Race Gas Question

[PEPwalshZ440]

Hey all,
I got a question about some race gas. So about a year and a half ago i bought a thing of VP 108 octane oxygentated race fuel and i opened it for about 10 seconds when i got it and then resealred it. It's been sittin there all this time. Do you think I could still run it?? And if i could, my quad has stock piston for 04' with the lid off, k&n filter, and TC pipe do you think i could run it without changing the jetting?? Any help would be greatly appreciated.
-Mike

[MR.BIG]

You could run it without changing your jetting but you are just waisting your money since you don't have a high compression piston. The gas should still be ok but maybe mix it with some fresh 93!

[PEPwalshZ440]

okay....i'll try that...thanks!
-Mike

[GPracer2500]

108 octane Oxy fuel from VP? The only one I know of that could possibly meet those specs is VP CSP. But that's 108 RON, not the MON they normally use by VP for labeling octane rating (CSP MON is 97). My guess is you've got VP C12. I say that for two reasons, 1) it's a very common fuel (CSP is not) and 2) its MON is 108.

But C12 is not oxygenated. And it WILL affect your jetting (along with most racing fuels). The primary factory in determining how a fuel affects your jetting relative to another fuel is the specific gravity specification of the two fuels. A typical racing fuel has a lower specific gravity than a typical pump fuel. The lower the specific gravity the richer you jetting must be.

Most pump fuels are gonna have a specific gravity over 0.750 and could be has high as 0.800. C12 has a specific gravity of 0.717. The less-dense C12 needs richer jetting to maintain the same air/fuel ratio you had when using pump fuel. If you're already jetted for best power (i.e. right on the edge of lean) then using C12 with no jetting changes could easily push you over the threashold of lean--you don't want that. If you're like many (most?) people and are jetted a little richer than "best power" jetting then C12 might bring you right to where you want to be.

ALWAYS CONFIRM JETTING WHEN CHANGING FUELS!

[PEPwalshZ440]

blahh i just poured about a gallon into my tank mixed with 93 and i've been running a little lean....guess i need to drain it or something cuz i don't feel like jetting it, i'm trying to sell it.
-Mike

[MR.BIG]

Correct me if I am wrong but doesn't race fuel run richer than regular gas!

[GPracer2500]

Originally posted by PEPwalshZ440
blahh i just poured about a gallon into my tank mixed with 93 and i've been running a little lean....guess i need to drain it or something cuz i don't feel like jetting it, i'm trying to sell it.
-Mike

As long as you're not holding WOT for long periods I wouldn't fret too much. Kinda depends on exactly how lean or rich you where before on straight pump. If you're worried just drain some out, top it off with pump, mix it around real good, and I bet you'll be fine.

[GPracer2500]

Originally posted by MR.BIG
Correct me if I am wrong but doesn't race fuel run richer than regular gas!

"Race fuel" is far too much of a generalization to be a useful term in any converstation about jetting. There are so many different race fuels with widely ranging make-ups that there are few "golden rules". It only makes sense to be specific about which fuels you're wanting to compare.

But like I said above, looking at the specific gravity of a fuel tells you a lot about how it needs to be jetted.

Specific gravity is a measure of weight. And air/fuel ratios are measured in weight (~13.5 parts of air to 1 part of fuel, by weight being the "best power" ratio for most engines). But carbs don't meter fuel by weight; they meter fuel by volume. So, if you've got a lower weight fuel (lower specific gravity) then you've got to add more volume of it to the air/fuel mixture to maintain the same ratio by weight.

Lets assume pump fuel has a specific gravity of .750. The difference between that and C12's .717 is 4.4%. So, your main jet would have to be 4.4% larger to maintain the same air/fuel ratio you had before. By my calculations that comes out to about 2 jet sizes (i.e. from a 180 to a 185).

It can get more complicated than that, but if you're not sure where to start when jetting for a new fuel than the specific gravity is the place to look first for guidence.

ETA: I should note that specific gravity has a lot to do with why people sometimes talk about "jetting consistency" regarding racing fuels. Most of the better racing fuels have a specific gravity spec that is set at one single number. Batch to batch it's going to be the same weight and that's where much of the "jetting consistency" comes from. Pump fuels and budget oriented racing fuels will list a specific gravity in a range (e.g. VP 110 is .720 - .735). Pump fuels can vary by quite a lot. Unless you measure the weight of your fuel with a hydrometer you don't really know where your particular batch of fuel falls within that range. And THAT is how one guy's 180 main jet might be perfect with his Chevron fuel and your identical bike and environment might be perfect with a 175 using Shell fuel. Or said differently, the fuel you bought yesterday might be a jet size or two off from the fuel you bought last week.

[PEPwalshZ440]

sweet....yea most it'll be on is someone riding it my backyard before they buy it hah. Yea...there was a little bit of pump gas when i put it in there but theres alotta race gas in there now. Thanks for all the info....this should probably be a sticky or something if there hasn't been another topic like this but im sure there has been.

[DirtDevilBT]

Well, the only problem with c12 is it's weight/ mixture is it has lead in it so even with the leaner/lighter/less denser fuel it should still run on that fine line ok.

but I don't know as much as some, just throwing that out there.

[GPracer2500]

Originally posted by DirtDevilBT
Well, the only problem with c12 is it's weight/ mixture is it has lead in it so even with the leaner/lighter/less denser fuel it should still run on that fine line ok.

but I don't know as much as some, just throwing that out there.

I'm not quite clear on what you're saying. But if you're suggesting that the lead in C12 throws off it's specific gravity measurement--it doesn't. All the components of a fuel are accounted for in it's specific gravity.

[DirtDevilBT]

lol, wasn't saying much but the point was:

Eventhough C12 is lighter in weight, because it has lead it should run fine being a little lean. The additives in C12 (w/lead) will allow it to run on that lean side without pinging or harmful affects.

Like I said though, just throughing that out there. Don't know much but was wondering if that had some kind of truth behind it.