VFR848RR Anyone ???

Regarding the power to weight ratio, the Duke 848 has 118hp to 195Kg of wet weight, so 0.60hp/kg. My VFR is already 25Kg+ lighter than standard & weighs 215Kg with a full tank, or 210Kg with an equivilent fuel load to the duke. So 107hp to 210Kg wet weight = 0.51hp/kg, if the big bore makes 130hp, then the power/weight ratio = 0.62hp/kg And if it made 140hp it would be 0.66hp/kg. So better than a standard duke 848 !

 

I like where you are going with this idea. From what you have already found out and shared, the 929 pistons sound like the best upgrade. If the center piston is the 929 I would machine off the lower skirts and I bet that would reduce weight to at least match the stock 954 weight.

I would also test fit to the OEM overbored cylinder head gasket. If the piston and gasket look good, run em. If not, then have a custom gasket made. Given the small difference in liner thickness over std. overbore (and considering industry standard failure is often calculated with 30% or so margins) I would hazzard that you can safely run the 929 pistons at 12.2 comp. ratio with no extra reinforcement of the liners. If I were you and had a spare engine, I would be running full speed ahead. Can't wait to see if you make this happen. :thumbsup:

Jose

 

I had been looking at the 929 pistons for some time & had intended to remove enough weight to make them equal to the VFR ones & to ensure perfect weight balance across all 4. I have them already, but only one 954 bought for test measurement purposes. It's still an appealing option & if your 30% industry standard is correct, then 7mm wall is 89% of the orginal 8mm & 6.4mm wall is 81% in thickness terms. I'm trying to find out how thick the 954 liners are as they are safely bored to 76mm, thus giving 980cc.

If I can make the 75mm bore it would be a bonus & definately provide more power But the VFR825F2 is an option !

 

FWIW, I remember a couple big bore kits way back when I bought my rev 5.
Dynammo Humm made them?
I seem to remember one being 830 (840?) and the other was something like 870?
The latter required new sleeves or something. Not sure, I haven't looked at bike mods for a long time.
But that would indicate 870 is certainly doable on a VFR800.

Does anyone know a shop that has experience doing the bore work on the Honda V4s?

 

Wondering if you ever tackled this project?

 

It's not winter yet ! Hopefully I'll have enough spare cash & time to tackle this later in the year when its cold and dark in the evenings & I've nothing better to do ! Watch this space.

For those interested in this I have received info from TTS & Dynamohum, basically the MMC sleeve liner can be bored to 74mm safely, so an 825cc big bore is an easy option, this may or may not require Nikasil on the bores, depending on how good your boring company are.

The 870 or even the 848 (76 & 75mm bore respectively) would require new steel liners & thus the CBR pistons are NOT best suited for this purpose, but could be used. The liners would be special order, so possibly expensive & only leaves 4mm alloy wall thickness to support it.

Going forward I'll be looking at the 825cc option using CBR929 pistons.

 

Well alright then .... 929 pistons it is.

Can't wait to see what happens. :madgrin:

Jose

 

How much do you figure the compression ratio will change given the new overbore?