33-outlaw

I am rebuilding my 2000 502 mag mpi motors i am having some mild porting done to heads and intake also changing cam nothing really big it is a comp cam xm 284 hr also will be upgrading exhaust i am looking to get like 500 hp out of each of them my question is will the stock injectors and fuel pump be good for this set up? thanks for any info

Boat1

The stock injectors are plenty but you need to do significant work to the intake, the runners are very restrictive. You need to cut the divider out as deep as you can and open the lower turn area. Take the lower intake to the porting service and let them look at it. It is usually cheaper to find a 500 EFI take-off intake and use it. The computer will need to be re-mapped for fuel and spark with the cam change. Everything else will support the power, the throttle body is your next restriction.

imagecat

iTrader: (2)

How much can the 502 MAG ECM be calibrated? If you stroke it to a 540 with a 525 intake could it be adjusted to work? Is the 502 MAG ECM a MEFI 3 ?

tunertech

There is no limitation within the ECU. Yours is likely a MEFI 3 16236999 series since it is MerCruiser.

articfriends

iTrader: (1)

The throttle bodys can be bored, I have a local source for getting them bored out. I made 1100 hp with highly modified 502 mpi intake and throttle body with a m-3sc blower running lots of boost. I also made around 650 hp with same motor (540 cu inch) with blower disconnected just to see what could be done, Smitty

Gimme Fuel

Articfriends........Who does the porting on those 502 MAG throttle bodies?

I built a 540 out of my 1997.5 502 MAG MPI and I am needing some more air flow and I think that is my next bottleneck. I have had the intake extrude honed, runners shortened, and port matched to my Dart Iron Eagle 308cc heads with a mild port job. Running a custom cam from Marine Kinetics (.620 INT/.618 EXH) for dry exhaust. I am in the process of upgrading the fuel system too....I'm a little too close to the limit for comfort based on what I have been reading (62 psi rail pressure, stock injectors, stock pump with adjustable regulator hat, stock fuel rail, Precision Marine ECM tune).


(BTW 33-Outlaw, it will be waaay cheaper and easier to buy a new intake and EFI system instead of highly modifying the stock one.......I know I wish that I did that instead)

articfriends

iTrader: (1)

I can't believe that Bob at Marine Kinetics hasn't mentioned you as you live only 35 miles from me. Do you have a 02 sensor installed in your exhaust yet? Did precision marine lock your ECU or can you fine tune it in the boat, I have MEFI burn, we need to get together, Smitty

Gimme Fuel

No, Bob never did mention you and I have spent many hours on the phone with him....haha. Yes I do have an O2 sensor in my exhaust along a pyrometer in the opposite bank. I dunno if Precision locked it or not. I would be very interested doing some tuning if it is unlocked. I also have a bunch of other gauges I added to help with the tuning processs with Mark Boos. I have had some issues with the motor and have not had a chance to really get to working with the tuning yet. We should get together for sure. Where do you usually do your boating at?

STV_Keith

I assume you were limited by the stock injection system programming? Did you do any of your O2 measurements before modding the motor?

GF, I'm curious at what A/F ratio your engine runs at through the RPM range. Do you have that data?

Some of the other engines I have looked at are very rich. 11.6:1 @ idle, 12.0:1 or richer below 3000, etc. How is yours?

Gimme Fuel

Keith, I am limited by stock injection programming, computer capabilities (MEFI1), fuel rail flow. The intake is my biggest restriction even though I have had extensive work done. It still cant flow as well as a nice short runner single plane. If I switched it all out for a new system and intake, I could probably gain up to another 50 hp and move my peak hp up more where Bob Madera wanted it. He wanted around 5800, I said I could maybe get her around 5600, but in the end I am betting it is 5300-5400.


Mark Boos told me to set it around 11.7 or so for break in (I haven't been able to get past that yet...haha). I set that with my adjustable regulator hat. I have modded the fuel rail slightly with removing the blow off regulator on the front end and making a block off plate. Once I set the regulator, the AFR stays constant through the entire RPM range. Mark has my injectors set to full pulse width at WOT and he figured I would have around 600 HP at 40 psi rail pressure. Once I installed a gauge I was at 62 psi to hit that AFR. I can set the AFR mostly anywhere I want and the curve in the PCM seems to be right on seeing as it keeps a satble AFR throught the RPM band. It will trim off at part throttle a little bit (12.3 or so) but once again, it needs much more fine tuning,

I am worried about being on the outer limits of my fuel system so I am planning some major upgrades this spring. I have learned of a few areas in the rail that I need to bore out, I want to install a better pump, increase line and filter sizes. (from tank to pump and to rail). I have access to some nice machine shops so it should be fairly simple. I am also boring my throttle body because I feel like it lacked good top end (the little bit I got there). I am also planning on installing a vacuum pump to help her seal up better. I built the motor to add boost later on and so my rings are hardened severe duty Total Seal rings.

And to be honest with you, this motor has not been run enough to fine tune yet. It only has around 5 hours on it......I switched breathers last year and ended up blowing the rear main seal out and messing a bearing so I have to go through her again.

Sorry about the long reply, I guess it comes with being an engineer.