Thinking about just dropping in a truck long block to ride out the season - that way I can take my time and maybe find someone to dyno my 489. Came across a low-mileage L29 long block out of a late 90's GMC dually for $500. I know I will need to swap the 11-lb oil filter bypass for a 30-lb valve, but aside from this, is this essentially the same thing Merc was dropping in for the 7.4L MPI? This would also give me something to drop in the boat if I ever sell it.

Thinking about changing out the wimpy cam for a Merc magnum roller if I can find one. Also wondering if a ZZ502 cam would run in this engine - yeah, I know, it has the smaller port Vortec oval heads and cast crank / pistons, but thought that might wake it up a little and at least sound a little nasty. I will probably go ahead and run my Holley and Lightning headers on it just to simplify things.

Anyone have a magnum or ZZ502 cam laying around that they want to unload cheap?

They are pretty much the same motor, but heads and intake. You can't get carried away with a cam without doing head work and changing springs. I have not done this conversion but have read about it many times on the truck forums. The springs should be replaced with new springs & rotator eliminators. The merc 12551622 cam, which is stock on the 454/502mag is what most of the truck guys go to if they don't want to go crazy and do a bunch of head work. You should be able to get a pullout cam pretty reasonable in the swap section. I don't know anything about the zz502, but would be concerned about reversion.

28, I think the ZZ502 cam is ground on a 110* LSA, so yes, it may be reversion-prone with stock exhaust. I think lift on that one comes in around .510. Not sure what the springs in the Vortec heads are good for. Might be safer to stick with the Mag cam, as it is about the same lift, just more duration. It should be pretty much a bolt-in. I don't want to get carried away with this engine if I elect to go this route - it is only meant to get the boat moving under its own power so I can drag the kids around the lake on the tube.

I sure wouldn't hesitate to do the same thing if my big motor was down, escpecially for $500. I probably wouldn't even mess with the cam change.

I wouldn't mess with the cam change either. longblock is essentially the same. The injection setup is a little different. You'd need the ECU from the truck to make it work, or put a carb on it.

Going to run a carb and intake if I go this route. Might even drop my old Q-jet back on it - it might fall on its face with the 800 Holley, even with stock jets.

That'd work. Really not bad engines. A definite step up from the old peanut port 330 flat tappet engines. The cam in them is factory installed retarded like 7 degrees or something like that. I suppose if you were gonna do the carb, then maybe slap the 454 mag cam in it if you can find one cheap. They're 9:1, I actually think with the mag cam, intake and carb it be a pretty decent running engine!

Yeah MT, sure wish I had that Mag cam back that I sent in to be reground - that bad decision is what started me on this misadventure!

Competition products used to sell them for 30 bucks, as takeouts. Just looked on their site and don't see them anymore. but there has to be a ton laying around in oso members garages on the cheap

Yep, I put an email in to them this morning, and they replied that their source has gone away. Hopefully I can find someone who has one laying around that they want to get rid of. I might also try some of the car and truck forums.