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Pump Gas versus "Race" Gas
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Author:  Frank [ Sun Oct 02, 2011 10:36 am ]
Post subject:  Pump Gas versus "Race" Gas
Are there any rules-of-thumb that can be used when using race gas (ex. VP100 from VP Fuels) as compared to pump gas? I recently had to run some in my T500 at a land-speed event where I had tuned on pump gas. The VP100 didn't work very well. Unfortunately I cracked a cylinder head before I could spend any time making changes. Initial evaluation was that it needed more main jet (based on plug color plus it wouldn't rev out at all although there was no audible detonation.) Ignition timing was probably wrong because of the slower burn of the higher octane fuel.

Thoughts, advice, etc. appreciated! Next time I'll get some ahead of time to tune with but any hints on where to start? I might run my H2 next time and want to learn more about how to approach this problem.

thanks,
Frank
Author:  Jim C [ Sun Oct 02, 2011 11:00 am ]
Post subject:  Re: Pump Gas versus "Race" Gas
From the experts I've talked to and articles read, there are no hard and fast rules as there are too many variables inlcuding engine type, porting, compression, altitude, barometric pressure, jetting, ignition, etc.

I do believe what this guy writes and is a pretty well regarded 2-stroke tuner and designer:

http://www.ozsuperkart.net/formulavee/T ... /Fuels.htm

BTW, I find it amazing that many of the gasoline classes at the track allow VP (and other) brands, as they often times have no gasoline in them
Author:  Jim [ Sun Oct 02, 2011 11:08 am ]
Post subject:  Re: Pump Gas versus "Race" Gas
Jim C wrote:
I do believe what this guy writes and is a pretty well regarded 2-stroke tuner and designer:

http://www.ozsuperkart.net/formulavee/T ... /Fuels.htm

Some good information under "How much octane do we need?":

Quote:
It's a commonly held misconception that higher Octane fuel slows down the flame speed which keeps the engine from knocking. Flame speed is a function of fuel chemistry, not the Octane rating. The component make up of the fuel will determine the flame speed whether it's a high octane fuel or not. . Racing fuels designed for high rpm applications tend to have higher flame speeds than normal to help reduce burn time.
Author:  Ja-Moo [ Sun Oct 02, 2011 11:20 am ]
Post subject:  Re: Pump Gas versus "Race" Gas
I haven't used race gas for years, but it burned so "different" you couldn't get a plug reading. Are you using a high compression?
Author:  Frank [ Sun Oct 02, 2011 7:47 pm ]
Post subject:  Re: Pump Gas versus "Race" Gas
Not really. I shaved the heads .040" and had static (cold) cranking pressure of 145 PSI. Jim C - thanks for the link. Interestingly, if I had run on pump gas already in the tank it's considered a "fuel" class. I wanted the gas record though (it was open) so I chose VP. I've emailed their tech support to explore this issue but haven't heard back yet. I'll try to get serious about learning more about combustion dynamics.
Author:  Jim C [ Sun Oct 02, 2011 9:04 pm ]
Post subject:  Re: Pump Gas versus "Race" Gas
Glad I could help Frank.
You might try sending Rich an email.
He answered many of my fuel questions on Dirtrider.net years ago and it would be worth a try to ask him his advice; I suggest giving him all the bike info as well as air and altitude date from your last run to encourage a response
Author:  scrambler73 [ Mon Oct 03, 2011 8:50 am ]
Post subject:  Re: Pump Gas versus "Race" Gas
on a related note.....

I use the highest octane fuel available when out riding, usually 92-93 Octane... All of it has at least 10% ethanol in it.

Yesterday, I ran the H1 just about dry and made it into a gas station that carries "non-oxygenated" 91 Octane, which from what I understand has no ethanol in it.

There is always a "hint" of detonation when you bring it up through the gears quicky and hold a high RPM for any amount of time.

So after filling with the non-oxy, it was noticably better...and not just Placebo-effect-noticable. I mean, I could hold it open much longer and the "hint" of deto was all but gone.

so why is this? Does ethanol burn hotter?, or is the octane rating inaccurate between oxy and non-oxy? (since the non-oxy was rated at 91 and yet detonation was less than with a higher-octane rated ethanol blend)
Author:  Jim [ Mon Oct 03, 2011 8:56 am ]
Post subject:  Re: Pump Gas versus "Race" Gas
Was it colder outside than usual? Also, ethanol requires richer jetting than gasoline, so with a 10% mix, the bike will run a little leaner than with no ethanol.
Author:  scrambler73 [ Mon Oct 03, 2011 8:58 am ]
Post subject:  Re: Pump Gas versus "Race" Gas
Jim wrote:
Was it colder outside than usual?



no, actually... it was a BEAUTIFUL 75 degrees fahrenheit.
Author:  Bill B [ Mon Oct 03, 2011 9:05 am ]
Post subject:  Re: Pump Gas versus "Race" Gas
This is one of my favorite subject, fuels can dramatically affect the way your engine runs. Alky burns much cooler than gasoline and is a natural octane booster. When running Alky in a race engine you bump the compression to near diesel levels and jet up about 100%. Many fuels have Teritary Butyl Esters that are an alky distillate and they increase octane and carry some oxy so they can clean up emmissions.

But when it comes to comparing pump gas to race fuels its get complicated. Race fuels vary significantly in specific gravity so you have to jet up and down to get your fuel/air mixture right. Pump gas and Avgas are fairly consistent but these are both grades of gasoline with some additives, Race fuel on the other hand has no gasoline in it, most are a mixture of high end solvents like Xylene and Toulene, you can call up the data sheet from VP's website.

So the simple answer to your question is....pick a fuel, tune to it and your good to go...how easy is that?
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