96 vfr750 cbr929 pistons???/

hi guys ive been reading around and heard that the cbr929 pistons are a direct swap with my 96 vfr750 set, can anyone confirm this??

i know they are bigger so an overbore would be needed (just asked a company would be about £80) but other than that would there be anything else?

one last thing, what effects would this have on the engine good or bad?

i think i read that it makes it a vfr837 and that sounds good to me!

thanks for any help as im seriously interested in doing this

v4vfrgixxer750

i know they are bigger so an overbore would be needed (just asked a company would be about £80) but other than that would there be anything else?

I doubt you can go this far with an overbore. You decide, here are some numbers:

[image: 929d.png]

929

[image: vfr750.png]

VFR750

[image: vfr800fi.png]

vfr800fi

The tables don't show compression height which is rather important too.

V4, can you send me the links to the pages as I am at work and cannot view them...mcrwt644 at yahoo . com

I've been researching this a bit and it might be something I'm going to undertake. I've got a line on a complete engine for ~150 and if I can get 929 pistons, a good set of rings, and have ape bore it, it would run me about 500 with gaskets as I would do all other work in house (valve job, jetting etc)

I believe the ape website says the JE/Wiseco kits raise compression to 836cc 2.599" / 65MM bore, application; Street 10.25:1 K836 mods to be madeCylinder boring only price; 564.44

This is the street application, the race app raises compression to 12:5

Now, you go this route, do you go ahead and lighten and balance the crank??

mcrwt644

I believe the ape website says the JE/Wiseco kits raise compression to 836cc 2.599" / 65MM bore, application; Street 10.25:1 K836 mods to be madeCylinder boring only price; 564.44

With compression height I meant the distance between the centre of the piston pin and the piston deck. If it is too large it will result in bend conrods (piston hits cylinder head), too low and you'll loose a lot of compression.

mcrwt644

Now, you go this route, do you go ahead and lighten and balance the crank??

At least balance the cranck and have the conrods polished (increases strength).

V4 Rosso

mcrwt644

I believe the ape website says the JE/Wiseco kits raise compression to 836cc 2.599" / 65MM bore, application; Street 10.25:1 K836 mods to be madeCylinder boring only price; 564.44

With compression height I meant the distance between the centre of the piston pin and the piston deck. If it is too large it will result in bend conrods (piston hits cylinder head), too low and you'll loose a lot of compression.

mcrwt644

Now, you go this route, do you go ahead and lighten and balance the crank??

At least balance the cranck and have the conrods polished (increases strength).

JE kit I'm presuming would fit flush, but I am not sure. I'm going to get a set of 929 pistons and pull this other engine apart and put the 929 pistons in. ....thinking now, that's gonna be REALLY hard with a 61.5mm bore....There isn't a ton of info on the web on this that I can find.

I'm taking my vfr by a local machine shop that said they might be able to do this today to see what they say.

If I undertake this? I'm probably going to go the 929 piston route, bore to 65mm, lighten and balance the crank , maybe have a 3 angle valve job done, possibly cams, jet kit and obviously a full exhaust. It'll take some time because this is NOT going to be cheap. It's very doable though, expeically with the availability of cbr parts.

I believe the hp gain was in the 40-45hp range?

Hopefully the wrist pin diameter is the same, and the top of the pin hole to the piston crown is at least close, so the top of the piston isn't meeting the valves. Even so, you would need to dry fit the pistons, bolt the engine together, and rotate the assembly with modeling clay on the piston tops to confirm clearance at tdc with the valves operational too.

The piston weights would be your next worry, and you may need to lighten or weight the crank to suit.

Veefer800Canuck

Hopefully the wrist pin diameter is the same, and the top of the pin hole to the piston crown is at least close, so the top of the piston isn't meeting the valves. Even so, you would need to dry fit the pistons, bolt the engine together, and rotate the assembly with modeling clay on the piston tops to confirm clearance at tdc with the valves operational too.

The piston weights would be your next worry, and you may need to lighten or weight the crank to suit.

JE kits have the wrist pins etc, but yo ubring up a good point with the crank...that's why this is probably going to be a year long deal

mcrwt644

Veefer800Canuck

Hopefully the wrist pin diameter is the same, and the top of the pin hole to the piston crown is at least close, so the top of the piston isn't meeting the valves. Even so, you would need to dry fit the pistons, bolt the engine together, and rotate the assembly with modeling clay on the piston tops to confirm clearance at tdc with the valves operational too.

The piston weights would be your next worry, and you may need to lighten or weight the crank to suit.

JE kits have the wrist pins etc, but yo ubring up a good point with the crank...that's why this is probably going to be a year long deal

Just curious. Why is this route better than buying a ready made pistion kit?

slowjoe64

mcrwt644

Veefer800Canuck

Hopefully the wrist pin diameter is the same, and the top of the pin hole to the piston crown is at least close, so the top of the piston isn't meeting the valves. Even so, you would need to dry fit the pistons, bolt the engine together, and rotate the assembly with modeling clay on the piston tops to confirm clearance at tdc with the valves operational too.

The piston weights would be your next worry, and you may need to lighten or weight the crank to suit.

JE kits have the wrist pins etc, but yo ubring up a good point with the crank...that's why this is probably going to be a year long deal

Just curious. Why is this route better than buying a ready made pistion kit?

I'm asking myself the same thing. I'm seeing 929 piston kits for like 1/6th the cost of a je kit, but that said, the je kit comes with new rings, wrist pins and circlips

V4 Rosso

I doubt you can go this far with an overbore. You decide, here are some numbers:

y'know rosso, you say that, but this is the typical size of the pistons in any 840cc overbore kit. I'm gonna start doing some research, cause he may just be onto something here....

just to put a little note on this thread...im about to absolutely lose my mind here, as I am looking at the same piston spec chart in the manual I have for the 86-87 VFR's, an already knowing beyond the shadow of a doubt that the 2nd gen VFR's used the same pistons for both the 700 and 750 motors (the extra displacement in the 750 bikes was accomplished via the crankshaft and connecting rods), and comparing these charts to each other, I am coming up with the following conclusions:

(1) these comparisons are being made under the assumption that the VFR750 piston spec chart is the one for the 96 model VFR

(2) all the numbers for the 2nd gen pistons match the #s for the 4th gen (96) pistons *exactly*

(3) the #'s in both the 2nd gen chart and the 4th gen chart also match the 929 pistons

(4) the wristpin measurements are listed in these charts, and they seem to match right on as well, implying that the VFR and CBR wristpins are the same, and there should be no problem mounting the 929 pistons on the VFR rods

(5) the only thing missing here is the total height measurement of the piston (ie center of the wristpin to the top of the piston). I would love to get this measurement, as this should be the determining factor in whether or not this will work.

(6) if all of these #s actually work out, v4vfrgixxer750 and Rosso may very well have accidentally found a MAJORLY money-saving alternative to buying JE's thousand dollar overbore kit, saving many VFR750 owners shittons of money on engine upgrade projects!!!!!

I've already found some very cheap sets of 929 pistons on eBay, and I'm dying to see somebody score a set just to complete the specs and measurements, and determine once and for all the answer to v4vfrgixxer750's question...

will the 929 pistons really work in the VFR750 motors as the coveted 840 overbore piston!!!???!!!???!!!??? :cheerleader:

hmmm seems ive really started summin here lol :biggrin: , i reckon it needs to be found out once and for all with a definitive answer.

my question is this, i pretty much know the 929 piston could work even if it hits the cyclinder head / valves as you can get the piston head machined / grinded slightly to be shorter.

the bigger bore piston kit (837cc) is like £500!! before machine work so it will no doubt be cheaper going this route.

BUT what effect will it have on a vfr750? will it giv more hp / torque? less reliable? etc AND if you do the overbore will you NEED to work on the crank etc or can the rest of the engine be left alone within reason (can imagine jetting would be needed and minor tweeks)

what perks and pitfulls would this have in comparison to doing more engine work?

ive been adding up whats needed (this is based on just an overbore not other engine work) £70ish for 929 pistons, £80ish for overbore work, £70 ish for gasket set and would probably buy new piston rings as well just incase........... thats not a bad price to look at to get a vfr840 :fing02:

thankyou for everyone whos chimed in and helped out so far!

hmmm seems ive really started summin here lol :biggrin: , i reckon it needs to be found out once and for all with a definitive answer.

oh yes. this thread could potentially open up one hell of a can of worms.

my question is this, i pretty much know the 929 piston could work even if it hits the cyclinder head / valves as you can get the piston head machined / grinded slightly to be shorter.

the bigger bore piston kit (837cc) is like £500!! before machine work so it will no doubt be cheaper going this route.

you wouldnt want to deck the heads, cause that would bring the top of the combustion chamber CLOSER to the piston, and right now, the biggest concern I have is piston/valve clearance. this could best be determined by measuring the pistons from the center of the wristpin to the top of the piston (and comparing the measurements), and also measuring the depth of the valve reliefs on each piston, from the top of the piston deck to the bottom of the valve relief, as WELL as verifying valve relief placement on the piston, so to ensure it would not interfere with the valves when the valves are open and the piston at TDC.

BUT what effect will it have on a vfr750? will it giv more hp / torque? less reliable? etc AND if you do the overbore will you NEED to work on the crank etc or can the rest of the engine be left alone within reason (can imagine jetting would be needed and minor tweeks)

what perks and pitfulls would this have in comparison to doing more engine work?

you're kidding right? there's an old proverb in the performance world that dates back to the beginning of engine performance itself. it says "there's no replacement for displacement". I believe that when it comes to the bore and stroke of the cylinders being compared to the HP/TQ, the size of the bore tends to affect horsepower more, where the length of the stroke tends to affect torque more. (i may not be correct here, so anybody is welcome to chime in on this at your leisure). but increasing the displacement of your engine definitely will result in more overall power,

now one MORE thing I've noticed, is in comparing the VFR piston to the 929 piston, it's quite obvious that the 929 piston doesnt have nearly as much material on the piston skirt as the VFR piston does. this could actually yield an added advantage, as the 929 piston may in fact be lighter, which will result in a lighter overall rotating assembly weight, which has an end result of the engine being able to spin up faster (ie reach higher RPM's with less time and effort). theres nothing at ALL wrong with that!

ive been adding up whats needed (this is based on just an overbore not other engine work) £70ish for 929 pistons, £80ish for overbore work, £70 ish for gasket set and would probably buy new piston rings as well just incase........... thats not a bad price to look at to get a vfr840

one thing to look into here is to find out whether the cylinder bores would have to be sleeved to accomodate a 4mm overbore, cause lets be honest, +4mm is a pretty huge bore. (at least to me it would be, i'm used to seeing cage motors bored in much smaller incriments....that having been said, the 840 kit IS a set of 74mm pistons, so this has been done plenty of times before).

if you do decide to move forward with this project, PLEASE keep us all posted as to your progress and success!

I heard once that the legendary Tony Scott once built a RC30 engine stuffed with Fireblade pistons for someone to race on the Isle of Man. (Or it could have been an over-bored VFR750F engine in an RC30 chassis--I forget.) Anyway, it blew up.

But don't let that stop you! You could be the next Tony Scott... :biggrin:

I have a TTS-built VFR837FP, which I definitely approve of, but if you're expecting huge power increases from that much additional displacement, well, don't. I expect a whole lot more from my A&A kitted RC46 (if I ever get it running...), but it also cost a lot more than a big bore!

If you're au fait with engine building and can get your hands on a couple of second-hand engines, you might be able to work out an OEM combination that would work. Honda does seem to like to use proven designs in more than one engine. The most interesting example I've found of this is that the V4 NC30 (and NC35) engines actually use the same exact pistons as the inline-4 NC29. :cool:

However, bear in mind that Honda VFR engine cases are notoriously difficult to over-bore accurately. I've heard of 750s and 400s that have been ruined by machine shops not familiar with the appropriate techniques. That "cheap" boring job may turn out to be anything but...

[FYI: Here's the old TTS big bore kit page--their current Web site is almost dead.]

[Oh, and another thing: Back in the day, only TTS and Dynamo Humm were selling VFR big bore piston kits. Both were made by JE, but to TTS' spec. Dynamo Humm in Canada actually had to buy the pistons from TTS, as JE (in California) would not sell them to Dynamo Humm directly. I don't know if TTS still has exclusive rights to those pistons or not. Dynamo Humm doesn't exist any more, but TTS apparently still does (even if mainly a Hyabusa supercharging shop now). Might be worth a call to JE/Wiseco?]

Ciao,

I'm looking into having the crank lightened and balanced, the pistons with possible carilla rods, overbore, valve job, cams, jet kit and obviously a full exhaust. Any and all machine work would be done by ape out in California. They are a full service shop. Just check out their website.

I've been looking for 929 pistons etc on ebay and they can be had with rods, for ~10 bucks each. Probably need new rings, but that's another story. The pistons I believe are lighter like the previous poster stated. I've got an opportunity at a gen four engine for like 150-, and I'll order a 929 piston and check at least the piston height from the wristpin. If that matches up, we're in business.

I do not know if a sleeve is needed on the boring job. APE would be able to address that. APE charges ~$340 (if I am reading their site right) for a full bore job to match the pistons you provide (trust me you want to do this as one time I had an overbore done, I sent the smallest piston, only one, and regretted it)

Lightening the crank costs ~250. Get the bottom end and pistons done, and you can do a valve job at home, leave stock cams in, and have it jetted on a local dyno. I'm going to seriously consider it.

mcrwt644

and you can do a valve job at home, leave stock cams in,

You can also have the cams reground for some more lift or fit VFR800 valves (and seats) which I think are about 1mm larger in diameter. The larger displacement engine has to be able to breath after all.

Keep any and all suggestions coming

V4 Rosso

mcrwt644

and you can do a valve job at home, leave stock cams in,

You can also have the cams reground for some more lift or fit VFR800 valves (and seats) which I think are about 1mm larger in diameter. The larger displacement engine has to be able to breath after all.

now this is a pretty good idea. i didnt know the VFR800 valves were only 1mm larger, which I think is an IDEAL size for a valve replacement. The questions here are, of course, whether the VFR800 valves are the same otherwise (ie the valve stem where theyd actually mount to the heads and vavle retainers, etc), and whether these oversized valves would interfere with the new 929 pistons.

as much as i hate to say it (only because of the involved expense), it sounds like this project would be best experimented on a donor engine from ebay. this way, youd still be riding your own bike during this motor build, and if anything did happen to go south, you're not jacking up the engine that you already depend on to run in your bike.

that being said, man i really hope you see some success with these ideas, cause you can bet your bottom dollar i'll be following suit with the super-viffer motor built on the cheap ;)

That is exactly what I was thinking ^^

I've got a line on a gen 4 engine for about 150, and it runs, so that is where all 'experimentation' would take place

mcrwt644

That is exactly what I was thinking ^^

I've got a line on a gen 4 engine for about 150, and it runs, so that is where all 'experimentation' would take place

wow, 150?! seriously?! dude thats WAY cheaper than id expect you to find a donor engine for a project like this. you should snatch that thing up, if for no other reason than to sell it and make a profit if you dont use it for the project rebuild!

I just found a page in the service manual for my bike that lists the specs and measurements of the valves in very similar detail to that of the charts that Rosso posted earlier in this thread on the pistons. If we can find the service manuals for the 4th gen VFR and the VFR800's, then that would help to compare the #s on the valves and determine whether it would be worth moving forward with that idea.

I have a 1/2 wrecked donor in my garage that I've been staring at and debating over for quite some time now...sounds like an interesting idea. Have a buddy that owns a motorcycle shop, bet I could talk his mechanic into helping out a bit.

does anybody have links for various VFR service manuals that can be downloaded in .pdf form? regarding this thread, I'm specifically looking for the manuals that would cover the gen 3-4 bikes, and the manual for the 5th gen 800fi bikes... (to start comparing #s and what not)

They are all right here in the files section. But if you're looking for valve dimensions, it's not in there.

Yes, 150 ish for the engine...80 ish for a frame with center stand (bill of sale only) local to me. This is going to get good in a hurry, I can tell. As long as the wrist pin to top of piston measurement is good from the 929, we could be in business.

Now, as Lee Shierts' shop asked, do I want to do carilla rods or would the 929 rods suffice?

I have NO experience mixing and matching Honda engine parts, BUT, I have done a ton of mixing and matching on small block Chevys and Fords. Some things that have been touched on here (Very Cool thread) bear repeating. Which rod- 929 or after market? I'd stay away from the aftermarket until a "proof of concept' engine can at least be assembled. I don't like alloy rods for street use, they don't hold up. Piston dimensions, especially wrist pin to top (don't forget bottom too, is the crank throw dimension in the VFR same as the 929?!) are critical. The short skirt on the 929 piston MAY be a concern in the VFR at BDC as the the crank starts to push it back up. Depending on the angle, the side load can overwhelm the rings ability to keep the piston centered in the bore, resulting in big time cylinder wall scuffing. Maybe. A Very Cool project, (like most of us need another one) love to hear what works. :fing02:

ok 3 replies in order of posting....

Rosso.....are you saying that the valve measurements arent in the factory service manuals for the 3-4 and 5th gen vfr's? I was able to easily find these measurements in a chart in my 2nd gen manual. let's start there to look for the info we need. (and wheres the files section?!)

mcrwt644.....as far as what rods to use, having determined that the wrist pins are the same outside diameter, I would use the existing VFR connecting rods and wristpins for this one. that way you dont have to worry about the potential different rod length of the 929 and youll use a rod you know works for that motor.

rangemaster.....i completely agree with you on the point of avoiding aftermarket connecting rods. it seems there'd be too much risk in that one. as far as the shorter piston skirts on the 929 pistons and the risk of the increased side load that the rod would put on the piston coming up from BDC, I'm not sure that would be as much of an issue as we might thing, simply because the 929 actually has a higher redline than any VFR that I know of, so wouldnt that translate to the 929 pistons taking (and subsequently being able to withstand) more side load than the standard vfr piston already? (just throwing this one out there to get other opinions on it)

This is crazy stuff, I can't wait to see where it goes. :fing02:

One thought; if the wrist pins are indeed the same diameter, would you not want to use the 929's with the 929 piston? You have the extra piston width, why not bear some of the combustion load with the full-length pin?

Tallboy

This is crazy stuff, I can't wait to see where it goes. :fing02:

One thought; if the wrist pins are indeed the same diameter, would you not want to use the 929's with the 929 piston? You have the extra piston width, why not bear some of the combustion load with the full-length pin?

legitimate point being made here.

flyguyeddy

Tallboy

This is crazy stuff, I can't wait to see where it goes. :fing02:

One thought; if the wrist pins are indeed the same diameter, would you not want to use the 929's with the 929 piston? You have the extra piston width, why not bear some of the combustion load with the full-length pin?

legitimate point being made here.

Absolutely. Sorry, I meant the location of the wrist pin in the 929 piston in comparison to where the wristpin's relative position is on the VFR piston. Clear as mud I know. But you guys are right, for sure use the 929 wristpin in the 929 piston. Looking at those JE big bore pistons just posted, the short skirt of a 929 piston doesn't look like it would be an issue. Just a thought, after you find out if this works, get the pistons, wristpins and rods all balanced as matched sets, makes a big difference in how it spools up.

Absolutely. Sorry, I meant the location of the wrist pin in the 929 piston in comparison to where the wristpin's relative position is on the VFR piston. Clear as mud I know. But you guys are right, for sure use the 929 wristpin in the 929 piston. Looking at those JE big bore pistons just posted, the short skirt of a 929 piston doesn't look like it would be an issue. Just a thought, after you find out if this works, get the pistons, wristpins and rods all balanced as matched sets, makes a big difference in how it spools up.

Chris71mach1

Rosso.....are you saying that the valve measurements arent in the factory service manuals for the 3-4 and 5th gen vfr's?

It doesn't mention the valve diameter, here is what it says about the valves:

[image: cylhead.png]

VFR750

[image: 800ficylhead.png]

VFR800Fi

You can go to the files section by clicking the files tab in the top menu bar. Then select "Owner manuals & others".

Knowing what we do about the 929's redline, wouldn't the 929 rods be 'heavier duty' , or are they the same part number? (I haven't looked at the fiche). I can do a proof of concept on this for about $200, and I'm going to probably get the engine on Monday.

I'm surprised that the carilla rods didn't fly? Of course it's a cost savings too.

Now, a question for the piston rings on the 929....does anyone make an aftermarket set, or should the existing unknown mileage rings be utilized?

Is the crank lightening 'necessary' or just 'cool'??

http://www.vfrdiscussion.com/forum/index.php/topic/68300-je-pistons-for-750-big-bore/page__pid__796973#entry796973

talk about timing!! I've inquired about the size of the overbore....

mcrwt644

http://www.vfrdiscussion.com/forum/index.php/topic/68300-je-pistons-for-750-big-bore/page__pid__796973#entry796973

talk about timing!! I've inquired about the size of the overbore....

god yes! looks like we MIGHT have a cheap big bore piston! gets ome used ones, moly coat the skirt, and throw em in :) ive already bought a set of used pistons to check out. ill measure the piston pin to top height when they show up. (ive also got ahold of someone with an engine for rebuild for this project, too)

flyguyeddy

mcrwt644

http://www.vfrdiscussion.com/forum/index.php/topic/68300-je-pistons-for-750-big-bore/page__pid__796973#entry796973

talk about timing!! I've inquired about the size of the overbore....

god yes! looks like we MIGHT have a cheap big bore piston! gets ome used ones, moly coat the skirt, and throw em in :) ive already bought a set of used pistons to check out. ill measure the piston pin to top height when they show up. (ive also got ahold of someone with an engine for rebuild for this project, too)

^^cool, where are you located? I'm in northern VA. I'm inquiring about picking up the engine today. I've got an e mail into APE in CA about the cost of having boring done as well as whether or not sleeving is necessary and what the turn around time is.

im in central illinois and my project engine is in north carolina, so i will hafta pay some decent cash to ship it. however there isnt really any local, and everyone wants a fortune for them.

i agree with the idea of using the 929 wristpins with the 929 pistons....that does make more sense than using the vfr wristpins. as for the rings, i think it would be best to buy new piston rings, as well as connecting rod bearings (if you're rebuilding your engine, bearings are one thing that should be replaced anyways).

also, the idea of assembling the pistons to the rods and having them all balanced is a really good idea. stuff like that really would help the motor after rebuild.

and after looking at the 2 charts that rosso posted earlier with the valve specs, it looks like the valves from the 800FI have a decent chance of interchangability with the 3-4th gen bikes, but theyre clearly different valves from the 2nd gen bikes. dammit. oh well, the 3-4th gen rebuild can at least serve as proof of concept for that one if the 2nd gen cant....

Those listed big bore pistons go +4mm = over 880c-thats BIG. The kits I remember went 840 tops, did JE make TWO sets of big (and really big) bore pistons? I would think 880 0n a 4th gen 750 case would be REALLY pushing it-840 would give the machinist much more (relatively) to work with.

rangemaster

Those listed big bore pistons go +4mm = over 880c-thats BIG. The kits I remember went 840 tops, did JE make TWO sets of big (and really big) bore pistons? I would think 880 0n a 4th gen 750 case would be REALLY pushing it-840 would give the machinist much more (relatively) to work with.

i have no idea where the # of 880 cc came into play, but the 4mm overbore uses the 74mm pistons (all 750cc engines, be they 2nd, 3rd, or 4th gen use 70mm pistons from the factory). the 74mm pistons end up giving the motor an overal displacement of 837cc (more frequently known as the 840)

mcrwt644

I'm looking into having the crank lightened and balanced, the pistons with possible carilla rods, overbore, valve job, cams, jet kit and obviously a full exhaust. Any and all machine work would be done by ape out in California. They are a full service shop. Just check out their website.

I've been looking for 929 pistons etc on ebay and they can be had with rods, for ~10 bucks each. Probably need new rings, but that's another story. The pistons I believe are lighter like the previous poster stated. I've got an opportunity at a gen four engine for like 150-, and I'll order a 929 piston and check at least the piston height from the wristpin. If that matches up, we're in business.

I do not know if a sleeve is needed on the boring job. APE would be able to address that. APE charges ~$340 (if I am reading their site right) for a full bore job to match the pistons you provide (trust me you want to do this as one time I had an overbore done, I sent the smallest piston, only one, and regretted it)

Lightening the crank costs ~250. Get the bottom end and pistons done, and you can do a valve job at home, leave stock cams in, and have it jetted on a local dyno. I'm going to seriously consider it.

Mcrw,

I started a big bore engine project on a spare 94vfr750 engine that I bought on eBay a few years ago. The project got aborted when the shop I had putting the lower end together for me bored right through the sleeve into the engine. I still have the JE pistons from that project and a crank that was precision balanced crank. According to the shop that did the work the cranks on these bikes are already balanced pretty close to damm good. On advice of other engine builders I did not lighten the crank though. Doing so could have affected the abilty of the engine to run smooth at the lower RPM range. The engine relies on the inertia from the weight of the crank to run smooth down low. One other bit of advice. Be very careful about the head work. Do not have the cylinder heads "decked" , "shaved" or material removed to increase the compression, you could run into a mess of problems with the gear driven cams. The overbored engine case it going to be turned into a end table....lol. Screw some long threaded rods into the the top of the engine to hold up a plate of glass, add some short legs to the bottom and viola! I'll post some pics of that when I'm done.

Ride safe everyone.

tireguy

rangemaster

Those listed big bore pistons go +4mm = over 880c-thats BIG. The kits I remember went 840 tops, did JE make TWO sets of big (and really big) bore pistons? I would think 880 0n a 4th gen 750 case would be REALLY pushing it-840 would give the machinist much more (relatively) to work with.

JE also made Dynamo Humm's 870cc pistons--but these required sleeves as well.

Ciao,

the kit I found in the classifieds, I believe is a 836cc kit

tireguy

mcrwt644

I'm looking into having the crank lightened and balanced, the pistons with possible carilla rods, overbore, valve job, cams, jet kit and obviously a full exhaust. Any and all machine work would be done by ape out in California. They are a full service shop. Just check out their website.

I've been looking for 929 pistons etc on ebay and they can be had with rods, for ~10 bucks each. Probably need new rings, but that's another story. The pistons I believe are lighter like the previous poster stated. I've got an opportunity at a gen four engine for like 150-, and I'll order a 929 piston and check at least the piston height from the wristpin. If that matches up, we're in business.

I do not know if a sleeve is needed on the boring job. APE would be able to address that. APE charges ~$340 (if I am reading their site right) for a full bore job to match the pistons you provide (trust me you want to do this as one time I had an overbore done, I sent the smallest piston, only one, and regretted it)

Lightening the crank costs ~250. Get the bottom end and pistons done, and you can do a valve job at home, leave stock cams in, and have it jetted on a local dyno. I'm going to seriously consider it.

Mcrw,

I started a big bore engine project on a spare 94vfr750 engine that I bought on eBay a few years ago. The project got aborted when the shop I had putting the lower end together for me bored right through the sleeve into the engine. I still have the JE pistons from that project and a crank that was precision balanced crank. According to the shop that did the work the cranks on these bikes are already balanced pretty close to damm good. On advice of other engine builders I did not lighten the crank though. Doing so could have affected the abilty of the engine to run smooth at the lower RPM range. The engine relies on the inertia from the weight of the crank to run smooth down low. One other bit of advice. Be very careful about the head work. Do not have the cylinder heads "decked" , "shaved" or material removed to increase the compression, you could run into a mess of problems with the gear driven cams. The overbored engine case it going to be turned into a end table....lol. Screw some long threaded rods into the the top of the engine to hold up a plate of glass, add some short legs to the bottom and viola! I'll post some pics of that when I'm done.

Ride safe everyone.

tireguy

why did they bore it like that? did they go too far down into the cylinder, or too big on the bore? is it something we need to be concerned with?

also, has anyone thought about using vtec or 800 connecting rods in one of these engines? i hear they are more stout than what came in these engines from the factory....

I'm not going with a local shop for the boring...I'll be going with APE racing in CA. This is all they do. I have an e mail into them about the boring and whether or not we need to do sleeves.

Tireguy, thanks for the crank information

The 86 VFR750 can be bored out to 74mm without sleeving. My 86 is now 837cc. The iron liners in the cases for the early VFR's, as well as the 3rd/4th gen are thick enough to bore to +4. I got my pistons from TTS/JE.

I found out the hard way that the liners on the RC30 are too thin to bore. That's why the oversize pistons for the RC30 are 70.2mm and 70.4mm. I got a set of TTS/JE 72mm pistons for the RC30, so it will end up being identical in displacement to the VFR800 (72x48.6). If I want to go larger in the future, I can always go for the 74mm kit now that I've had the RC30 sleeved. For boring or sleeving, I've had good luck with Millennium Technologies in Wisconsin, they just did my RC30 cases earlier this year. The sleeving ain't cheap though. When I had the 86 cases bored (several years ago) I sent them to Mike Velasco, not sure if he's still around.

If I can find a 929 piston, I can compare the pin to deck height with the RC30 piston, but I don't know if I still have any of the stock 86 VFR pistons laying around. I think as long as that measurement is good, this will be a lot cheaper (and faster getting parts) than going through TTS. The big advantage of the non-original pistons for the RC is the three ring piston design, stock was two ring (one compression, one oil ring)

Pic below of the stock 86 piston compared to the JE 74mm. It's an old pic, taken from a crappy camera, but you get the idea.

[image: post-5940-0-40496800-1313963345_thumb.jp]

[image: post-5940-0-34168200-1313963356_thumb.jp]

'Mike Velasco' that name sounds very familiar from my days at a speed shop in San Diego...I'm wondering if he did my 99 F4 1mm over in 01.....

Ok, so 929 pistons are very much less expensive.

My question regarding those pistons is what do you do for rings? Use the ?? mileage rings that are on the piston, or is there an aftermarket source that makes rings for that application? It sure would be cheaper than buying the JE kit...but I'm fairly sure if you go new oem from the dealer? the rings would cost more than the JE kit NEW.

So far? I'm very close to getting the JE kit from Tireguy. I should have the fourth gen engine this week.

evl_twn

The 86 VFR750 can be bored out to 74mm without sleeving. My 86 is now 837cc. The iron liners in the cases for the early VFR's, as well as the 3rd/4th gen are thick enough to bore to +4. I got my pistons from TTS/JE.

I found out the hard way that the liners on the RC30 are too thin to bore. That's why the oversize pistons for the RC30 are 70.2mm and 70.4mm. I got a set of TTS/JE 72mm pistons for the RC30, so it will end up being identical in displacement to the VFR800 (72x48.6). If I want to go larger in the future, I can always go for the 74mm kit now that I've had the RC30 sleeved. For boring or sleeving, I've had good luck with Millennium Technologies in Wisconsin, they just did my RC30 cases earlier this year. The sleeving ain't cheap though. When I had the 86 cases bored (several years ago) I sent them to Mike Velasco, not sure if he's still around.

If I can find a 929 piston, I can compare the pin to deck height with the RC30 piston, but I don't know if I still have any of the stock 86 VFR pistons laying around. I think as long as that measurement is good, this will be a lot cheaper (and faster getting parts) than going through TTS. The big advantage of the non-original pistons for the RC is the three ring piston design, stock was two ring (one compression, one oil ring)

Pic below of the stock 86 piston compared to the JE 74mm. It's an old pic, taken from a crappy camera, but you get the idea.

ill have my 929 pistons in sometime next week if you like i can bring one over so we can compare the two, since your very local to me lol

mcrwt644

'Mike Velasco' that name sounds very familiar from my days at a speed shop in San Diego...I'm wondering if he did my 99 F4 1mm over in 01.....

Ok, so 929 pistons are very much less expensive.

My question regarding those pistons is what do you do for rings? Use the ?? mileage rings that are on the piston, or is there an aftermarket source that makes rings for that application? It sure would be cheaper than buying the JE kit...but I'm fairly sure if you go new oem from the dealer? the rings would cost more than the JE kit NEW.

So far? I'm very close to getting the JE kit from Tireguy. I should have the fourth gen engine this week.

if you do choose to use used 929 pistons, then id highly suggest treating it like a standard engine rebuild. clean up and essentially recondition the 929 pistons, use NEW piston rings, NEW rod bearings, and maybe even replace the main bearings while you're at it. It wouldn't hurt to give the heads a good once over as well while the motor is apart (ie clean all the carbon from the combustion chambers and valves, inspect the valvetrain and cams, etc). this way you can ensure as long a life out of your new 840 powerplant as possible.

Chris71mach1

mcrwt644

'Mike Velasco' that name sounds very familiar from my days at a speed shop in San Diego...I'm wondering if he did my 99 F4 1mm over in 01.....

Ok, so 929 pistons are very much less expensive.

My question regarding those pistons is what do you do for rings? Use the ?? mileage rings that are on the piston, or is there an aftermarket source that makes rings for that application? It sure would be cheaper than buying the JE kit...but I'm fairly sure if you go new oem from the dealer? the rings would cost more than the JE kit NEW.

So far? I'm very close to getting the JE kit from Tireguy. I should have the fourth gen engine this week.

if you do choose to use used 929 pistons, then id highly suggest treating it like a standard engine rebuild. clean up and essentially recondition the 929 pistons, use NEW piston rings, NEW rod bearings, and maybe even replace the main bearings while you're at it. It wouldn't hurt to give the heads a good once over as well while the motor is apart (ie clean all the carbon from the combustion chambers and valves, inspect the valvetrain and cams, etc). this way you can ensure as long a life out of your new 840 powerplant as possible.

i plan to get the pistons cleaned and skirts coated when they get here.

suddenly i'm curious..... are the CBR900RR and CBR954RR pistons still 74mm like the 929 pistons are? this comes down to the question of whether the displacement difference in the 900RR, 929RR, and 954RR engines were made by the crankshaft (stroke) or the piston size (bore). answering this might just open the door for a whole lot more pistons that might be used for this one.

ok i answered my own question on this one....the 900RR piston is only 71mm and the 954RR piston is 75mm, so the 929RR piston is the only one that will substitute for the straight out 840cc, +4mm overbore conversion for these bikes.

Does anybody have any new developments on this? Im still waiting.on my pistons...

just got em, they are either 23 or 24 mm from top of piston to middle of wristpin. i will get a more accurate measurement tomorrow.

flyguyeddy

just got em, they are either 23 or 24 mm from top of piston to middle of wristpin. i will get a more accurate measurement tomorrow.

24mm from top of piston to center of wristpin.

:lurk:

Please do the test run with you standing behind a thick Lexan shield......

:cool:

Dutchy

Please do the test run with you standing behind a thick Lexan shield......

well one trick ive seen engine builders use is to check the valve clearances to the piston using playdough or silly putty. basically, put the motor together (at least install the rotating assembly), and then install the heads and valvetrain to where you can manually turn the engine over with a wrench. now BEFORE you install the heads onto the motor, apply a thin coat of silly putty to the tops of all the pistons. install the heads and then start turning the motor over SLOWLY. (obviously, leave the spark plugs OUT so you dont build up any real pressure in the combustion chambers...this is just to make the valves open and get as close to the pistons as they would during normal operation). after turning the motor over a few times manually (enough times to get all valves in all 4 cylinders to open and close so to verify clearances in all cylinders), pull the heads off and carefully inspect the indentions on the silly putty. if the valves went all the way through the silly putty and touched the piston, the deal is off, and you dont want to use this combo. if on the other hand, there is still silly putty left between the valve and the top of the piston, you're very likely good to go.

(testing something like this with the motor actually running and firing and stuff would be just ASKING for it to fly apart anyways!)

anybody have the measurement for the 750 piston?

Chris71mach1

ok i answered my own question on this one....the 900RR piston is only 71mm and the 954RR piston is 75mm, so the 929RR piston is the only one that will substitute for the straight out 840cc, +4mm overbore conversion for these bikes.

Did you find out what the stroke was for those bikes? If the bore is only a bit bigger, but the stroke is longer, then you could get even more torque out of the engine. Unless you're tracking the bike, you'll probably get more of a kick out of more torque than top speed. Still would have it's problems though.

tireguy

I started a big bore engine project on a spare 94vfr750 engine that I bought on eBay a few years ago. The project got aborted when the shop I had putting the lower end together for me bored right through the sleeve into the engine.

tireguy

Is this because they bored more than they should, or because you couldn't bore to 4mm?

Hope this is helpful?

A guy from this side of the pond sent me these details: from the label on the box of his 837cc TTS JE Piston kit.

TTS PERFORMANCE ENGR LTD

ACCT 6916

CUSTOM ORDER

PO 5317

HONDA M/C 750cc VFR750

Bore 2.913

Comp Height .900

Forging 75M

Pin Dia .669

Pin Length 2.050

JE .050 Wire Locks

Dome .155

Top Ring .8mm

2nd Ring .8mm

Oil Ring 1.5mm

Piston weight 176

PART 150871

JOB 421787

VFR750 Bore and Stroke 70 x 48.6mm

CBR900 70 x 58

CBR919 71 x 58

CBR929 74 x 54

CBR954 75 x 54

ok to start with, YoshiHNS, you did pose 2 good questions. the 837cc kit is an overbore only. this basically replaces the stock 70mm pistons with 74mm pistons. and yes, the VFR engine cases can in fact take the giant 4mm overbore, as it has been done plenty of times in the past.

as for the stroke, i can tell you that the difference in the 700 and 750cc engines in the 2nd gen bikes is the stroke. this is how honda achieved the extra 50cc's of displacement, was by using a different crankshaft (and in conjunction, different connecting rods as well).

the reason tireguy's machinist screwed up his engine cases had to be due to inexperience with these motors. thats the only thing i can think of, as if you read earlier in this thread, evl_twn had his cases bored successfully and has a strong running 837cc motor.

Eddy, I have a 750cc rotating assembly out in the garage, I just need to find my set of calipers so i can get the exact measurements off of the piston. I'll post back on this thread when i get to it.

I should have my 837's original pistons in the garage. Which measurements are needed?

The RC24 was originally designed to be 750cc (or 748 or whatever); the VFR700F was designed afterwards (RC26), so it would be more accurate to say that Honda achieved the reduced capacity by shortening the stroke on the 700s, rather than lengthening the stroke on the 750s!

Ciao,

JZH

I should have my 837's original pistons in the garage. Which measurements are needed?

The RC24 was originally designed to be 750cc (or 748 or whatever); the VFR700F was designed afterwards (RC26), so it would be more accurate to say that Honda achieved the reduced capacity by shortening the stroke on the 700s, rather than lengthening the stroke on the 750s!

Ciao,

the measurements needed are just the distance from the center of the wristpin to the top of the deck on the piston. comparing this to the same measurement on the CBR929RR piston should verify whether the 929 piston can be used for the big bore project as a more economical alternative to the ragingly expensive JE set.

Looks like the big bore pistons are 22.83 from center of pin to top of piston. Would 1mm be too much more? Perhaps removing 1mm from the 929 piston?

VFR750FP piston, measured from centre of the 17mm OD piston pin:

22.85mm to top of piston (where "IN" is located)

25.40mm to top of crown

Note, however, that the earlier FL-M RC36s appear to have different part numbers for the pistons. I can't imagine them being different, but they do have different part numbers, and it doesn't appear to be entirely due to supercession (from MT4 to MY7). These pistons are marked "MY7" on the top.

Ciao,

Hmmm. Do u think 1mm would be too much rise?

flyguyeddy

Hmmm. Do u think 1mm would be too much rise?

at this point, a proof of concept using the silly putty idea i posted here earlier might actually be necessary....

The stock RC30 pistons measure (at least as well as my eyes could gauge) 19.5mm from center of wrist pin to top surface of piston, and 25mm to the top of the dome. I wish I would have seen this thread BEFORE putting the bottom end of the engine together, now I'm curious how much more of a dome the TTS pistons have. I might be able to get a close estimate if measuring the top to dome with a piston at TDC.

Chris, don't use Play-doh, it's too soft. I was recommended the use of modeling clay, as it's more stout. I still need to pick some up, I think my heads are finally done and on their way home. Also when doing the clay test, leave the head gasket off. That way you know you have that little bit of extra clearance for valve float, and you don't end up wasting a set of gaskets.

evl_twn

The stock RC30 pistons measure (at least as well as my eyes could gauge) 19.5mm from center of wrist pin to top surface of piston, and 25mm to the top of the dome. I wish I would have seen this thread BEFORE putting the bottom end of the engine together, now I'm curious how much more of a dome the TTS pistons have. I might be able to get a close estimate if measuring the top to dome with a piston at TDC.

Chris, don't use Play-doh, it's too soft. I was recommended the use of modeling clay, as it's more stout. I still need to pick some up, I think my heads are finally done and on their way home. Also when doing the clay test, leave the head gasket off. That way you know you have that little bit of extra clearance for valve float, and you don't end up wasting a set of gaskets.

i was thinking about milling the top of the piston down that little bit to make it match the height of the vfr piston. seems like the 929 piston is plenty thick enough to handle this. thoughts? it would be something around .030 off the top, thats not much at all.

gotta give this topic a bump just cause its too cool not to...

and eddy, your idea of machining the tops of the 929 pistons (if theyre too tall from the wristpin centerline to the top of the piston deck, that is) is actually a REAL good idea. are there any adverse effects or bad consequences that can come of machining a piston like that?

Too thin = potential dome breakage?

If you machine too much material off the top of the piston you might end up with a broken ring land:

[image: ringland.gif]

Interesting thread.

I would like to note that polishing a connecting rod does not make it stronger, it makes it less prone to breaking due to removing any potential stress risers. Splitting hairs, I know.

i dont really think that the very minimal amount of machining that is required to get these to go in would really be a concern, in my opinion. the piston has 6mm from the top to the first ring groove, and i would guess that the interior of the piston would be similar. HOWEVER, only a small portion of the edge would need to be removed, sort of a bevel to match the head. might get a slight compression bump from this too. im gonna look into it a little further.

next question, how do we deal with the head gasket? is there a big bore one we can buy?

I have heard of folks carefully trimming a stock head gasket, but I don't know how far one can go with that.

The big bore head gaskets used by TTS and Dynamo Humm are (were) modified OEM. Brian Law once told ne how he did it (using an air grinder, I believe), but I ended up having TTS install the kit and mod the gaskets for me.

Ciao,

So has anyone got any further along with this? I gonna kick in a few things. If you want to know how much you have to play with getting the pistons decked; take one and cut it in half with a band saw will tell you much about how much material is actually there. Did it with a junk head from a Toyota pickup, I was porting the replacement. Did a lot of good cause I ripped the frame in half not two weeks after rebuilding it.

i dont have a spare piston to cut in half or else i would.

im going to soda blast them all and try to machine the tops off.

i talked to a local speed shop, and we did some rough calculation based upon my guessing of the piston popup of the vfr. if i trim the piston tops to match the vfr deck height JUST enough to clear the squish area on the vfr head then i will be sitting about the same compression as before with stock bore/pistons.

im also thinking of running two 900rr ignition units on this engine. one fro the front bank one for the back. ive heard they have a little more timing advance to them and i want to see how much it would affect things. i will be machining the pistons today, ill post pictures of my progress later today.

also, where would someone send the upper half of the block to get it bored? i was thinking APE.

i just called millenium tech and they quoted me 250 to bore and hone to my pistons for this build. not bad!

also, i got in touch with a custom gasket manufacturer for the headgaskets for this and he quoted me 100 each for big bore headgaskets.

I ended up over here from VFR World. Considering bike projects and this was pointed out to me. Sounds like a GREAT thread (so far).

flyguyeddy measured his 929 pistons, and came up with ~24mm from "top" of piston to center of wrist-pin.

The TTS pistons listed a comp height of .900 and a dome of .155. Assuming that together those are the total height of the piston from the wrist-pin center, in inches, 1.055" gives you 26.7mm... Which seems awfully tall vs. flyguyeddy's numbers.

Futher, the .900" comp height (anyone know exactly what dimension this is?) is 22.8mm, which matches the numbers from JZH..

So, are we (ok, you guys, until now), all taking the same "top" on the pistons??

From Wiseco's site:

"Compression height is the distance from the center of the wrist pin to the deck of the piston (not dome)."

flyguyeddy: were you measuring to the top of the dome, or the deck of the pistons?

('cause yes, I'm REALLY interested in this, maybe in a new 4th or 5th gen bike as a fun project)

yes we are referring to compression height of the piston. the 929's are a little taller than the vfr around the edges. i plan to chuck mine up in the lathe at work and cut off just enough to clear the squish zone in the head.

Thanks for the clarifcation. :)

I'll go back into lurk mode now...

flyguyeddy

yes we are referring to compression height of the piston. the 929's are a little taller than the vfr around the edges. i plan to chuck mine up in the lathe at work and cut off just enough to clear the squish zone in the head.

ooh, pics please?

you will have to probably have to cut the valve pockets also when you cut the pistons.

Hey, this one dead in the water?

no its just stalled. i need to get my pistons machined and i havnt had the time.

[image: View Post]V4 Rosso, on 19 August 2011 - 05:46 AM, said:

[image: View Post]mcrwt644, on 18 August 2011 - 06:35 PM, said:

[image: View Post]karhawk, on 21 April 2012 - 07:24 PM, said:

[image: View Post]flyguyeddy, on 21 April 2012 - 08:43 PM, said:

Ok i have started to machine my pistons. As discussed earlier .030 needed to be removed from the areas that will interfere with the head. So i chucked each piston up in the lathe and centered off the area between the middle ring and the oil ring, using the ring land from the oil ring to center the face of the piston. Touched off each face, backed the cutter off and moved it in .030. Then touched off the side of the piston and went in .154" (as read on the dial of the crossfeed wheel, which means diameter not radius). I came up with this number by subtracting the vfr piston diam from the 929 diam measured above the top ring. After i finished that cut i then did an angle of 22.5 degrees (as close as i could measure the vfr piston to) out until it stopped cutting. The result is this.

[image: 3e0ce7e0.jpg]

You can see the one piston marked with yellow paint. That area also has to have .030 removed from it and i will blend it all into the valve relief pockets in the middle.

What do ya'll think?

Sweet. Was it a pain to get them to run true in the late?\

So just need to lap the top surface then? Grind or mill? Or both?

Here is a side view, with both pistons sharing a pin.

[image: d28d0e95.jpg]

It wasnt all that hard. Ill post a picture of my setup being as im doing 8 pistons total.

Cool.

What will your displacement be with this setup?

And what about the weight of the pistons vs the Vfr ones? How is that going to affect the balance?

[image: feb90f87.jpg]

836cc. Im hoping to not lose too much compression with the smaller dome.

Piston weights with pin and clips are vfr=224.75g and modified 939 minus coatings is 231.9g. Not a whole lot of difference, really. I imagine it wont matter. This was actually discussed in either this thread or the other big bore piston thread

[image: View Post]Bmcmanus87, on 27 April 2012 - 11:11 PM, said:

[image: View Post]flyguyeddy, on 21 April 2012 - 03:24 PM, said:

[image: View Post]flyguyeddy, on 21 April 2012 - 03:24 PM, said:

[image: View Post]NakedViffer, on 30 July 2012 - 10:34 AM, said:

[image: View Post]Mohawk, on 30 July 2012 - 12:18 PM, said:

[image: View Post]NakedViffer, on 30 July 2012 - 10:34 AM, said:

[image: View Post]Mohawk, on 30 July 2012 - 08:04 AM, said:

My 5th Gen version of the same thing;- http://www.vfrdiscussion.com/forum/index.php/topic/75247-vfr848rr-anyone/

Got a set of used 929 & 954 pistons, plus a spare engine to play with. Only problem now is I work away from home all week every week & a shortage of finances.

But this was a winter project, so my yet turn into real metal. I may destroy my upper crankcase to get the real deal on the MMC liners dimensions fitted in the bore. Then buy a spare set of crank cases to rebuild it in if there's enough meat in them to make it feasible..

Still have a new set of Bigbore pistons for the VFR800Fi / VFR800 Vtec (TTS)

Willing to sell

Something for my 750 4th gen would be nice...

Any developments?

Can anyone tell me if the rc36 engine has the same type of liner that the vfr800's do? It sounds like dynamo humm sleeved all the big bore engines they made, making this project way more expensive.

I thought they were sleeved because they were bored out so far that it was a strength issue.

flyguyeddy

Can anyone tell me if the rc36 engine has the same type of liner that the vfr800's do? It sounds like dynamo humm sleeved all the big bore engines they made, making this project way more expensive.

MMC (metal matrix composite) was not used on the RC36 engine

Oh, thank god.

JZH

'flyguyeddy

836cc. Im hoping to not lose too much compression with the smaller dome.

So you're effectively making your own TTS Big Bore kit? If that is the case, then the main issue will be with boring the cylinders. Back in the day, when Brian Law at Dynamo Humm sold the TTS kits and built the engines, there were a few stories of ruined engine cases, incorrectly bored by engine shops that had no experience with VFR-type v4 engines. Brian used OEM head gaskets, hand-reamed using an air grinder. If my 837cc 3rd-gen is anything to go by, there isn't a huge difference from the extra 89cc, though it does feel stronger.

Ciao,

"If my 837cc 3rd-gen is anything to go by, there isn't a huge difference from the extra 89cc, though it does feel stronger."

I fitted the TTS 837cc kit to my RC36II based track day bike, in conjunction with a slip on can, Dynojet kit and a modified airbox.

The result made my standard road VFR feel flat by comparison... Mainly a boost to the alraedy strong mid range.

Probably the best $$ per BHP mod you can do to a VFR in my opinion.

"If my 837cc 3rd-gen is anything to go by, there isn't a huge difference from the extra 89cc, though it does feel stronger."

I fitted the TTS 837cc kit to my RC36II based track day bike, in conjunction with a slip on can, Dynojet kit and a modified airbox.

The result made my standard road VFR feel flat by comparison... Mainly a boost to the alraedy strong mid range.

Probably the best $$ per BHP mod you can do to a VFR in my opinion.

Hi Andy,

I have an RC36 motor going into an RC30 frame - and I'm looking to do the big-bore conversion.

Who did the rebore for you and what did it cost you all-in can I ask (PM me if you don't want to post it up here).

Many thanks,

JB

TTS did mine. I had several "issues" with their work, but it was a long time ago, really.

Ciao,

anything new? thread was a great read

ChiefGodzilla

anything new? thread was a great read

HighSideNZ has a great thread on his 5th gen big bore engine mounted in a 6th gen RWB... ~140 rwhp.

Makes a great read and he is quite a mechanic!