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Recommended octane for 496MagHo

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Old 06-09-2007, 08:43 PM
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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.
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Old 06-11-2007, 07:19 PM
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pcm is programmed for 87 anything higher is a waste of money.
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Old 06-12-2007, 11:20 AM
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Originally Posted by Mentalpause View Post
You get the most HP on 87. Buy 93 and you spend more to produce less HP.
YUP ...........
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Old 06-12-2007, 11:31 AM
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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.
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Old 06-12-2007, 12:40 PM
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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.
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Old 06-12-2007, 02:03 PM
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Quote:
Originally Posted by Gunrunner72 View Post
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.....
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.
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Old 06-13-2007, 12:15 PM
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Quote:
Originally Posted by saubouin View Post
pcm is programmed for 87 anything higher is a waste of money.
How about the whipple stage 2 reprogram? It states 91 or better?
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