Fuel type? 87, 89, 91 octane?

[Moor]

Most of the marinas in the area and a few land based filling stations near our larger lakes (Cumberland and Dale Hollow in KY/TN) are carrying the Rec-90 (ethanol-free, 90 octane unleaded gasoline blend designed for use in recreational/marine engines). I've never believed in running any special gas in an old 10:1 compression ratio big block, but my boat LOVES this rec-90... Maybe it me subliminally justifying paying $3.89/gal on the water, but I swear the boat runs better on it!

Unless you changed pistons, your 454 has around 8.5:1 CR, same as mine. It will run on damn near anything lol. And no, your not crazy, All of my carburated engines run better on Non-ethanol fuel. I think the lack of Ethanol is what you notice more than the higher octane.

[NorCalPR]

Yep. No ethanol is nice because it doesnt go bad and you get more power, but is it absolutely necessary? Not for a old iron block chevy/ford...

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[cadunkle]

I've always used 89 in my PCM 454. The Supra manual doesn't mention octane requirement of any engine. PO said he rebuilt it and no idea what pistons he used so not sure if it's a 8.5-9:1 compression ratio or something more, or even if it's stock bore and pistons and was just freshening up with rings and bearings. I want to run it low and try 87 to see it it detonates at all. The spread used to be 5-10 cents between octane ratings, now it's more like 30-40 cents more for 87 and another 10-20 for 93. Extortion for those of us who built engines to run 93 specifically because the engine would be more efficient and have a lower cost per mile or hour of operation than lower compression on 87.

[Moor]

if the compression ratio is kept below about 9.25:1 then running 89 octane shouldn't cause detonation if the engine is tuned properly. Anything above that, i'd recommend at least 91 octane.

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thanks everyone 87 it is!