what octane do you use?
 

ok to run 87 in my 2008 X15? Not sure why higher would be needed.

you don't have money to burn!

330 Black scorpion, 87 for over 600 hrs. Whatever your manual prescribes is what I would use.

91 or bust. Indmar 383 Hammerhead.

91 -- 383 hammerhead

The manual for my PCM 351 says to use 89 minimum. I typically run 91.

i put 87 in my 330 black scorpion <100 hrs..... dont think its bad for it???

91...Only thing they have at the Marina

I run best that I can.....I figure I spend a ton of money on the boat, why the hell would I worry about an extra $400 a summer on gas. Think about it guys..... $0.25 differnce a gallon (at worst) on 50 gallons is only $12.50. For us we use about 10-15 tanks of gas a month. We ride for 4 months about.... so I would rather just run the $400 and call it a day then put bad gas in that has water, and everything else in it. Just my $.02

87

Indmar recommends 89 minimum. That's what I run.

Gas is rated on its ability to resist combustion. Higher the octane then higher its resistance to burn.

Running 93 octane in a motor designed to take 87 can actually cause a performance decrease.

Running 87 in a motor designed for 93 octane is normally a higher compression motor or has a fair amount of timing advanced. The lower octane gas can actually combust before the spark plug ignites causing "detonation" or pinging. This is BAD for engine internals.

Run what the owners manual says.

87 on the nautique and LSV

I have to say I agree with Matt. I can tell you that when we bought our Malibu this year i literally researched this issue like crazy. What octane is too little and what octane is too much, top tier fuels, 10% ethyl or not etc. I would be happy to give you all of the websites I checked as well as the engineers, mechanics, manufacturers etc but the bottom line is to read the owner's manuel and stick with it. Your motor is designed to function with a certain type of fuel in it and that's what you should do. For me it's 89 octane. I have been told that I can run 91 in it but I would just be paying extra for the same performance. Which is exactly what I do. In general 87 is too low, 89 is what my manufactuer recommends, 91 is a "safe but probably useless extra", and anything higher is too high.

Are you saying that higher octane gas cant go bad? I agree with Matt as well and very familiar how gas works. I guess my Title for this Thread should have been

"Anyone know what Octane Rating is reccomended for a 2008 X15 with MCX engine"

If he is then he is completely wrong. =)

Octane is not based on how much water there could be in the mix. If thats the case then a higher water content would actually raise the octane rating similar to the effects of water/methanol injection :D

Wow, ok maybe I knew nothing about gas. I am reading this and do understand do what the manual says, not an idiot. Mine says 89. I never run 93 only cuz I can't hardly find it. But, I do run 91 almost always. So you are saying that 91 isn't good for my boats? Doesn't make sense to me, but again maybe I know nothing about gas. I always thought the higher the octane the "cleaner" it was. Maybe I am totally off there. Again, forum post on WW to learn something go figure huh...lol

Higher octane has nothing to do with the cleaniness of the gas. In fact I would be weary of filling up with 91 or 93 in extremely rural areas, since there is no telling how old that gas is. You can rest assured that the 87 or 89 tank has been replenished more frequently.

PCM says to run 89. I always run 87 or 89.

I have to agree with Matt F on his comment on gas selection as well.

This is a direct cut and paste from PCM's website:

http://www.pcmengines.com/owners_inf..._questions.php

Q: With today's rising gasoline prices, what octane rating is recommended for my Pleasurecraft engine?
A: Pleasurecraft fuel injected engines are calibrated to operate on 87 octane fuel and maximum performance is obtained when using this fuel. The ignition timing set by the factory requires the use of a high-quality lead free regular gasoline with an octane specification of (R+M/2)

The best thing to do is to call Mastercraft and ask for their recommendation.

Mario-

Mercruiser 350 Mag MPI, 87 octane for 250 hours, no problems.

99% of gas stations have a low grade and high grade tank. They blend the two in order to get your 89 or 91 octane ratings (if 93 is the high grade)

The only exception would be is Sunocco 94 which would be its own separate tank

Matt is 100% correct!!! I was a mechanic for years, it is a highly mis-understood fallacy that burning a higher octane fuel is either BETTER for your engine, or will give you MORE power. Neither of these are true. You may think you are giving your boat the BEST, but you are just wasting money foolishly, and will most likely not achieve full fuel burn and end up leaving deposits and residue behind, which results in actually DAMAGING your engine.

A lady once randomly asked me this same question because she wanted to pass an emissions test tail pipe sniffer. I tried to explain that higher octane gas may actually hurt her more then it will help her.

She said "oh, ok" and then put 93 in her old car anyway.

The only time you go against the mfr recommendation is if you increase compression by changing pistons or shave the head (works sometimes).

Or, you have a modified ECU to increase timing.

Wow, learned something today! No wonder my head hurts. Guess I have money now for a new board. THANKS GUYS! I will be showing my wife this thread to tell her I can get a new board and bindings even maybe with the money I will save this summer! YES YES YES ! Wow, very cool thread!

[QUOTE=alans;1590730]Higher octane has nothing to do with the cleaniness of the gas. In fact I would be weary of filling up with 91 or 93 in extremely rural areas, since there is no telling how old that gas is. You can rest assured that the 87 or 89 tank has been replenished more frequently.
QUOTE]

That's if the station has 3 tanks for 3 grades. Often times they will have two tanks and a ratio blender to make the 89. Blending 87 with 91/93 to make 89. I know because I used to manage a gas station and when we added Diesel, that's how we did it to still offer Premium and Plus.
Just a cliff claven moment.....

Edit - Oh and I run 87 in my 8.1 fuel injected Volvo-Penta, same but different as Mercruiser, per my owners manual.

I run 89 in my 08 x-15ss but thats the lowest the marina has. Ive never had problems but have always wondered if im doing any damage

Matt is dead on. -another gearhead

In my cars and boat (2010 Axis A22) plain old unleaded evry time and no issues

98 RON when available otherwise 95 in our 350 Performer. Spendy.

Great thread.

I'm at high altitude, so I run 87. If I was at a lower altitude I'd run 91. 25 cents extra in a 42 gallon tank adds up.

Ya from a clean fuel stand point, get your fuel from a place that is reputable and sells A LOT of gas. Often times they have the best prices also but the less time that fuel spends in the tank the better!

One more variable in the mix, fuel degradation over time.

I have heard that gas drops a octane over time, something like 1 point ever two months? I want my boat to run on 87-89 octane gas. If there is gas that is over a month old I will blend in some higher octane 89 or 91 to bring that weak fuel back up a point or so. If the tank is empty and I expect to burn the gas the same day I buy it then it gets 87 octane.

If the octane drops below 87 the boat may start to knock and the computer will retard the timing reducing the power. I also agree that running gas over 89 octane may reduce performance as it does not flash quite a quickly.

I also avoid marina gas like the plague. I try to use only Chevron gas from the popular station near my house (which is also the closest Chevron gas station to Chevron's US corporate headquarters so I think the gas is good at this location).

The only time you need to use high octane fuel is if you have a high compression engine OR you hear knocking. Octane is an 8-chain stable hydrocarbon that is able to resist compression related pre-ignition. It does not inherently burn any hotter or cleaner, and it won't give you additional hp. 89 is fine for nearly every marine application. Anything above that is total waste of money. Spend the difference on beer.

manual says my black scorpion 5.7L runs best on 87 so thats what it gets!