Compression ratio

[beyer05]

I am new here and have been browsing around. By the way, lots of good information. This is a cool site. I was curious why alot of you run a 10.8:1 piston on your 400EX's? Why not a 13:1 or 12:1 or something like that? Can you still run pump gas with 10.8:1? Or is it a reliability factor? I want to put a piston, cam, exhaust, and carb. on my 400 and trying to figure out what would be best for me (racing MX).

[VegasEx'r]

At 11:1 or higher you need to run race fuel in an air cooled engine. I think that reliability also comes into play. At 13:1, you'd be putting an awful lot of additional stress on the stock bottom end.

[Tommy 17]

i can run 94 octane on my 10.8:1...

[beyer05]

So, does anyone run a JE 13:1 piston? Here is what i was thinking, maybe you guys can give me a heads up if I am about to do something wrong:
JE 13:1 (or 12:1) piston (406), cam from GT thunder, exhaust from Hetrick or Curtis Sparks, hard faced rocker arms, heavy duty valve springs, port and polish heads, and a carbuerator (probably FCR39). Where is the best place to get the rocker arms and valve springs and how much are they?

[beyer05]

Anyone?

[Tommy 17]

if i were u that sounds good... the only thing i would do is go to a tc cam... i think they are the best out there but thats my opinion...


with this cam u don't need to harden ur rockers or get differnt valve springs... u can use stock as long as they are in good shape..

[beyer05]

Which cam can you use the stock stuff? The TC or the GT thunder? It doesn't hurt anything to use them anyway if you have the money does it?

[deansfastway]

I send the rockers out for CRYOTHERM treatment (Cold tempering process by deep freezing) It is cheap and pretty quick turn around. Also send out the clutch components and Third gear mainshaft . These parts seem to last longer .FASTWAY MOTOSPORTS