502/502
 

I have the oppurtunity to make a purchase on a GM crate motor (502/502). I'm wondering how good of a marine motor this would make right out of the crate.

Would I have to make any changes (cam, headwork etc)?

I'm getting a real good deal on it so if changes would have to be made I think it would be worthwhile.

Joe K.

Check out www.1800runsnew.com . They have marine crate motors up to 585 hp. Do not use a car motor in a boat!!!!

Teague on tech covered this some months ago. All the wrong parts in zz's pistons,cam,no inconel valves,wrong valve springs etc.

Yea, What Birddog said! I think it was the Oct or Dec issue of PowerBoat in "Teague on Tech". He talked about the ZZ502 and it's marine ability. Check it out.
Eric

I have a pair of these engines, and have had good luck, BUT, you need to make changes. Roller rockers, Inconel exhaust valves, marine cam and marine carb. You also have to know what you're doing when you set up the oiling system with remote filter and cooler. Depending on your existing motor mounts, the eight quart pan that comes with the engine may not clear the mounts. If you are replacing a Mark IV engine you need an electric fuel pump.

"Really good deal" should mean having $1500 - 2000 left in the budget to do these changes. The compression is OK with premium gas, especially if you step up to more cam, but then you better have good exhaust with the water introduced way down the pipe.

You can also buy the Short block of a ZZ502 and add heads. Then you could add what ever heads you want. You could also buy the Accel fuel injection system with the thier intake.You can get a short block for about $4k. This is what merc. uses for the Hp500 bottom end but they run a diff. Cam.


Pyle

are the 1800runsnew engines crate motors? Or rebiult crate motors built to marine specs? Or do tehy take new crate motors and marinize them?

I ahve always heard fgood thing abotu thier engines and people here have had luck with them nust not sure exactly what they are.

They are marine crate motors. I have 2 502's with prochargers and they run great!

The engine is out of a truck and has only 600 miles on it. The engine already has roller rockers. I have a marine carb that I would be putting on it and already have an electric fuel pump. I also have a oil pan that will work. The engine would be purchased for 3700.00. Biggest concern would be the effects of reversion with the stock cam (I've heard bad things). I have a set of Gil exhaust with 6inch risers.

I will surely look back to the article on this engine and find out what I can.

Thanks for all the info.

Joe

Just read the article in Powerboat. I may think about rebuilding my 454 mag instead. Could probably get better results putting the 3700.00 into it.

Thanks Again,

Joe

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.........:p

502/502
 

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