Cammo wrote:As blueflag says, using rvf400 pistons (vfr are discontinued) will increase the compression ratio. Easier than skimming the heads and the rest of the work.

I don't know how much this increases the c/r by, anyone have any idea?

Mike Norman told me that skimming 0.5mm off the head on the VFR engine increases the compression ratio by about one point, so 11.5:1 to 12.5:1

http://www.ebay.co.uk/itm/RVF400RR-RVF4 ... 2ec0429053 Bit cheaper..

Second hand set in good nick with new rings will do the trick. It's the cost of a head gasket that's the head scratcher. (no pun intended)
If you go the offset gear route, just weld it better than I did! Lol!
For what it's worth, and it is only a feeling but I SEEMED to have more power with the V4 pistons. Different dynos but with the offset gear it was putting out 56 ish, now after some expert carb set up by a mate (on another dyno) it's putting out 60.7 and feels stronger everywhere. (Alright, yes, I won the championship this year )
Keep us posted what you do.

As with all racing, its the guy with the most money that wins.
From experience 87-2012.
V4 pistons are hard to get and a gasket set is £30 and I can do all the other work myself.
There are loads of stories of engines with V pistons blowing.? any ideas? before I commit?
The thing about the cam gear mod is getting the cam timing right after.
If all I want is raised compression, why can't I just skim the head and elongate the cam gear mount holes to offset them a little?

Head gaskets (NC23) are around £60 each,
If you really want to do the mod you might as well remove the quietening gears on your cams and make them adjustable, I did this when I offset my cam drive gears but I found it a reall pain in the backside setting the cam timing. I reckon it's worth doing but I would caution doing it unless you have access to a dyno and plenty of time.
I paid about £30 quid for my pistons......
I understand your worry about blowing an engine if you put the V4 pistons in but in my limited experience they worked just fine. I did check the valve / piston clearance though!
After my engine fail I took out the adjustable cams, modified idler gear train and standard pistons and threw them a long way away!
Just my tuppence worth.....

Cammo wrote:As blueflag says, using rvf400 pistons (vfr are discontinued) will increase the compression ratio. Easier than skimming the heads and the rest of the work.

I don't know how much this increases the c/r by, anyone have any idea?

Calculating Compression ratios


http://www.csgnetwork.com/compcalc.html

dunkenb wrote:http://www.ebay.co.uk/itm/RVF400RR-RVF4 ... 2ec0429053 Bit cheaper..

This auction is only for the pistons. We sell the rings seperatly on our eBay store. Can supply the pins and clips as well.

Summery:

Piston SET, for one RVF400: £175.00 ( buy on our ebay store)
Ring SET, for one RVF400: £139.00 ( buy on our ebay store)
Pin set ( X4 pins): £39.00
Circlips set ( X8): £12.00
Combined Shipping, all above: £20.00

TOTAL: £385.00

Let us know when you are ready.

Kind regards,

Ido Kats
ISI Co., Ltd.

Web Site: www.isicar.com