kentuckydiesel
05-30-2014, 01:40 PM
Hey guys, I don't race, but I have been soaking up the knowledge on this forum for a while. I tend toward the technical/performance aspects of engines, and most other forums lack that sort of discussion. You guys, on the other hand, seem to really know what you're talking about.
I have two Johnson 70s. One is a '74 model (70ESL74M), and the other
is a '79 model (70EL79R).
The other day I pulled the reed plates so I
could inspect the reeds. To my surprise, the '74 manifold and reed plate are two
separate pieces. The '79 has a one piece reed plate/manifold.
Looking at
the parts list for the '79, it appears that the short shaft model came with the
two piece, while the long shaft version (which I have) came with the one
piece.
www.boats.net/parts/search/BRP/JOHNSON/1979/70EL79R/INTAKE%20MANIFOLD/parts.html (http://www.boats.net/parts/search/BRP/JOHNSON/1979/70EL79R/INTAKE%20MANIFOLD/parts.html)
Was one style better than the other for any reason? I have a spare one-piece unit on a parts engine that I could swap onto the '74, if it'd be worthwhile.
While I'm at it, are there any decent all around performance upgrades for these engines?
I was thinking about decking the heads to bump up compression, but after a dry/cold compression test yesterday, I'm not so sure I want to bother. The '79 has between 140-148psi across the cylinders, and the '74 has 154-158psi across the cylinders. Not too bad for 30 and 45 year old engines that have never been opened up. :thumbsup:
Thanks,
Phillip
I have two Johnson 70s. One is a '74 model (70ESL74M), and the other
is a '79 model (70EL79R).
The other day I pulled the reed plates so I
could inspect the reeds. To my surprise, the '74 manifold and reed plate are two
separate pieces. The '79 has a one piece reed plate/manifold.
Looking at
the parts list for the '79, it appears that the short shaft model came with the
two piece, while the long shaft version (which I have) came with the one
piece.
www.boats.net/parts/search/BRP/JOHNSON/1979/70EL79R/INTAKE%20MANIFOLD/parts.html (http://www.boats.net/parts/search/BRP/JOHNSON/1979/70EL79R/INTAKE%20MANIFOLD/parts.html)
Was one style better than the other for any reason? I have a spare one-piece unit on a parts engine that I could swap onto the '74, if it'd be worthwhile.
While I'm at it, are there any decent all around performance upgrades for these engines?
I was thinking about decking the heads to bump up compression, but after a dry/cold compression test yesterday, I'm not so sure I want to bother. The '79 has between 140-148psi across the cylinders, and the '74 has 154-158psi across the cylinders. Not too bad for 30 and 45 year old engines that have never been opened up. :thumbsup:
Thanks,
Phillip