Do I really need to run different gas

[shogs]

I have fmf fatties, vf3 reeds, a pro design cool head (unaware of dome size atm), about to have +4 timing, and also about to install a 2into1 carb kit. The guy I'm buying the carb from says I need to run 100 octane with +4 timing. Is this true? Also what dome size do you guys think I should run for best performance in trails? I'm trying to have everything together so when I get it I can install it and ride but I don't think that will be the case.

[278]

You need to do a compression test on the motor the way it is and let us know. Then we will be able to tell you. Oh and whats your elevation that will help too

[shogs]

My elevation is about 300 above sea level or so. I could take it to the shop and do a compression test but I plan on putting a new topend on it either way. Its my first banshee and I bought it used so odds are it needs a new one soon anyway.

[BUILDER]

My elevation is about 300 above sea level or so. I could take it to the shop and do a compression test but I plan on putting a new topend on it either way. Its my first banshee and I bought it used so odds are it needs a new one soon anyway.

 

Compression is what really matters as far as running ras gas. I am not sure of the numbers but if you do a search on here i am sure you will find it. You are run 4 degrees on your timing and not run race gas but if you compression is to high thats when you need to worry about your gas.

[dirtfreak]

under 150psi is ok for pump fuel.im at 360ft asl.

for pump gas i would think the domes should be 21cc you might get away with 20cc domes.

just have to compression test it.

[shogs]

Yea the only reason I asked was because its been running fine with high test from my gas station. There probably 21 or 22 I cant imagine them being any lower than 20. So timing has nothing to do with what gas I run?

[Misssppelllleddd]

Compression ratio and timing advance is what really matters in choosing race fuel. Yeah you can do a compression test to see how many lbs of compression you have but it really matters on compression ratio and timing advance. If you have too low of octane fuel you can have problems like detonation. When you put your top end back together make sure you torque your spark plugs to the right torque spec. If the spark plugs back out then you have a detonation problem. Either your timing advance is too much or you have too low octane fuel.

 

All in all you have to determine the compression ratio first. Figure out how much octane would run on that ratio. Then figure in your timing advance and add the octane rating from there.

[dajogejr]

Agreed.

While it's apart...measure it out to get your compression ratio. At 4 degrees timing advance...it would hardly change your octane requirements. But if your compression ratio is right at the ragged edge of pump gas vs. the need for more octane, the heat from a +4 could put you over the edge.