High Octane!!! Worth It or Not?

[DudeHoss]

Does 93 Octane with 10% Ethinol make a measurable differnce in the 496 HO EFI. The owners manual says its designed for 87 Octane. Who actually notices a difference???

If you Notice a Differnce is it worth the extra $$$ per Gallon?

[David Ochs]

Higher octane fuel burns slower and has a higher ignition point.
The only reason to use higher octane fuel is to help prevent pre-ignition due to higher compression.
You will not get more power out of higher octane fuel with an engine that does not need it. It is absolutley fuelish to spend the money on it if it's not neccesary.
If the book recommends 87, use it!

[Formula Jr]

Good Read on Octane.

http://www.prime-mover.org/Engines/GArticles/octane.html

:propeller

[mphatc]

I agree with Poodle and David, but have to disagree . . . to an extent :wink:


My shop builds alot of HO performance engines using street fuels, and we have recently had numerous complaints of detonatioon, preignition etc. from some users when running engine on fuels with ethanol. Please note . . some of these engines were built to run on 93 octane fuel . . . and these customers have had to retune or buy a higher octane race fuel and dilute their mixtures . .

So what happens to a 496 HO . . . ? Truthfully I don't know, and in a marine engine you would likely never know if you're having a problem . . . but rational thoughts lead me to be cautious . . as any fuel with ethanol seems to have a lower effective octane from my own and few other experiences.

In discussions with other tuners and shops the ethanol fuels seem to cause this problem in motorcycles with advanced electronics as well.

Possibly 89 octane fuel is enough of a margin . . and certainly coolant water temp and how hard you're running may effect you as well.

For those with huge investments . . a water jacket installed knock sensor may be a cheap tool to warn you of a problem before it happens.

Your mileage and results will vary, I only share this info from my own experiences, and I for one will continue to run 93 in my engine as it is a whole lot cheaper than the beer I'll need to rebuild another . . .

FWIW,
Mario :boat:

[RedDog]

I believe the 496 has a knock sensor..??

as does the 502 MAG MPI?

If I understand correcly, the knock sensor retards the timing if pre-ignition occurs and therefore the concern of damage is minimized. Ergo - run the recommended fuel which is 87 octane.

I have also heard that running a higher octane fue lin the502 MPI or the 496 results in a sooty (black) transom.

[Sofa King]

Also u will get better tq wut 87 :eek!:

Iffin u have too much money i'll give u my address and u can mail it too me.
Arip

[Carl C]

Higher octane fuel burns slower and has a higher ignition point.
The only reason to use higher octane fuel is to help prevent pre-ignition due to higher compression.
You will not get more power out of higher octane fuel with an engine that does not need it. It is absolutley fuelish to spend the money on it if it's not neccesary.
If the book recommends 87, use it! This response is right on the money. It's amazing how many people don't understand this. And, yes, most EFI engines have knock sensors and will retard timing to stop preignition and some can actually determine the pinging cyld. and adjust timing only on the offending cylds. Use the recommended fuel or slightly higher for max. power but if you must buy low octane dock gas you should be OK but may lose a little power.

[Pismo]

In the 502 Mag, if using 93 or higher octane gas the knock sensor may not detect knock and it will then go into a base mode of very conservative timing which will cost you hp. So in a 502 Mag 93 or higher will porbably cost you hp, use 87/89.

[ChromeGorilla]

Run 87.... the 496HO has been dynoed with higher than 87 and has seen slight decrease in #'s. It performs best with 87 octane. This is a pretty well known fact about the 496HO.

[Shanghied Again]

Run 87 anything more and your throwing your money away, we run 525s on 87 Octane thats all they need.