Max RPM and Compression Ratio

[lindsey]

I have a couple of ? I have a 1973 evinrude 85hp im curious to know what is the compression ratio and i keep reading stuff about running the motor at a higher rpm is safer to do because of the ethonal blended fuels? Any help would be greatly apreciated

 

[Silvertip]

Re: Max RPM and Compression Ratio

Compression ratio is probably 6:1 to 6.5:1. Two strokes don't run very high compression.
5500 RPM at WOT is fine. Ethanol or not. Two strokes do not like to be "lugged".

 

[lindsey]

Re: Max RPM and Compression Ratio

Thanks. I think i worded that wrong about the compression. I want to know how many psi for each cylinder

 

[ugadawg187]

Re: Max RPM and Compression Ratio

Im not sure exactly about the compression but from what i hear anything over 110 per cylinder is fine as long as each cylinder is within 10 psi of each other. From what ive seen some of the bigger motors like the 225's & 250's have around 90 psi on each cylinder while some of the smaller outboards have a higher compression.

 

[lindsey]

Re: Max RPM and Compression Ratio

Thanks yeah there all between 115 and 117psi so i'm good