Compression?

[300ex07]

What is the highest compression you can safetly use on pump gas

[Knips178]

i think 11:1 you can run like 89 octane, and 12.x:1 you need to run 93 octane. then if you get up to around 13:1 you better be running race fuel 110 octane.

[Hondaluva]

I normally hear 11:1 on 93 octane. Anything above that and you will want to be mixing 93 with cam 2 (110 octane).

[UglyMotha™]

Originally posted by Knips178
i think 11:1 you can run like 89 octane, and 12.x:1 you need to run 93 octane. then if you get up to around 13:1 you better be running race fuel 110 octane.





man where did you get that info :huh 12.1 is definantly going to need race gas atleast a mix, normally 11.1 is borderline it can go either way most cases you can get away with 93 but some cases some people have to run a race mix, pre-detonation shouldn't be your only deciding factor on what type of fuel you run, the higher the compression the more heat your goin to generate and a higher octane fuel is goin to cool the piston

[wilkin250r]

It's possible to get up to 12:1 using pump gas, but it takes a very precise setup that is usually very expensive, you're not going to find in a prepackaged "kit", and certainly not going to find it in an air-cooled engine.

[UglyMotha™]

Originally posted by wilkin250r
It's possible to get up to 12:1 using pump gas, but it takes a very precise setup that is usually very expensive, you're not going to find in a prepackaged "kit", and certainly not going to find it in an air-cooled engine.



man wilkin you always gotta bend the rules :mad:



considering the ex never came with a liquid cooled motor other than fst's your not goin to to see 12 on pump :p

[cals400ex]

yeah, sparks told me that a true 10.5:1 is about the highest they would run on pump gas. i run a 10.8:1 piston, but that isnt a true 10.8:1. if i removed the base gasket and only ran one layer of the headgasket, i may be alittle closer. i have never compared race gas to pump gas in my bike. so, i don't know if it will run better with it or not.

[Knips178]

obviously it differs between machines and their setups, but i'm in the middle of installing a wiseco high compression 440 kit, which is like 12.3:1 and I think I can run a mix of 93 octane and 110 race fuel. am i way off on this?

[UglyMotha™]

you'll just have to build then see, i can tell you for sure that you won't be able to run straight 93 you might be able to get away with a mix you'll just have to run it and see if you get any pre det or how hot she is running that is the only way your goin to know, your elevation and temp also has a lot to do with it

[Knips178]

is there any difference in performance in the following?
Use a 12.3:1 high comp piston and make the final compression actually 11:1
vs.
Use a 11:1 piston and make it spot on at 11:1 final compression
??????

is there a different flame travel from the domed head that make it worse or better? or should they perform the same?

[wilkin250r]

Obviously something designed for 11:1 spot-on will work best. If a 12.3:1 detuned to 11:1 worked better than a true 11:1, then wouldn't the true 11:1 be designed just like the 12.3:1 detuned?

There are lots of different things inside an engine that affect power, it's not just displacement and compression. Valve placement and size, dome shape, flame travel, squish band, ect. A true 11:1 compression piston will be built to optimize all these factors at 11:1. Likewise, a properly designed 12.3:1 piston will optimize all these factors at 12.3:1, but they may not necessarily be optimized at 11:1.