RPM's

[billysboat]

Its at the point now I can happily ask this question. After about a month of taking my boat out on the weekends finding problems and then coming home and during the week fixing them ( sometimes twice ). Fortunately they were not expensive, just time consuming all while wondering if I was doing it right.
My boat is a 1966 17' speed boat with a ford 351 set up. It has an old Holman Moody Volvo outdrive with a 14x22 three blade stainless steel prop. It now jumps right up on plane in no time. I can cruise at 4000 rpm's with the motor sounding just right. It will go to 5100 rpms and then starts to miss a little (sounds like popping). I was told 5100 is a little too high to be running for a long time.
What I want to know is what would be the max. rpm's I should be running at with this motor and would a prop change do any good? .....oh and the popping at high rpm's, is that normal?
P.S.
Thanks for all the other help in getting me this far along.

 

[Alumarine]

Re: RPM's

Hi there.

I don't know the spec's for that motor but 5100 seems a bit high.
The popping sound could be caused by the valves floating.

I've seen one spec that says WOT is 3800-4200.

Maybe someone will come along with the right spec.

You might check out manual # 2 at this link.
http://forums.iboats.com/showthread.php?p=1693398#post 1693398

 

[Howard Sterndrive]

Re: RPM's

valves might be starting to float at 5100, thus the popping.
The Fords usually had a fairly low max rpm...ditto Marc C

Sounds like you need more pitch....maybe 24P, but double check your tach with a portable shop tachometer or phototach.

It's possible the lower unit of your drive has been swapped for one with different gears.

Probably had an AQ model 200 drive with the 1.59 ratio originally.
that lower is a bit rare....

I don't know the why that drive was 1.59 and not 1.61 like later V8's either...have never found the teeth counts for that unit.

 

[airdvr1227]

Re: RPM's

Max on my 351 is 42-4400.