View Full Version : Which is better with gas?

06-24-2012, 12:18 AM
87 oct NonEthanol or 89 with 10% ethanol?
Since I've moved back south I have a station on way to lake that has NonEthanol 87. I may mix in some 93 some just to improve oct but thinking I'd rather run 87 nonE
EtxCat 340 engine.

06-24-2012, 12:38 AM
thinking I'd rather run 87 nonE.

I like your thinking.

06-24-2012, 02:29 AM
I wouldn't even think that one over. If I can run non-ethanol I do it. If you look at the Indmar manual for most of these engines it says run 87 anyway. The Moomba manual says 89 though, I think. I trust Indmar and performance will be better and less chance of vapor lock with the non-ethanol. In fact, I've never experienced vapor lock.

06-24-2012, 07:56 AM
everything i run is 10% ethanol, all you can get in texas. ive never had vapor lock either

06-24-2012, 08:31 AM
Brad, run NE gas if you feel the performance slipping them back to E 89 with treatment like stabil or sea foam

06-24-2012, 08:44 AM
I can't recall ever putting anything but 87 in any boat that I've owned. Non-ethanol is just much better for moisture issues.

06-24-2012, 08:46 AM
Since your boat is a 2011, and ethanol is nothing new, I would hope the entire fuel system is designed to run ethanol and will not suffer any deterioration due to it. 2nd, Its always best to run the engine manufacturers recommended octane level, but there is ZERO advantage to running a higher octane level. The marketing hype you see on TV about "Premium" is just that, marketing hype.

Higher octane fuel has a lower volatility, meaning it needs a higher temp before it ignites. This is the how and why higher octane prevents/resists pre ignition or spark-knock. As the piston comes up and compresses the air/fuel mixture, the combustion temp rises. If its too high, the lower octane ignites before the spark. This is pre ignition. Higher octane resists this due to its ratio of octane and heptane molecules. Once ignited, 93 octanes rate of propagation and its BTU's is about the same as 87 oct. So there is no performance gain in the fuel. If an engine is designed to run 87 oct, and its spark-knocking, running the more expensive 93 is not the fix, although it might subside the pre ignition.

So, if a boat's fuel system is compatible with ethanol, then the only thing we need to fear about running ethanol, is water absorption during lay-up over the off season. There are additives specifically for ethanol.

Since spark-knock is soo hard to detect in a v-drive boat, I would be more worried about it, then ethanol.

06-24-2012, 10:29 AM
the debate over 87 v 89 could go on and on. My plan is to run 87 nonE and put Ina little high test. Hat way I'll be running less percent of ethanol

Cigars n scotch
06-24-2012, 10:42 AM
Supra's manual says to run 89 in your motor, I have the same one and I run 89. I don't have anything to add on the debate though.

06-24-2012, 10:57 AM
everything i run is 10% ethanol, all you can get in texas. ive never had vapor lock either

Here's a link to find ethanol free gas stations. There may be better ones out there, but this seems to be accurate. Use the map function or click on your state at the bottom. Given the choice, I wouldn't put the ethanol in, but you don't always have a choice. I keep a bottle of Stabil marine formula in the boat for all fill ups.


06-24-2012, 11:23 AM
I add stabil just for winterization and run nothing but 89 octane E10. No problems as of yet! And during the summer my boat lays up up to three weeks at a time without any stabil or ethanol treatment.

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06-24-2012, 11:42 AM
I mostly run the ethanol gas also without problems. I add the stabil every tank now only because a two week layup turned into the entire winter last year. I was wishing I had put the ethanol treatment when that happened. It's probably overkill using every time, but it makes me feel better in case my boat has to unexpectedly sit for a while. Definitely not required if you're using your boat frequently.

06-26-2012, 05:23 PM
I run 91 octane due to being non-ethanol in it vs. 89 or 87 with.
Figure the major benefit is being ethanol free :)

ps.....if i can find 89 e-free fuel I will use it but far and few between carry it.

06-26-2012, 07:12 PM
NonE station was closed Sunday so I added none.
We'll see this weekend. Prob run 89 e10

06-26-2012, 07:49 PM
I run 91 octane due to being non-ethanol in it vs. 89 or 87 with.

you are both wasting money and potentially degrading the performance of your boat. you shouldn't run higher than what the manufacturer recommends. premium is designed for higher compression/force fed motors and has different burn characteristics than it's lower octane bretheren.. you might not ever know the difference, but with the load that we place on these motors weighted down, I'd run what indmar/skiers recommend.
ethanol-laced fuel will run just fine in boats if you run the blower and keep the heat out of the engine compartment and don't leave untreated fuel in the tank for extended periods of time.