502 mpi cam advice
 

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...

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.

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

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.

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....

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

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-

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.

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.

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.

Griff/Smitty,
Thanks for the feedback. Griff, a leakdown test performed on one of the engines showed one cylinder a slightly low due to a valve (I do not have the paperwork from my mechanic with me at work to give the specifics on int/exhst), so he recommended a valve job may be in order. We will perform a leakdown on the other engine sometime next week. Other folks I have talked to and posts I have read also state a freshing of the heads on these engines @ about 300-350 hrs is a good idea. I am sure some have done it sooner and some much later...

Smitty, thanks for the contact, I will give Bob a call and get a plan in order for what I am looking to do and what he thinks would be the best path.

Jeff, thanks for your assessment of my knowledge base. I understand completely what the ecu monitors and the adjustments it makes based on many engine parameters. What I don't have is the limits of the stock program that it can be pushed to in order to require modification to the fuel, air, and ignition curves. We all know the merc program is set up conservative and the fuel curve is fat to protect the engine. I am simply looking for someone who has understood what can be modified on the engine to not compromise it. I'll call Bob as suggested, thanks.

Just a suggestion: I'm not sure if remapping the ECU's is an option you're considering or not, but if it is, talk to Mark at Precision first- he strongly suggested I use a custom Comp grind that he has experience with. Otherwise, he was very uncomfortable with the idea of remapping the ECU for a cam he hadn't tested. Good Luck-

What part of the world are you in? I know a guy that does some good stuff to the MPI motors.

Goodpoint. I will be sure to consult the programer prior to selecting a cam if I am forced to reflash...

Jason, Huntington Beach, CA

Check out Tyler Crockett marine engines he has a 100hp kit for the mpi's. If i keep the fuel injection thats who im going to use

Bob is a true engine expert. I gained 5MPH just from a cam and matching parts.

Dave, I wasn't trying to insult you. The tuning is very important and any change you make to the engine requires calibration. If you go lean you will destroy your engine. I have a Holley MPI kit with wideband O2, I program mine with the laptop on the fly. Every time I modify the engine, I have to go in and change the map.