21’ donzi hornet3, had a Mirage 23P behind a TRS and a stock. merc 330 hp 454. Now has a gen6 502, a rev 4 23 was recommended, any other advice?

I would recommend using what you have first to get a baseline with the new motor. I know you likely have a baseline with the previous motor but don't go changing a zillion variables at once. Run the new motor with the existing Mirag 23P, THEN if the propeller doesn't perform as expected or the motor is not operating in the rpm band where it makes peak HP start looking for a new propeller.

No mention of how it did with the 7.4...could you hit max rpm? How was the hole shot? What are you looking for...more top-end or low end grunt for towing watersports or...? Figuring out these things will go a long ways towards getting your answer. In practice you gained what...85 hp?

Back when the 330 was running strong I’d get 60 mph at 4600 rpm, last year I was down to 52 at 4200….

the hole shot was great, I’m looking for more top end, but stable, another hornet 3 with a 502 and a rev 4 23 is hitting 67…

I agree best practise is to run the mirage and see what 8 get and go from there, I’ll post results of that, then go from there, thanks for comments,

Sounds like a good Plan. I've used both Mirage Pus and Rev 4 in same pitch and the difference in the hole shot is noticeable, with the 4 blade just OWNING the 3, and really only giving up MAYBE 2 mph in the top end...

To hit 67 68 mph with a 23 would take a VERY efficient hull at 10% slip running 5200 rpm...

The Rev 4 is a really good prop. I like it better than the Bravo.

Is the boat still a TRS? I've been cautioned about running a 4-blade on the TRS drive. It puts a heavier load on the lower pinion (the only real weak point of the TRS). Might not be an issue with the light weight of the Donzi - just thought I'd mention.

Yes still running trs….

For top speed with a TRS, your best prop will most likely be a Mirage or Mirage Plus. Run the 23 Mirage prop you have and see where the WOT rpms are and adjust from there.

If I remember back a million years, target rpm for the 502mpi was 5100rpm. So, your current prop may end up being still the right one.