After I did my 3800SC series III swap, a 3.4" pulley was installed. The final series 3800 with the series V Eaton Supercharger and the smaller pulley brought the boost to 11 psi. At this point KR.s became a problem so I began tuning the PCM but those efforts on further modifying fueling and timing proved unsuccessful. Next was the addition of the ZZ Short stack intercooler. This eliminated the KR's but I still sought an extra degree of safety. Just for extra KR protection I tried adding Lucas Octane booster to the gasoline but this left an Orange residue on the Oxygen sensor. Didn't believe that was good so the final solution came to my town in the form of Sunoco 94 gasoline that I now use regularly.
My point is that if you run a modified or boosted engine you've got to be very careful to avoid KR's (detonation) An amount of kr's on a full throttle 1/4 mile run can blow a piston and kill your engine. If you run a smaller pulley on your 3800SC or an engine with high compression; for safe operation you will most likely need Sunoco 94 high octane gasoline.
For track only cars E85 seems a good choice but for street you will get lower gas mileage. You could make your own E85 but alcohol and gasoline do not mix well. You will also need to add an "exciter" to the gasoline like Amyl Acetate or Acetone.

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" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

[This message has been edited by Dennis LaGrua (edited 04-29-2025).]

$$$ per mile is probably a better metric when evaluating fuel choices for high hp engines than simply mpg.

You likely will find the cost savings from e85 will offset any mpg loss, especially when you compare it to 93+ octane or needing to add octane booster to each tank.

Newer GM ecms or aftermarket ecms also will allow you run flex fuel. This allows you to fill up with gas to maximize mpg when cruising and E85 to maximize performance when you plan on beating on it. This also allows you to mix the fuels as you fill up. E50-E60 is the sweet spot for detonation resistance and maximixing fuel economy. So lots of opportunities when you opt for newer technology with ecms.

Never had any trouble with the 98 octane fuel we have here in France?
There are a lot of racers who go ethanol here, but I don't see the need for my car and the track time that I do per year.

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"Turbo Slug" - '87 Fiero GT. 3800 turbo. - The fastest Fiero in France! @turboslugfiero
https://youtu.be/hUzOAeyWLfM

I run 10.5-1 CR naturally asperated and 94 octane Chevron fuel. with my setup I can run 87 octane or E85 without changing my tune. I stay away from E85 because my car sits for extended periods of time and E85 is a water attractant fuel. I only run 2 or 3 tanks of fuel per year and would likely get corrosion from ethanol content in the fuel. as long as I can buy premium fuel with no ethanol I will gladly pay the few cents extra per gallon. sleek

quote Originally posted by Frenchrafe: Never had any trouble with the 98 octane fuel we have here in France? There are a lot of racers who go ethanol here, but I don't see the need for my car and the track time that I do per year.

The best that we can do here in the USA is Sunoco 94 Octane or ultra expensive $12/gallon race gas. You got us beat on that pump octane. I choose to avoid ethanol on primarily a street/strip vehicle. E85 is also not widely available in my state. Regularly scan for KR, LTFT , fuel pressure and O2 sensor readings. If one of these is way off it can cost your your engine. Maybe I am a bit paranoid but I want to keep my $5000 engine and I do take it to the red line on occasion.

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" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

I think 98 here is equivalent to your 93?
The 94 that you talk about would be 100 or plus here. And yes, then it's race fuel. We pay expensive as well, but I've never needed to put that in my 3800 turbo setup.

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"Turbo Slug" - '87 Fiero GT. 3800 turbo. - The fastest Fiero in France! @turboslugfiero
https://youtu.be/hUzOAeyWLfM

[This message has been edited by Frenchrafe (edited 05-01-2025).]

The biggest problem with E85 branded fuels is the US government mandates the E85 branded pump fuel only needs to contain a minimum of 51% (and a maximum of 83%) ethanol to be sold as "E85". Testing I've done on the fuel dispensed by E85 branded pumps in my area throughout the year have shown the composition varies wildly (usually between 60 - 75% ethanol content) depending on the time of year and the gas station.

Unfortunately, GM never made a flex-fuel compatible 3800-powered vehicle; so there is no factory 3800 PCM that has flex-fuel capability. I would NOT attempt to run any super or turbocharged 3800 off of "pump E85" unless the actual fuel composition was tested at every fill-up and the PCM tune was adjusted to work with that specific fuel composition.

People with serious builds who use "E85" as fuel in their cars around here typically buy a 55gal drum of pure ethanol so they can adjust the E85 branded fuel they get from the gas station to ensure a consistent 85% ethanol blend fuel that they fill their tanks with.

Another issue, specific to the Fiero is that there are several components used in the stock Fiero fuel system that are NOT compatible with ethanol. These components would all need to be replaced if you planned on running "E85" in your Fiero. One of the major components that is not compatible with Ethanol is the fuel tank.

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More is more. Less is not enough.

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