zz502 vs. merc 502mag
 

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....

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.

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

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.

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.

75ish will not happen cheap , unless you just happen to have a spare 525 sitting in the corner of your shop. :picard1: On the other hand I guess it all depends on what you consider cheap.

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.

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.

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.

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

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?

Whole EFI setup, complete with injectors, wiring harness, ECU, distributor, and fuel pump and sensors, etc. will bring $800-$1,500, depending on how long you want to hold onto it and what ECU you have. Pistons and rods are $100-250 if they're in good shape. A crank that needs to be ground may bring $100-150 if it can be saved. $50-75 for your stock cam if it is still good.

You can keep your old dist. and ECU, but you're better off selling it with the EFI system. Parted out you'll only get $400-600 for it, complete they're worth a lot more.

Your old marine heads may still bring $250 or so needing valve jobs or??? Why do you think they're bad?

You're right to use the zz heads, I didn't realize that they were aluminum/decent heads. You won't need to flush if they're fresh water. You may want to upgrade the valves to manley SD valves though. I'm sure others will chime in.

also the guy has a msd 6al box that comes with the motor... could i use this or not? any issues with marine conditions? obviously it will work

Sounds like you are on the right track. I have not heard good things about MSD in the Marine world, they seem to rust. I use the Marine DUI and it works well. The heads should be GM perf parts, they are similar to the Edelbrock oval ports. The 30 psi valves are cheap just get a new one. Get new hoses and fittings for the oil lines.

ok so from what i have found so far here and in other forums my list is as follows....

mech advanced distributor
mech secondary carb
my 502mag alt and starter
30psi oil valve
bigger oil cooler
longer exhaust risers
bigger oil hoses

______________________________________________
these are my questions before i finalize this whole thing.....

my distributor will work right?
what carb should i buy or what should i do to the one i have?
how big of a cooler should i go with and how big should the new hoses be?
and finally where is the best place to find exhaust and do i need totally new exhaust or just taller riser?

thank you so much to everyone especially @jeffswav and @rotax454

also my current exhaust is factory manifolds and risers with captains call....

also my efi set up came with the mechanical pump hooked to the water pump and a electrical pump.... do i use both or do i need a different pump what are my options with that... shouldnt a carb be fine with just the mechanical one?

last question....

i got to thinking about the oil cooler situation and started wondering....

you obviously cant run a radiator for cooling the motor cause you lack the wind you would need but in the case of an oil cooler why couldnt you run a conventional with a fan hooked to it?

http://www.summitracing.com/parts/DER-15800/

something like this^ which is pretty big even for automotive apps

i'm running MSD with the 6al box on my 509. I pulled the dist and it was rusty, so i took it apart cleaned it up, coated it with some rust inhibitor, and put some dieelectric grease on it. Will be keeping an eye on it, to see how it holds up. Havn't had any problems with the 6al box either. My dist is lockedout, and havn't had any problems with except for the rust.

good luck.

what do you have your timing locked in at and is your 6al retarding it any?

what kinda set up are you running cam compression etc

502 block bored to 509. Aluminum heads, don't remember the specs on the cam off the top of my head, but its pretty aggressive. Roller rockers/lifters. Lightning water reduced headers (due to the high lift cam) Pro systems carb.

When I bought it it was set at 34 degrees. Motor is 10:1 In michigan 93 octane is pretty easy to find. In Iowa about the best I can do is 91 (92 once in awhile) so I bumped back to 32 degrees, and run the 91. I've been reading the plugs pretty frequently, and so far so good. I put about 35 hours on last summer. to my knowledge the box is not retarding the timing, but I will admit, I am not a guru on MSD ignition.

I also run an electical fuel pump, with no mechanical pump.

Hope this helps. I mainly lurk here, and always pick up some good info.

Here is the one I use, the auto oil coolers will not work http://www.eddiemarine.com/store/car...l&p=13577&c=47
Distributor http://www.performancedistributors.com/marinedui.htm

The #6 MSD box does not alter the timing. You can lock out the timing and use this timing control from MSD. Carry with you a few retard "pills". Set your total for 36 and place a 0 in the box. When needed, replace the 0 pill with a 4 and presto, you have 32 degrees of total timing. The start setback is sweet too.

http://www.msdignition.com/Products/...ed_Retard.aspx

We dropped a new GM ZZ502/502 in my 23 Wellcraft Nova several years ago, 2002... I think. My ZZ came with brass freeze plugs so no problem there. We took the Thunderbolt IV ignition system from my 7.4 and used it on the ZZ. We also changed over the circulating pump, oil pan, alternator, and starter. I switched to a 23x3 combo oil and power steering cooler. And, my engine guy changed the head gaskets. After running the engine/boat for about 1/2 the season I was having oil tem issues so I yanked the 11 lb. pressure relief valves from the oild filter pad, and replaced the side valve with a 30 lb. Been quite a while since we made the swap so I'm sure I'm forgetting something.

Anyways, for the 1st season I ran the ZZ with the vac Holly 850 that came with the engine, and ran the stock Merc exhaust, with Imco Sound Advantage. There was no cam change. The ZZ cam is very similar to the older hp500 cams, which I understand did have reversion issues. Due to that I kept the idle at +750. Realizing the potential for reversion, after going thru no wake zones and after docking, I'd make it a point to crack the throttle a few times to clear any water from the exhaust manifolds. The 2nd season I changed to the Revolution Marine exhaust. That exhaust was affordable, and had/has more rise than the Merc exhaust. I also had the carb "marinized" by Nickersons to conform with coast guard regs. btw... the engine ran just fine prior to sending the carb to Nickersons.

The only problem I had with the ZZ was oil temps, even with the bigger cooler. My oil temp sensor was (and still is) connected to a port on the remote oil filter housing. I have it there because I figure that's where I'm going to get temp readings at their highest. Allot of guys like the sensor in the oil pan, which will give an ambient oil temp, and likely lower than what I see. Regardless, and not to start an oil war... I always used (and still do) Mobile 1 V-Twin 20/50, due to its ability to withstand higher temperatures.

Prior to yanking the ZZ and having it turned into a 557, I ran it as described above, for four seasons in my 23 Nova. Speeds were anywhere between 69 and 73 on GPS with a labbed 25 Mirage Plus, depending on the water I was running in. Again, as described above, the engine ran flawlessly. And I ran it HARD... ALLOT :o)

Now, this was a brand new ZZ crate engine that no one had phuk'd with. When my engine guy tore the ZZ down for the 557 project it had about 140-150 hours on it, and the internals looked to be in great condition. As we looked things over, he commented that the engine/internals would easily go another few hundred hours.

IMHO if the ZZ502 you have is "stock" and has not been messed with, you should be able to run it with the carb and cam it came with.

Good luck and lett'r rip......

thanks kidnova your amazing i think im going to run down and pick it up next weekend im super excited to see how she does....


and thoughts on the locking of the timing and or retard boxes

From what I hear about MSD's you won't need to worry about locking out the timing... it'll rust up and lock up on its own :o/ However, reading the post by ROTAX454, he seems to like the MSD and he knows far more than I do about the subject. So I'd pick his brain. I ran the ol' faithfull T-bolt IV on my ZZ502 and it ran just fine. I did however use a T-bolt V ignition module to get around the rev limiter. In fact, I'm still running the T-bolt on the 557 ... bored, stroked ZZ502. I run the T-bolt with a Crane box on the 557.

The 557 also runs like a dream, with a mild solid roller. I thank rmbuilder aka Bob Madara for the cam. Bob was also key in picking out and furnishing the AFR 315 heads w/complete valve train, and 454R intake. And he was great with advice about the rotating assembly, which is Callies.

If no one has gotten their grubby paws into the ZZ you're looking at, and it's been maintained (oil changes/good oil), and if it hasn't been abused, you should be fine. I'm no guru so if I were to spend any real $$ on a used engine, I'd have a trusted pro look it over before buying it.

so i have been looking at exhaust for the last 3 hours online... prices between 1000-6500 and dont understand how one exhaust has a better ability to stop reversion more than any other.... i need some help making some choices here.... only thing i found online proving it had the ability to stop resonance reversion was this super long article about how there has only been a few manifolds ever built that have lips in them to help stop the water from coming back into the motor... any thoughts?

any suggestions?
anyone know what i might be missing minus the fact that some are shinny some are aluminum some are stainless etc

Performance exhaust introduces the water further back from the exhaust port so the water has to climb further uphill to get into the cylinder head. The ones most resistant to reversion are dry all the way through the transom. Don't worry about them getting hot, they are water jacketed. The MSD will work fine. Use the black bushing in the distributer and set it for 34 degrees at 3000 rpm.

ok well i feel like a complete retard here but can anyone explain more in depth to me which bypass valve i remove and which one i replace?

i get the idea and have no issues with that what i dont get is which one is which and or where it is at? center vs side of pad...

nvm i figured it out.... do i need to install a 30psi or could i go with tapping it and plugging the hole all together like in a race application?

Some plug the hole and some put a 30 lb valve in. I went with the 30 lb valve. From what I've read/heard, the side valve only opens if the filter gets plugged, but I can't swear to that. I change oil/filter every +,- 20 hrs. so makes no difference to me.

As far as exhaust is concerned, see PatriYahts post.... decent exhaust exposes water further back. I came across a used set of KE headers. KE's are the best bang for the buck, if you can find some used, and in good condition. If the ZZ cam is a reversion concern contact rmbuilder/Bob Madara and he can set you up with a good cam. Plus with an rmbuilder cam you'll likely see more tq/hp than with the ZZ cam. But as I mentioned before, I never ingested water into the combustion chamber. At least none that I'm aware of.

There are two bypass. The center one you remove and throw away. The second is closest to the bock, put the 30 lbs bypass in that one. All you have to do to remove them is screw a 3/8 bolt into it and yank them out.

Read this article it probably has the part number in it. I get mine at local chevy dealer for $8.

http://www.offshoreonly.com/forums/g...ass-valve.html

Good go'n 1BIGJIM. I remember that thread well now lol

There are two sets of EMI exhaust on this site in the swap shop. I also saw a set on Speedwake in the classifies section.

send me the links woulda ya please im going to be away for a bit!