Race gas vs pump gas on lower compression street/strip motor

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B3422w5

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Wondering if anybody has ever ran both 110 and raced a car and pump premium and raced same car and what if any difference did you see.
I am taking something 10 to 1 ish with aluminum heads that runs fine on pump swill
 
I did this in my mid 10sec car. Use to run 110 race gas. Switched to a fuel station that sells 93 with no ethanol cut and the only change I saw was a slight water temperature increase. Still runs 10.63's. If I remember I changed the timing ever so slightly. Something like 2 or 3 degrees.


Big block motor with aluminum heads
 
The last three small blocks I've built have all been around 11-1. The 340 and 408 were faster on pump 93, the 434 made 30 more hp on the dyno on pump 93 than crate 98 race gas. This was after the engine was tuned for the 98, no other changes than the gas.
 
Back a few years ago we did R & D on a restricted sb chevy on the dyno at 10-1 compression on vp 110 and 93.3 pump gas back to back. pump gas made 6 more hp than vp. We tuned for the best pull with each. Not earth shattering but in a restricted engine every bit counts. Yeah I know...it was a chevy...results are results.
 
Opinion:

The higher the octane the slower it burns.
Race gas in 10 to 1 or lower compression Will cost some HP, burns too slow.
But ... Motors like the lead :)... Cats don't :rolleyes:
I'm 'happy' mixing Leaded AV Gas 100 and 87 UL pump at doses of 50/50 at 10.5 to 1
Some alcohol could actually be helpful in passing water while you're 'passing gas'. At <5% in the above mix not much concern over the Crusty Carb Syndrome while sitting.

"your mileage may vary based on driving habits" :steering:
 
If it doesn't spark knock on pump gas with the timing set to optimum, race gas will not help a thing.
 
Correct : 110 octane gas burns slower to prevent detonation . Street engines with comp ratios 10.11:1 or less can use 93 octane with a small amount of octane booster . 165 psi of cylinder pressure is about the limit with 93 octane . I'm using 93 octane with 2 ozs. of Race Gas per gallon to raise the octane to 97-98 , no problems .
 
383Scampman said:
Correct : 110 octane gas burns slower to prevent detonation . Street engines with comp ratios 10.11:1 or less can use 93 octane with a small amount of octane booster . 165 psi of cylinder pressure is about the limit with 93 octane . I'm using 93 octane with 2 ozs. of Race Gas per gallon to raise the octane to 97-98 , no problems .
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I'm pretty sure octane rating and burn rate are not related.
 
yellow rose said:
I'm pretty sure octane rating and burn rate are not related.
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Elaborate please @YellowRose. I’m not saying you’re wrong, I am saying I am uninformed. One of my girlfriends high school friends is a crew chief for a fuel funny car. In the pits they fire the engine on 87 octane. When I asked why he said “it burns slower”, among a few other things. I’ve always heard that same thing.
 
High octane fuel has a higher flashpoint, burns slower and harder to ignite.
Less energy when used in lower compression engines.
The result is slower ET's
 
Hey TT5.9, I don't believe pump gas burns slower than Nitro and here's why. You can spill nitro on the floor and take a propane torch to it, you will have to try very hard to get it to light. Try that with street fuel and you won't be happy.
Now since Nitromethane carries a good bit of it's own oxygen, when it does light it goes up at a very much faster rate. It takes lots of pressure to set the stuff of but, that's why the cars are so forceful, moving the air around them. That fuel is liquid dynamite, literally.
 
TT5.9mag said:
Elaborate please @YellowRose. I’m not saying you’re wrong, I am saying I am uninformed. One of my girlfriends high school friends is a crew chief for a fuel funny car. In the pits they fire the engine on 87 octane. When I asked why he said “it burns slower”, among a few other things. I’ve always heard that same thing.
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That may have more to do with gasoline not having any Oxygen in the molecular structure. Nitromethane has 2 Oxegen atoms. That oxygen is the same as popping a little nitrous oxide in your street engine. it oxidizes any fuel in the chamber more efficiently... need oxygen to prpmote the burn.

An engine will run better when the octane is just enough to keep out of detonation. When I raced in some restricted forms, I used to tell guys my stuff had a special blend I got from a local refiner specifically for our class. It was from the 91-93 pump at our local 76/Arco/Chevron... etc. When we dyno'd the engines, they ran better on pump swill.
 
TT5.9mag said:
Elaborate please @YellowRose. I’m not saying you’re wrong, I am saying I am uninformed. One of my girlfriends high school friends is a crew chief for a fuel funny car. In the pits they fire the engine on 87 octane. When I asked why he said “it burns slower”, among a few other things. I’ve always heard that same thing.
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You'd be better off going to the Rocket Racing Fuels website and reading about it there.

Pump gas has a different burn rate than race gas, as a run of the mill surface transportation vehicle is lucky to see 4000 RPM every once in a while.

An engine with an 8000 RPM speed needs a fuel with a faster burn rate (which also affects ignition timing) because there is much less time to burn the fuel at that RPM, and if you had a slower burning fuel, you'd be jacking the timing through the roof.

On the same line of thinking, a bracket car shifting at 7000 might need the same octane, but a slower burn rate.

Racing fuel is quite complex.

But burn rate and octane are not tied together. The Rocket website explains it much better than I can.
 
70 Buster 340 said:
Mixing Fuels and Calculating Octane
Sunoco Race Fuels
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I read a couple of those last night. From what Sunoco is saying...they tie burn rate to specific gravity.

I went to the Rockett Fuels web site and can't find the article I referenced above. It may have been an article in a magazine by Tim Wusz but I didn't look through all the articles.
 
The engines I mentioned above were 10.8-1, 11.4-1 and 11.2-1, all have smallish 55-68 cc chambers with good tight quench. There is more involved in octane tolerance than just static compression. I'm no expert but have taken advice from some sharp guys and so far it has worked pretty well.
 
I run 92 in my Scamp with a 440. I tried race fuel that I have for my truck and the car did not run the same. Throttle response was even different. Car felt like it loading up. Track time was only a tenth or 2 slower.
 
My 9.4 compression (stock) 340 would detonate 1000 foot out. with 91 Premium. But only in the heat of the summer. one gal of 110 to 10 gal 91 would fix the problem.

If i understood then, what i do now, i would have cut a hole in the hood and seal it to the carb instead of adding High Octane Fuel.

There is many many variables as to why you should or should not run pump fuel. and "X" amount of compression is not the answer either.
 
My old 408 with Econo W2 heads ran 9.80’s with BP93 pump gas. Crazy thing about that was I would stop on the way to the track and buy 10 gallons of it and use it in my Duster, quad, and generator. Well when I switched to alcohol in my Duster I would just grab 87 for the quad and generator. They didn’t like the switch one bit and it took some track tuning and cleaning to get them running smooth again. They were spoiled.
 
justinp61 said:
The engines I mentioned above were 10.8-1, 11.4-1 and 11.2-1, all have smallish 55-68 cc chambers with good tight quench. There is more involved in octane tolerance than just static compression. I'm no expert but have taken advice from some sharp guys and so far it has worked pretty well.
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Those are decently high static CRs, do you mind sharing cam specs from those motors?
 
TurboGLH said:
Those are decently high static CRs, do you mind sharing cam specs from those motors?
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The 11.4-1 was a 340 with a hydraulic flat tappet, 237/242 @ .050" with .584/.592" lift. The 10.8-1 was a 408 with a flat solid, 260/264 @ .050" with .638/.642" lift, or really close on the lift. The current motor is a11.2-1 434 with a solid roller, 263/271 @ .050" with .711/.719" at the retainer.
 
justinp61 said:
The 11.4-1 was a 340 with a hydraulic flat tappet, 237/242 @ .050" with .584/.592" lift. The 10.8-1 was a 408 with a flat solid, 260/264 @ .050" with .638/.642" lift, or really close on the lift. The current motor is a11.2-1 434 with a solid roller, 263/271 @ .050" with .711/.719" at the retainer.
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Interesting info, thanks. That's substantially more dynamic compression than what's considered the "safe limit" on pump gas, so it's good to have actual data to compare.
 
higher octane fuel has less BTU per lb than regular fuel, but it resists knocking so you can use higher compression to extract more power from it, but it wont help a 'normal' engine. Propane has even less but its octane rating is like 130 so you can run 13:1 and extend the duty cycle of the injectors to get it up to gas specs and higher. My SC required 93 'use premium only' on filler cap, and I can tell the MPG's are lower using cheap. I think the computer manipulates the spark advance on the fuel grade. Got a Flex-fuel Caravan and the MPG sucks on E10 but its cheap, 2.97 here in CA.
 
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