what octane to run????

[buckw13]

hello all. i have a 1990 larson senza with a mercruiser 350 260 hp. I have heard many different ideas on what gas to use. I took a safe boating course and the instructor said you should always run at least 89 octane. Then other people have said you can run 87 octane with no problems. I usually put gas in it before i get to the water so 87 is available. i have ran both, not noticing any different but i have not taken 60 gallon tank below half. all answers are greatly appreciated

 

[Kessi]

Re: what octane to run????

I'm sure I'll catch some arguments on this but, 89 min. at sea level and 87 at higher elevations. Having higher octane doesn't hurt, just a waist of money when you don't need it.

 

[1976SRV190]

Re: what octane to run????

I'm sure I'll catch some arguments on this but, 89 min. at sea level and 87 at higher elevations. Having higher octane doesn't hurt, just a waist of money when you don't need it.

I believe you are right. I use 87 but sometimes run a few gallons of 90 in it. I hear that at higher altitude you loose part of the need for high octaine fuel, but that may be wrong.

 

[buckw13]

Re: what octane to run????

i run in upstate ny in the finger lakes at about 900 to 100 ft. altitude.

 

[JustJason]

Re: what octane to run????

87 unless it knocks...... then pick one... run 89 or 93 or pull back the timing a few degrees and loose a few ponys...

 

[Fishermark]

Re: what octane to run????

Run good old "regular" - 87 octane. Like captJason says - if you have trouble you can go up from there... but no need to run higher octane than you need.

 

[Kessi]

Re: what octane to run????

At that low of an elevation I would run 89 and not even look back, no harm, no foul, no chance of ping.