Prop RPM

[Red Rider]

I have five 'rudes from 6hp to 40hp. I have a couple of induction tachs so I can take the engine RPM off of a spark plug. But how do I find out what the prop RPM is?<br /><br />It has to be simple, but for the life of me I can't figure it out. Must be a case of can't see the forrest because the trees are in the way.

 

[ob]

Re: Prop RPM

You need to know what the lower unit gear ratio is to determine the propshaft revolutions as compared to the crankshaft.

 

[Red Rider]

Re: Prop RPM

OK, now where do I find out what the lower unit gear ratio is? It isn't in my repair manual.<br /><br />I have the following Evenrude motors:<br /><br />1966-6hp / 1971-9.5hp / 1972-40hp / 1977-35hp / 1984-20hp / 1988-40hp(Tracker) / 1988-90hp. I wasn't relly concerned with the 6hp and the 90hp but thought what the heck, include them.

 

[Dhadley]

Re: Prop RPM

The 90 is 2:1.<br /><br />To find the rest, count the turns on the flywheel while someone watches the propshaft (forward gear). Stop when the propshaft has turned 10 times. Note the flywheel turns and divide by 10. You can go by one turn of the propshaft but its more accurate to do 10.<br /><br />In the case of your V4, the flywheel will turn 20 times when the propshaft has done 10. That gives you the 2:1 ratio.<br /><br />On a typical V6, the flywheel will turn 18.6 times to get the propshaft to turn 10. That gives you the 1.86:1 ratio.<br /><br />Good luck!

 

[Red Rider]

Re: Prop RPM

Darn! I thought the internet was supposed to save me work? Oh well I guess I'll have to do the manuel labor <br /><br />Hey thanks.

 

[ob]

Re: Prop RPM

Just curious as to why you would want to figure the prop rpm.Just for grins?

 

[Red Rider]

Re: Prop RPM

Prop Rpm is supposed to be figured into what type prop you should use for what speeds etc.<br /><br />But yeah mainly for grins. <br /><br />I kinda wanted to compare the rpm at the prop for my different engines.

 

[Spidybot]

Re: Prop RPM

Here's a bunch of info. For those models listed under one brand it is OK to assume the same specs for the equivalent model under other brand<br /><br />Format is Model, RPM range at WOT, gear ratio<br /><br />Evinrude Outboards,<br /><br />5 hp 4-Stroke,5500-6500 rpm, 2.23 ratio, <br />6 hp 4-Stroke,5500-6500 rpm, 2.23 ratio, <br />8 hp 4-Stroke,5000-6000 rpm, 2.42 ratio, <br />9.9 hp 4-Stroke,5000-6000 rpm, 2.42 ratio, <br />9.9 hp HT 4-Stroke,4000-5000,2.42 ratio, <br />15 hp 4-Stroke,5000-6000 rpm, 2.42 ratio, <br />25 hp 4-Stroke,4700-5300 rpm, 2.09 ratio, <br />30 hp 4-Stroke,5200-5800 rpm, 2.09 ratio, <br />40 hp 4-Stroke,5200-5800 rpm, 2.27 ratio, <br />50 hp 4-Stroke,5900-6500 rpm, 2.27 ratio, <br />70 hp 4-Stroke,5200-5800 rpm, 2.42 ratio, <br />75 hp Ficht,4750-5250 rpm, 2.00 ratio, <br />90 hp Ficht,5250-5750 rpm, 2.00 ratio, <br />115 hp Ficht,5250-5750 rpm, 2.00 ratio, <br />135 hp Ficht,4750-5250 rpm, 1.86 ratio, <br />150 hp Ficht,4750-5250 rpm, 1.86 ratio, <br />175 hp Ficht,5250-5750 rpm, 1.86 ratio, <br />200 hp Ficht,5500-6000 rpm, 1.86 ratio, <br />225 hp Ficht,5500-6000 rpm, 1.86 ratio, <br />225 hp Ficht HO,5500-6000 rpm, 1.86 ratio, <br />250 hp Ficht,5500-6000 rpm, 1.86 ratio, <br /><br />Johnson Outboards,<br />2 hp,4000-5000 rpm, 1.85 ratio, <br />3.3 hp,4500-5500 rpm, 1.85 ratio, <br />3.5 hp,4500-5500 rpm, 1.85 ratio, <br />4 hp,4500-5500 rpm, 2.08 ratio, <br />5 hp,4600-5400 rpm, 1.92 ratio, <br />6 hp,4500-5500 rpm, 2.23 ratio, <br />8 hp,5000-6000 rpm, 2.23 ratio, <br />9.9 hp,5000-6000 rpm, 2.23 ratio, <br />15 hp,5000-6000 rpm, 2.23 ratio, <br />25 hp,4500-5500 rpm, 2.15 ratio, <br />25 hp,5200-5800 rpm, 2.15 ratio, <br />30 hp,5200-5800 rpm, 2.15 ratio, <br />35 hp,5200-5800 rpm, 2.15 ratio, <br />40 hp,4500-5500 rpm, 2.23 ratio, <br />50 hp,4500-5500 rpm, 2.23 ratio, <br />60 hp,5000-6000 rpm, 2.23 ratio, <br />70 hp,5000-6000 rpm, 2.23 ratio, <br />90 hp,4500-5500 rpm, 2.00 ratio, <br />90 hp OP,4500-5500 rpm, 2.00 ratio, <br />115 hp,4500-5500 rpm, 2.00 ratio, <br />115 hp OP,4500-5500 rpm, 2.00 ratio, <br />135 hp,5000-6000 rpm, 2.25 ratio, <br />135 hp OP,5000-6000 rpm, 2.25 ratio, <br />150 hp,4500-5500 rpm, 1.86 ratio, <br />150 hp OP,4500-5500 rpm, 1.86 ratio, <br />175 hp,4500-5500 rpm, 1.86 ratio, <br />175 hp OP,4500-5500 rpm, 1.86 ratio, <br />200 hp,5000-6000 rpm, 1.86 ratio, <br />200 hp OP,5000-6000 rpm, 1.86 ratio, <br />225 hp,5000-6000 rpm, 1.86 ratio, <br />225 hp OP,5000-6000 rpm, 1.86 ratio, <br />225 hp HO,5000-6000 rpm, 1.86 ratio, <br />250 hp OP,5000-6000 rpm, 1.86 ratio,

 

[Red Rider]

Re: Prop RPM

Hey UU, Thanks a lot, Just what I was looking for.

 

[ob]

Re: Prop RPM

Dang UU.Nice job.Thanks for the info on all of those gear ratios.