Well i have had my yfz450 for almost a year now, and have the basic mods done to it. I have a rossier pipe, rossier intake, once thoes were on i rejetted the carb. Recently i had some bad luck when i was on the trails, my chain came off and hit my shifter and cracked the case. Soo since i have to take the whole engine appart anyway to replace the cracked case. I figure i would do some engine work but i have a few questions.

First thing is the kit iam going to go with is this one http://www.maxpower-engines.com/big-...78-icecube.htm. Its a 478cc big bore kit comes with a piston and new cylinder. Now there is 3 compression ratios i could go with 10/1 , 12.5/1 , 13.5/1, which one would be the best for 93 0ctane gas? Also what other things would i need to go alone with this kit? could i rejet my stock carb to handle the bigger displacemnet? Or would i have to go with a aftermarket carb?

Will my engine be able to rev as high as it use to? If not maby instead of getting the big bore kit maby ill just get a high comp piston. well thank you!

 

Consider a stroker kit since you have to take the bottom end apart. It will give you much more performance than a big bore kit. You can run 93 oct with 13.5/1 compesssion without a prob. Some people will tell you 12.5 but I think you will be alright.

Yes you would have to rejet but you dont have to buy new carbs.

Yes your engine will rev as high as usual.

 

Thanks for the reply! Belive me i wish i could go with the stroker but its double the price of the big bore kit. Its around $1200 for the big bore kit to make it 478cc. And for the stroker its around $2500 and it makes it a 523cc which would be awsome. If what you said about the 13.5/1 compression ratio being able to run 93 octane gas, i will be getting that ratio for sure. Also thats great about me not haveing to go and buy a new carb and just rejetting the stock one. But is there any benifit to going with a bigger aftermarket carb? thanks again!