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Hatch7
06-03-2013, 12:11 PM
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

CantRepeat
06-03-2013, 12:32 PM
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?

SP Maristar
06-03-2013, 12:50 PM
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.

Table Rocker
06-03-2013, 12:56 PM
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?

east tx skier
06-03-2013, 01:00 PM
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.

CantRepeat
06-03-2013, 01:33 PM
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.

TxsRiverRat
06-03-2013, 03:15 PM
I use 87 with no issue. I do not use additives of any kind.

slink976
06-03-2013, 03:23 PM
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.

FrankSchwab
06-03-2013, 03:27 PM
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.

east tx skier
06-03-2013, 03:35 PM
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.

thatsmrmastercraft
06-03-2013, 03:44 PM
At 9:1 compression and the timing advance these engines run, 87 should be just fine. That said, I run 89. Like Doug said, it's not much difference in price when filling a tank

CantRepeat
06-03-2013, 03:45 PM
I hear ya and tend to agree, that when gas sits around it drops a bit in the octane department. I just fail to see how any motor with a static compression of 8.8 or 9.0 would need more then 87. I always assume, from what EngineNut posted, that Indmar just went with the 89 based off of gas sitting around. He did go onto say that 87 would work just fine without any loss of performance.

Hatch7
06-03-2013, 03:51 PM
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?

I have heard mixed reviews on the additives but most are in the snake oil camp. What about Marvel Mystery Oil? I know nothing about it's composition but could that help or hurt?

I do use Stabil on a regular basis both during the season and the appropriate amount for winterization.

Hatch7
06-03-2013, 03:55 PM
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?

I usually make it a practice to use all the gas before we leave or fill all the equipment and boats etc and add stabil but some could have been left and inadvertantly used. Fortunately for my wallet we go avoid the marina fuel.:D

Hatch7
06-03-2013, 04:04 PM
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.



I plan to run what is in there out and see how she does - it could have just been a bad tank of gas what ever the octane. I hope it's not he carb going but will keep checking all the possibilities. I'll be back on the lake next weekend to see how it goes. Thanks to all for your help!

By the way, I don't always sign in but have become additcted to this site and continue to learn something new every day. My wife thinks I'm nuts/obsessed (she's right) but I have come to see that I'm in good company!

thatsmrmastercraft
06-03-2013, 04:11 PM
I plan to run what is in there out and see how she does - it could have just been a bad tank of gas what ever the octane. I hope it's not he carb going but will keep checking all the possibilities. I'll be back on the lake next weekend to see how it goes. Thanks to all for your help!

By the way, I don't always sign in but have become additcted to this site and continue to learn something new every day. My wife thinks I'm nuts/obsessed (she's right) but I have come to see that I'm in good company!

Welcome to the support group. My name is thatsmrmastercraft and I have MCOCD...........

Hatch7
06-03-2013, 04:23 PM
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?

Someone went out to pick up the gas so if there was old gas in one of the tanks we use or condensation it could have caused the problem.

There was no sputtering or pinging just the delay and some coughing. As long as I go slow at the start it doesn't seem to happen.

CantRepeat
06-03-2013, 05:04 PM
I have heard mixed reviews on the additives but most are in the snake oil camp. What about Marvel Mystery Oil? I know nothing about it's composition but could that help or hurt?

I do use Stabil on a regular basis both during the season and the appropriate amount for winterization.

I've always heard good things about MMO. However, I have not used it in anything other then 2 stoke engines back when I was a kid.

The one "rumor" that I like best and need to start using is the MMO or 1/2 quart of tranny fluid before oil changes.

Welcome to the support group. My name is thatsmrmastercraft and I have MCOCD...........

Indeed, we are a support group for sure. I get a great feeling after someone comes here and gets good info that turns out to fix their troubles. It doesn't matter if it's my advice or someone info from any of the other great people here, it's always nice to see MC owners helping each other out.

I enjoy learning from great post that go up here!

thatsmrmastercraft
06-03-2013, 05:26 PM
I've always heard good things about MMO. However, I have not used it in anything other then 2 stoke engines back when I was a kid.

The one "rumor" that I like best and need to start using is the MMO or 1/2 quart of tranny fluid before oil changes.



Indeed, we are a support group for sure. I get a great feeling after someone comes here and gets good info that turns out to fix their troubles. It doesn't matter if it's my advice or someone info from any of the other great people here, it's always nice to see MC owners helping each other out.

I enjoy learning from great post that go up here!

I know TT made my learning curve much more enjoyable. I had my boat for nine months before I was able to put it in the water, so I was able to learn a lot of the things I shoud and shouldn't do before I had a chance to do them.:rolleyes:

Team Talk is truly a great place to be.