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1980's Johnson/Evinrude 20/25hp conversion to 30hp with pics
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<blockquote data-quote="thill" data-source="post: 373918" data-attributes="member: 4972"><p>I know that somewhere before 1990 they increased the HP output of all their motors, to rate them at the prop, instead of at the powerhead.</p><p></p><p>Because of this, my 1995 is WAY stronger than my 1981, although the compression is lower. It makes almost a 10 MPH difference. The older motor runs excellent, but it's just not as stong at the prop. I've found this to be the same across the board, especially with my 70 HP motors. The older ones run flawlessly, but just don't have the same grunt as the 90's motors.</p><p></p><p>It depends on how they achieved the higher HP, as to how you proceed. If they increased the bore and stroke, increased the carburetor and intake volume, increased the max RPM, or whatever, it changes how you take advantage of the differences.</p><p></p><p>Any idea of WHY the 1982 heads are supposed to be the best?</p><p></p><p>Of course, this is all theory to me, as I have not actually looked at the specs, and I'm not very experienced with making serious modifications to motors. My job is to get them running well, and keep them as close to stock as possible, so my opinion is not worth too much in this discussion.</p><p></p><p>-TH</p></blockquote><p></p>
[QUOTE="thill, post: 373918, member: 4972"] I know that somewhere before 1990 they increased the HP output of all their motors, to rate them at the prop, instead of at the powerhead. Because of this, my 1995 is WAY stronger than my 1981, although the compression is lower. It makes almost a 10 MPH difference. The older motor runs excellent, but it's just not as stong at the prop. I've found this to be the same across the board, especially with my 70 HP motors. The older ones run flawlessly, but just don't have the same grunt as the 90's motors. It depends on how they achieved the higher HP, as to how you proceed. If they increased the bore and stroke, increased the carburetor and intake volume, increased the max RPM, or whatever, it changes how you take advantage of the differences. Any idea of WHY the 1982 heads are supposed to be the best? Of course, this is all theory to me, as I have not actually looked at the specs, and I'm not very experienced with making serious modifications to motors. My job is to get them running well, and keep them as close to stock as possible, so my opinion is not worth too much in this discussion. -TH [/QUOTE]
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1980's Johnson/Evinrude 20/25hp conversion to 30hp with pics
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