Recommended octane for 496MagHo
 

I always use Premium in everything I own, but I've been told that Mercury actually recommends Regular (87) for the 496. Is there any merit to this rumor? I'm looking at a boat with a 496MagHO and if I can save the extra dough and still make it run right.....

496
 

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I use 93 if the boat is going to sit for weeks. Otherwise I mix 87 and 89. Depending on the availability.

87 is the recomendation on 496ho.Anything more is wasting money.

I was always told there wasn't much to gain in a low compression engine and to save my money. I always ran 89 in my 415s and never had a fuel-related problem.

There was some time ago that the electronic spark advance relied on the knock sensor to tell it to stop advancing the timing. If you had 93 the engine sometimes didn't EVER knock and the timing was advanced too much. I'm sure after MerCruiser warrantied a few engines they changed that situation in the computer.

I don't know how true that is, I never remember to ask the right people.

Not sure if it is relevant or not but same thing with the 502 Mpi' as well. Owners manual even says to only use 87

Good, clean, waterless, non-junk filled 87 octane is all thats needed. But remember all bad fuels are bad fuels so if you expierence a lot of knock events on your 496 or other fuel related problems find a new fueling station!

Regards,
Ray @ Raylar

Only 87.

87

I own I gas station, so I know what's going in the tank is good stuff.:D

You get the most HP on 87. Buy 93 and you spend more to produce less HP.:mad:

Just as posted above....don't waste your money on high test. Computers are set up for 87. They do not like 93! It will actually make the engine run even more rich than it normally does and will turn the transom black.

pcm is programmed for 87 anything higher is a waste of money.

YUP ...........

Common misunderstanding that high octane means more hp. Higher octane burns slower which is needed on a high compression (or blower) engine which will allow the engine to make more power with the compression and advance. High octane in a engine designed for 87 octane will lose power.

Very few engines are designed for high octane fuels anymore. As mentioned above, high octane burns slower allowing for long combustion strokes. Lower octane burns faster for the shorter strokes. The mentality of higher octane is better came from the 50's and 60's in the era of big block long stroke engines and everyone associated premium with higher HP.

496HO's can be ran on either 87 or 89 octane. Might be okay to run some 89 in ethanol fuel that has sat for awhile since ethanol fuel starts degrading in roughly 30 days.

Look in the technical forum or his web-site and click on the big red button on the left. bobl dyno'd both 87 and 93 and posted the results and a lot of other good info. 87 wins. :D

How about the whipple stage 2 reprogram? It states 91 or better?