I ran my ZZ502/502 for 4 seasons with the ZZ cam. Ran it for 1 season with the stock Merc exhaust and then for 3 more seasons with Revolution Marine exhaust. The only "reversion" experienced was about a table spoon (if that) of water in the bottom of the 4 exhaust ports. However, realizing the ZZ cam was/is border line reversion prone, I made it a point to keep the idle around 750-800 RPMs. And would always rap the throttle a couple of times before shutting down the engine, to clear out any water that may have accumulated in the exhaust. The ZZ cam has a real nice lope to it. But if I were to "do it again" I would consider a cam change. For both reversion, and a little more "oomph"
IMO rmbuilder of marine kineticks would be the man to talk to if you want to look into another cam.
The entire Thunderbolt ignition from my 7.4/330 was easily transferred from the 7.4 to the ZZ502, no problems/issues. This includes the starter also. Your marine circulating pump and power steering will also bolt up to the ZZ. All the brackets relocated nicely.
More hp = more heat. So, you'll need a bigger oil cooler. I used a Hardin Marine that included power steering cooling. Overall length is 22 inches. I don't remember the model number but according to Harden, it is good up to 700 hp. It also has a built in thermostat to warm the oil to operating temp.
There are two bypass valves in the block at the pad where the oil filter would go in an auto/truck application. You will need to replace the 11 pound valve in the side of the pad, with a 30 lb valve, I don't recall the part number but someone reading this thread might pop up with it. Also, take the bypass valve in the center of the oil pad out, and leave it out. If you don't do this, oil circulation is restricted, One more on oil/cooling... I always had oil temperature issues. Eventually I got the temps pretty much under control. But the one thing I did not do was change the stock Merc oil lines. Merc calls their oil lines 1/2 inch. Could be, but the fittings are barely over 3/8 in, and I think the 3/8 fittings are too restrictive for a 500 hp engine. I suggest you get rid of all the Merc oil lines and fittings, and switch to 5/8 in. or -10 lines and fittings... no smaller. You might also want to consider a larger oil pan. I think the ZZ comes with a 6 qt?? I'd go with an 8 or 10 qt.
I'm not qualified/knowledgeable enough to know if your Gen IV heads will work on the Gen VI block. There may be issues with the water passages. I think they will work but hopefully a gear head will chime in and comment on this. Anyways, large ovals are a good choice for the ZZ502. The Edelbrock heads that are bolted on from GMPP are large ovals and work well on the engine. I'd use MLS head gaskets from Felpro or Cometic. ZZs come from GMPP at 9.6:1 compression with the Aluminum Edelbrock heads. You'll need to know how many CC's the combustion chambers are to determine what thickness to go with for the head gaskets. Quench would also be a consideration. Are you going to have the block decked ? All stuff to throw into the mix :shocked:
What about an intake and carb? ZZs come from GM with a vac Holley 850 on a GM high rise duel plane intake. The 850 worked great on my ZZ. Not sure who made/makes the intakes for GMPP.
It's been several years, but I think we used the flywheel from the 7.4 on the ZZ502. Not sure though.
Oh... might wanna install brass freeze plugs.
I'm sure there's more. I'll edit this post when/if more comes to mind.