morrowcarl72

hey so i have a boat with a 502mag.... last owner didnt drain water so im looking at a motor with a cracked block...(cracked bad)

i found a guy with a zz502 forsale in my area and was curious how interchangeable these would be.... technically it would be a little more hp and a little more ft lbs.... but could i use my mag intake on it and what are your thoughts about the swap....

wjb21ndtown

I'm guessing you have a mag carb motor, 415 hp? You will probably want to take the cam, intake and heads off of your motor and put it on the zz motor to correct the power curve to fit a marine app. The reason for the head swap is that I would tend to think that you'd be better off with whatever valves that Merc uses opposed to the valves that GM puts in their zz motors. Make sure it is a brass freeze plug motor. Someone else may know about the zz valves and be able to provide more info though.

Double check the compression ratio of the zz motor, but I thought it was 8.5 - 8.75. If it's over that with your iron marine heads you could have a problem.

morrowcarl72

mine is a 95 efi mpi mag motor

my plan was to use the whole zz502 but take the carb and intake off and use mine.... plus my oil pan and oil cooling plus all my fuel system and alternator distributor and starter....

those were the major things i picked up from this forum.... most guys said they even ran them factory with no issues for many seasons....

like i said this motor is cheap with little to no hours on it.... (less that 50 in a car)
mine is all toast (intake is the only good part)

im looking to do this as cheap as possible but still be able to go 75ish!!!!

boat is a 95 mirage intruder 217.... external hydralic steering 16in trim tabs bravo 1 and a 25p mirage 3 blade

Griff

You would need to have the ECM recalibrated for the ZZ502. Also, I don't think the cam in it usaeable with stock Merc exhaust as it would revert water.

jeffswav

Also if they used the long block zz502 it will have GM performace parts large oval heads. Your intake is rectangular port.
Why don't you just find a used block and have all of your parts switched over? A good machine shop can do this for you.

Ok, I just read your last post. Now you want to go 75 ish. Get out your wallet because you are going to need 500HP or so to do that.

jeffswav

Here is another idea for you. Buy the engine complete, get a marine carb, marine distributor, aftermarket exhaust with long risers. You will need to upgrade the oiling system, bigger cooler, bigger better lines and fittings. That would get you your 500HP assuming the engine it what he says it is. That should get you near 70 MPH on GPS. The "Dream O Meter" will always read faster.

wjb21ndtown

I agree.


You can sell your stock EFI unit for a decent price and cover the cost of most of the swap. You'll have to go to a carb or spend a ton of money to get that efi system over 500hp.

You could probably sell your old rotating assembly, cam and lifters, EFI system and the 502zz large oval heads and cam out of the zz motor for decent money (around $2k for everything if the crank, pistons and rods are still good). You would be better off with a HP500 cam or a crane upgrade, keeping your heads, and getting an Edlebrock airgap or single plane intake. As mentioned though, you're going to need to upgrade your exh. system to the tune of around $800-1,200 if you want to make this happen.

ROTAX454

The average ZZ502 GMPP crate motor will have an honest 510-515 HP at the listed 5200rpm. I tend to agree with Jeffswav on the route to take.

More "stuff" needs to be done to make the motor marine friendly. Don't be alarmed. It is a short list. I.E. oil bypass valve.

PM me and I can fill in the details.
ZZ502 with a dash of PC.

Raylar

Most of the GM Performance ZZ502's are equipped with some medium size aluminum oval port heads that unless your MPI efi setup is the small oval port type it will not mate up with the heads on the ZZ502 and unless you boat in fresh water or have closed cooling, running the aluminum heads will require careful flushing after uses. You might want to buy the ZZ502, sell the heads and use the money to upgrade your MPI heads if they are rectangle port.
A good cam change in the ZZ502 similar to the HP500efi cam, brass or stainless freeze plugs, swap your marine oil pan and such and the ZZ502 base block will make a good build up platform.
As you probably already know finding a good 502 gen 5-6 bare block or a new one will set you back $1800 -$2500 if you can find one so buying an existing ZZ 502 may be a better move.

Best Regards,
Ray @ Raylar

morrowcarl72

so can you set me up with a list of what i would need for the zz502

say by chance i use:

my starter, alternator distributor all of my raw water cooling....(never going to leave lake washington always will be flushed and stored in a garage) and all of my oil system
i would like to use the aluminum heads mine are toast and i found out today that the crank will need some serious help so buying this motor would be a replacement deal

the list of needed things would be:

oil relief valve ( does my 502 have the right one?)
mechanical secondaries
bigger oil cooler
long exhaust risers


please add to this list and let me know any other thoughts of what i would need if i went with the zz502

also how much is my whole efi set up worth?