What octane to run?

I have a 07 YZ250F with Stage 1 Hotcams, Wiseco 13.5:1 high-comp piston, and FMF full factory 4.1 exhaust with powerbomb. I doubt the exhaust has anything to do with octane, but anyway, I can get either Sunoco 110 or Sunoco 112. VP has some nice fuels but they are outrageously expensive. For the Sunoco, it's 11.75 per gal for the 110 and 13.75 for the 112. Whats the best for the cams and piston? The guy I talked to told me 112 for sure, since 110 only tolerates up to 13:1 (even though it can tolerate higher comp in smaller bores, it would still be pushing it). I think the MON is 106 for 110 and 109 for 112. Yet, I've also heard 112 is overkill...for some unexplained reason. Can someone enlighten me?
 

SRAD97750

Moderator
Staff member
Have you done a compression test?
If you are under 200PSI cranking compression in a modern 4T, you can run on 91 pump gas.
My GSXR makes 14:1 compression/14,000 RPM and runs great on pump gas.

I suggest trying 91 from the pump. If it pings or runs funny, you can mix in race fuel at 1/5 and I promise you'll be fine. -BIG DAN:thumb:
 

James

Staff member
I have a 07 YZ250F with Stage 1 Hotcams, Wiseco 13.5:1 high-comp piston, and FMF full factory 4.1 exhaust with powerbomb. I doubt the exhaust has anything to do with octane, but anyway, I can get either Sunoco 110 or Sunoco 112. VP has some nice fuels but they are outrageously expensive. For the Sunoco, it's 11.75 per gal for the 110 and 13.75 for the 112. Whats the best for the cams and piston? The guy I talked to told me 112 for sure, since 110 only tolerates up to 13:1 (even though it can tolerate higher comp in smaller bores, it would still be pushing it). I think the MON is 106 for 110 and 109 for 112. Yet, I've also heard 112 is overkill...for some unexplained reason. Can someone enlighten me?

I don't see any reason that you need to be running anything higher than premium pump gas (unless it's knocking). The KX250F's have been running 13.5:1 or higher for years now and they run on pump gas. It's been 13.8:1 since 2013.

Couple other things, running a higher octane than needed will actually rob you of power thanks to the higher ignition point. Plus unless you're racing in the top classes you're just throwing money away.
 
Big Dan and James are absolutely correct.

Run the lowest octane you can without pinging (preignition).

In the 250s, if you are below 14.5:1, it will run fine on 91 oct pump fuel.

Running higher octane rated fuels will yield you a much slower burn rate. This means at higher rpms, more of the fuel/air charge will exit the exhaust unburned. This yields less power.

Most people think octane is a power additive...it is exactly the opposite.
 
BigDan if you want to run something with a bit of a kick. And is safe to run in your stosk engine and will not rob you of any Hp. Buy Vp's U4.4! For stock engine's that is the best. Mix it 50/50. It feels like you did engine mods or even a new pipe. Its that good. Expensive 98 bucks for 5 gallons. Well up here where I live anyway. central NY.
 
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