world is a VERY SMALL PLACE now thanks to the internet!

say you dont want to post bad reviews all over links that they have..

Holy crapola, they must have screwed it up big time. Hope they sort it out ASAP. We feel for you :(

Hey, NZ is a small country and suppliers are hard to find.

I've already had to pay a 50% deposit for the cam reprofile, so if I didn't go them halves on their f$#k up they would have sent the cams back as is.

I feel it is the best of a bad situation.

All I want to do is get my gear back in a usable state.

I'll have my revenge after the fact. I know enough people in the bike racing scene so a few choice works in the right ears will do what I want.

Payback is a bitch..... :-)

Hi guys

Just got back in to the build and have burretted the chambers and an assembled piston/head assembly.

The front head measures 14.4cc and 14.3cc for the chambers

The back head are both 14.0cc

The assembled unit measures 16.0cc on #1 (14.0cc chamber)

From my calcs, this is going really high in CR with a static CR of 13.89:1

This would give me a dynamic CR of 12.39:1 (inlet closes 45 deg ABDC)

I feel I'm going to have to open the chambers up to say 15.5cc (this would be a measured 17.5cc assembled)

With this size I'll end up with a static of 12.78:1 and a dynamic of 11.41:1

Anyone got any thoughts? Trying to keep the bike trackable on the road.

Cheers

Phil

Further to the above.

I cannot open the chambers up to 15.5cc and after balancing all chambers to 14.4cc it looks like I'm stuck with that.

From my calcs, I get the following:

Chamber volume = 14.4cc

Gasket volume = 3.44cc

Piston volume (including gasket) = 2.2cc (piston has a negative impact as it is higher than crankcase surface)

So with a swept volume of 206.4cc (74mm bore x 48mm stroke)

Working chamber volume = 16.6cc

Static CR = 13.4:1

Dynamic CR (45deg ABDC inlet close) = 11.98:1

Looks like it will need to run on 98 octane, but it should make some power. Here's hoping. Maybe 95 at a pinch.

Working back from what I've measured today, the standard CR for a Gen5/6 VFR doesn't seem correct at 11.6:1, unless they are talking dynamic and even then it is low.

From my calcs, the standard static CR is 12.77:1 based on a 14.4cc chamber. Dynamic would be 11.96:1 (35deg ABDC close)

So from this, I'd have to say I'm in the ball park.

are you going to dyno it when you get it running

HighSideNZ

Further to the above.

I cannot open the chambers up to 15.5cc and after balancing all chambers to 14.4cc it looks like I'm stuck with that.

From my calcs, I get the following:

Chamber volume = 14.4cc

Gasket volume = 3.44cc

Piston volume (including gasket) = 2.2cc (piston has a negative impact as it is higher than crankcase surface)

So with a swept volume of 206.4cc (74mm bore x 48mm stroke)

Working chamber volume = 16.6cc

Static CR = 13.4:1

Dynamic CR (45deg ABDC inlet close) = 11.98:1

Looks like it will need to run on 98 octane, but it should make some power. Here's hoping. Maybe 95 at a pinch.

Working back from what I've measured today, the standard CR for a Gen5/6 VFR doesn't seem correct at 11.6:1, unless they are talking dynamic and even then it is low.

From my calcs, the standard static CR is 12.77:1 based on a 14.4cc chamber. Dynamic would be 11.96:1 (35deg ABDC close)

So from this, I'd have to say I'm in the ball park.

Dude,

Glad to hear you are making progress. I'm traveling for work so I don't have my spreadsheets to confirm the calcs... I do know that measured working combustion chamber volume is like 1.8 cc less than calculated.

Pictures?!?!

Hi Phil, Hmmm interesting. I calculated std at 18.4cc assuming the 11.6-1 claimed was true. Dynamic was 10.98 iirc.

I'd go with the principle that you know it worked regardless before, so you know how much you have added, so can do some basic calculations.

Remember that cam timing is NOT the same both ways, that's why I asked if you had done a cylinder pressure test. The 235 degrees is at 1mm lift, so you still lose some stroke before the cylinder is sealed, except at peak torque where you would expect a higher compression ratio, as cylinder filling is generally better than 100% at that point ! Likewise engine load has a serious impact on how the compression ratio reacts, as in high load high gear can produce pinking, but a lower gear freer revving engine wouldn't ! Should be good to go.

Hi Mohawk

Yes, I did the same, taking the advertised CR at 11.6 as being correct. Extrapolating that out with the increased swept volume I got 11.9:1 static CR.

But, I'd have to say that the chamber volumes I've measured are as I stated, 14.4cc. Did the measurement many times as I balanced out the 4 chambers.

Using these:

Chamber volume

[image: post-25941-0-88128300-1409905598.jpg]

Burette

[image: post-25941-0-03113100-1409905607.jpg]

Spark plug hole adaptor (5.8cc volume)

[image: post-25941-0-20774200-1409905616.jpg]

The standard head gasket thickness is 0.8mm which gives a volume at 72mm of 3.26cc and at 74mm of 3.44cc

When I measured the installed chamber volume, I sealed the piston in the bore with grease, dialed the piston to TDC and greased both sides of the old head gasket, then screwed the head down.

Then I fitted the spark plug adaptor above. I again sealed the thread with grease.

With the head leveled in both directions, I filled the chamber via the burette to the top of the adaptor.

The volume measured was 22.4cc less 5.8cc for the adaptor left me with 16.6cc for the working chamber.

So, static CR is:

(Swept volume + working chamber volume) / working chamber volume. (206.4 + 16.6) / 16.6 = 13.43:1

I've used a couple of online dynamic CR calculators and both give the same results at 11.98:1

Does this all look valid from an outsiders point of view?

Cheers

Phil

Add  some  video  and  they  will  probably  rename  the forum  to "HighSide VFRD". :goofy:

Hi Phil, Been a few weeks, hows the bike going ?

Hi Chris

The weather has been fairly crap here so it has given me a chance to get the single nut conversion rear wheel well underway.

The bike has been going really well when I've had a chance to ride.

Should have the rear wheel conversion completed next weekend.

Just waiting on a couple of new 38mm axle nuts to arrive from the UK at present.

Got everything in place yesterday and it has shaved about 3.2kg off the unsprung weight on the rear.

Just need to button it all up once the nut arrive.

At that stage I'll create a new post and upload the drawings I've made of all the mods.

Cheers

Phil

Holy crap... I'm envious of your time and skills.

Yes it seems to be the Mohawk and HighSideNZ show LOL

Chris comes up with the ideas and the prototype, then I have a go!

Must be my time to lead.

Going back over my figures I reckon on 3.0-3.1kg with my steel bits.

Was a little optimistic with my maths.

Got to be a good overall effect on the rear suspension, and with the reduction on the front end with the R1 gear and no linking, not sure if I could get it much lighter without a metric butt load of $$.

Pics please :)

Hi CRRC46

There is a completely separate thread for this mod, with pic's and drawings.

http://www.vfrdiscus...ersion-6th-gen/

Cheers

Phil

Wow, what a read, what an adventure, way to stay the coarse,  I'll need to preserve this thread for future referencing.. Nice job,  talk about dedication.  Those numbers aren't to bad either  ;)   Hey! Honda,  you see this?

Veefer46, 6/14/2016 at 7:02 AM

Hi Mohawk,

due to the fact that I keep my standard cams in first place I am caluculating static CR. I'd just like to compare the values respectively ask what you think could be possible with 95 Octane (98 would be possible as well).

Thanks,

Julian

Just dropping in over bore, higher compression pistons and tuning for fuel alone on only euro 95 RON octane fuel (only 91 US ron+mon / 2) Is not going to let you go up much on the compression ratio. 12.15 static may be possible, but like mohawk was saying, it all comes down to the dynamic compression ratio and some other tuning and factors. The VFR800 comes with relative mild cams with very little overlap, which keep the dynamic compression relatively high, compared to the static compression ratio. If you were able to degree your factory cams and add some more over lap (this might not be cost effective on a gear driven valvetrain), you could bleed off some dynamic compression and raise your static compression much higher.

There are many more factors to address for knock resistance than just fuel octane rating and compression though.

First, obviously using 98 RON or 93 (RON+MON)/2 will allow much high compression or much safer operation on a given compression, versus 95 RON or 91 (RON+MON)/2.

Also as mentioned earlier, dialing in more valve over lap with factory (slotting the cam gear/sprocket bolt holes and rotating the cams relative to the gears a few degrees) or bigger custom cams will bring dynamic compression down to safer levels while adding more top end power and not losing too much low end if dynamic compression is kept at the same level.

Secondly, retarding your ignition timing will reduce combustion pressures by igniting the air/fuel mixture later in the power stroke so peak pressure is applied later on, as the piston is accelerating downward at a faster velocity, causing less chance of detonation.

Third, reducing temperatures in the combustion chamber can also make your engine less prone to detonation on higher compression levels. This can be done with a manual fan switch and spark plugs that are a temperature range colder.

Another way to reduce temperatures is a full high flowing exhaust system (I am not talking slip ons and ebay headers...) That is catless and ceramic coated. Also a slightly richer air fuel ratio will help lower temps too.

There are other things like deburring and smoothing the piston tops/valve reliefs/heads and ceramic coating the piston tops and combustion chambers, but that is probably out of the scope of this discussion.

Thanks for your detailed explanations.

I just didn't get the concept of DCR right and thought it would increase with more overlap due to the better delivery degree in higher rpm-ranges. Now I know better.

This gives me the answer that I cannot go as high in static CR as Phil because of my std. cams.

98 RON, Ignition timing and avoidance of hot spots on the piston should do the trick for 12.1:1 with standard cams.

I guess the standard VFR runs fine on even less than 95 RON because of the bad fuel quality in some countries. I don't think they used different maps for e.g. CN-versions like Porsche does.

My target is not to gain the highest power output possible but perhaps a little bit more low- and midrange-torque. This is my first engine build, so I'll start small  :blush:

Decatted and ceramic coated exhausts were used in our formula student cars, hence I know the prices and you are fully right - this is out of scope of the discussion  :goofy:

Yup the VFR was built to run on 90 RON and 87 (RON+MON/2) from the factory and there are no higher state of tune variants of VFR800's for different country's. Also there is no knock sensor, so there is no way for the bike to adjust for different fuels. But, yeah, I would imagine 12.1:1 would be very safe with optimized ignition timing and 98 RON and some other heat management tricks.

Back in the 80's, I think it was Lamborghini that was having financial difficulties and didn't have the money to design, build, and test an all new engine. They bored out the cylinders as much as possible (for additional displacement) but realized it wasn't enough. They then put spacers in between the block and heads to increase the stroke for even more displacement. Wow.

2FAST4U, 6/14/2016 at 6:26 PM

Back in the 80's, I think it was Lamborghini that was having financial difficulties and didn't have the money to design, build, and test an all new engine. They bored out the cylinders as much as possible (for additional displacement) but realized it wasn't enough. They then put spacers in between the block and heads to increase the stroke for even more displacement. Wow.

Deck plate spacers, with longer sleeves, have been used by hot rodders for a while, but it's hard to believe a manufacturer would do that lol. Man I'm sure the reliability and maintenance on those engines must be even worse than the already bad usual super car stuff.

17 hours ago, Veefer46

I just didn't get the concept of DCR right and thought it would increase with more overlap due to the better delivery degree in higher rpm-ranges. Now I know better.

I think you were on track with your train of thought, because I believe cylinder pressures could be higher, at higher RPMs with bigger cams, due to better cylinder filling (Ram air effect), but I think most engines are less prone to detonation at higher RPMs, being that the piston is moving away from top dead center, at a faster rate of speed.

I think detonation is more of a concern at lower RPMs, when the engine is lugging, as the piston is moving away from TDC at a much lower rate of speed, so when the fuel is ignited, it doesn't have as much time to expand, therefore running the risk of detonating if it expands at a faster rate than the piston will allow.

This same concept is why retarding the ignition timing (igniting the air fuel mixture later) will allow more safety (possibly at the cost of power) as when the combustion starts expanding, the piston is already moving away from TDC at a high rate of speed, so it is allowed to expand at a safer, more controlled rate.

It is when the flame is not allowed to expand outwards fast enough, that combustion pressures spike and the remaining unburnt air/fuel mixture detonates all at once and you get knock or worse, a smashed bearing or new window in your block.

Tuning is always a compromise, even more so on a daily driven street engine. You want to make as much power as you can, but not at the cost of reliability. That said, I do believe that there is a lot of room for safely making more power on the VFR engine, when using higher octane fuel, as Honda has tuned it to last forever on very low grade fuel and very mild cams.

21 hours ago, CandyRedRC46

because I believe cylinder pressures could be higher, at higher RPMs with bigger cams, due to better cylinder filling (Ram air effect)

This is exactly what I meant.

Your explanation regarding higher piston speeds sounds plausible, though.

I guess retarding ignition is only useful to the point when ignition is really triggered by the spark plug and not by hot spots on the piston/chamber.

But as you already pointed out, egalizing all sharp edges should help a lot.

Another question:

I'm about to choose new crankshaft bearing. Via Plastigauge I measured clearances of ~0,05mm. Therefore I want to replace with the original bearings according to the code-stamps on the weights of the crankshaft and on the housing.

Upper crankcase reads A-A-A

Crankshaft reads 3-2-1

This gives me colour codes brown-green-yellow according to the table in the service book.

Is there any way to countercheck with the codes on the bearings itself?

Example brown bearing:

According to the spare-parts catalogue this is "13315-ML7-691 BEARING C", the bearing reads "MZ5 817L".

All three bearings have different numbers stamped in so I guess it must have something to do with the colour codes. I just don't know how to transcode it.

I want to order the OEM parts in the US so sending them back won't be an option. Hence I'd like to double-check if possible.

You are beter off using plasti gauge to work out the shell bearing clearances. The factory codes are a good start & excellent for a quick build at the factory, but less accurate than your own measurements.

The cylinder filling efficiency can be better than 100% but ONLY at the peak torque RPM.  Cylinder filling can reach +10% or 110% in total, but that is already the case, so for the current dynamic compression ratio which according to my calculations is around 10.86/1 which +10% wold be 11.95/1 which is within tolerance at higher rpms. Normal 95RON fuel can be used at 12/1, so if you increase static compression then you MUST increase the valve overlap to maintain a safe DCR, or as CR46 says pull the ignition back in the peak efficiency rpm range.

Regarding Knock which is caused by the piston location after spark plug ignition as described by CR46. I feel you may be confusing Knock with Pre-Ignition.

Pre-ignition is caused by the heat or hot spots in the combustion chamber & is unplanned & often happens before the piston reaches TDC & can destroy an engine in short order.

This is normally caused by a combination of over heating & too high a compression ratio, take your pick !

YMMV

2 hours ago, Veefer46

I guess retarding ignition is only useful to the point when ignition is really triggered by the spark plug and not by hot spots on the piston/chamber.

But as you already pointed out, egalizing all sharp edges should help a lot.

The thing is, advancing ignition timing will raise combustion pressures and in turn temperatures, while retarding timing will lower pressure and temperature. So yes pulling timing will be useful while spark is triggering the combustion, but also it will lower temperatures and in turn further lower hot spot ignition/combustion/detonation as well.

1 hour ago, Mohawk

You are beter off using plasti gauge to work out the shell bearing clearances. The factory codes are a good start & excellent for a quick build at the factory, but less accurate than your own measurements.

The cylinder filling efficiency can be better than 100% but ONLY at the peak torque RPM.  Cylinder filling can reach +10% or 110% in total, but that is already the case, so for the current dynamic compression ratio which according to my calculations is around 10.86/1 which +10% wold be 11.95/1 which is within tolerance at higher rpms. Normal 95RON fuel can be used at 12/1, so if you increase static compression then you MUST increase the valve overlap to maintain a safe DCR, or as CR46 says pull the ignition back in the peak efficiency rpm range.

Regarding Knock which is caused by the piston location after spark plug ignition as described by CR46. I feel you may be confusing Knock with Pre-Ignition.

Pre-ignition is caused by the heat or hot spots in the combustion chamber & is unplanned & often happens before the piston reaches TDC & can destroy an engine in short order.

This is normally caused by a combination of over heating & too high a compression ratio, take your pick !

YMMV

My bad, you're right. :)

In all of these situations the best approach is to make sure there are no points in the combustion chamber that can give rise to hot spots.

Retarding the ignition should really only be used as a last resort to curing detonation as it is very hungry on power production.