I've had my SC3800II Fiero for nearly six months, but just started driving it. What is the best octane to use with this engine. I know most engines with forced induction require higher octane. I filled it up with 93 octane yesterda, but if not needed, why spend the extra cash for higher octane.

i had a SC'ed bonneville,the book states nothing less than 92

as mentioned before nothing below 92.. all they have around here is 93 or 94, course I fill with 93 at Amoco, Sunoco has the 94. It's needed may not seem like it, but if you ran the lower grade you'll get KR and a good chance of burning a hole in a piston.

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88 5spd Modified 3800 Series II SC Formula
Modifications 2004 - Intercooler | 2.8 pulley | 1 inch drop | Interior | 17 inch wheels

Like the others have said, my 3800 sc Buick request 92 octane. Mostly 93 is the minimum I've seen here. I have used 89 or 91 a time or two with no apparent adverse effects. But I'm also not blasting the sc unit much.

quote Originally posted by topcat: I've had my SC3800II Fiero for nearly six months, but just started driving it. What is the best octane to use with this engine. I know most engines with forced induction require higher octane. I filled it up with 93 octane yesterda, but if not needed, why spend the extra cash for higher octane.

You could just run 87 octane, but why even bother with the SC motor then?

The computer will compensate for lower octane gas by pulling timing back. I would guess that your mileage will suffer slighly with lower-octane gas, but I cannot verify, because I run premium in mine.

Also know that the PCM takes a while to re-learn if you've been running regular & then switch to premium.

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84 Fiero, 3800SC Series II conversion.
--------------Sleeeeper---------------
Best 1/4 mile to date: 13.033

quote Originally posted by TimGully: You could just run 87 octane, but why even bother with the SC motor then? The computer will compensate for lower octane gas by pulling timing back. I would guess that your mileage will suffer slighly with lower-octane gas, but I cannot verify, because I run premium in mine. Also know that the PCM takes a while to re-learn if you've been running regular & then switch to premium.

I never got a owners manual, or any other info as to the type of fuel to run. I know a little about engines, and figured that the car would need higher octane, ergo the question to verify what I already thought. If running anything lower than 92 is going to affect engine performance in anyway at all, I would always use the higher grade fuel.

Thanks for the response anyway.

I just looked up the fuel specs on my 98 Regal GS. I don't know if that's a Gen II, but I think it is.

They call for 91 octane. I have been using 89 for 3 years, because when I bought the car used, that's what the guy said. I haven't had any problems, that I'm aware of, but now that I read the manual (duh, where was I before!) I'll try higher octane to see if I feel a difference.

See, this is why I still frequent this board, even though I no longer have a Fiero. There is always something useful to learn.

-L

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