jonholmb9

Hi i have a newly bought Sea Ray Pachanga 22 with an Mercruiser 350 mag mpi from 2000. My question is what is the best octane to use ?. Mercury recomends 95 Ron but is it better to use higher or will the effect drop since it burns slower. Please give me some advice.

All The Best Jon

RedDog382

I don't think you would gain anything with higher octane. It actually doesn't seem like you would even need to run 95 unless it is supercharged.

What was your source for the Merc recommendations?

I think even the 575 SC motors run on lower octane. I would think 89 to 91 or 92 would be adequate for this engine.

cuda

I'm almost sure they were designed to run on 87. 95 is way beyond what's needed. I run my 468's on 93, and it has 10:1 compression.

JaayTeee

I don't remember hearing of any
Merc's production ( non blue)
engines needing anything more than
87 octane.

You should be fine with the 87



jt

jonholmb9

Hi Thanks for the advice i think you are mixing the octane levels i live in Europe we use the Ron system so 95 Ron is not so high in the Us. Iam not sure what 95 equals to maybe 82.

All The Best Jon

restabr

92 ron = 87 by US (R+M/2 I think is the formula for octane in the US). 92/87 is the recommendation for the Merc Racing 525 EFI. I would think it would be the same for your setup.

Good Luck.

obnoxus

575SCI's need 92 octane. Stock 350 I would use 87.

SSComp

FYI most pump gas in the US is R+M/2 many other counties use RON:

The pump octane is also referred to as the Anti-Knock Index (AKI). AKI is determined based on an average of the Research Octane Number (RON) and the Motor Octane Number (MON). The formula is RON+MON/2 normally abbreviated as R+M/2 on the pump.

The MON is a measure of the gasoline's ability to resist knock under sever operating conditions. MON affects high speed, part throttle and performance (under load such as in passing). The RON on the other hand, is a measure of gasoline's ability to resist knock under less severe conditions. RON affects low to medium speed knock and engine run-on (dieseling). For a given AKI, RON is typically 8-10 points higher than the MON. As an example, 87 AKI (pump octane) fuel would have a MON of 82 and a RON of 92.

You should use the minimum pump octane (AKI) fuel that will run in your engine without knocking. You're wasting your money on higher octane fuels if there aren't needed to control knock. The two most common myths regarding pump octane (AKI) are that it will increase performance and result in better fuel mileage. You may see improvements in your ride due to the cleaners in higher grade, higher quality fuels, but octane by itself will not have any effect.

Dave M

I have no idea who RON is but I use 87 Octane in my 454 Mag MPI.

SSComp

MON - Jamacian (roughly means you)
RON - American (short for ronald)
AKI- Jamacian (means pain)

Used in a sentence by Jamacian:

"Ron-mon, I have an aki in my back, mon."