dave-01

I have twin 2000 502 mag/mpi's with 330hrs that I am going to freshen the top ends on in about 8 weeks or so...The engines are stock except for emi w/stainless risers (with corsa silent choice) and K&N air filters.

My plan was to pull the heads, install new severe duty exht valves, stainless int, clean up the bowls a little and maybe cut the surfaces to slightly up the compression (9:1 max) and install new springs and all related hardware including roller rockers...
I would like to upgrade the cam while I have this apart. I want to leave the silent choice on...don't really want to touch the ecm and definitely stay with the fuel injection... what cam can you recommend? Has/Is anyone currently running a setup like what I am looking for?
I have also been told to leave the cam alone and simply go with 1.8 rocker arms...


Any specific advice would be appreciated...

jeffswav

Without a ecm upgrade you are waisting your time. In fact you could do damage without it. With the short risers and silent choice you also limit your options. Unless you use Long risers (no silent choice) and reprogram your computer with wideband O2 I would leave it stock. I would not use 1.8 rockers, it changes the geometry.

29scarab

Good answer! that's exactly what I would have said.

obnoxus

I went through this a few yaers back.

Dennis Moore and I got together and figured out the biggest cam I could run for my 272.

Its not huge gains mind you as I didnt want to mess with ecu programing, but it was a small gain and if your rebuilding ,,,, you might as well use the biggest you can.

Dont have time today, and I dont remember if it was her, or Speedwake,,,, but do a few searches and you will come up with the cam number.

This was in 2000, 2001,,,, and the boat is still running.

dave-01

Thanks for replies. Keep in mind, the top end is coming apart anyway for valve job or new valves (most likely), new parts will be purchased, the heads will get massaged, why not get what I can since the workscope is the same...just looking for past experiences from folks who have done it...I have done multiple searches on this and found no real straight answers or specifics...just looking for someone with first hand knowledge....

swan2

I would not change the cam just freshen it up leave it like it is. Or go ahead and putt some serious money into them and make some horse power. If you did find a cam and did those things to the motors that your talking about you would take it out and most likely gained no mph or not even feel the difference. I have done alot more mods than that in the past to fined out its just not worth it unless you put lots of money into it. Just my 2 cents

ctuck0659

I did the top end of my 502's last winter. I followed the mods recommended by Mark Boos at Precision Marine in La. and had him remap the ECUs. I have a Formula 357 and no BS, picked up 9 mph on GPS. I went from struggling to break 60 to 68.9. The eng's had about 400 hrs on them. Mods were basically cams, larger intake valves, some head work, K&N air intakes, Gil exhaust, 22 to 25P props and a bunch of smaller mods. If you want more specifics, let me know-

jeffswav

He said he did not want to remap ECU. That is why I told him to leave it alone. He does not understand how things work.

Griff

Why are you taking it apart in the first place?????? 330hrs is nothing for a 502 mpi. You should be able to go at least 500hrs before needing a valve job and head gaskets. No reason you should need new valves either.
Doing a few very minor mods is a waste of money. You won't gain anything.....well, maybe 1-2mph max.

Smitty

iTrader: (1)

Go ahead and put a new cam in those motors. But order them from Bob Madera at Marine Kinetics. Give him a call at 585-654-8583.

He will make you a cam that will work perfect for your application.

Tell him Smitty refered you.

After you get the cams ordered, send your computer to Mark at Precision marine for a new calibration.
www.pmefi.com

You will be making 40-60 more hp per motor when you are done.