I put 700 hours on a set of 2000 385 Mags. Usually ran 1 tank of 91 to 3 or 4 tanks of 87.
No porblems.
NOW boat is over 900 hours and STILL runs like a top.

87. I have 1999 454 Mag EFI's. I have put premium through it with no noticeable performance gains, and that includes LOTO Shootout runs.
The premium will also put a nice black residue on your transom. It wipes off pretty easy, but it's mildly annoying.

Folow your manuf guidlines.

Never spend money for fuels of a higher octane that is required by the compression ratio,
or super/turbo charging of the engine. If you do, you are just burning your money.

For fuels with an octane rating below 100, the octane rating is simply stating, that this
mixture will perform in terms of compressibility, the same a fuel with the same ration of
iso-octane and heptane.

Iso-octane is hydrocarbon and an alkane, 2,2,4-Trimethylpentane, an octane isomer
which defines the 100 point on the octane rating scale.

Heptane is a straight chain hydrocarbon and an alkane, which defines the 100 point on the
octane rating scale

87 octane rating fuel, performs (compression/detonation) same as 87% iso-octane and 13% heptane mixture.
93 octane rating fuel, performs (compression/detonation) same as 93% iso-octane and 7% heptane mixture.

Octane rating does not correlate to the energy content of the fuel!

It is simply a measure of the fuel's tendency to burn in a controlled manner, rather than
exploding in an uncontrolled manner. In other words, how much it can me compressed,
until it detonated (explodes).

FYI: Where the octane number is raised by blending in ethanol, energy content per
volume is reduced.

Now there is some sound advice. Use it.

+1

My truck says to use 87 and if I use 87, my truck sounds like a diesel just my experience

TexomaPowerboater;3465281]Premium. Boats often sit for long periods of time without use. If you run 87 you will increase the risk of detonation. Its cheap insurance. Also, if your running a boat that has sat for longer than a month you should stay off the throttles until you get some fresh gas in there.


Makes sense. Fuel loses it's octane when it sits. Even though using a higher octane than recommended doesn't benefit performance it will retain more octane over the time you're not using your boat. If you use your boat daily it doesn't matter but if your tank lasts a month it's worth using the higher octane.

I may have the wrong motor. I think this motor runs slower with 93 then 87. The ecm would run the motor just before detonation. With 93 the ecm would not see any sign of detonation from the knock sensor and would think the knock sensor was bad, and run with reduce timing, thus giving less performance that 87 octane.

I used to run the minimum octane required(87) but with todays questionable fuel I run 89 just to play it safe. Cheap insurance IMO.

Owners manual will tel you what octane Hi test I think on the mags!?