I popped my 502 mag mpi gen 5, and replaced with a band new long block gen 6 502 mag mpi. Ive got about 7-9 hours on the new one.
The old motor 73.3 MPH with a 25 P High Five, 4800 RPM

The new motor 69.5 MPH with same prop, 4650 RPM

a 23 P Mirage spun at 5200 RPM and 71.6 MPH

Is the motor broken in? How much time did you put on it before going to the wood with it? Are the conditions the same and was the speed checked by GPS?. Is the replacement the exact same as it original? Somewhere in one of the many Vapor posts I remember some changes to the computer, injectors and fuel pressure and addition of headers. Did you get the VST problem worked out? It sounds like there is still a lot of tweaking to do after the motor is properly run in.

Sorry missed the 7-9 hours but that may still not be enough to do comparisons. Have you changed the oil and filter yet?

the motor was run for 20 minutes then changed oil. then i wanted 10 hours of break in and then going to change again. I hope this is enough hours. the company from Mass. told me 5 hours, merc told me 20, i just thought i would meet them half way???

Sorry about my impatience, its the story of my life.
there is a 100 boat poker run coming up that i went to last year here in WI, and i want to ready for it.

thanks allot

Also is the 5 blade killing my top end, it has been lab finished???

Is the cam in the new engine the same as the original? It may have a different powerband than original and you may need to do some more prop testing.

I just put a 502 crate in mine and make sure your timing is correct. I gain 300 more MAX RPM going from 32 degrees of total timing to 34 degrees. At 34 my MAX RPM is 5000. AT 32 it was only 4700.

Just curious, but was it recommended to change your oil after the first 20 min.? The only recommended to me was not to run synthetic oil until after the first 40 hrs.
You need to be 100% sure your rings are seated before converting your motor to synthetic oil or you'll be pulling it back out of your boat

I'll tell you one thing I wish I could get the speed your getting. I turn my Bravo 1 24' at 5000 RPM and get only 64 -/+ GPS Speed. When I tried my Mirage Plus 25. Forget about it.....5100 MAX RPM and major slip. MAX speed 60 GPS. If i go by the speed that my regular speedometer says (non-gps) it reads over 70 mph. Are your reading from a GPS?

73.3 must be GPS (or does anyone know of a water pressure speedometer that reads of tenths) I suppose, but getting those figures out of a high five prop on a 502 seems pretty amazing to me.

Anyway, a boat or auto motor doesnīt (and shouldnīt be expected to) give itīs full potential after only 9 hours, unless you hammer it from hour one ( and then its all over after 25...)