Octane Race and AV Gas?

[Excaliber]

I've heard it said "race gas" does not make "more power". I've also heard it said, it DOES!

Assuming you have ENOUGH octane to keep detonation and pre-ignition from occuring WHY would you use more? Only reason gotta be "more power" I would think.

I'm pitting for a new FF team, "we" are still working out the details and bugs. The 1600cc iron head engine is 9.5 to 1 C.R. The other teams are using 108, 110 octane, some are using AV Gas. One guy is using 103 octane. I'm thinking the 103 octane guy is onto something!! With only 9.5 to 1 C.R. why wouldn't 92 octane pump gas do the trick?

And whats the deal with AV gas anyway? I've heard you should NOT use it in a car. WHY is that?

[Hotfingrs]

First the easy part....AV gas burns slower, because of the conditions air plane engines are subject too, and oxygen at different altitudes. Don't know all the specifics, but something along these lines.

Octane, is the gases ability to control detonation. The higher the number the more control it has. A 9.5-1 needs more than a 13.0-1. You might want to advance the timing on your 9.5 and more octane will help control detonation. More timing=more power. If you use more octane than you really need, you're just wasting your money.

There's a lot more that goes into this.....but this is the short version....as I know it.

[Yetiman]

There are many factors involved, but it depends partially on how much ignition advance you want to be able to run, and how hot the engine gets.

That said though, if your running all the advance you want to, and have no detonation issues when the engine is as hot as it will ever get, there's no reason to up the octane any further.

Also, if you run Av gas, i wouldn't go telling people that.

[Excaliber]

Jack I think you got that dsylexia thing going on,

I assume you meant 13. to 1 needs more octane than 9.5 to 1 C.R.?

Hmmmm,,,, burns slower, IE "more controlled"? That is my take on higher octane fuels in general, a more controlled burn (slower?) thus NOT as sensitive to detonation as a lower octane fuel would be. Another way to say it, "Harder to light off" a higher octane? How that equals "more power" baffles me!

Why not "tell people" if your running AV gas (and were not)? Is it illegal or something?

[Hotfingrs]

Yep a little dsylexic.... higher octane doesn't equal more power, it what you do that requires the higher octane, that makes the power.

[Yetiman]

At least in my state, If the people supplying you Av gas know it's going into anything but an airplane, they can be subject to big sanctions. It's taxed differently.

[DAVID GAGNARD]

Slick;

Jack is right on all counts.........We used to use AV gas in the dirt track car,it ran very good,but AV gas has a number of additives for high altitude and air cooled avaition engines and will leave a nice black coating (have NO clue exactly what the stuff is) through out the internals of your engine..........

I have done a good bit of research on octanes and such and by all counts burning more octane than you need is just wasting money,higher octane will not make higher HP.......... actually the minimum octane needed for any given engine will make the most hp.........

Some people use a little higher octane for added insurance against engine knock while racing and running at prolonged high rpms.........

The drum (55 gal.) I have of 110 leaded gas right now states on the tag that this fuel should suffice for engines up to 15 to 1 compression,around here we have 110 and 114 avaliable in drums,my race motor is 13.5 to 1 compression,that's why I use the 110...........

David

[scottj]

There is much more to race fuel than octane rating.

Race fuels, such as VP Race Fuel, are blended for specific applications.

For instance, the VP Ultimate 4 that I run in my motocross bikes is only 92 octane but, it makes 6% more power than 92 octane pump gas.

The VP Late Model Plus that I run in my dirt car is 113 octane, like the Sunoco that I used to run but, it burns cooler AND makes more power than Sunoco (about 1%).

But, in my bikes, VP Late Model Plus made less power than VP Ultimate 4, or pump gas.

It's all about the blend. Certain blends do make more power when used in their intended application.
Scott

[DealsGapCobra]

AvGas (100LL) contains lead, so you don't want to use it if you are using O2 sensors.

[Steve R]

Homemade Octane Boost ??

[Excaliber]

Good link Steve. It is basically a discussion of how to raise octane. My question is more simple, WHY would you want to?

I know the main reason is: High compression and a fellow needs more octane. The Formula Fords are only 9.5 to 1 C.R., I suspect even "pump gas" would work fine (depending on timing issues, inlet air temperature, engine temperature, etc.).

Scott makes an interesting point, if I read it right. It suggests that there IS some "horse power" to be found using "race gas", a KEY part of the answers I'm looking for! Pretty hard to nail down WHY or HOW that extra horse power is to be had using "race gas" however.

[Allan A]

Ernie,

You will need all the help you can get from what I hear, I talked with one of your island brothers the other day Kei. Do you know him, he mentioned that his little CSX 8000 car smoked you at the drags. How could a little slab side eat your lunch with that big side oiler you have.

[Steve R]

Gas article
http://www.ducatimeccanica.com/gas.html

[Excaliber]

Ha ha,,,,oh yeah I know Kei really well, and yes he "smoked" me at the drags. Locally I'll always have a hard time living THAT down, and now it's GLOBAL??? Sheessssh, thanks a lot.




...I missed the third gear shift, but no one believes me ( ). Kei's car IS fast, make no mistake!

Good article, thanks for the link Steve.

[Allan A]

[John-Tucson]

Re. AV GAS. They do not use the same octane rating system that the automotive guys use. As previously stated, the AV gas, 100LL, does have more lead in it. John

[ToyCollector]

You need to be aware as stated above that even 100 low-lead Avgas still contains gas and one weekend it will ruin your O2 sensor (I speak from experience). I would not be as concerned about legal implications if using AVGAS OFFROAD.

Running higher octane than needed can lower running temps, which is why many people will still run 100+ octane NO LEAD in a late model street car that is being tracked.

[Dave24]

You may also find that at certain tracks they test the fuel at impound to make sure no one is running anything illegal. Sometimes...local pump fuel will not pass inspection. Fuel purchased at the track will.

[speed220mph]

I run 100LL Avgas in my 12:1 427. It works great, or as good as race gas and I pay a lot less at my flying club for it. I run premium pump gas in my 9.5:1 HiPo 289, also with great success. I give it a shot of 100LL every once in awhile to put some lead on the valve faces. As for using 100% race gas or Avgas in a 9.5:1 engine, it's a waste of money. Besides the slower burn of either doesn't do your exhaust valves any good. And backing off spark lead to be able to run low-octance gas is giving up potential power. As for O2 sensors, I don't need no stinking O2 sensor.

[Excaliber]

Well I've been researching this octane/race gas issue more in depth. The opinions stated here are very good.

Several things I keep hearing: Runs cooler, burns slower and makes more horse power. It seems all the above are relative terms and each holds some truth.

1. Runs cooler, I think we can test that! There is no fan and the engine running temperature during a race is around 210-220. Changing fuels may impact engine temp? Perhaps "runs cooler" means lower combustion temperatures? That could only be tested with a pyrometer (were poor, aint got one).

2. Makes more power (assuming carb, timing, etc. are not changed! Compared to WHAT? ScottJ's findings are interesting and valuable! At the highest levels of "race gas", like 116 octane used by the sub 7 second cars that IS certainly true. But that gas is something like 85% additives and only 15% "gasoline" (and cost an arm and a leg). That 116 DOES "burn faster" and needs to because the engines are turning 9000 rpm! But does "makes more power" apply to the more typical race gas available? 103-108-110? I suspect not. It appears that the "burn rate" is pretty much the same for all of them, including pump gas (exception being the really "high end stuff").

Interesting note on AV gas I came by, usually has a "dual rating:. Like 100-110, for "lean and rich" settings. As mentioned above also APPEARS to use a different octane score than other gas. Making it difficult to nail down what the equivalant octane really is! Being "less dense" (weighs less per gallon) than pump or race gas the effective fuel amount delivered through the main jet is LESS. This has the effect of "leaning" out the mixture! Therefore the main jet size should be increased to account for this.

Conclusion: Man this stuff is deep, VERY deep! I'm thinking 103 octane (available locally) will be enough. I would not be surprised to find that 92 pump gas may work just as well! The research continues (on the track and on the computer)!