Differences between Merc 90, 115, 140

What are the differences between the 90,115 and 140 HP Mercury outboards? I have a 81 Vector with a 115 HP. When I look in my service books the only difference I can find is the RPM  the Horsepower is rated at. Does this mean I can turn my 115 faster and get 140 out of it?

Thanks, Rick.S.

Rick, 

The porting in the 3 motors is different. Think of 2-stroke porting, as the camshaft in car motors. The hotter camshaft, the more power, but at the expense of low-end torque. Turning your 115 more RPM than it's peak will result in less horsepower, not more. If properly ported, then the peak will be at a higher RPM and the result is more peak power. 

Randy

 

 

Please submit whatever questions you have to IHRTechTalk@yahoo.com.  All questions and answers selected will be displayed on this page as they come in.  Note: though all boaters are welcome, priority may be given to I.H.R. members.  Randy can not be held responsible for any advice given.  Though his information and expertise is second to none, he has no control over what you do with your boat.  It is up to you to boat safely and act responsibly, and his advice is only to be used as a guidance for your high performance boat/motor of which you are the one responsible for the risks involved.

Thanks,
Mark C.

 

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