07-03-21, 05:02 PM
(06-03-21, 09:12 PM)ruckusman link Wrote: Partially correct, we're planning to basically overbore the FZR400 from 56mm to 62mm with either YZF600 or FZS600 cylinders & YZF600 cylinder head - various rod/piston combinations/choices to get compression height spot on - this may go into an FZR250 or an FZR400 - TBD
then a possible combination of cylinder block and conrod and pistons @62mm bore - fortunately there's quite a few pistons available in 62mm, because a straight swap of say YZF600 top end, with the same squish band with the reduced swept area would see compression fall from 12:1 -> 9.78:1 - not good!
Now it's starting to make more sense
Don't quote me, as I may be wrong as it's been some years since this kind of thing was asked. Back in the day many tried all manner of ways to get more power out of an FZS600 motor, including using parts from the YZF, like heads and blocks, I don't know of anyone succeeding. The FZS is one of those bikes that was already getting close to it's limit out of the factory and any real power improvements required major engineering, which just wasn't worth the costs. As mentioned the YZF is a very different beast to the FZS and I seem to remember someone trying to fit a head to a FZS block and it wouldn't, due to cam chain issues, water/oil galleries don't align and the same sort of issues when a YZF bloc was tried to a FZS cases. Not to mention pistons, con rods etc.
The other drama was with mounting the airbox in the FZS frame, as the YZF doesn't have a traditional tank layout like the FZS. The YZF uses the tank area to mount it's airbox because the intakes are at right angles to the cases i.e. from traditional 9 O'clock position to the YZF 12 O'clock.
Now anything can be done, if your prepared to throw enough money and time at it. But from what you saying money isn't something your prepared to spend much of, if it is then I hope you've got deep pockets. Personally I would look at the R6 option I mentioned earlier, with the 08 -09 (127bhp ish) being the most powerful next was the 06 - 07 (125bhp ish), quite why the later models produce less power and torque, emissions probably. Although the latest 17 - on produces less power but more torque than 06 - 09 models. Shoehorning one of these into a 250 or FZS 400 would be a real hoot and would require just fabrication work to the frame, tank etc but you'd need the, fuel system and electronics from the R6. Again unless it's just to prove you can and for fun there's little point just buy a R6.
I wish you the very best of luck mate and please do keep us posted, its a very interesting project.
Later