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Old 06-03-2013, 11:11 AM
Hatch7 Hatch7 is offline
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Fuel Question

First time out was Memorial Day weekend the boat (93 Prostar with std 351) ran great. When I winterized I had filled the tank with 93 octane. As the weekend progressed new fuel was added which I found later to be 87 octane. After the refill she started sputtering when dropping the throttle at the hole shot. The boat now has a full tank of the cheap stuff. The question is: Does anyone have any experience with adding octane boosters? Would it be recommended or not? I'm sure it could be something else but fuel seems to be the likely culprit since she ran great out of the gate.

Thanks,
Hatch
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Old 06-03-2013, 11:32 AM
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Originally Posted by Hatch7 View Post
First time out was Memorial Day weekend the boat (93 Prostar with std 351) ran great. When I winterized I had filled the tank with 93 octane. As the weekend progressed new fuel was added which I found later to be 87 octane. After the refill she started sputtering when dropping the throttle at the hole shot. The boat now has a full tank of the cheap stuff. The question is: Does anyone have any experience with adding octane boosters? Would it be recommended or not? I'm sure it could be something else but fuel seems to be the likely culprit since she ran great out of the gate.

Thanks,
Hatch
They are all snake oil and not worth your money.

Unless someone has done a lot of work on that engine you are kind of wasting your money running 93.

Did you put any kind of fuel stabilizer in when you winterized?
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Old 06-03-2013, 11:50 AM
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I used to use it on my Porsche 944 Turbo and it really helped smooth out the motor. It is already a fantastic motor design with counter rotating balance shafts, but the higher octane with the turbo made it even better. Not sure how much a non turbo motor would benefit.
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Old 06-03-2013, 11:56 AM
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Was is sputtering or pinging/detonating? Lower octane causes detonation in higher compression engines.

Where did you get the gas that you later found to be 87? Could it have been old gas? Gas that sat in a can for a while, gas that sat in a marina's tank over the winter?
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Old 06-03-2013, 12:00 PM
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east tx skier east tx skier is offline
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Run 89 in that motor as recommended in the manual and keep it stabilized (even during the season unless you are burning through a tank every two weeks). You could siphon off the gas and use it in cars or lawn equipment or you could add some 93 back to whatever is left of the 87.

2 parts 87 to 1 part 93 = 89.
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Old 06-03-2013, 12:33 PM
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Originally Posted by east tx skier View Post
Run 89 in that motor as recommended in the manual and keep it stabilized (even during the season unless you are burning through a tank every two weeks). You could siphon off the gas and use it in cars or lawn equipment or you could add some 93 back to whatever is left of the 87.

2 parts 87 to 1 part 93 = 89.
Doug,

Everything I've read says 87 for 351w/302 and that's all I ever ran in my 92. I guess it's just a matter of how long it sits before use and whether or not that it was stabilized.
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Old 06-03-2013, 02:15 PM
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I use 87 with no issue. I do not use additives of any kind.
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Old 06-03-2013, 02:23 PM
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I only fill with 91 (highest in cali) first rides of the year after that I pump 87. 91 really only matter on cars/boats with turbos. For me the 91 on the first ride is just to freshen up the remaining 87 from past year.
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Old 06-03-2013, 02:27 PM
FrankSchwab FrankSchwab is offline
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In general, the higher octane fuel REQUIRES higher compression to work well - putting 93 into an engine designed for 87 is going to REDUCE performance, not enhance it.
If your engine is pinging or knocking, going to higher octane will probably help, and may increase mileage/performance due to getting rid of the ping/knock (and any timing retarding done by the ECU), but otherwise it's just money down the drain.
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Old 06-03-2013, 02:35 PM
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Originally Posted by CantRepeat View Post
Doug,

Everything I've read says 87 for 351w/302 and that's all I ever ran in my 92. I guess it's just a matter of how long it sits before use and whether or not that it was stabilized.
Here is the page from the 91--93 Owner's Manual. I believe the reason they recommend 89 (per Indmar) is that 87 is okay, but 86 is not. Boat gas sits around. For what it's worth, the 351 (GT40) in my 98 Ski Nautique calls for 89 as well. I'd feel more comfortable putting 87 in that boat since it has a knock sensor. But I don't.

As the saying goes, your boat, do as you like. But the manual for that year undoubtedly says 89 octane.

For a full tank, that's about $3--5 more around here. I don't tend to miss it in the grand scheme of things. Then again, my VW takes 93. So getting to put 89 in something is a picnic.
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