NOBODY

This has nothing to do with fuel pressure.
The higher the specific gravity the fuel is denser therefor the fuel is packed tighter in the same amount of space which makes it weigh more.
Air/fuel ratio is measured in weight therefor a 12/1 ratio will be 12Ibs of air to 1Ib of fuel. So if your carb pulled out the same amount of fuel in volume and it had a lower specific gravity there would be less fuel for the air that passed the booster. Then the only way to correct this would be to add heavier fuel or increase the jet size.
It is important to know your specific gravity when tuning because .01 difference in specific gravity usually means 1 jet size difference and if your already on the lean side good luck.

Linster

I would suggest you follow your thoughts. I did a 572 with 9.2cr, ran 4.5 lbs with just 93 fuel and its still living. Watch the timing and keep the heads cool. A 26 Velocity went from 86 to 98 GPS. Had to go up quite a few jets to get the plugs looking good from a normal blower carb setup. He still stops at every fuel station, but gets there quick.

RumRunner

It's not all just the Specific gravity of the fuel, there are other factors.

That being said we'll look at Nobody's example. As fuel gets hotter it looses some of its high end additives, and the Specific gravity gets lower. If you had your engine calibrated to run with a fuel at .750 SG, and it dropped to .680 SG. That is a change of about 9%. That change moves with the flow area of a fuel jet. Bottom line meaning if your carburetor had # 90 main jets in it with fuel at .750, and the fuel got to .680 you'd have to go up to a #93 or #94 main jet. Big change!!!

Rich as safer!!!

thunderusone

Does this hold true for regular race gas...this got started talking about AV gas.

NOBODY

Very much so.
When you buy or look at the web sites that sell or manufacture the fuel they should list the specific gravity for the model number fuel they sell. If they don't all you have to do is call and ask them what it is.
Here are some examples:
Sunoco-111---------.725
Sunoco-112---------.715
VP RED--------------.742
VP C12--------------.710
VP C14--------------.690
VP C16--------------.730
AV GAS between---.650 and .700
93 pump fuel average .750

Sean H

i think i would go with rum runner on this....

Nordicflame

PM Bobl...
He is currently working with Dustin on a 565 with 9.4:1. Appears the cam is a big savior here also. He can give you the details.

FASTERDAMITT