Knowing the prop won't help. A 5.7 in a 20' bowrider might have a 25"
pitch and the same engine in a 25 ft cruiser would have a 17". There
might be an adapter to hook an engine to a prop shaft. Boring the
cylinders only adds a few cubic inches, 30 over is about 6 cubic
inches. Cam, heads, intake, and carburation have the most effect on
these engines.

Tim wrote:
I've thought about that James, I've never heard of anybody reasonably
hooking a dynomometer up to a prop shaft, but I'm sure it's been done,
in high-performance marine use.
James Sweet wrote:
Tim wrote:
My Monarch, is a 1977 model, and has had the enggine replaced a few
years ago with a Four Star reman. Now, It was origionally rated at
something like 225 hp. or something like that, and there's really no
reason I should think that the reman wouldn't be the same. But engine
rebuilders hafe interesting ways about them, like boring cylinders 20,
30, and even 40 thousands oversize, PLUS the cam may or may not be to
origional specs.

I'm really not that concerned about the hp, because I know it will be
enough to handle the boat. It has for a few years. But I belive Four
Star located in Indianapolis went out of business a few years ago, and
was wondering if seriel numbers might tell the hp rating,t hat is, if
alll the variables were to remain stock. Has anyone ever heard of
putting a marine engine on a dyno right at the prop?

If so, it would be interesting to see what the true rating of this
engine and "R" Drive really are, instead of merely going with what is
on the valve cover decals.?



You ought to be able to get a reasonable idea of the HP just by the RPM
you get with a given prop. Is the prop original?