Converting 4.5 to 7.5 - Possible?

[Duelfuel]

Hello,
I recently purchased a 1981 Evinrude 4.5hp Integral (internal) tank, and went on to Ebay and purchased a service manual for it.

I did not realize that the 4.5 & 7.5 were lumped into the same group (i.e. 9.9 and 15hp).

Has anyone tried to convert or tweak a 4.5 to generate higher horsepower? You see it all the time with 9.9/15, but I have not seen anything regarding 4.5/7.5.

Any thoughts from forum members would be appreciated.

 

[Chinewalker]

Re: Converting 4.5 to 7.5 - Possible?

No - very different powerheads. They're lumped together as they share a similar chassis - similar lower ends, clamp brackets, cowlings, etc. The 4.5 is a smaller bore engine, shares it's lineage with the old 3hp Lightwins of the 1950s. As such, 4.5hp is about as much as they got out of the old 3hp block... The exhaust housing is different so you can't bolt a 7.5 powerhead onto the 4.5 housing...

 

[Duelfuel]

Re: Converting 4.5 to 7.5 - Possible?

Thanks... the technical specifications in the manual looked quite different, so I wondered if anything was possible.