I just boaught a 1984 cimmaron 18 ft with 3.8 ltr omc stern drive the boat is in great shape and runs good i know nothing about omc or what size prop to use the prop is 14 1/2 -19 i get about 35 mph at 4100 rpm pulling a tube or not it seems to over rev any info will be great thanks
1984 cimmaron
- Thread starter tweeter
- Start date
Hi tweeter - welcome aboard. 
Basically, what you'll want to do, is find the max RPM range for your motor.
You'll then want to prop your boat so that it runs in the max rpm range, when you're at wide open throttle (WOT).
Putting on a prop with a higher pitch, will lower your RPM's at WOT and putting one on with a smaller pitch, will increase your RPM's at WOT.
As an example...
If you're running a 19" pitch and running at 4100 RPM's at WOT, then if you put on a 20", your rpm's will drop down to something like 3950 or so. Put on a 18" and your max RPM's will go up to 4250 or so.
Make sense?
-Chris
Basically, what you'll want to do, is find the max RPM range for your motor.
You'll then want to prop your boat so that it runs in the max rpm range, when you're at wide open throttle (WOT).
Putting on a prop with a higher pitch, will lower your RPM's at WOT and putting one on with a smaller pitch, will increase your RPM's at WOT.
As an example...
If you're running a 19" pitch and running at 4100 RPM's at WOT, then if you put on a 20", your rpm's will drop down to something like 3950 or so. Put on a 18" and your max RPM's will go up to 4250 or so.
Make sense?
-Chris
Fun Times
Active Member
Also you might get lucky, Try looking at your engine for a sticker that might have some of your basic engine specks info on it, Normaly that info will tell you your engines max rpm it should be running at. some times it is on top of the flame arrestor, Or on a valve cover, Some where in that area, As long as it is still stock.