13:1 and race fuel.

[Prednizone]

Question for Rudy, but anyone can chime in.

I'm told there's a 13:1 piston in my '05 450R. Does running that piston require straight race fuel? Or just premium? Or a 50/50 mix?

[panici33]

In my opinion, if you have anything higher than 11:1 but less than 13.5:1, you can run race fuel but you don't have too; you get better performance with race fuel though. I ran Klotz 100 in my stock YFZ450 and I saw a noticeable difference. I started running VP U4.2 in my LTR450 with stock compression and I saw a difference again in performance. I have a little bit more compression now but won't change fuels. U4.2 performs really well. Most guys I know that run 50/50, want the performance of race fuel but are trying not to break the bank. 13:1 I don't think is potent enough that you have to run race fuel.

Its all about performance; you will have a slight edge with race fuel vs. pump. You should check out VP's website. They have a fuel for all types of compression.

Plus race fuel smells good.

[ElderGeek]

Plus race fuel smells good.

Yes, Yes it does......

[Jeremy]

Interesting to hear what Rudy has to say...


Run the lowest octane you can without detonation. That is where the power is at.

[Prednizone]

Thanks for the replies guys.

Rudy...anytime. Haha!

panici - that's kinda what I had heard. Thanks for sharing that. I'm at 50/50 right now, which I know is not the best way to get a real MON, but yeah, it eases the wallet a bit.

Jeremy - I think I knew that. But the question is...what is that MON for my engine, and how do I get it? Haha!

[Jeremy]

IMO you're fine with a mix. With a 13.5:1 with shaved head and cylinder I'll stick with straight race fuel!

[DFR Rudy!!!]

the 50/50 mix will be ok, but keep in mind you are right on the borderline. A hot day or the jetting a bit on the lean side could get you some detonation leading to engine damage. I feel its worth the extra money to know for sure that you are protected in all conditions.

[Prednizone]

Good point. Better safe than sorry. 100 or 110?

[QuadRacer28]

I am contemplating the same thing on my KTM which runs a 12.5:1 compression piston. Has anyone had any experience with Sinclair race gas sold at certain stations? They sell 100/110/120 race fuel in 5 gallon "tins" for $54, definitely cheaper than the VP and Klotz equivalent. I was thinking about trying the 110 and mixing it with pump 91. Does anyone see any disadvantage to running pump race gas versus specialized race gas?

I've also always wondered how you can switch from pump unleaded gas to race leaded fuel without causing any problems?

[Prednizone]

The race fuel I run is out of the pump. Sunoco 110 from the Love's truck stop next to Firebird. Never had a problem.

The difference is that the underground takns that the pump fuel sits in is vented. That fuel probably sits in there for quite awhile. The venting will actually have the effect of dropping the MON (motor octane number) slightly the longer the fuel sits vented. If you get it in a sealed metal bucket like the shops sell, the MON is better controlled.

Personally, I never thought my engines were wound THAT tight to where it made enough of a difference to pay twice as much for 110 out of a bucket vs. the pump.