I purchased a used 42' '98 Fountain w/ I think are rebuilt
500's. Pat Musi did the rebuilds.They were dynoed @ 697 hp. But they do not have copies of the sheets. The props that were on it were 32p and ran about 4400 rpm's wide open. I recently put on hydromotive labbed 28p. and ran 5100 rpm wide open. How would I find my max. rpm to run at?

Pull an engine and dyno it again. Or if you can find a propshaft dyno that will accommodate that much power. You need to find peek HP and prop to that. Running an engine loaded in its high torque range isn't really good for it.

Do you have any specs for the engines??? cam size, heads, comp ratio, etc??? Are they NA???

I would guess 5600rpms.

Thanks Guy's-- I was trying to prop it --but I guess I will have to pull one. I was hoping I was on the safe side with 5100.

I don't have any spec's the sheets were lost in a shop move.

X2. Atleast 5600, if it's a built motor and makes that kind of power N/A on pump gas.

For any 500-540" motor to make 697hp down around 5600-6000rpm and on pump gas is a down right nasty piece. IMO, they'd have to be some kind of Big Chief headed deal that would probably make well into the high 780-790hp at 7000+rpm. (Maybe more, but I like to be conservative).

Do you think I would be conservative @ 5600 Rpm? And drop to 26p?
Are 26p Props to small of a wheel to get any more speed?

I'm not a prop expert.

5600 should be fine. Are these blower motors?

You could be doing more harm than good by running too low of a wot rpm. It puts too much load on the engines.

Are they naturally aspirated or supercharged????

If they are NA, they probably need to be spun in the 5600-6000rpm range to make 697hp. If SC'd, then probably 5200-5600rpms.

They are NA. All motor