bcarpman

I had a 502 built up last year. It dynoed at 540hp. Since then I've made some minor mods which required more fuel (about 4 jet sizes), so I wouldn't be surprised if it was making around 550-560hp now. It has the following specs:

Crate 502 (all forged parts)
9:1 comp
Dart Pro1 310 Rec alum heads
Dart single plane manifold
reworked 850 carb
Crane 268761 cam
(this is a 18726543 firing order cam, .598 .610 230/[email protected] 114LSA)
1.75 rockers

I've managed to get this combination to Idle VERY smoothly (adjusting four corner idle, various combinations of carb spacers, plug gaps, Crane 6 marine spark box w/ 24deg at idle)

In fact the idle is almost too smooth! Not that I'm complaining, but I could easily sacrifice a little idle quality for more power. I did a quick "Desktop Dyno" sym on this combo with the current cam and a 741. The 741 showed a 50hp gain.

I'm taking the engine out for some hull work this winter, so it would be a good time to make the change. Any thoughts? I'm thinking more along the lines of the HP525 cam which I'm told is a 741 on 114LSA.

Anyone run the HP525 cam in a carb motor? How's the idle?

Anyone got one sitting around? Anyone want to trade for what I have now (about 25 hours)? It's got the ford firing order which I'm told actually makes a couple extra HP. Not sure about that, but it has a very cool sound to it. Kind of raspy like it's got a lot of compression.

formula 382 sr-1

If you want a cam that works with what you have PM Rmbuilder he can help.

Back4More

What is your WOT RPM?....also what exhaust do you have?
I don't think your going to feel much going from the 761 to the 741.
Plug the 771 in your desk top and have a lookie at those numbers...

Jammin'

I put the HP525 cams in my carb'ed 500HP's with M1 Prochargers. I haven't gotten the boat in the water yet so I can't tell you about idle, but they made 700 hp at 5700 rpm at around 5-6 lbs of boost on Nickerson's dyno.

Griff

Your cam is a 731 with the 4/7 swap. I highly doubt you will see anywhere near a 50hp gain going to a 741 or 525EFI cam. It all depends on your head flow numbers. Chances are, you will need to spin the 741 a few hundred rpm faster than you are spinning now to make its max hp.

PatriYacht

Keep in mind, the 741 cam was designed for use with the Chevy iron head and it's crappy exhaust port. That's the reason for the much longer exhaust duration. The Pro 1's have a much better exhaust port so you should go for a custom cam that better matches the heads breathing ability.

Pat McPherson

From the dyno results I have seen, the 741 makes about 25HP more than a 731 in a 502.
What kind of exhaust are you running?
If you have wet with short risers, don't go bigger.

bcarpman

Ok, this is embarassing, but I can't remember the name of my exhaust system. Brain dead this morning I guess. Stainless Marine sticks in my head, but they don't look identical to the current Stainless Marine stuff.

It's a cast, big, short tube header, dry all the way to the back where I put just a little water into the pipe just before the flappers. Tyler Crockett sold them to me used with the assurance that they would be good for as much power as this motor was ever going to make.

bcarpman

Currently makes max HP at 5300. Wouldn't mind moving it up a couple hundred rpm.

Yikes! the 771 looks like a pretty big jump in duration. Got any experience with how it idles. As the others have been kind enough to point out, reversion is one concern I had forgotten about.

Pat McPherson

I have a friend that has a Comp Cams XM296HR in a 502 built similar to yours.
It made just shy of 620HP@6000 on the dyno. Probably 50HP less in the boat with wet exhaust and accessories.