Compression and Fuel

[sixer3]

well i've been searching a bit and cant find an exact answer

What compression ratios use which type of fuels? would it vary by bike type? and would a higher compression with a higher octane fuel require bigger head studs even at stock bore?

i have a 400ex if it would matter for my situation thanks

[bradley300]

it will vary, but cam overlap has alot to do with it. the key is to use the LOWEST octane possible

[JOEX]

Originally posted by bradley300
it will vary, but cam overlap has alot to do with it. the key is to use the LOWEST octane possible
I'd like to know more info about how overlap affects other aspects of the performance of a motor.

I remember a little from back in HS autoshop but that was a long time ago:p

[nakomis0]

In general 11:1 on a air cooled bike you can run 93-94 octane.

Liquid cooled and you can go 12:1 and still run 93-94 octane.

Compression is good and bad. Its power but it can be to much. Pulling head studs is 1 issue. It can actually make your top end speed slower if you have to much..

On a 400ex 11:1 is about the most I would recommend going with the stock head studs. Basing that on my own experiance I run stocker studs and have no problems.

[Rico]

11:1 for a 400ex is as far as you want to go on pump gas.

I run a 10.8:1 JE piston with cometic flex steel gaskets and can run pump gas just fine. It runs much stronger with a 50/50 mix of 110 octane when I can afford it..> LOL

I did recently have to put in Heavy Duty head studs because I had one start to pull thru. GT Thunder did the work and all is good now.

[bradley300]

Originally posted by JOEX
I'd like to know more info about how overlap affects other aspects of the performance of a motor.

I remember a little from back in HS autoshop but that was a long time ago:p

from what i read (and it could be wrong) if the cam has the valve open at all during the compression stroke, the time that its open is called overlap, correct?? anyway, during this, the motor cannot build compression, so even with a big domed piston, there is not enuff air/feul in the cylinder after the valve closes to achieve the comp ratio that the piston advertisies