Old motors; Elevated RPM ranges

[jddenham]

I have read numerous times in this forum about running older motors at higher RPM's due to the inferior gas we now use.

I am wondering about one of my particular engines, a 1958 Johnson 'fat fifty' V4 50HP.

The transom plate lists 4000 - 5000 RPM as acceptable range, and 4500 at peak HP. This seems a bit lower than other V4's from say 1970 or so, but again this was the first V4 engine so maybe it wasn't capable of 5000+ RPM's?

Just curious if anyone has ran this motor higher than 5000, or if any of the experts would recommend running it higher. If so, how high with a light load, how high with a normal load?

Thanks.

 

[jimmbo]

Re: Old motors; Elevated RPM ranges

That engine is approx 71 cu.in, very large for 50 hp. It didn't have to rev up much to make its power. As for proping it. I think there is only one prop being made for that engine. 12-1/8" X 14" OEM# 278155, Michigan # 012033

My service manual says the 50 was rated @ 4000rpm and full throttle range was 3500 - 4500

 

[jddenham]

Re: Old motors; Elevated RPM ranges

Would it hurt the motor to occasionally run it at 5500 or so for a few minutes?

 

[walleyehed]

Re: Old motors; Elevated RPM ranges

No......