What Octane Should I Run

[coolhuh]

I just rebuilt my 400EX and now it is a 440EX with stage 2 cam. I checked the compression and it is 180PSI. Can I still run 92 octane?
Thanks

[2004exrider]

if its 11:1 comp ratio, then yes. 12.5:1 no.

Jimmy

[coolhuh]

It is the 11:1 piston, does the compression sound right?

[2004exrider]

sounds pretty damn good to me;)

Jimmy

[Kilabanshee]

If you're running a 11.1 comp piston you'll have to run atleast 94 octane. That might even be too low. I remember with my old 416ex 10.8:1 piston didn't like anything below 93 octane. Some motors are different. You can try running the 92 but I doubt it will run very well. If you hear the piston knocking you know your gas is no good.;) My friend in his 11.1 440ex runs a 50/50 mix of vp c12 and 93 octane. If racing gas is available to you I'de sugjest you run it. The difference in how the motor runs is huge!

[Rdhanded2]

If you have a a 440 then I would run higher octane fuel just for the heat issues.

[troutman561]

just a question kinda of off topic.. howcome on the 06 450r u can run pump gas with a 12:1 but alotta ppl or 50/50 on 11:1 pistons..is there something im missing here?

[JOEX]

Originally posted by troutman561
just a question kinda of off topic.. howcome on the 06 450r u can run pump gas with a 12:1 but alotta ppl or 50/50 on 11:1 pistons..is there something im missing here?
From what i've read a water cooled motor can handle a lower octane than an air cooled motor.

[wilkin250r]

"compression ratio" is just a general guideline. In reality, there are numerous factors involved, but it mainly comes down to heat.

The 450r is just better at removing that heat.

[dirteater74]

compression and cam profile work together, I read somewhere that your ability to run pump gas depends on how high your compression is and what type of cam you have in your motor. that's why the 06 450 can run on pump gas, because of the more aggressive cam that it comes with not because of better cooling capabilities.

[Chino886]

Originally posted by dirteater74
compression and cam profile work together, I read somewhere that your ability to run pump gas depends on how high your compression is and what type of cam you have in your motor. that's why the 06 450 can run on pump gas, because of the more aggressive cam that it comes with not because of better cooling capabilities.


I don't think the cam has anything to do with what type of gas you can run. A more agressive cam makes your motor run harder. If you read your statement above, it would be the exact opposite:

agressive cam=race gas
less agressive cam=pump gas,

not the other way around as you stated above....not flaming just for clarification, please correct me if I am wrong.

To answer the original question, if you have a 440, I would run higher octane fuel, especially with the heat that the 440 makes.

I am sure Wilkin250R is typing a more detailed post for you as I post this though...........

[Honda5]

the cam does make a big difference if you run a big cam with a lot of overlap you can get away with a lower octane fuel but using a stock cam will have a higher psi in the head causing detination problems and excess heat.