Originally Posted by TomZ (Post 4811803)

That’s what I thought too.

Perhaps the diesel created a change in the mixture and that’s where the extra “power” came from?

I just don’t see diesel being beneficial.

Originally Posted by CDShack (Post 4811843)

That is old school!!! I remember the old schoolers did it not for octane, but BTUs. Diesel has quite a bit more BTUs per gallon than gasoline. Not sure how that plays into the "mix"! (See what I did there?)

Originally Posted by CDShack (Post 4811840)

Not to step into the whirlwind of expertise contained here, but I just watched Engine Masters Sunday, and they did a myth-busting episode on Octane. Now to avoid boost and turbo and other variables blah blah, they had a 540hp LS3 NA engine on the dyno. They tested 87 and 91 pump, 110 and 116 Sunoco, and E85. For each grade, they completely drained the engine between each run, did 'calibration' runs for each octane, (timing, AFR, etc) before hitting it for the official run.

(Surprised me!)

Oddly, the engine liked 29-degree timing for max power on all fuels. Cranking timing up and down didn't help power. For each to make max horsepower, they fiddled with the AFRs. In the end, the best run from 87 octane to 116 octane, the engine horsepower/torque difference between them all was just 1-3 points. (91 pump did the best of gas, but E85 topped them all by a smidge)

Their conclusion was timing for max power is about what the build of the engine wants, not the octane. In a controlled environment, 87 was as good a anything else, but all noted they would not run it on the street with a good motor because of extended load, underhood heat, etc.. Octane level was only a matter of where the engine detonated, if it detonated, not horsepower, and the old myth of raising the octane and cranking in timing to get more horsepower was totally unfounded. Use of 110 and 116 was a waste on a NA street rod as they couldn't make is make more power out of it with anything they did. The E85--made the most torque and horsepower, but they had to crank what would be 'gas' AFR to around 8.5, burning more fuel compared to gas. They noted under boost, E85 made significant gains over gas-based fuels because of its cool charge and high oxygen content.

It shed some light on a lot of my old beliefs and theories. I like octane, so don't kill the messenger, but I feel a little better knowing if I'm on fumes and have to splash in a little 87 octane dock gas to get home, it's not the end of the world.

Pretty cool episode! I love those guys!

Originally Posted by ICDEDPPL (Post 4811941)

Was that the same episode where colder fuel made a bigger difference than a cold iced down intake? After that episode I thought about using a cooler to cool the fuel.

Originally Posted by ICDEDPPL (Post 4811941)

Was that the same episode where colder fuel made a bigger difference than a cold iced down intake? After that episode I thought about using a cooler to cool the fuel.