Fuel substitution question

I currently have a Sunoco 100 octane, and Gulf Mach 116 race tune. I'm looking for a safe substitute for both. It's my understanding that the Stoichiometric value of the fuel is the most important thing. I don't want to lean the car out. Obviously finding fuels that have equal stioch would be ideal, but I'd like to know which way, up or down would be safe?

The Stoich on the Sunoco is 14.1.

Gulf states the Mach 116 has a range of 14.77 to 15.

locally I can get VP and Sunoco, but oddly enough, I can't get the Sunoco 100

VP MS103 or street blaze 100 would work for your 100 octane tune. Sunoco 260 GT Plus should work too. Most of the tunes out there are plenty safe for a little stoich difference. But I don't think you will find any other unleaded 116 fuel. C16 has the same stoich as the gulf but its leaded.

The lower you go with the stoich is when the car will run leaner if tuned to a higher stoich value. IE Sunoco 260 GT Plus at 13.7:1 stoich will run leaner than your Sunoco 260 GT 100 octane fuel at a stoich of 13.9:1 in the chart below, but by only 1.5%. So if your WOT AFR on the GT is 11.5:1 then the GT Plus would be at 11.67:1 at WOT. Plenty safe.

You were probably running the 260 GT

Here is the stoichs on a bunch of fuels

Pump Gas Non-ethanol: ~14.64:1

Pump Gas E10: ~14.08:1

Turbo Blue Unleaded (100 octane): 13.9:1

Turbo Blue Unleaded Plus (104 octane): 13.7:1

Turbo Blue 110: 14.7:1

Turbo Blue Advantage: 14.9:1

Turbo Blue Extreme: 15.0:1

Sunoco MO2X UL: 14.5:1

Sunoco 260 GTX: 14.4:1

Sunoco 260 GT: 13.9:1

Sunoco 260 GT Plus: 13.7:1

Sunoco Standard: 14.8:1

Sunoco MO2X: 14.5:1

Sunoco HCR Plus: 14.8:1

Sunoco MaxNOS: 14.9:1

Sunoco Supreme Leaded: 14.95:1

Sunoco Maximal Leaded: 15.01:1

VP Street Blaze 100: 14.16:1

VP C10: 14.53:1

VP 110: 15.09:1

VP 113: 14.26:1 (leaded / oxygenated)

VP C16: 14.77:1

VP C12: 15.00:1

VP C23: 14.93:1

VP C44: 12.87:1

VP MS103: 14.26:1

VP MS109: 13.41:1

VP Import: 14.15:1


Read more at: Stoich Points of Race Gas - Page 7

Thanks for the super detailed response. It was really helpful.

No problem.

All you need to do is have a wideband that will let u switch the reading from wideband numbers to Lambda numbers. Lambda when at 1.00 that is your stoichiometric with any fuel. Then below 1.00 is richer and above 1.00 is leaner. I don't use a wideband to tune I always use Lambda.