If you upgrade a stock 400EX with one of the 440 kits, do you need to change the carb? or will the stock carb be enought to feed the 400? Which is better, the 11:1 or 12.5:1? Pro's and Con's of each?
Thanks,
James

 

yes, the stock carb, with necessary jetting, will be more than sufficient for a stock ported 440. A new carb would excentuate the increased power gained though. With the compression ratio's, It all depends on how availiabe race fuel is. It has been said that you can run premium on a 11:1 piston. The 12.5:1 would deffinatly need over 100 octane. The power gained over the addition 1.5 compression points is negligable at best, I think anyway. But, i do hope you will be going with a hi-rev cam too. Just a big bore, hi comp piston wont yield what you are looking for.....

 

Thanks for the reply. I am still considering this and have not made up my mind if I really want to upgrade the 400. I am currently testing a 450R and I have been told the 440 is actually faster, would like to test this for myself.
James