Probably somewhere between a 23 standard mirage, and a 21 plus.

I have a Rinker 236 with a 502EFI Mag and use a 3 blade 21 Pitch Mercrury Mirage and run 4800 RPM's . When I use a 23 Pitch it drops me down to 4500 RPM's. So I would also suggest dropping down to a 21.
It use to be that Mercury Marine gave out blue colored props to Marinas as for ppl to try so they could decide which prop worked best for them . Don't know if they still do it though . You'll have to ask your local marine shop about that.

A 4 blade prop is popular for ppl who like better hole shot and quicker planeing. Although I do know some ppl who swear they get better top end from a 4 blade . I tried one and it took off 3 MPH off my top end.

Also with those motors I believe Mercury suggest you use a Solid Hub prop because of the torque the Mag motors put out.

All true with the exception of the solid hub, Flo-torque hub is rated to 400HP. Solid is nice, but if you strike something with the prop, you will not only be buyng a new prop, but also a propshaft, not cheap!!!

Im trying to trade a 23p Mirage Plus for a 21p if that could somehow help. Thanks, Rob
http://www.offshoreonly.com/forums/s...us-rh-21p.html

Alright, just tried out a 21p 3blade. Not impressed, I felt way under prop. The first thing I noticed was a lack of bite, I knew my hole shot would be slower but I had to rev to 4000 rpms just to get on plane, I think I was slipping a lot. Once i was cruising and went for top speed I stopped at 4800 rpm, I wasn't at WOT. But I didn't want to push the engine any more than that. As for top speed I was able to get to about 57gps (top with 4blade23 was 54). So I'm thinking that going with other suggestions of a 23p. Any other suggestions from people way more qualified than me, haha!

Wat brand and diameter was it? Makes a BIG difference.

any boat with a stock big block or stock small block in the range of 19 to 23 ft with a v-8 and has 1.50 gears in drive is going to run a 21-23 p prop in a 3 blade, but my guess would be a 21 p in a good clean stainless. its got to be a 14.5 or 143/4 diam. prop

The brand is a mercury marine laser II. The number on the side is 48-16546 21p. Not sure of the diameter maybe these numbers will help.

I believe the laser is a small diameter, hence the reason for so much slip. If you go with a 23, go with a laser, or else you will open up another can of worms, if you go with a larger diameter 21 with a lot of cup such as a mirage plus, the slip will probably be gone, if you go with a large diameter 23, you may not turn the RPM's ya want.

Sorry for my ignorance but when you say cup, what are you referring too?