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Octane Grade

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BeeJay View Drop Down
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    Posted: September-15-2017 at 10:04pm
   I am original owner of a 1997 Ski Nautique competition model.From the time I purchased it I have always run 87 octane gas through it. Until just recently I noticed something in the Pleasure Craft manual that I have missed all these years - "recommend 89 octane fuel for this motor". I think I will try this on my last fill up for the season. However. In doing automotive tune ups in years past, most of the time it was recommended to set the spark advance for the particular fuel grade used. The question is-do I have to reset the timing to accommodate an upgrade in octane, and if so was the engine already timed for 89 octane when it was purchased? . Engine is a carbureted 351 Windsor with no extras except solid state ignition which is merely a switching transistor that replaces the points. As it stands right now the engine turns the standard four bladed prop at 4600 RPM WOT and idles like beautifully.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote MrMcD Quote  Post ReplyReply Direct Link To This Post Posted: September-15-2017 at 10:15pm
If all is running well with no pinging your tune for the elevation you run at is probably really good for the octane you are using.
You can always put a tank of premium and see how it affects the engine.
If you gain a little power under hard loads you answered your own question.
FYI: On my carbureted engine I was happy with regular. With my Fuel Injected engine it does perform better with premium. I believe the better gas allows the computer to add more timing giving a slight improvement in power on the GT40.
I have not looked to see if this engine has detonation sensors, if it does not the computer is not adjusting for the fuel but it just feels smoother when I run it hard.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote phatsat67 Quote  Post ReplyReply Direct Link To This Post Posted: September-16-2017 at 10:07am
GT40 has knock sensors in the ends of the head FYI.
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Post Options Post Options   Thanks (1) Thanks(1)   Quote KENO Quote  Post ReplyReply Direct Link To This Post Posted: September-16-2017 at 11:06am
Originally posted by BeeJay BeeJay wrote:

Hello All
I have a '97 Cmpetition Nautique with a 351 Ford PCM engine and PCM transmission. Altho the tranny oil looks and smells good, I figure its about time to change oil in it. The wortless factory manual that came with it tells me nothing. I see no evident drain port, so attemted to pump it out of the fill hole. An ounce or two was the best I could do and then nothing. What is the method used to drain that oil?


Here's a quote from an old transmission fluid post of yours, I couldn't help but notice the mention of the worthless factory manual

I guess you have to read it to get some value out of it.

The good 97 Correct Craft/PCM manual I have says to back the timing off 4 degrees if you're going to run 87 octane instead of 89.

Spec was 10 degrees BTDC at idle for 89 octane so it would have you going to 6 degrees BTDC at idle and the timing will be 4 degrees less over your whole operating range.

Maybe you know where it's set now, maybe you don't but that's where to start.

Figure out what you have for timing.

You've run it for 20 years this way with no problem.with whatever you have for timing.

You'll get different opinions on where to set it, but that's what the manual says..

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bri892001 Quote  Post ReplyReply Direct Link To This Post Posted: September-16-2017 at 10:56pm
Haha, not to get off topic, but I recently picked up my manual and read the piece about transmission fluid change. It turns out that the PCM 1:1 transmissions do have a drain bolt. I've always struggled with sucking it from the fill hole; I thought that's how everyone on here did it. I kind of hesitate to loosen that drain bolt after all these years, not to mention there's not much room for a catch pan other than the bilge itself.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote BeeJay Quote  Post ReplyReply Direct Link To This Post Posted: September-18-2017 at 1:08pm
   Thanx for your inputs. Tank is close to empty now so I think I will pump about 15 gal. of 89 into it for our final run and see how it performs. If no improvement, I will top it off with 87 on the way back home for winter storage. Have to pull boat early this year as I have a narrow window for winter storage coming up in a week. But right after oil change I will check the timing as factory set just out of curiosity.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote MrMcD Quote  Post ReplyReply Direct Link To This Post Posted: September-19-2017 at 5:40am
Fuel will degrade a little with time. I think Premium is the better bet for sitting all winter.
In the spring run whatever you wish after the first tank.   If you store it with 87 octane and it degrades to 85 octane or less you might not be happy.   Maybe a engineer can jump in and give better advice but it seems to me that in my many years of boating the boats are sluggish till we burn that first tank out after the winter storage. The second tank of fuel seems to fix this.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bri892001 Quote  Post ReplyReply Direct Link To This Post Posted: September-19-2017 at 11:21am
That's good advice. Store it with a higher grade.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jonny Quest Quote  Post ReplyReply Direct Link To This Post Posted: September-19-2017 at 3:17pm
Do a little research and stay away from fuel with BTEX (benzine/toluene/ethyl-benzine/xylene). I would do long-term storage with ethanol-free fuel. 90+ octane if you can get it. Most of the higher octane ethanol-free fuel is higher quality than the lower octane 10% ethanol stuff.

IMO, gasoline additives like MTBE (methyl tert-butyl ether) and BTEX coupled with ethanol should be avoided. I'm in the petroleum industry and this advice comes from some very intelligent petroleum engineers.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote BeeJay Quote  Post ReplyReply Direct Link To This Post Posted: September-20-2017 at 2:22pm
Hi All
Your inputs have provided some good food for thought here. In my 40 years of running inboards of all block, sizes, I have always just topped the tanks off at storage and never had a problem. I think my saving grace was that in my neck of the woods the storage temperature (6 months of storage) was rarely above 55 degrees at each end and more like 20 degrees in the middle (-29 two years ago). At these low temperatures gasoline is very inactive. However, several years ago I started having minor fuel problems and I am sure its due to that damn Ethynol. Now I add Stabil just as a precaution. This goes against my grain as I never had faith in any fuel additives especially "Perfomance" types. But in this 'wonderful ' Hi-tech world we live in today, all the old rules seem to be going by the wayside.
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