Hey guys getting ready to freshen my 91 502 mags (carbed), have 700 hours thinking the time is coming. Have read many of the previous reccomendations on combinations of components etc but curious of the cam specs that are in it now, also are my heads decent, with valve job/ porting. I would not be looking to make big horsepower just want to enhance while I am in there. I am economically limited but want to do it right. thanks

Randy, consider emailing Tyler Crockett. He went through my HP500's recently, and netted me an extra 100 hp via heads, (which you have already done), cam, & ignition.
Carder

Randy,
Have the same eng's I have redone each twice. I have kept them stock. I have all the receipts for all work. You definately need to have heads checked. I recommend you call Donnie at northeast machine 716-796-3300 or 800-888-3760. He knows me and my motors very well.Tell him Charlie with the Sutphen told you to call, he's come along on some poker runs . Great guy eager to help. Any other info you need E-mail me and I will give you my Ph. #. Send me a private message with your e-mail or ph. #.

The stock cam is 220/220, .510/.510 flat tappet on a 115.5 lob sep.

Heads are fine.

A good budget cam is Crane 134242

randy,at 700 hrs on your 502s how did they still perform?i have 400hrs on my 502mpi and wondering if i should pull and rebuild?

It might be due for valve springs, but doubtful that it would need a full rebuild at 400hrs.

At 400 hours i would do a valve job at the least. Do a leak down and compression check and that will tell you if you need to do a full rebuild.

I am not having any problems at 700 hours no oil usage between 40 hour changes, dont run WOT very often lot of 3200- 3600 use just want to do it before problems excessive wear Randy

We just took apart my almost 800 hour 454 MAG MPI that ran great. The gimbal ring needed replaced, so the engine had to come out. May as well go through it right? Everything inside looked great. Crank is good, cylinders are well worn with a ridge as expected, but nothing out of the ordinary. Only thing was the cam retainer plate bolts were coming loose. They were all no more than finger tight, and one had backed out a full head thickness. All I can say is good thing we took it apart. We'd have been looking at a monster failure if the cam had moved forward in the block. Taking it apart now was the difference between an easy rebuild and staring over. My compression checked out great as well. Compression and Leak Down are great tests, but they can't measure the intangibles.

Randy, in the early 90's I built a pair of 454s and used the Merc 465HP / 502 cams with the Crane HI Intensity lifters. I was happy with that combination as it idled well with no soot or loading (a little loapy). They also had plenty of low and mid range power to get on plane and pulled strong to 5450 RPMs. The boat was a 34' Scarab III with TRS drives which weighed 9400 lbs and ran 69 MPH on GPS. I went with this cam thinking that Mercury Marine had more time and money to develop the cam spec than I had patience for trial and error. If you find yourself interested in this combination I have one of these cam and lifter sets I purchased for a project a few years back that I would sell for $275. The Crane part numbers are 13H000036 for the cam and 93977 for the HI Intensity lifters. Current intenet pricing for these is $244.98 and $109.95. I spend most weekends in Grand Haven if you would like to see the parts (let me know in advance and I will bring them over). Good luck with your project.