Is their occasions were 92 octane pump gas can out perform race gas.We had two cars at the track last night one with race gas aprox. 112 Octane and the other with pump gas, this car ran race gas the time before.The pump gas car picked up a tenth or two and the race gas car dropped Two tenths. This track is at 2600 ft above sea level, so we lose 4 tenths Anyway. Neither car is running over 10-1, I ran 101 trick gas with mine Last time and I run 11.5 to 1 I am going to try the pump gas next time,
Could this be attributed to burn rate?

A couple things:
Pump gas doesn't have lead in it. "Race" gas usually does.

High octane gas is for high compression engines (11.5:1+). The gas needs to be compressed sufficiently to combust, plus it can't pre-ignite before the engine is ready for it to burn. On top of this there's usually a potent ignition that can ensure the gas detonates when it's supposed to.

The 10.0:1 engine doesn't compress the gas enough for it to do what it's supposed to do, which is why the car ran poor.

It's more complicated than this obviously.

My understanding/experience is that you should only use a high enough octane that will allow you to set the timing curve the way the engine runs the best without any pinging. In other words if you can run pump gas and it doesn't force you to pull the timing back (from where the engine runs the best) to keep from pinging there won't be any benefit to adding higher octane gas to it.

The higher the elevation the higher the static compression ratio you can run with the same octane gas. A 10:1 cr at an elevation of 2600 ft with pump gas sounds do-able depending on cam timing, etc. I would guess with your 11.5:1 that you will need more than pump gas. I think the trick gas half and half with pump gas will be close to what you need.

}Neither car is running over 10-1,

}and I run 11.5
I thought the 11.5 was your ET, I assumed both cars were at or below 10.0:1 as indicated by the 1st statement.

I run 11.5 to 1 compression in my car, the others last night are running 10 to 1 or less
sorry for the confusion. I still can’t figure it out about the gas I always thought more was better for any motor when it came to octane. Their was a guy at the track that worked with a dyno and he said he has seen this on motors on the dyno. I was just wondering if anyone else has experienced this or seen it on dyno testing.

no, but the fact remains the more you compress a gas the more volitale it becomes, the octane rating is a way to express the resistance to this, a higher octane makes it not as combustable at a lower pressure (compression ratio). The higher the octane you go the harder it is to burn. Running the higher octane in the low compression engine it might not get a good burn meaning it might not burn all of the fuel in the chamber which in turn makes less power due to the fact that there may still be raw fuel (unburnt)left in the cylinders. I hope this helps

as bob mentions, higher octane allows you to advance the timing since the gas will resist pre-igniting. This can increase power to a point. (before you reduce timing and advance the cam) - this can be proven on a dyno, to a point. You'll also be able to see power fall off if you over advance it or give it the wrong type of gas.

But assuming your engine is set up the way it is and timed & tuned properly, you want to run the minimum octane required before you get pinging or detonating. Anything more is a waste of money and as you found out, often times counter-productive.

Here's some good reading material. http://www.medfordfuel.com/frequently_asked_questions.htm

Take a peek at the nitromethane section. http://www.camaros.net/forum/smile.gif

[This message has been edited by NastyZ (edited 03-23-2002).]

I used 101 trick gas in my car for its first time out it was picking up ET everytime we bumped the timing up, finally at 45 total I did not want to go any more. I will mix pump gas with the remaining 101 for the next time out in April. What types of fuel do the rest of you guys run in here?

Ultra 94 unleaded from Sunoco. NOTHING else. There is a Sunoco 3 blocks from my house. http://www.camaros.net/forum/biggrin.gif

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79' Z28 4-spd- built 355, TRW 10:1 forged flat tops, WP SportsmanII heads, Crane Energizer 228* duration .480" lift, Edelbrock Victor Jr., Holley 750cfm, Dynomax headers, dual 3" flowmasters :) 3.73 Posi 10-bolt

A higher octane rating does NOT mean the fuel has more power or means to do such. Actually, the higher the octane the slower the burn rate. Octane mearly allows you to tune an engine to produce more power, if so needed.

It is a complicated subject, but if you go to my tech links site at www.inccn.net/jacksandslinks.htm (http://www.inccn.net/jacksandslinks.htm) and cruise on down the page there are a few large articles and others on fuel and octane. Great info....be ready to read for awhile.

The reason your engine was faster on lower octane is because it was tuned for it. IF you switched and did not reset timing etal then you lose. As one poster pointed out...use only what you need.

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STEVE JACK
ConceptOne Pulleys and Brackets

What a great website HOTROD SRJ I would recommend it to the other members to read.
Really liked the Z-28 found in a barn story. I have one of those stories but it involves a 1957 corvette.