Alex

Anyone done a successful cam upgrade on a Merc 502 MPI?

I have seen extensive intake mod's only, making a few more hp's but it really doesn't seem worth it.

I do have the possibility to remap but I wouldn't like to start all over. Some fine tuning would be ok ...

kennyo

Alot of people have done it. To go big enough to notice a difference you would need to change springs and rocker arms, then get the ecu remapped.

ZXXX Donzi

You will also need to use a big enough cam to require a better exhaust if you want to see any significant changes.

kennyo

See, we just spent $3000 for you!

Alex

Keep it up guys, it's for my customer - not me

Seriously, I was asked about the cam swap and I do have the possibility to remap myself but as long as he's stuck with the stock cast iron manifolds my advice is that it's not well spent money (or time).
A successful upgrade to me would include at least the exhaust ...

ZXXX Donzi

I would do the exhaust first. Why is he so bent on a new cam.? By the time you pull the engine and swap the cam you could buy some entry-level manifolds. That will net you your 1-2 mph right there and be ready for an even bigger cam when the time comes.

Alex

Skills? Maybe that's why he's the customer and I'm doing the work
I'm replacing both his long blocks due to a totally incompetent rebuild earlier that caused a real mess inside.
While at it he probably tried to find some cheap extra hp's but I've already adviced him against it since I also thought there is not that much to gain without the more expensive exhaust upgrade.
Just wanted to doublecheck with you guys if I've missed a secret or two.

ZXXX Donzi

Ahhh. That makes much more sense. I would expect that while you are in there you can stick in a little more agressive cam for 20 hp or so that will work with stock exhaust and then maybe reflash the ECU. I think that one of the guys on the Donzi site did that with a stock-ish type of exhaust. I would expect someone around here knows which cam will work. If not, I can check with him.

obnoxus

Comp Cams XE268H with 224/230 intake and exhaust duration and .515/.520 intake and exhaust lift with a 110 degree lobe separation angle. This will work without the need to change valve springs or go to adjustable rocker arms. The stock ECM will also work fine.

I ran this cam with Gil headers for years

billet marine

We have new, billet, gen VI, GM 502 take out cams for $140. They are 115 lobe centers, .226 int/exh duration @ .050 (254 advertised) and 545/540 lift.

We also have them as "100% new / then reground" billet cams comparable to HP500 specs. $200.
They have 115 lobe centers, 232/236 duration @ .050 (258/262 advertised) and 602/612 lift. These can be used with stock roller lifters but there is no room for error on the lifter travel in the lifter retainers. (Dog bones) I would recommend using the longer travel Crane roller lifters just to be safe. (Or at least double check all tollerances) The HP500 cam could also "right on the threshold" of reversion issues if the stock exhaust is retained...

Send me a message if interested.
Thanks, Curtis @ Billet Marine