Stock 1990 Twin 454mags. I have heard that I should be using premium, and I heard that I should be using regular. Gas prices aside what is better for these engines.

I run 87-89 in my '97 MAG MPI's. In my old 1994 454 Mag I ran 87 with no problems.

The mpi is a differnt world then a carb mtr, for the 1990 better to run the 92 octane..........

you can run the 87 if you are running factory timming specs but still better to run the 92

Thanks that is what I was looking for

I read somewhere that the higher octane fuel burns slower. Logically that should require more ignition advance in order to maximize the power output. If you just increase the octane, power goes down a little, everything else unchanged. Conversely, it would be logical that a faster burning fuel (lower octane) and less ignition advance should produce more power, given that the octane rating is high enough not to selfignite at the compression in question. In order to take advantage of the higher octane you would need to raise the compression or put a blower on it. Conclusion, dont use higher octane than necessary.
Am I out on deep water here?

The engine build + environment it's put in set's octane requirement.

You don't.

The only way you can set the requirement yourself is in your choice of parts + machining practices before/as engine is put together.

mats. I understand what you are saying ,It makes sense to me how ever reading the other posts here you can see why it s getting confusing.

I think it is safe to say that on a stock engine, with stock timing etc, it is perectly safe to use the octane recommended by the manufacturer ie 87 octane in this case. Also, you can always use a higher octane but it may cost power and definitely more money.

sb you forget about timing

No, I did not forget.

I'm a firm believer that the engine + what it's put in determines timing rquirements.

If you have to adjust timing because of fuel quality, then you really didn't build the engine totally correct for it's intended usage.

If I build an engine or have an engine built for 93 octane, I'm sure as heck not going to reduce/play with my timing for it to run on 89 octane. Meaning, I'll make sure 93 is used at all times. I would build/buy it for 89 octane if this was what I was going to use for fuel.

Hard to type these things sometimes. Sorry if it appears I'm making no sense. LOL.