which gas - ZR-1 Net Registry Forums

Perry Mitchell · 05-26-2022

In my area, I have three choices of gasoline, Ethanol based 91 octane, non- ethanol 87 octane, and 100LL Avgas. Which would be the best fuel to use in my stock '91 LT5 that doesn't get driven a lot? Which fuel lasts the longest in the tank?

spork2367 · 05-26-2022

Quote:

Originally Posted by Perry Mitchell

In my area, I have three choices of gasoline, Ethanol based 91 octane, non- ethanol 87 octane, and 100LL Avgas. Which would be the best fuel to use in my stock '91 LT5 that doesn't get driven a lot? Which fuel lasts the longest in the tank?

Ethanol based 91? Or 91 octane with ethanol? "88 Octane" is E15. So I'm guessing you mean regular 91, but with ethanol. Typically 10% or less. That is the best choice, with replaced injectors. Original injectors are not ethanol compliant. Non-ethanol 87 is on the low end for the high compression ratio. 100LL is not only not legal to run, but extremely costly and will damage your catalytic converters over time.

Perry Mitchell · 05-26-2022

Yes, I mean regular 91 octane with ethanol. My injectors have been replaced with Jerry's FIC units. I don't have cats on the car as this motor is in a 67 Camaro. The problem with ethanol gas is it doesn't stay good for long. I've been running non-E gas in my other collector cars and equipment without issues.

spork2367 · 05-26-2022

Quote:

Originally Posted by Perry Mitchell

Yes, I mean regular 91 octane with ethanol. My injectors have been replaced with Jerry's FIC units. I don't have cats on the car as this motor is in a 67 Camaro. The problem with ethanol gas is it doesn't stay good for long. I've been running non-E gas in my other collector cars and equipment without issues.

Obviously, the LT5 was designed around non-ethanol fuel. 87 octane is just a bit on the low side. Even without cats, I don't think I'd run 100LL (if for no other reason than the price). You also have to remember that it has slower flame propagation than mogas which will tend to increase operating temperature a bit. It will also kill your O2 sensors eventually.

CamP · 05-26-2022

Since you replaced the injectors, I'd say run the 10E 91 octane pump gas.

100LL is one of the best storage fuels, but the lead will kill the cats and eventually foul the o2 sensors.

I blend 87 non-ethanol and 100LL for my C3 big block.

05-26-2022	#1
Perry Mitchell Join Date: Nov 2018 Location: Washington Posts: 98	which gas In my area, I have three choices of gasoline, Ethanol based 91 octane, non- ethanol 87 octane, and 100LL Avgas. Which would be the best fuel to use in my stock '91 LT5 that doesn't get driven a lot? Which fuel lasts the longest in the tank?

05-26-2022	#3
Perry Mitchell Join Date: Nov 2018 Location: Washington Posts: 98	Re: which gas Yes, I mean regular 91 octane with ethanol. My injectors have been replaced with Jerry's FIC units. I don't have cats on the car as this motor is in a 67 Camaro. The problem with ethanol gas is it doesn't stay good for long. I've been running non-E gas in my other collector cars and equipment without issues.

05-26-2022	#5
CamP Join Date: Jun 2012 Location: fort worth Posts: 183	Re: which gas Since you replaced the injectors, I'd say run the 10E 91 octane pump gas. 100LL is one of the best storage fuels, but the lead will kill the cats and eventually foul the o2 sensors. I blend 87 non-ethanol and 100LL for my C3 big block. Last edited by CamP; 05-26-2022 at 03:23 PM.