1987 IMP 5.7 L Prop size

[K.C.IMP]

New guy here,
I have a 1987 IMP 20 foot open bow with a 5.7 L OMC I/O. It has a 14 1/4 x21 prop on it now and will only turn about 3700 RPM and run 35 to 40 MPH. We normaly run with 4 adults and 4 kids 3 to 9 years old on a small (930 acre) lake. Tubing and sking are our main activites. I have done some research and I think I'll try a 17 pitch stainless prop. Does this sound right???

 

[180shabah]

Re: 1987 IMP 5.7 L Prop size

I think you need to first determine, is that 3700WOT correct? If so, you need to figure out why. A good running 5.7 should have no problem spinning a 21" prop in a boat that size.

My 4.3 will spin a 23" powershift to 4300, my 21" hustler hit 5k with light load and me runnin solo.

 

[180shabah]

Re: 1987 IMP 5.7 L Prop size

Sorry, forgot this above.

You shoud post in the I/O forum, for advice on finding the missing power in your engine. Some quickies though:

Complete tune up(cap, rotor, plugs, wires)
set timing, what is you total advance?
Compression test.