Beeman ?

[Steve H]

Out of interest what piston did you end up running in your SRX ?. I know you had a few piston issues to start with, just wondered what make piston and CR you ended up with

[beeman]

Sorry about the delay, dragon rally and being ill has meant limited time on the computer.

Wiscoe piston 634cc I think, the comp ration was about 10-10.5:1. no problems with it, touch wood for 12k
did have problems with the cosworth piston previously used had 12:1 comp. Ist blew head gasket(genuine yamaha) then it seized up after being put back together. Problem was no info on clearances etc. The race tuner who did it thinks he should, in hind sight, have given it a slack 3k clearance and not a tight 3k clearance. which we think caused it to seize (bugger).

The coswoth piston certainly gave it more instant power.
Presently the bike is running 45bhp at the back wheel and max torque at 3k all the way to the red line. and beyond (oops)this is up from 31bhp standard srx on the dyno. Please note not yamaha quoted outputs.
Top speed is about 110mph on standard gearing and a sub 6 sec 0-60mph. easy to start and fuel economy seems not to be affected.

[Steve H]

Cheers for that, did you have a problems with pinking/detonation when you were running the 12:1 Cosworth piston ?.

Steve

[Steve H]

Interstingly the clearance on the box containg the cosworth piston states .020 mm or 0.8 thou, which is half that of a stock piston. I have read that cosworth use low silicon (or high silicon) alloy reducing the expansion rates. However half that of stock seems optimistic

[beeman]

I ran in on shell optimax mostly and never got passed 1000 miles before self destruction. Didn't get any pinking problems. Only damage on the piston itself was where it picked up when it seized. if I wasn't using the bike for work could be tempted to go back down that route. Would consider changing con rod first for safety tho.