General Question. If you had a motor with 13:1 compression, wheter it be a car, bike, quad, whatever, what octane fuel would you need? I'm thinking at least 104 but I don't know. Is there a formula for this? Thanks.

 

I think it all has to do with the design of the combustion chamber.......

 

Hmmm, well then I'll have to wait [img]i/expressions/face-icon-small-smile.gif[/img]

 

Has a lot to do with a bunch of things

timing
cam
combustion chamber
water/air cooling
rpm the motor is running
oxygenated/non-oxygenated fuel
brand of fuel

But I'd say 104 would be a minimum

 

It's my understanding - I admit it's limited - that compression is the primary factor that defines whether or not higher octane fuel is reqd. Gasoline will ignite sooner under higher pressure. That's often why ya get pre-ignition (pinging) on cheap pump gas. Gasoline with a higher octane rating ignites later (is more resistant to ignition) and this suits the higher compression effects. Mix in all the other factors mentioned by Jay and it's really hard to exactly predict the correct octane.


A 13:1 motor will surely need higher octane that pump. My desert race car has 12.25:1 compression (high revving VW motor) and likes anything higher than 103/105.

I'd consult an engine builder who is experienced with the specific engine to be sure.

One thing I can guarantee - dont waste your money on race gas unless it's truely necessary - running anything other than premium in a stock motor is just $$ down the drain.

 

If you use high octane or race gas on just a..say... stock utility quad, will this damage the engine? will it give a noticable increase in power?

 

You will most likely loose power if you you race gas on a stock quad.

 

Alright then, screw it. Anyone know if they make a 13:1 raptor piston in 102mm? I found a 105mm but that requires a sleeve and I don't want to go there. EDIT Ok I found a 101mm kit [img]i/expressions/face-icon-small-smile.gif[/img]

 

Compression, sea level, and fuel have alot in common. Normally above 1500 feet you dont need race fuel, atleast on a two stroke. Also, a 13:1 will most likely require race gas. The higher compression needs more of a flash point when it ignites.