Man that is a great thread! Wish that discussion was going on a few summers ago when we put the ZZ502 in my Nova. Sure would'a cut down on some of the trial and error stuff, and $ spent.

I have an automotive crate engine in my boat, GM ZZ502/502. And when all is said and done, I'm real happy with it. Very dependable and a strong runner. This is season number three with it. We dropped it in the boat just about "as is" from the crate, with the exception of the head gaskets. I also sent the carb to Nickerson's for marinization and tweaking. And swapped the oil pan off my old 7.4 that was yanked. Also swapped the ignition, starter, alternator, sea/fuel pump, and complete Merc exhaust from the 7.4 to the ZZ. Kept the 110* LSA Cam, and kept the SS exhaust valves. Two seasons ago I took the Merc exhaust off and installed Revolutions. Plus a bigger/better oil cooler.

The engine has performed very well. And I'd do it again. But whether or not you go with an auto type crate motor I think would depend on how hard you intend to run it. I've done a couple of sustained 20-25 mile just about WOT runs with no ill affects. But I think that might be pushing it a bit too hard.

Most of my WOT is limited to just a few minutes at a time {wife screams at me and gives me dirty looks}. Rest of the time we're just cruising around at about 3500-4500 rpms or so.

I think if you're gonna go out and WOT every now and then like we usually do, a crate motor is just fine. But if I was gonna add a blower and or lean on the sticks allot, I'd opt for a properly built marine blower motor.

Disclaimer.....Just my .02......I'm no mechanic, just a dumb azz rambling on about my own experience with a crate motor. Good luck with your decision.

thanks for all the help this is the latest info I have gotten .

I spoke to a well known marine and car engine builder and they have a complete marine division . They sent me the specs on a 540 non blown car and boat motor . All specs were identical (HP was about 650 on pump gas) as far as torque curve rpm horsepower everthing .I dont have them in front of me or I would list them . Anyway the car engine was 12000 the marine was 16999 both engines turn key. I asked the differences for the extra money and I was told maching and etc. is all the same but the marine motor has inconel exhaust valves , hardened and coated valve seats , fuel pump and system was marinized, 10 quart pan, he included a billet breather and nice valve covers, but he said the biggest difference was the 12 month warranty and that he spends 8 to 10 hours on the dyno getting the fuel curve perfect on the marine engines . I guess my point and or question is , is it really worth it ? I dont run the boat to death but I would like to go a bit faster sometimes . The crate motor with a few upgrades is really seeming to be the way to go , and I can just have the upgrades done when they build the motor .

J and E piston manufacturer recommends more clearance between the piston and bore.... about .002 more... the thinking is the piston is going to run bigger because of the added heat from more load... and the bore is going to be smaller because of the cooler block than a car. ( If you are running raw cooling).

That would make sense .

17K sounds like allot of $. But then 650 turn key hp built right is some pretty serious stuff. That include the exhaust?

Bert,
So the engine you are looking at is a marine crate motor, not an automotive crate motor?

Torque curve and where peak torque comes in (RPM) is everything.
Inconel exhaust valves and cylinder bore clearances also very important, as previously mentioned.
Stay away from the automotive stuff.
Regardless of what you build, build for intended application and use.
Don't compromise. You will ultimately pay in the end.

About 10K or more under what the larger marine motor builders will do one for and half of what a 600 merc will set you back

Exhaust not included in the price . I have been looking at and comparing both car crate and complete marine engine's .

I would like to add a little something to this subject. I am an ASE cert. master machinist and engine builder. I have built both automotive and marine engines for the last 19 years. Before that I worked at a GM dealer. First off, the GM performance parts catalog specifically states that the engines in the catalog are NOT intended for marine applications. That is not to say people haven't used them in a marine application. Some people have had good luck with them and some haven't. I think it depends on how hard they are run.

The above mentioned references to increased piston to bore clearances are right on the money. This is especially important with open cooling systems. Not nearly as much block expansion. There are other differences that most people on here know about and have been listed.
Sorry for the long post. Thanks for listening.