502 mag mpi questions
 

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

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.

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 ?

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

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

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)

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

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?

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?

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.

Thanks for the thorough reply. :) I'm not an engineer, but appreciate the technical info. Coming from the automotive world, I've been suprised to see how rich the engines run in the marine market. A stock 502/500hp we put a wideband on a few weeks ago idles at 11.6:1! That's super rich.

In the automotive world, 14.7 (stoich) is where they try to get the motors to idle. These days, they all do idle there, sometimes leaner.

While playing with the injection on the 500hp, we found it would idle just fine at 13.0-13.5. That 500hp was rich (never leaner than 12.0:1) all the way up until 3250rpm, where it progressed to 12.8-13.2, what I expected to see for peak aspirated performance. We leaned it out to 13.0 in the lower ranges and it picked up quite a bit of fuel mileage. At one point, 28%! It went from 2.8 to 3.5mpg. This was in a smaller, 22' Stoker.

I'm still curious as to the reason Merc runs them this fat.

Where do you plan to set your motors to run once they're broke in? If your fuel curve makes a nice, flat A/F curve that can be raised and lowered simply by adjusting fuel pressure, it sounds like you've got a pretty good tune already. Too bad you can use the wideband you have for closed loop feedback and just tell it what you want for A/F huh? ;)

Yea......I wish I had a newer MEFI controller to use. Running closed loop would be nice. I havent felt like re-pining all of my harnesses...haha. I imagine if I go on to adding boost, I will wind up doing that or getting completely away from the MEFI's ang going with a GM controller. I was trying to save money by adapting what I had but that faild so now I am stuck with it for a while. My friend and I have the HP Tuners software and a Mustang chassis dyno that we do a lot of tuning for GM and Ford vehicles on.

I would have to say that Precision Marine guessed the tune pretty much spot on. I can mess with the timing curve by messing with the distributor too. I have been nothing but impressed with Precision Marine and Marine Kinetics. They both worked together on the tune and the cam to make it right for the setup.

It is amazing how much more power and mileage the factory leaves out of their tuning. I think Merc leaves them fat because they know the motors are going to be abused and they don't want extra warranty claims. Just like what I have experienced with snowmobiles and such....very fat from the factory to keep them from burnin holes in the pistons. It is all about reliability.

My truck has an 8100 Vortec (496) and WOT AFR was over 15:1 stock!!!! My guess is they wanted to eek some mileage out of them, didn't work though. No wonder why they all burn the rings out and burn oil when used hard. I gained about 60 RWHP and 2 MPG on that truck.....runs awesome now and has since slowed on oil consumption. I would love to throw some Raylar parts at that thing.

Gimmee fuel: I run the Saginaw river ocassionally. Your ASFR's are WAY too rich for a N/A motor, we need to get together and give it a on the water tune. I have talked to Mark before, he is a nice guy. I redid my afr's on my N/A tune in about 2 sessions of river tuning 2-4 hrs each time, we set afr's at 13.5-14-1 at light throttle and at the higher rpm's we set them in the low 13's/high 12's. I built custom twin fuel rails with bigger injectors on my mpi set-up, if you go back and look at my old post from around 2004-2005 I put exstensive pics and detailed writeups on here about it. Like I said too, I bought 2 spare throttle bodys and had them bored to sell on a exchange basis, 1 is early style, one is late style. When we did our river tuning, we loaded motor hard with tall prop and tabs dragging and loaded motor light with short prop to set all the fuel tables at different map settings so it would be right no matter what. It really brought the cruising mileage up and cleaned up the transom, you got my number from my pm, if you need to try some props I have a shelf full of 24's, 26's and28's too, Smitty

Smitty, does your software have you map the fuel table as RPM vs. MAP or some other reference? Is that the MEFI-burn software?

I have the mefi-burn program, it lets you do alot of stuff, you can work on the fuel tables in different rpm bands-ie-idle to 1200 1200-2400 etc or something close to that, Smitty