Dennis Moore

The 502/502 is a 502 HO partial engine assembly with the bigger camshaft. The cylinder heads are known as the GM Signature Series heads with 290 cc intake runners and 110 cc semi open combustion chambers. These heads are made by Edelbrock for GM Performance parts. The heads were shipped to GM from Edelbrock assembled and included with the engine package loose (not installed). They did not have the GM manufactured valves, springs or retainers but valves, springs and retainers sourced from the aftermarket by Edelbrock (good stuff, by the way, I did an article on the Edelbrock heads and they are a very good product). That is why the first 502/502's didn't come assembled. Now you can get one assembled as a complete crate motor.
By the way, I am sure that it comes as no surprise to anybody that the aluminum oval port intake manifold for the 502/502 is also made for GM by Edelbrock.
To make an excellent marine motor buy the 502 partial engine assembly, 502/502 camshaft and single row timing chain set and then purchase from Edelbrock the hard anodized aluminum marine heads #61459 (oval port 290 cc with 110 cc chambers and inconel exhaust valves) and oval port intake manifold. Install a GM marine oil pan, marine water pump, marine ignition and marine carburetor and then build it with the rest of the parts from the 502/502.
For the complete story on the Edelbrock hard anodized marine heads locate a copy of the March 2002 FAMILY AND PERFORMANCE BOATING MAGAZINE.
Sincerely
Dennis Moore

rjcardinal

Dennis,

Thanks for the part number for the hard anodized heads. I have a stock 502EFI now in a 27 Fountain at 70 hours and I am thinking about changing the heads, cam, and exhaust this winter. I am researching as to how much I can change the engine and use the EFI system with some mods. Any thoughts?

Ron

Dennis Moore

I think this will be controversial but with a port injected EFI you don't need to change to smaller 290 cc port heads to increase port velocity. Because the fuel is injected into the engine you do not need high port velocity to have a sharp draw on a carburetor. While the stock rectangle port heads are total overkill for a carbureted engine they work like gangbusters on a tuned port EFI engine like yours. Change to a good flame arrestor, good exhaust system, an adjustable fuel pressure regulator (these things may help a little) and if you really want some more speed (along with a lot of work) send the camshaft to Comp cams and have it reground, but that is a whole nother subject!
Sincerely
Dennis Moore

obnoxus

I dont mean to jump into the middle of your post, but it is exactly what I was looking for advise on. I will be rebuilding a 95 502 MPI in the off season and was looking for opinions. I want to get another 500 hours out of this engine without touching it, should I do a completly stock rebuild, or will it handle a larger cam with no ill effects, I am running Gil headers and K and N flame arrestor, otherwisw bone stock. I have an adjustable fuel regulator sitting in the garage just in case. Any/all input welcome.

Dennis Moore

Dear Obnoxus
If you are not going into the computer I would be carefull what camshaft you choose. The stock camshaft has 224 degrees of intake duration and 224 degrees of exhaust duration @ .050 lift on 115.5 degree lobe separation angle.
Installing a high performance camshaft that has aproximately the same duration (on the intake) but is more radical (opens the valve quicker and closes the valve quicker) will increase perfomance without screwing up the computer too much. I would also go with a dual pattern camshaft with about 8 - 12 degrees more exhaust duration. The lobe separation angle should be 114 degrees (for the computer to work well).
To make this all work a little better with the computer you should also use fast bleed down lifters. These lifters shorten camshaft duration at low speeds and restore it at high speeds. The fast bleed lifters are particularly important for closing the exhaust valve quicker. This helps prevent water reversion at idle speeds (water being sucked back up into the exhaust port).

My suggestion would be the Crane Cams H-278-2. It has 222 degrees intake duration / 234 degrees exhaust duration with .529 intake valve lift / .525 exhaust valve lift. The lobe separation angle is 114 degrees. This camshaft will work with the stock valve springs and the stock non adjustable rocker arms. Fast bleed down lifters (Crane calls them Hi Intensity Lifters) are available from Crane #99377-16.
Hope this helps!
Sincerely
Dennis Moore
FAMILY AND PERFORMANCE BOATING MAGAZINE

ursus

Re the Crane H-278-2,, So are you suggesting going to a flat Hydraulic Lifter cam instead of using the stock Hydraulic Roller cam configuration on Gen VI 502 mags ?

Wouldn't the flat hydralic be less radical,, open the intake valve slower, than the hyd roller with the same duration ?

Dennis Moore

Dear Ursus,
I am sorry but I was replying to the question that Obnoxus gave me. He has a 1995 MPI with a flat lifter camshaft.
Sincerely
Dennis Moore

Cignificant

In case anyone's interested, I have a 502 / 502 hydraulic roller camshaft (0.527" / 0.544" lift, 224 / 234 degrees duration @ 0.050" lift) for sale - it's new - pulled it out of a new short block. With lifters and retainer.

$200 (cost at gmpartsdirect.com is about $300)

ursus

ok thanks Dennis,,, I have looked for wondered about a hydralic roller cam upgrade for the gen VI 502 mag with about 224/230 .525ish lift but with 114 degrees seperation so as not to mess up the putr and be able run thru prop exhaust still, most of the hyd roller seem to be on 110 degree lobes and with 234 or 236 of exhaust.

Perhaps no one makes these cuase the improvement would be to minimal ?

Perhaps a good question for you, how to get decent additional power with thru prop/quiet exhaust, noise laws are becomeing very restrictive for some of us.

obnoxus

Thanks Dennis,

I dont mind going into the computer at all, but dont want to sacrifice reliability. I hae a guy in Wisconsin who can do computer remapping while its on the dyno, I am thinking this is the best way to approach it instaed of someone " guessing " what my motor will need with " these " parts istalled.

That was my biggest reason for sticking to a stock rebuild, I dont want the headaches.