I recently dynoed the car and ran 375HP 400ft/lbs on 93 octane. The car has 12.5:1 compression via flat top pistons and stock cc LT1 heads, so I was running with ~26 degrees of advance (using an MSD box to control timing). Its what I call street tuning.

Today I mixed a 50/50 mixture of 93 and 101 and went back to the dyno. I ran full advance (36 degrees) and ended up losing 30 ponies. My air fuel was fat by about a point and a half (can that be worth 50hp?)There was no detonation.

My question is - am I being optomistic about making 400HP with race gas? is it possibe the car is optimized with 26 degrees of timing and pump gas? Or do I need to lean it out and add even more timing (like 39 degrees)to get full power.

I'm not sure what direction to go but I would prefer to be able to go from street to race with the least hassle.

BTW the car is a 383 LT1 with stock heads/intake and 306 cam + bolt ons.

 

There's no more energy in a gallon of 101 octane as there is in 93 octane. All the octane level does is resist detonation. If your car wasn't pinging or knocking with 93 then increasing the octane level does nothing except lighten your wallet.

26* of full timing seems low. Most cars like 32-38* full advance.

Go back to the dyno and play with timing and your fuel curve. That's what the dyno is for. Change one thing at a time and make a pull.

I'm assuming the 101 octane fuel you used was unleaded? If it wasn't you'll kill your O2 sensor and plug the catalytic converter.

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Stephen's racing page
or check out the race car

87 IROC SuperPro race car
461 big block
Best ET on a time slip: 11.418
Best MPH on a time slip: 117.01
Best corrected ET: 11.051

Altitude corrected rear wheel HP: 468
Best 60 foot: 1.595
Member of the Calgary Drag Racing Association

 

I realize that there's likely more energy in 87 octane than the 101. Read my post again. The reason I ran race gas was to run more advance (ie I ping with 93 octane and anything over 26 degrees)

My problem is I made LESS power with more timing (~36) and I did NOT change the previous fuel curve that netted my near 13.1 air fuel. It would seem that the added timing should lean things out, even with the race gas. Instead I ran near 10.1. Again, do you guys think the answer is in the fuel or spark?

 

When considering the energy content of fuels, you need to look at "specific energy", not BTU/#. Only by looking at the BTU/gal will you get the true effect of a volume based delivery system like a fuel injector. Many high octane fuel are rich in "light" components, meaning that the density (#/gal) is lower, meaning that the mass (#) of fuel delivered by one pulse of the injector is less. That will affect your A/F ratio (did you check the A/F ratio when you were running the higher octane fuel, or did you simply assume since it was 13.1:1 before, it was unchanged?), and it will alter (reduce) the amount of energy contained in that fuel.

You need to compare the specifications of the fuels, including density, and BTU/# to see how it will affect your tune. I use (and the engine was tuned for) VP Fuels C16, a relatively dense high octane leaded fuel. If I were to change to a lighter (less dense) fuel, I could get into serious trouble on the mixture. You might be seeing similar effects on energy content. Seems like an awful big HP loss for just energy content though. I think you need to check to see if the A/F ratio leaned out a little too.

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Fred
94 Formula A3+1: 381/TH400+OD/N2O

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11.513@115.59 on motor; 11.162@127.67, 1.643 60' on a 125-shot. Going with a 275-shot this year

 

I guess the verdict is I should attack the fuel mixture as my timing would seem normal. I have been using VP 100 octane performance unleaded. Here is link to my dyno graph, including air fuel readings.
http://image1ex.villagephotos.com/pu...asp?id_=585170

 

Injuneer thanks for the response - thought you might get a kick from this - take a look at a pic of my car.
http://image1ex.villagephotos.com/pu...asp?id_=129140