johnson service motor

[niesenracing]

can someone please tell me how to tell the difference between a px50 and a po

[Skoontz]

Not sure which letters were which, but one was a 6 stud, the other a 4????Correct me if I'm wrong here..... According to Russ Hill, probably the most knowledgable on the PR, PX, PO series on this forum, the crankcase was not to efficient on one, better on the next, but still really not the best.....

Anyhow, ask him when he gets back from the midwest.....

[BRIAN HENDRICK]

Some one step in here with better info, but a PR was an external rotary valve racing motor, a PO was an internal rotary valve service motor produced thru the early '50s, and the PX I have never heard of. :confused:

[Allen J. Lang]

The Johnson POs were as stated internal rotary valved engines. The P50 series of engines were like the PRs, external. Several P50s are running the C Service classes now.
Hope this helps. :cool: