502 mag efi rebuild
 

I'm currently rebuilding a 1995 502 mag efi for my boat and would appreciate any input on things I should do differently or something I might have missed. So here is what I've come up with so far.


It's a Gen VI block bored .030 over. J & E flat top pistons. Block "parallel" decked (just enough to make sure it's straight). The crank is turned .010 - .010. Stock rods. Balanced rotating assembly. Surface the heads. Manley Severe duty 2.25 intake and 1.90 inconel exhaust valves. Some mild porting. ARP head bolts and rocker studs. Crane gold roller rockers. Cometic head gaskets. Crane roller cam. Lift .576 in .598 ex Duration 222 in 230 ex 114 lobe separation (grind #HR-222/339-2S-14 IG) Intake runners shortened and shaped.(but not extrude honed like the AZ Speed intake) Revolution Marine exhaust manifolds. Corsa "captain's call" exhaust. Mefi 3 Computer programmed by Mark at precision. (my harness has already been re-pinned for it) Stock ignition with an MSD replacement coil.


Originally I was going to rebuild the engine basically stock and put a Vortech supercharger on it but I just couldn't quite afford the blower kit this year. I wanted to keep that as a possible option for next year so I am keeping the compression ratio near stock.

Can I go any bigger on the cam and still keep the selectable exhaust or am I pushing it already?
Will the VST fuel system be able to keep up?
Are there any decent full-time mufflers reasonably priced?
What lifters should I use?



Any input would be greatly appreciated.

Doug

Re: 502 mag efi rebuild
 

use ARP rod bolts, and have the big ends resized.

your cam choice is fine.
I'd use the longer Crane stock replacements that locate with the GM dogbone key plate. No link plate to give you troubles.

Re: 502 mag efi rebuild
 

Any thoughts on the VST system?


Doug

Re: 502 mag efi rebuild
 

I scrapped mine, remodeled the fuel rail to take 8-an lines in and out, electric fuel pump before, thru the fuel rail, thru a regulator, return line to the tank. I had problems with that system cooking my fuel, motor would diesel when you went to shut it down, they added the cool fuel sytem in later models, I don't know which one you have. Mine was 1996 model, gen v. Weldon makes some nice pumps and regulators, remodel the fuel rail, thats a project!

Re: 502 mag efi rebuild
 

I would be looking at a 231/ [email protected] with a 110 lobe separation for better bottom and mid range. If your oil pump drive rod has a nylon collar throw it away. The gen 6 motor has a 6 bolt timing cover, just incase you're not sure what you have. Look at GGB.ca for mufflers.

Re: 502 mag efi rebuild
 

Wouldn't that cam cause reversion with my short risers and Captain's call exhaust?

My block is a Gen VI with a 6 bolt timing cover but the dress is 1995 Gen V without the fuel cooler.
Any idea why the factory fuel injection systems do not return to the tank?
I do have an extra fitting in my tank that is plugged.

I seem to remember Dustin Whipple saying something to the effect that it's not coast guard approved to return it to the tank which is why they return it to the suction side of the pump in their systems.

Thanks for all the good ideas so far,


Doug

Re: 502 mag efi rebuild
 

I ran the 231/239 in a 454, great low and midrange torque, had the captains call, no problems at all. My opinion, the 114 lobe separation is a turd, in the boat and on the dyno. Just an opinion.

Re: 502 mag efi rebuild
 

If you change the cam, you must recalibrate the computer. These are speed/density systems. Any time you change the induction/cam/exhaust...the computer doesn't know what you have done. You may "correct" one area and make another "bad". Your computer has been calibrated for ONE particular circumstance, consult the programmer.

-Dick

Re: 502 mag efi rebuild
 

I've been talking to Mark at precision, who is programming the computer for this engine, and will DEFINATELY talk with him about any changes being made as I am building it. He has the final say as to what is going into the engine because I'm going to be running a program he has already written for a similar combination instead of mapping it on a dyno.


Doug

Re: 502 mag efi rebuild
 

..

Re: 502 mag efi rebuild
 

I scrapped the stock fuel pump ,vst and all the other garbage feeding my efi,ran a -10 from tk to larger than stock filter into a large inline sx pump,runs through a fuel cooler thats actually a small oil cooler. Drilled out fitting holes on efi rail,threaded and plumbed with twin -8 hoses feeding it. Ran 2 tees out of fuel pump,2 of lines are ones feeding rail,third goes to bypass return regulator to suction side of pump. If you re-design fuel system and change the pump,don't try to run new pump off old pump wires in harness,instead use the power wires to energize a nice hd relay,Smitty

Re: 502 mag efi rebuild
 

Boatally Insane

Listed are the 3 camshafts in question. These EFI motors like high vacuum and strong intake signal, so overlap must be kept to a minimum. Of the two choices available to reduce overlap, pulling duration out of the cam would have a greater impact on performance than spreading the lobe sep, hence the LSA of 114* and 115.5*
502 HP carb
284/292.... 222/230.... .576/.598 110

502 EFI
292/298.... 230/236.... .598/.610 114

502 Mag MPI
................224/224.... .483/.483....115.5
The carb Crane recommended was essentially the HP 502 with the LSA spread from 110* to 114*
Bob

Re: 502 mag efi rebuild
 

Boatally,
Specs on the 525 EFI camshaft
298*/306.....*236*/244......610/.632.....114*
Bob

Re: 502 mag efi rebuild
 

502 HP carb
284/292.... 222/230.... .576/.598 110 ........ is this right the LSA at 110 on this came ????

Re: 502 mag efi rebuild
 

Crane spec'd that cam with a 114 LSA because I'm running Revolution Marine Manifolds and short risers with Captain's Call, and didn't want any reversion issues. I certainly wouldn't mind going bigger if I can. My two limiting factors are definately the EFI system and my exhaust but I don't want to give up either one..so could I get away with more cam?

Thanks,


Doug

Re: 502 mag efi rebuild
 

Rob,
Here is the cam card. Even though it's on a 110* LSA, becase of the relatively short seat duration it has 64* overlap as compared to the 731s 69*.
http://www.cranecams.com/?show=brows...11&lvl=2&prt=5
Bob

Re: 502 mag efi rebuild
 

It looks like Merc is using the Gen VI 731 on 114s for the 500EFI and the Gen VI 741 on 114s on the 525, correct?
Will the MPI intake support the hp this combo is going to make?
Also, beings you have just kissed off the decks are you considering using the Cometic .027 gaskets to improve the squish area and bump the CR a tad?
Thanks,
Dave

Re: 502 mag efi rebuild
 

So the 525 cam is a 741 with a 114 lsa.. I wonder if the 741 Crane would make much diferance between the 112-114 lsa

Is the 731 close to what came in my 500efis?


Rob :D