Teach me. . .Race Gas.

Duke wrote: Every time someone mentions octane ratings, I try to preach that octane is not a "power" rating for fuel. High-octane fuel is NOT more powerful than regular, nor is it more efficient (higher mpg); it simply resists preignition better. In fact, higher-octane gas is actually *less* effective (less power output per volume burned) than lower-octane gas. It is merely that engines can make better *use* of it by running higher compression ratios, more spark advance, or more boost without preignition knock. All these strategies increase the power output of the engine more than is lost by using the less-volatile high octane gas. Virtually all modern cars have a knock sensor that retards the spark when it sense preignition, so you are less likely to damage your engine by running too-low octane than in the old days. However, it will lower your power output due to the retarded spark. If you run higher octane, the ECU will advance spark *if possible*, making more power. BUT: there is almost always a limit to how far it will advance the spark, no matter what gas you run. So if your owner's manual says that your stock car is optimized for 89 octane, there is absolutely no reason to run 91 octane in it. All you are doing is wasting money because the ECU will never advance spark enough to take advantage of any higher octane. That's even more true with ultra-high-octane race gas.

Duke Octane is about knock, not pre-ignition. While often confused, they are not the same thing.

Second, as you say, octane isn't a measure of energy- and high octane fuel has the same energy as low octane fuel. Assuming that the oxygenate the same amount, it will be the same energy.

(as an aside, it's commonly claimed that high octane burns slower, which is also not true- burn rate is identical, especially when in cylinder turbulance is a much bigger driver of burn rate than the fuel ever will be).

EdenPrime wrote: In reply to red5_02: For my uses, it'd be in a 2ZZ Toyota Celica. It takes premium, but i heard Race Gas is 110 Octane. It sounded trepidatiously volatile.

I think its been covered...

But you had that one there backwards. 87 is gonna be way more volatile than 110. That is kinda the whole point. Race engine compression/timing requires a less volatile fuel so that it does not combust before it is ignited in a controlled manner.

Put a lower octane in a race engine and the injected fuel will ignite from the conditions in the cylinder, all at once in a bang... we want the fuel to hang on long enough for us to light one side of it and have it burn slowly and completely to produce a nice continuous force down on the piston.

92CelicaHalfTrac wrote: What standalone do you have installed in your car to take advantage of the added octane?

It isn't necessarily the added octane, so much as race fuel tends to be a lot more volatile than pump gas.

May be crucial depending on what state you live in. My bridge ported 13B runs just fine on Ohio gasoline. Illinois gasoline makes it run like dog poo at low throttle, like a lean misfire. Must be a different formulation with a lower vapor pressure. Race fuel should have the opposite effect.

I'm not about to throw down $18/gallon to find out, though.

alfadriver wrote: (as an aside, it's commonly claimed that high octane burns slower, which is also not true- burn rate is identical, especially when in cylinder turbulance is a much bigger driver of burn rate than the fuel ever will be).

Race fuel can burn faster than pump, depending on what it's made of. If you burn the fuel quicker, it has less time to detonate.

RedS13Coupe wrote: But you had that one there backwards. 87 is gonna be way more volatile than 110. That is kinda the whole point. Race engine compression/timing requires a less volatile fuel so that it does not combust before it is ignited in a controlled manner.

Unfortunately, it's a lot more complicated than that. Combustibility and autoignition don't directly correlate. You can have fuels that burn very easily and don't detonate, and you can have fuels that are difficult to ignite yet love to spontaneously combust with just a little more heat and pressure.

Where the monkeywrench gets thrown in is that, bluntly, race fuel is formulated for engines to make power, while pump gas is formulated for emissions. Most emissions nowadays is evaporative and the rest is cold-start, so pump fuel needs to have low volatility so that it doesn't evaporate so easily, but it still has to be volatile enough to burn cleanly in a cold start. Different regions have different standards, since you'd want a different formula in the high desert than in Minnesota.

Ever notice that pump gas doesn't evaporate cleanly anymore? It forms a tall, oily puddle and leaves a residue. C16, however, still evaporates quickly and cleanly like brake cleaner

The conspiracy theorist in me says that the real reason why ethanol is blended is that it's an expedient way to bring the octane rating of junk heavy hydrocarbons up, since we've used up most of the really good ones. Nothing to back that up, of course, but if there was good backup for it, it wouldn't make a good conspiracy theory...

My lt1 powered 240 will lose a second and a half in the quarter using race fuel verses 91. No changes to programming in the ecu. Runs like crap on 87. I had to once due to fuel shortage on the way to challange one year.

Knurled wrote: The conspiracy theorist in me says that the real reason why ethanol is blended is that it's an expedient way to bring the octane rating of junk heavy hydrocarbons up, since we've used up most of the really good ones. Nothing to back that up, of course, but if there was good backup for it, it wouldn't make a good conspiracy theory...

You need a conspiracy theory other than lobbying dollars from ADM and other giganto farming corporations who want to use the government's regulatory powers to force people to buy their products? :)

As for octane -- it's a measure of one thing and one thing only, the resistance of the fuel to ignition due to compression. Changing the fuel composition to increase octane will naturally change other characteristics of the fuel as well, but it's difficult to predict exactly what those changes will be because it depends on how you change the octane. Tetraethyl lead, toluene, and ethanol will all bump the octane up a bunch, but they're very different chemicals and will have significantly different other effects.

If you're really really bored, there's lots of info here: http://www.faqs.org/faqs/autos/gasoline-faq/part1

I guess this is where I point out again that in Spec Miata, most everybody runs Shell 91 octane in Central Florida Region. It makes one to one and a half horsepower less than the $30 a gal. oxygenated stuff, and a half horsepower more than 100 oct. unleaded race gas. Von Charbeneau won his SM national championship with Shell 91 oct.

What the edit is for: Everybody talking about 91 and 93 octane in here, and I put 91 in my post. It should be 87 octane.

codrus wrote: You need a conspiracy theory other than lobbying dollars from ADM and other giganto farming corporations who want to use the government's regulatory powers to force people to buy their products? :)

I like how there are some people who whill denounce ethanol in fuel while singing the joys of oxygenation. Adding alcohol to gasoline is done because it oxygenates the fuel.

Hmm.

Duke wrote:

EdenPrime wrote: In reply to Duke: I didn't know that-- thank you. Admittedly, when i run 93 instead of 91, it feels as though the car is "woken up," a bit.

In that case, it seems like your stock ECU is able to advance the spark enough to take advantage of the higher octane - cool!

My truck has 2 timing tables. It defaults to the more advanced one on start up, then after seeing 3 "knock events" reverts to the lesser advanced, or standard setting. Running 91 in it makes a significant difference. As far as I know, it's not mentioned anywhere in the owners manual. Don't know why they wouldn't?

the proper answer is E85..

By the way, the latest issue--in the mail now--has a fuel dyno comparo: pump gas, E85, race gas, etc., etc. Hopefully that answers some questions.

Knurled wrote: The conspiracy theorist in me says that the real reason why ethanol is blended is that it's an expedient way to bring the octane rating of junk heavy hydrocarbons up, since we've used up most of the really good ones. Nothing to back that up, of course, but if there was good backup for it, it wouldn't make a good conspiracy theory...

Here's an alternate/additional conspiricy.

On top of the junk, heavy HC's, they are also using lower energy HC's. How many times have you seen people claim a +10% reduction in FE when E10, when the energy reduction of E10 should be something like 3% by volume. Seems as if the base make up of the fuel got a lot worse with E10, so that the octane increase of the ethanol was more than made up with the terrible base fuel. Which begs the question- why does bad fuel cost so much?

But now we are teetering on political, and can't talk about that.

Seems to me that peoples fuel economy claims cannot always be trusted.

David S. Wallens wrote: By the way, the latest issue--in the mail now--has a fuel dyno comparo: pump gas, E85, race gas, etc., etc. Hopefully that answers some questions.

hmm I think i'm missing an issue... will have to contact you guys... I'm planning to run e85 in the volvo s10 thing... volvo guys have had great luck with it and it's avl so why not :)

alfadriver wrote: Here's an alternate/additional conspiricy. On top of the junk, heavy HC's, they are also using lower energy HC's. How many times have you seen people claim a +10% reduction in FE when E10, when the energy reduction of E10 should be something like 3% by volume. Seems as if the base make up of the fuel got a lot worse with E10, so that the octane increase of the ethanol was more than made up with the terrible base fuel. Which begs the question- why does bad fuel cost so much? But now we are teetering on political, and can't talk about that.

Which brings us back to my earlier comment about name brand premium E10 vs no-name E10.

^pardon my cross threading. that comment was in the ethanol strkes again discussion.