I just rebuilt my 502 mag. Everything is stock other then exhaust, and I changed valve terrian over to roller. And also probably made a bad choice in cam selection. I put in a crane 139721.

After rebuild I changed my prop, Performance with the first prop was 60 mph (GPS) at 5000 rpm w/ a 21 pitch 3 blade. But with that prop it just felt like I was blowing it out (spinning in place). And forget about triming it out. No grab at all.

Now I have a Bravo 1 26 pitch 4 blade on it. What a difference, now it grabs with trim up in any position. But the kickers is the top speed is still 60 mph (GPS) but the max RPM I can get is 4100. I know I should probably get a smaller pitch prop. But is there anything else I can do like changing the cam to say something like a 139731. Will that give me some more RPM. Or can I get away labbing it. Or am I to far off a pitch for that?

The boat is a 1990 Carrera 27 ft V-Bottom Bravo 1 1:50 Stern

It seems to be overpropped to me. Can you borrow a 22 pitch Bravo 1 from someone? This should give you less slipage than the 3 blade and get your rpm back up, given the couple of changes you made.

Do you have access to a 23" 3 blade or a 24" bravo 1 for a test run??? Looks like your at the opposite ends of the spectrum with the two props your running, you might find something in between will work better and get you into the rpm range your looking for. Those 4 blades are really heavy and take the hp and torque to spin them.... I'd like to see what a 23" 3 blade will give you in rpm... if your still bumping 5 grand with it, then go to a 25" 3 blade....... though not knowing your boat or it's weight, a 25" might be to big for it.... I'd start with a 23 mirage and 24 bravo 1 or hydomotive...

Good luck!

I live on the West Coast and Teague Marine does'nt offer Prop exchange anymore and I took a gamble and bought the 26 pitch Bravo 1. Labben the 26 pitch would'nt work I take it. I really dont want to go back to a 3 blade. I really like the way the boat handles with a 4 blade. Maybe a 3 blade will handle better with a bigger pitch. Ill try and get my boat weight. Thanks for the info..At least I know where to start.

You're overpropped for sure and are not getting into the powerband of the engine. Changing to the 731 cam will only move the powerband up farther.
I think you will need to go down a 22" Bravo.

Check with Throttle Up or other good prop shop and give them your engine specs and some info on your boat like X dim, dead rise, weight, and what ever else they ask for. They can take a lot of the guess work out of the prop selection process.

I agree with Griff....over propped.

I agree w ECB.
Borrow a 23P and work up or down from there.
You may be able to sell the 26P on ScreamandFly.com
Outboards have the gearing to swing 26P props, you can buy and sell alot of used props on S&F and ebay without loosing too much money in the process.

I really lked the Michigan Wheel "Raptor" 22P on my Donzi and want to try it in a 23P.

Good Luck

The 721 cam is the same cam that Merc used in the 420 and 525sc (both 454s) engines. It's not all that bad of a choice.

Keep the prop & add more HP. Add a whipple, procharger or vortec. That and a new cam shaft should get you there.

prop it right and you should be good to go wouldnt bother with more engine mods unless you have a big pocket then would make more changes but would first I would see what she will do with the right prop!!!!!