More compression, More power ?

[G DANE]

When i rebuild my 35Hp Evinrude, i had used parts from 3 motors to choose between.<br /><br />I had two cylinderheads, one with round edges in combustion chambers and one older with sharp edges in combustions chambers. I used the round edged as it was newer. I mesured the room with oil and the sharp edged would give 10% more compression.<br /><br />My question is: Is the roundedged cylinderhead from a 20HP or just a newer design. Will higher compression always give more power, or can combustion chamber shaping maybe give the same power ?

 

[hondon]

Re: More compression, More power ?

A compression boost can certainly give your engine a new verve ,but to much will cause detonation, hard starting ,and possible rod journal failure.Are you ready to experiment?

 

[G DANE]

Re: More compression, More power ?

Hi Hondon thanks for reply. All three cylinderheads are original Evinrude - none of them modified to increase compression. One of the motors i got parts from, was a 1979 20 Hp, the others were 35HP, a 1984 and a 1976. The 20HP had replacement powerhead in 1999, but broke crankshaft after only 3hrs, due to wrong propeller pitch. ( studendts used on a rubber boat ! ) Problem is i am afraid i used the cylinderhead from the 20HP, i dont feel my 35 Hp has the right power. Compression is 113 on both, cold. I mesured on my old 25HP, 1983 it has 125 on both.<br /><br />Can i possibly identify the right cylinderhead by part nr. ? Where can i get the partnr checked ?

 

[G DANE]

Re: More compression, More power ?

Once again: the partnumber i need i the correct cylinderhead for 1979 35HP Evinrude.<br /><br />Thanks