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fuel 87 or 89


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hey guys,

just curious about fuel octaine... has anyone noticed a huge difference between 87 and 89 gas?

i know the manual says 89 octaine, just wanted to get some info from other people,

thanks

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If your engine manufacturer recommends 89, then its best to use 89 or higher. Higher octane fuel is less volatile in order to resist pre-ignition. Higher octane requires more heat to self ignite, then lower octane fuel. This prevents the unwanted "spark-knock". Once ignited, 93, 89 and 87 all have about the same BTU's, so no performance advantage from the fuel itself. Another thing to consider, spark-knock is not as easily detectable from a boat engine while under way, as it is while sitting in a nice quite car interior. So running too low of an octane level, means you are relying 100% on the ECM to detect the knock and adjust accordingly.

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MalibuNation

If your engine manufacturer recommends 89, then its best to use 89 or higher. Higher octane fuel is less volatile in order to resist pre-ignition. Higher octane requires more heat to self ignite, then lower octane fuel. This prevents the unwanted "spark-knock". Once ignited, 93, 89 and 87 all have about the same BTU's, so no performance advantage from the fuel itself. Another thing to consider, spark-knock is not as easily detectable from a boat engine while under way, as it is while sitting in a nice quite car interior. So running too low of an octane level, means you are relying 100% on the ECM to detect the knock and adjust accordingly.

+1 ... very well put MLA.

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The dealer here told me to use 87. Said the higher octane stuff has too much ethanol in it. Said 87 isn't the best but it is the best we got here (Colorado)

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i have always used 87 never thought to read manual...the last few years it seems that im fighting performance issues, loss of power, running rich, etc (THE NORMAL)

but i just never paid much attention to gas type... just curious what others thoughts were...

Iam thinking is sounds just like what MLA (post #2)has said....

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These boats have 89 recommended for a reason. I have a friend who just had to replace an engine due to low octane fuel.

AL FUEL in a boat loses SOME octane rating due to the open vented fuel system and expansion/ contraction of temperatures.

In addition, the conditions you ask your boat to run is the equivalent to if not worse than asking you truck to tow your boat to the top of a mountain in 5th gear with a full load in the boat. Boat engines run at 4000 RPM plus, car engines rarely see these higher rpms .

Pre detonation from low octane fuels kills engines. PERIOD.

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The dealer here told me to use 87. Said the higher octane stuff has too much ethanol in it. Said 87 isn't the best but it is the best we got here (Colorado)

detonation is elevation dependent. very unlikely you'll detonate on 87 in CO.

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@ Racer: I would rely on the pump octane rating for determining the ethanol %. By law, there should be a sticker on the pump or by the nozzle that is, by law, supposed to state to what percentage the ethanol level should be. But, theres a problem with that. The ethanol, along with all the other additives, are added at the end of the pipeline as each gas brand/distributor, pumps their allotment out. Up to that point, everything that comes down the pipe is all the same gasoline, whether its Shell, BP, exxon or Marathon that pumps it out. So there is no guarantee that the blend will be at or below the required 10% max. I have read articles where samples have been indipendantly tested and contain a varying levels of ethanon and in a lot of cases, above the 10% level.

@ JIMJON: What do you mean 100%, 0% ethanol? What octane is the 100% gas you are using? Can you still get 100% 87 or 89, or is it blended? Ethanol blended fuel has less BTU then 100% gasoline, so comparing pump octane to octane, there is a difference in performance and fuel consumption. With blended, performance goes down and usage goes up.

@ Grandude: All grades of gasoline spoil (loses its potency) at about the same rate and its volatility goes down as well as its BTU's. This means it take more heat to ignite and it packs a lesser punch. This contradicts what most people think. There is no correlation between the gasoline's pump octane rating and its volatility after aging. No advantage in this department to use 89 or 93 oct over 87 for a boat or other toy that sits for periods of time. Its bets to use the recommend octane that the engine is designed for, based on its compression ration, and then supplement with a storage additive. I agree 100%, that using a fuel with too low of an octane can damage an engine.

When it comes to ethanol, if you can get 100% non-ethanol fuel and trust its ethanol free, then use. If not, I wouldn't sweat using ethanol blended fuel in a boat thats 10yrs old or newer, but the fuel system maintenance needs to be stepped up.

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@ JIMJON: What do you mean 100%, 0% ethanol? What octane is the 100% gas you are using? Can you still get 100% 87 or 89, or is it blended? Ethanol blended fuel has less BTU then 100% gasoline, so comparing pump octane to octane, there is a difference in performance and fuel consumption. With blended, performance goes down and usage goes up.

The gas station by my house that sells 100% gas (no ethanol) is 89 octane. I ran 5 tanks of that gas back to back and noticed no perfromance or economy gains. After that switched back to 87 octane 10% ethanol and boat never missed a beat.

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The dealer here told me to use 87. Said the higher octane stuff has too much ethanol in it. Said 87 isn't the best but it is the best we got here (Colorado)

Did the dealer build that motor? and is he going to fix it if it breaks?

The info about the amount of ethanol in the fuel is also incorrect. The percent of ethanol in all grades of E10 is the same.

Run 89. Indmar is smarter than your dealer, and us.

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Did the dealer build that motor? and is he going to fix it if it breaks?

The info about the amount of ethanol in the fuel is also incorrect. The percent of ethanol in all grades of E10 is the same.

Run 89. Indmar is smarter than your dealer, and us.

Colorado doesn't even offer 89 & you have to go find E10, it is not a standard here

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Colorado doesn't even offer 89 & you have to go find E10, it is not a standard here

What do they have as a mid grade, 91? Like TLC said, Dont go chasing waterfalls.....um, i mean, ethanol, please stick to the stations and pumps you are used to :lol::whistle:

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As Shawndoggy stated elevation makes a difference.

In fact if you run high octane at high elevation then you are burning less fuel and not going to get as much power out if each gallon. You also create more in your exhaust gas which will increase smell from exhaust.

At high altitude I think 87 would actually run better and get better mileage then 91. Especially when the ambient air temp is high. High temp does the se thing as higher elevation, lowers the air density.

Run what the motor manufacture recommends unless you are high altitude then go lower. Do not go higher then the manufacture has tuned the motor for, period. You are wasting fuel and money if you use too high of octane.

Mike

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Colorado doesn't even offer 89 & you have to go find E10, it is not a standard here

Just replying to what your dealer told you about 87 and 89. Why did he even tell you anything about E10 if its not in general use there?

If you don't have E10, then you are ahead of the rest of us because you don't have to deal with all the issues of ethanol.

If you don't have 87 there, what octanes do you have?

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If your engine manufacturer recommends 89, then its best to use 89 or higher. Higher octane fuel is less volatile in order to resist pre-ignition. Higher octane requires more heat to self ignite, then lower octane fuel. This prevents the unwanted "spark-knock". Once ignited, 93, 89 and 87 all have about the same BTU's, so no performance advantage from the fuel itself. Another thing to consider, spark-knock is not as easily detectable from a boat engine while under way, as it is while sitting in a nice quite car interior. So running too low of an octane level, means you are relying 100% on the ECM to detect the knock and adjust accordingly.

This is mostly true, unless the 93 you're running is ethanol free since a pound of ethanol contains about 30% fewer BTUs than a pound of gasoline, in which case there is a performance advantage.

Say there's 10% ethanol in all grades of gas (and for the sake of comparison let's pretend the 93 hasn't been sitting in the gas station tanks forever since there's less demand for it), an engine will still have the most power potential at the threshold of detonation, so ideally you want to run as low of an octane rating as the engine is designed for to prevent pre-ignition.

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Always amazes me that people will go out and spend $40K, $50K, and more on a boat and then cheap out on the fuel.

The "average" boat owner puts about 50 hours per year on their boat. If the boat burns roughly 6 gallons per hour that's 300 gallons per year. Mid-grade is what? 10¢ / gallon more the regular? That's $ 30 dollars a year that your saving. Indmar says to run 89, run 89. Or you could always sell your Malibu and buy a Bayliner with a POS little 6 cylinder and run 87.

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NorcaliBU

It's not just about being cheap. I have no problem spending the money for better fuel. But spending more on higher octane that actually gives me less performance is double stupid.

It's a misconception that higher octane is better. The fact is the most important thing is the right octane.

Now if I wanted to remap and change the spark curve on motor to take advantage of the higher octane then great but I am not going to do that on this motor. The only other way to take advantage of higher octane is higher compression and I am not going to do that either.

So use the right octane for your engine tune and your air density.

It's a fact that at higher elevation on my Indmar 8.1 I will get better performance out of 87 octane then 91 octane regardless of the price of the fuel.

Mike

Edited by PyleDriver
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