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Old     (tbonus)      Join Date: Oct 2005       07-20-2006, 4:44 PM Reply   
What octane rating gas do you use in your boat, or any vehicle for that matter?
Do you use a fuel with an octane rating as recommended by your engine manufacturer or a higher rated fuel or a lower rated fuel.
If you run higher rated fuel than recommended, why? Why pay more than what the manufacturer recommends? What do you benefit from running a higher rated fuel?
Old    bigrich            07-20-2006, 4:53 PM Reply   
Thanks to you T 91 only for me.
Old     (iagainsti)      Join Date: Apr 2004       07-20-2006, 4:57 PM Reply   
Go with the manufactors recommended rating. If you use higher your wasting $$$ and getting less performance. The higher the octane the more compression to ignite the combustion chamber so if your running 91 in 89 recommended motor your igniting the gas before the motors full stroke. On my Dodge hemi truck it recommends 89 but says 87 is acceptable but specifically says higher octanes then 89 will degrade performance and mpg
Old    bigrich            07-20-2006, 5:08 PM Reply   
Agree but dont the higher octane fuels also have better/more detergents in them or is that also another myth
Old     (iagainsti)      Join Date: Apr 2004       07-20-2006, 5:14 PM Reply   
Okay after rethinking this I might have it backwards. Lower octane with pre-ignite sooner and higher will ignite later ? Your motor will retard the spark with lower octanes, I think ??? Anywayz go with the recommended and you'll be set
Old     (awf_axis)      Join Date: Aug 2002       07-20-2006, 5:49 PM Reply   
My MC supposedly has this Northstar ignition, that will adjust to the cheap gas I choose to use. At $4.60 a gallon at the Marina, and $3.29 locally, I just can't justify premium.

Old     (tbonus)      Join Date: Oct 2005       07-20-2006, 6:06 PM Reply   
Rich - say it is not so, I though I had you at 89 at most.

KG - your rethinking is correct: too low of octane = pre-ignition, to high of octane = un-burnt fuel, buildup, harmful deposits, clogged ports, etc.

My theory on the additives is this: The oil companies convinced us to buy the higher priced fuels long ago because they said it is better. They found out that over the long run (100k+ miles) this high octane fuel will harm the performance of our vehicles that do not need it, which is most of us. So that they can continue to sell us the expensive fuel, they have developed the additives to clean out the crap that is left behind in the engines that donít need the expensive fuel. Basically, selling a product to clean out the product they sold us that we did not need in the first place. (pure marketing genius)
Old    bigrich            07-20-2006, 6:19 PM Reply   
Ok but if you start using good gas from day one then there is never build up because the additives keep things clean right? Also you got me reeling now so I talked to some reliable sources. Octane in simple terms is the gasolines ability to resist detonation (higher octane= slower burn). Modern engines marine or automotive that are computer controlled have the ability to adjust ignition timing. Since the actual spark from the spark plug happens before the piston reaches top dead center the higher the octane rating the sooner before top dead center the spark plug can fire giving longer burn time and increased performance. Whewww!!!
Old     (hudd007)      Join Date: May 2006       07-20-2006, 6:35 PM Reply   
91 only in my boat.
Old    smooth_worm            07-20-2006, 6:41 PM Reply   
Nothing but 94 in my Turbo Supra... in my truck 87 (I only run it on gas when towing, normally I use propane) and usually 89 in the boat.
Old     (attila916)      Join Date: Oct 2005       07-20-2006, 6:43 PM Reply   
Old     (tbonus)      Join Date: Oct 2005       07-20-2006, 6:58 PM Reply   
That is right, using 'good' gas from the start will clean out the 'good' gas you purchased but were not able to fully burn.
Excellent point on the computer controlled ignition. But, doesn't advanced timimg (firing before end of stroke) take it's tole on an engine over time. Easy way to add performance to older cars was to advance the timing, but your engine would die sooner. Also, I wonder if I could feel the increased performance like I can feel the $9 left in my pocket after filling up my 90 gallon tank.

If i can save one person, just one person, 10 cents per gallon, it will all be worth it.
Old     (jayc)      Join Date: Sep 2002       07-20-2006, 11:43 PM Reply   
In the UK you can't buy anything less than 95 octane, of course we are paying close to $10 per gallon but at least its not that watered down rubbish you guys have!
Old     (dkjbama92mariah)      Join Date: Dec 2005       07-21-2006, 12:34 AM Reply   

Europe uses a different method for measuring octane. But I do agree, our gas sucks.
Old     (trace)      Join Date: Feb 2002       07-21-2006, 9:10 AM Reply   
EFI marine motors do not run in closed-loop, so you should absolutely run the octane your motor is set up for.
Old     (wakerider42)      Join Date: May 2002       07-21-2006, 11:23 AM Reply   
Just for everyone's education, what IS the manufacturer's recommended octane for some boats? I've never actually looked for my '02 Malibu VLX with the Monsoon engine. I usually run 89, but wonder if 87 is recommended or acceptable. I know most inboard boats use but a few engine builders (Indmar, PCM, etc...) Anyone know what these manufacturers recommend?

Old     (iagainsti)      Join Date: Apr 2004       07-21-2006, 11:36 AM Reply   
Danny-Most motors are 87-89 rated. There is recent link on the new MC motor which is 93 rated ? Anyway if your boat is rated for 89 and you put 87 in it the ECU will retard your timing. Your boat will run fine and you probably wont notice any "seat of the pants" diffences in power, but the motor wont be running optimally.
Old     (mackr0s)      Join Date: May 2006       07-21-2006, 12:27 PM Reply   
I run cheapo gas.
Old     (trace)      Join Date: Feb 2002       07-21-2006, 12:40 PM Reply   


Anyway if your boat is rated for 89 and you put 87 in it the ECU will retard your timing.

Are you sure about that?
Old     (iagainsti)      Join Date: Apr 2004       07-21-2006, 12:47 PM Reply   
Honestly Im not sure of anything anymore
Old     (wakerider42)      Join Date: May 2002       07-21-2006, 12:56 PM Reply   
I'm pretty sure that is a true statement. Higher octane reduces "pinging" or pre-detonation. If you run a lower octane fuel, your engine is more prone to pre-detonation because the fuel is combusting too early and creating the pinging sound because the piston is meeting the pressure of the combustion too early. So if the computer detects pinging (presumably from too low of octane, in this case), the computer will retard the timing, thus making the burn come a bit later when the piston is more near TDC as it approaches.

Hopefully that makes sense, I think that's right.

P.S. this does NOT mean that you have to run a high octane fuel to avoid pre-detonation. As we know, many newer engines are DESIGNED to run on lower octane (i.e. 87) fuel.

Have a great weekend, I'm OUT (unfortunately no wakeboarding this weekend. I'm 23 and all my friends are getting married, thus cutting into wakeboard time).
Old     (trace)      Join Date: Feb 2002       07-21-2006, 2:03 PM Reply   
I'm not sure now either. The fuel/air curves are fixed in a boat due to no O2 sensors, but I'm not sure what it looks at for the timing. My Monsoon has a knock sensor, but I think that's just to throw a code.
Old     (biz)      Join Date: Mar 2004       07-21-2006, 2:10 PM Reply   
Ahhh... the beauty of a carb engine and the ability to run 87 octane and a lot of ballast.
Old     (peterc4)      Join Date: Aug 2005       07-21-2006, 3:19 PM Reply   
Old     (attila916)      Join Date: Oct 2005       07-21-2006, 7:20 PM Reply   
06 RTP-1 manual says run 89
Old     (attila916)      Join Date: Oct 2005       07-21-2006, 7:22 PM Reply   
I would venture to guess that the guys and Indmar know more about their motor then I do, so I run what they recommend.
Old     (mobv)      Join Date: Jun 2002       07-21-2006, 7:40 PM Reply   
Centurion Mercruiser 330hp run 87 octane as recommended by Mercruiser
Old     (lake_side)      Join Date: Jan 2004       07-21-2006, 8:49 PM Reply   
91,93,112 I like that purple taste great and less filling.
Old     (azwakekid)      Join Date: Apr 2005       07-22-2006, 8:15 AM Reply   
100ll for me
Old     (luchog)      Join Date: Jun 2002       07-22-2006, 8:37 AM Reply   
My old Ford engine is rated for 87oc, but I use 94 and You can really tell a difference in performance. Have ran on 98 too but it was the same so I stuck with 94.

I think that:
In EFI or MPI engines you run what is recommened by the manufacturer, or at least as close to it as possible.

In Carburated engines you can run higher octane and then compensate with carburation and timing (like in my case)

In both cases if you have standart coil ignition you can adjust timing for different fuel octanes.
Dunno if you can do that on electronic coils.
Old     (trace)      Join Date: Feb 2002       07-23-2006, 6:04 PM Reply   
OK, I am now pretty sure the ECM in a marine EFI motor only looks at the MAP sensor to advance the timing. There's no closed feedback loop, and the MAP has no idea what octane you're running. Run what the mfr recommends.
Old     (ktmwakeboarder)      Join Date: Jun 2004       07-25-2006, 5:16 PM Reply   
87 in the car
87 in the boat

That's all they calls for, that's all I can afford, that's all they'll get haha
Old     (duffy)      Join Date: Feb 2006       07-26-2006, 12:56 PM Reply   
I use to build fuel stations and have lots of knowledge on fuel. I can only speak for Indmar motors because Ive only owned Moomba and Malibu. There rating is at least 89. These newer boat are like sportcars in the water and you wouldnt put 89 in a vet. The more octane the better because not only does it burn hotter and cleaner but you actually get better fuel efficiency because the motor doesnt have to work as hard. See that high octane fuel burns out all of the impurities in your system and keeps them out therefore making your boat run stronger and cleaner.When you use cheap gas your motor is working overtime because of all the impurities in the system.I use premium in my boat.Cars are different they dont take the abuse a boat does unless you have a high performance car than thats different.Also to high an octane can be bad as well (AV gas) to high an octane(generally not available to the public) can be bad as well making the motor run harder than it should. If you have a newer wakeboard boat you should run the higher octane it cost more but your boat will run better and last longer.Hope I helped!


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