I also run the ZZ502 in my boat. I am very happy with it. I did send it to the machine shop and have it balanced and totally blueprinted with ALL clearances on the loose side! Changed to Crane hyd roller, Crane rockers and stud girdle. I kept the oil pan off my GenV 7.4L. It will also require a 502 flywheel.

Since i can't lay my hands on the article, just what exactly did he say was wrong with the cam that comes with it? Dennis Moore in his book 'Building Big Block Chevy for Marine performance' reccomends that cam. Just wondering what was wrong, cause i'm considering it.........

I also have this motor in my boat and love it. I added heads, cam, and exhaust to my old 7.4 and smoked the main bearings after 1.5 years of hard running. So I bought the 502 shortblock from GM ($3700.00 delivered new) and used my heads. It comes with the 502/502 cam, roller lifters, and retainers. I cced the heads and milled for compression ratio of 9.4 to 1. I also changed to inconel exhaust valves and Comp Cams 930 springs. It runs great, has a nice lope at idle, and pushes my 22 Scarab into the upper 70's.

The shortblock can with the timing cover and oil pan already installed but I removed them and disassemlbed the bottom end and measured all the clearances. To my surprise they were right on.

Anyway, as mentioned above Dennis Moore in his book Big Block Chevy Marine Performance recommends this cam and it runs great in my boat. There are others on this board running this cam with no problems. Some are even thinking of going to a more radical cam.

Hope this helps

Ron

Rebuild the mag you have. You will be happier, and probably wealthier.

I have (2) brand new zz502 short blocks if you are interested.

502/502 - no inconel valves (unnecessary if not supercharging). 110 degree lobe center cam (will tend to suck water back in unless you use dry headers). You will need to change valvesprings to something with 135-140# seat pressure and 400-420# open pressure.

the HP500 cam is a Crane Powermax hydraulic roller with .570/.611 lift and .050 duration of 224/236 with 112 lobe center

good luck

I have purchased the motor but for now (with all the changes that have to be made) she is going into a pickup until I decide to "boatarize" her.

mcollinstn. Thanks for the info.

Joe

Okey you guys have got me all confused now. I thought the 500HP came with a Crane # 169611 which has 222/230 @ .050 and 576/598 lift w/110 deg. LSA. (I got that from their web site just to make sure)?

Now for the confusing part. The 502/502 comes with the following cam specs; GM # 12366543 224/234 @ .050 and 527/544 lift w/110deg. LSA.

I thought that anything between 109-112 deg. was good for no reversion, at least that's what the bible said (Dennis Moore Book). It must also depend on other factors?

Now this is where it really gets confusing. A 502 "Marine" Crate motor comes with the following: GM # 12551622 224/224 @ .050 and 483/483 lift w/115.5 deg. LSA.

So what am I missing here??

Thanks Bob

Bob

I was spewing specs off the top of my head for a Gen4 motor (pre '95).

You are right for the Gen5, Gen6 motors. The HP500 cam is the one you mention. It is indeed the 110degree lobe center, but is set up to close the exhausts AT tdc, so as to stave off reversion (essentially a 5degree "retard").

With that in mind, I reckon you could retard the 502/502 cam 5degrees and end up in the same situation. Maybe that would be sufficient. Shouldn't kill bottom end enough to matter. Don't know if the ramp profiles are different enought to cause the intake valves to get too close to piston, but should be easy enough to check.

As far as the "marine" cam, if you look in the Crane catalog for the hydraulic flat tappets, you will see 115degree centers fairly common. Nonperf newer motors use the same basic grinds with the hydraulic roller setup.

With lobe center, I like to stay over 110 when able. Once had a Mopar 440 with a custom-ground 104 degree solid roller cam. Made all the right noises, but narrowed powerband significantly. Had it reground to a 110 degree center and made all the difference in the world - did lose some of that "sprintcar chatter" though.

With a 110 degree lc cam, I'd rather not be the guy who recommends it to a guy running stock center-rise Mercruiser exhausts.

In reference to the Teague article about the ZZ502/502, most of the concerns revolved around the camshaft (lobe center), the valvesprings (too wimpy), the headgaskets (not stainless), and the aluminum heads and intake not being "salt-duty" (no brass water crossover liner in the intake).

Reversion most certainly does take several factors into consideration in addition to the camshaft lobe center (and specifically the closing point of the exhaust valve). Length of the exhaust primaries is a big factor (shorter is more prone: and leaking exhaust gaskets essentially shortens the primaries and becomes a factor), as well as the entire exhaust system (4 into 2 into 1 versus 4 into 1). It has been argued that Dual-plane intakes are more prone to reversion than single-plane intakes in an otherwise apples-to-apples comparison (less effective volume to spread the "sucking" action for a given cylinder). The list goes on...

M