Well I never saw myself going down this road, however my carbed 502 mag needs a rebuild. Its smoking worse than a weedwacker, wont idle, and is pretty much gutless. I have done some reading and from what I can tell the stock 502 mag and the HP 500 are similar as far as internals, block, crank, rods, pistons, heads(with the exception of valves, rockers, springs, lifters) etc.

I guess I am stuck at what to do. If the motor needs to be rebuilt anyways is it worth it to turn it into a HP500? I do not want to build a high hp un-reliable engine. I just figured that Mercury already did the R&D on the HP 500 so cloning it would give me more HP but not lose reliability.

Has anyone done this build and have part #’s for the parts needed for the conversion?

Gofast- Do a compression check. A big block smoking as much as you say is not normal. They do eat oil. But you need to figure out if you need rings and it sounds like it. In that case pulling the whole engine is needed vs just doing heads while motor is in the boat. How many hours? HP 500 is more stout than a mag and they use different heads. If your valves are shot you might want to go to a complete new set of Dart heads. The Iron eagles are good. A new roller cam and Dart intake and Holley carb and you should be at 500 hp no sweat.

Wannabe

I can hook you up with an hp 500 intake, carb, flame arrestor and cam. All out of a genuine merc 500. I have two sets. Also have lifters but i wouldn't bother putting used lifters in if you're going to do a complete rebuild. Message me if you're interested. Im going to tear them down soon and no issues. Just building blower motors.

You will need aftermarket exhaust with long risers to use an upgraded cam like the 500HP uses. It will probably cost you an extra 2k plus exhaust to turn it into a 500hp clone.

The motor has stainless headers on it now with the mercury silent choice that comes on the fountains

sending PM

Swap to a Crane 168731 cam and all the other necessary valve train parts to go with the cam.
Then you will need an Holley 800cfm #9022 carb and Dart intake.
That is about all you need.

The Crane 731 cam is better than the stock HP500 carb cam and very close in specs to the 500efi cam.

Thanks alot for the info everyone.

Griff I appreciate the cam info.

I just figured if the motor is coming apart I mind as well stick a couple more bucks into it to get some more power

I recently built 2 502mag engines for a guy wanting more. I used 139011 cam (replaces obsolete 731), morel retro roller lifters, 800cfm carb, air gap intake, severe duty intake valves, inconnel exhaust valves, cometic head gaskets, pro mag rockers, used stock rect port heads, which were the same as hp500 heads, new springs and retainers. Total parts and machine work for one engine was 4k. He already had aftermartket exh manifolds but we did extend the inner tube of the ss risers to the transom. He gained approx 600rpm at wot on a 38' baja.

Griff

As far as lifters, rockers, and springs what do most guys run?