Cylinder head swap

[89retta]

I have a 1990 115hp Johnson. The compression is 115 on all four and the engine runs great. I was thinking of putting a pair of 1983 heads on it from my old 140. The reason for doing this is i have read that the 140s have a higher compression head. Would i see any benifet to doing this and also will they fit ? Both engines have bubbleback exhaust and are crossflows. Thanks for any help.

 

[emdsapmgr]

Re: Cylinder head swap

Your 115 does have low compression bathtub heads. The early 140's had really high compression heads, which began to change in the 81 model year. Despite that, the 83 140 heads should bolt right on and provide an upgrade from the current heads you have on the engine. You should see higher compression numbers and slightly better performance. Do a complete "before and after" compression test to see what your results are. A couple of concerns. After the swap, the powerhead should be run on 91 octane gas only. Possible that you may need to rejet the high speed jets slightly (larger) in order to keep the cylinders cool. The 1990 engine WOT timing is 28 degrees-probably the same as the 83 model.