Vfr848Rr Anyone ?

[JES_VFR]

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

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

First Mohawk thanks for sending the Email to Brian.

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

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

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

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

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

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

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

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

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

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

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

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

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

what about stroking the vtec engine?

Well you don't have the limitation of the cam gears, but you still have the limitations of the VFR block.

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

[Mohawk]

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

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

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

[Dutchy]

Keep at it boys!

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

[douglasthecook]

Dutchy, one can only hope!!!

[daword2011]

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

[Rush2112]

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

[daword2011]

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

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

Then report here haha

[The Phantom]

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

[GadiantonRob]

This is something I want to do to my bike.

But like for realsies.

Not just talk.

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

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

[The Phantom]

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

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

[Rush2112]

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

@ G-Rob:

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

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

This mod has been done... for realsies!

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

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

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

[daword2011]

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

@ G-Rob:

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

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

This mod has been done... for realsies!

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

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

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

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

[GadiantonRob]

@ G-Rob:

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

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

This mod has been done... for realsies!

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

That's why.

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

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

Relatively speaking.

[Rush2112]

@ G-Rob:

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

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

This mod has been done... for realsies!

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

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

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

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

[Mohawk]

This is something I want to do to my bike.

But like for realsies.

Not just talk.

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

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

OK for real, the main issue is that the VFR series have the bore cast into the upper crankcase, thus boring them requires a total engine strip, not just a top end like many other bikes !!!!!! That adds huge cost to the project unless you do the spannering yourself.

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

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

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

[spinalator]

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

[Rush2112]

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

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

[Ranger77]

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

[Mohawk]

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

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

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

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

[Veefer800Canuck]

Interesting.....

[keef]

Oh hell yes!

[Switchblade]

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

[spinalator]

That won't buff out! ;)

[Mohawk]

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

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

[douglasthecook]

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