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Great motors, I will say that the heads are set up a little tight for a marine application. With the aluminum heads you may want to take them apart and have the valve guides clearanced, besides that they run great. I have two GM crate motors which I'm very pleased. One is 454 HO motor in my cruiser that I have been running for 8 years now, I has had 3 intakes on it, several different sets of headers thru transom and dry and it starts every time. The other is a GM 502/502 short block with AFR heads and custom solid roller cam with a tunnel ram producing 740 hp. I disassembled the lower end for inspection after a year of racing and all the bearings look brand new.

That motor will give you many years of reliable service. Just make sure that you open up the valve guides a little.
 

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i have a 450 hp marine 502 it runs great, the insides are bone stock has an edelbrock intake and 850 double pumper and basset headers turns 52-5300 rpms with my berkely pump and b impeller the only drawback is that you have to run an electric fuel pump.
 

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classic hot boater
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502/502

We had this alum head 502 in a gullwing we added a 420 mega blower it was great. Had a few problems with it.. I would change the stock roller rockers.
I agree with widowmaker on the heads i did drop a vavle one time with the blower,also broke a roller rocker and a roller off the lifter. But I think they are great engines and will be great with a tunnel ram but may go with bigger carbs but i ran two 850 dp with the blower.
On a 454 30 over i was running 750 dps on tunnel ram so u could say i like a bigger carb. You can always jet down if you need to.

Good luck with this.:)devil
 

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Discussion Starter #7
Thanks guys for all the positive input. I ordered it this morning from the local Chevy dealer. Supposed to be here in 3-4 days. :D
 

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My personal experience with the ZZ502 and the ZZ572 have been tight lifter bores, out of spec line bores (size good but not straight) valve guides and snug piston to wall on non t stat engines (all). These all caused some sort of failure except the line bore issue. Luckly it was corrected. Just go through them completly. Put another couple tenths on the lifter bores with a brush hone, a couple tenthes on the guides, one thou on the bore with a torque plate and correct the line bore if even needed. Oh and check all the other stuff these guys have found. Good luck.
 
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