octane?

[Sparky416ex]

I picked up my 400ex from lancaster ohio a couple weeks ago, i have ran about 2 tanks of gas so it is basically broke-in. I went to the local speedway and bought cam 2 race gas, the octane was 115. I mixed 3 gallons of race gas and two of premium. It felt awesome the 416 kit kicks. I was wondering if there is a better octane besides 115 to run. On my next ride im going to run the race gas straight. Make sure you know what you are talkin about i dont want to blow up my engine. lol THX

Look in the faq section,,there's a thread on octane and compression.

[Scott]

It depends entirely on your compression ratio, which you didn't mention. Displacement doesn't mean a thing, you can have a 660 running on pump gas and a 125 that needs racing gas.

Do a search for threads about 416 or 440 kits on here. There have been a million of them, and most of them got into what octane fuel you need for what compression ratios. If it were me, anything over 11:1 I'd atleast run 50/50 with race gas. Much higher than 11:1 and you're going to have to use 100% race gas.

[Sparky416ex]

OK thx for your time, i have a xr 400 cam in it

[RideRed400EX]

VP fuel 108 octane is designed for a compression ratio between 10.5 and 12.5, anything higher is overkill. It's also about a buck cheaper too.

[Scott]

10.5:1 does NOT require 105 octane. Higher octane isn't doing you any good, it's just emptying your wallet faster...

[RideRed400EX]

I didn't say it was a requirement I said that a particular gas is formulated for a specific compression range. Try READING the message before blasting a person for something they didn't say.

[emiliano22]

Originally posted by Scott
It depends entirely on your compression ratio, which you didn't mention. Displacement doesn't mean a thing, you can have a 660 running on pump gas and a 125 that needs racing gas.


It is not fully true, a 125 with 11.5:1 probably work with pump gas and a 660 not, because in a bigger bore size is hard to control the detonation.