SHO Fuel requirements

[white mudbug]

All, I am considering the purchase of another boat that has a 250 SHO, my question is does it require premium fuel to be ran at all times? If so what happens if it isn't ran always? Thanks in advance!

[Rich Z]

89 octane is whats recommended. It will run just fine on 87 with little less power.

[printman71]

I have one on my Basscat PUMA. 89 is suggested, it is my understanding that if lower octane is used, it senses this and retards the timing and performance.
I am fortunate enough that there are several gas stations here that have 89 ethanol free in my area, at a reasonable cost, so that is what I run in mine.
I ALWAYS add Yamaha ring free with every re fuel.
What boat are you putting it on?
What did you have previously?

[wpaul]

Stick with the 89 and you’ll be fine.

[SmlRanger]

Ethanol free 93 and you’ll say weeeeeee!!!!

[Wackyjig]

Ethanol free 93 and you’ll say weeeeeee!!!!

Not for $1 more per gallon

[SmlRanger]

Not for $1 more per gallon

You can buy cheap fuel and your money will last longer. Get the best fuel possible and your motor will last longer

[Rich Z]

Anything over 89 octane is wast of money. I do agree that E-free fuel regardles of grade is better for the fuel system components on the motor.

[kry29]

I never believed going from 87 to 89 would make a difference. Honestly, I guess I never read the manual right and just saw it said 87 in there so that's what I was using. Finally saw enough people on here say 89 so I looked again and sure enough it says 89. So, I ran out almost all the gas I had and put some 89 in. It made a difference for sure. Sadly, i really needed gas and the only thing the station has is non ethanol 87 so I got some to finish the trip. Again, you could tell a difference.

[Meleagris1]

I notice my engine runs a couple mph faster on 89 vs 91. I only run 91 because it’s nonethanol.

[SmlRanger]

I only run 93 due to my higher altitudes

[printman71]

I only run 93 due to my higher altitudes

I've never heard that logic. Why?

[LOSTTEXAN]

The higher the altitude, the lower the the octane needed, unless perhaps a turbo or supercharger is involved.

[Randy T]

The higher the altitude, the lower the the octane needed, unless perhaps a turbo or supercharger is involved.

This! Because the air is thinner, there is less air to compress. Compressed air heats up, and higher octane, requires a higher temperature to burn. The result is compressed air heating up and reaching the flash point of the octane before the spark is produced by the plug. The more air induced, the higher octane required because more air means more compressed air, which means more heat. The less air induced, the reverse occurs, and the lower octane required.

This is a major reason why 89 is recommended by many on the VMAX HPDI 3.3L blocks. Cylinders 1&2 were the most problematic to damage not resulting in injector failure. They were the hottest 2 cylinders in which aided the on 87 octane to ignite through compression and not spark plug.

If a higher than needed octane is used it is a waste because not all of the fuel is being burned for the air inside the combustion chamber. If a lower octane is being used expect combustion before the spark, and will result in damage to components, and is sometimes avoided by knock sensors. Either rob power because full combustion is not occurring at the correct time. However, higher octane rarely shows because the results are so very minimal where as lower octane is seen by expensive repair bills.

To the OP, run what the manual says to run. Yamaha built the engine with the given compression ratio, and based the required octane off of that to achieve best performance.

[Rich Z]

The higher the altitude, the lower the the octane needed, unless perhaps a turbo or supercharger is involved.

Agree^^^. Randy, you confusing pre-ignition with detonation. Two different phenomena and both can destroy an engine. Unlike detonation, pre ignition has very little if anything to do with octane level.

[Randy T]

Agree^^^. Randy, you confusing pre-ignition with detonation. Two different phenomena and both can destroy an engine. Unlike detonation, pre ignition has very little if anything to do with octane level.

I'm using pre-ignition as a term meaning fuel/air combustion before the normal spark. Poor word choice for those who know what both is, but corrected.

[SmlRanger]

Im just running off of experience with most gas motors up here. If you dont use 93 you get spark knock. Id rather waste some unburned fuel rather than destroy hard items

[Rich Z]

The SHO, has a variable timing advance and knock sensor. If octane level is low it will reduce timing to protect the engine.

[krindgen]

Not for $1 more per gallon

You'll say WOOOh.