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Old 07-18-2006, 10:52 AM
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MCX Engine - 87 vs 89 Octane

okay, sure this has been discussed before but couldn't find a post that just focused on this issue...

got my 2005 197 with MCX 350/350 which calls for 89 octane fuel...i've got a bunch of buddies that swear the 87 runs fine, that the 89 requirement is just for california emissions...

any thoughts on this, certainly a big difference in price here in New England...for 87 our price here in New Hampshire is $2.95 but for 89 it is $3.05...

so for every 10gals looking at $1 extra for 89...
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Old 07-18-2006, 11:06 AM
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We ALWAYS run 89 in the MCX....
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Old 07-18-2006, 11:07 AM
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Quote:
Originally Posted by erkoehler
We ALWAYS run 89 in the MCX....
my problem is, sometimes get ski buddies who bring 87 octane claiming it is 89...but they run 87 in their boat?!?
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Old 07-18-2006, 11:11 AM
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If your using it the same day, it isn't as crucial, but MC does recommend 89 octane in the MCX engine.
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Old 07-18-2006, 11:20 AM
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Quote:
Originally Posted by erkoehler
If your using it the same day, it isn't as crucial, but MC does recommend 89 octane in the MCX engine.
I believe that's the reason. Engine Nut once posted here that it has to do with assuring that you get at least 87 octane in the engine. So if you know it hasn't been sitting at the station for too long and you plan to burn it all up in a week or so, then it'll probably be alright. As he said (not a direct quote), 87 is fine, 85 is not. This may be more applicable to my carb'd motor where it cannot retard timing. Plus, my motor is low compression at 8.5:1.
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Old 07-18-2006, 11:22 AM
phecksel phecksel is offline
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I can tell the difference in pull between 87 & 89, and to a lesser extent, even 91
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Old 07-18-2006, 11:28 AM
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Quote:
Originally Posted by east tx skier
I believe that's the reason. Engine Nut once posted here that it has to do with assuring that you get at least 87 octane in the engine. So if you know it hasn't been sitting at the station for too long and you plan to burn it all up in a week or so, then it'll probably be alright. As he said (not a direct quote), 87 is fine, 85 is not.
trust me skiing almost everyday, can't tell by my buoy count right now, but the gas doesn't sit in there for very long...
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Old 07-18-2006, 11:51 AM
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If I know I'll burn thru the tank in a weekend I have ran 87 octane. If it's going to sit a week before I burn it off I'll run 89. I have ran 91 in it and you definetely can tell between all grades which one provides the most giddy up. 9 times out of 10 I run 89 octane.
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Old 07-18-2006, 11:53 AM
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This has been covered here ad nauseum…. If you want the boat to make less power then run 87, the engine is equipped with knock sensors that will retard timing. This serves as the engines way of protecting itself from detonation from running low octane fuels with high stress loads (i.e. pulling up slalom skiers or running the course at 36mph). However, when the engine pulls this timing out it will make less power…so what you might say? Well it will then take more throttle to achieve a given speed or power output. In other words it will need to burn more fuel to make the power required since it cannot extract it from the lower grade fuel without the possibility of hurting itself.

BTW, as hot as it is this situation only gets worse…hot air doesn’t make power.

Tell your friends 89.
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Old 07-18-2006, 01:15 PM
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Quote:
Originally Posted by MYMC
This has been covered here ad nauseum…. If you want the boat to make less power then run 87, the engine is equipped with knock sensors that will retard timing. This serves as the engines way of protecting itself from detonation from running low octane fuels with high stress loads (i.e. pulling up slalom skiers or running the course at 36mph). However, when the engine pulls this timing out it will make less power…so what you might say? Well it will then take more throttle to achieve a given speed or power output. In other words it will need to burn more fuel to make the power required since it cannot extract it from the lower grade fuel without the possibility of hurting itself.

BTW, as hot as it is this situation only gets worse…hot air doesn’t make power.

Tell your friends 89.
makes sense especially since skiing 36mph and want times to be good...wonder if that's why we're getting varying times on glassy water with perfectpass...
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