Correct Prop? RPM Range?

[Bryant Davis]

I just purchased a rebuilt 1982 Johnson 150, and am trying to determine a correct prop for my conditions. I have a 20' Bayhawk boat w/ hydraulic jackplate.<br /><br />First off, can someone tell me the correct max RPM's I should be turning? Someone told me there is a few years (early eighties) that turned less RPM's (about 4,500) than other years on the V6's.<br /><br />Currently, I am trying a Raker 14.5 X 24 and am running WOT 44 mph at 4,400 RPM's with the engine tilted up. I gain a LOT of RPM's just by trimming.<br /><br />Is this correct, or am I over pitched and if so what MPH should I expect with the correct prop. <br /><br />Bryant

 

[voodoo]

Re: Correct Prop? RPM Range?

5500 rpm

 

[walleyehed]

Re: Correct Prop? RPM Range?

5500 is the book value, but I would shoot for 57-5800 with yourself in the boat.<br />The 1982 200 is the exact same block, pistons, etc., and it's max is 5750.<br />Keep in mind, that's a pre-propshaft rated engine and puts out approx. 135HP at the prop.<br />17-19" pitch will be the range you will need...4400 will burn that engine up in short order....

 

[jimmbo]

Re: Correct Prop? RPM Range?

The 200 has the same displacement, however it does not share the same block as the 150. Engine breathing is restricted by smaller and milder porting, smaller carbs, and less refined exhaust tuning. Proping this engine in the upper half of the rpm range let alone exceeding 5500 results in less than the rated horse power.