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  1. #1
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    502/450 hp gm blocks whats the mystery ?

    Ok somebody explain to me what the difference between a 502/450 HO gm crate motor and a 502/450 gm crate marine motor other than the slight cam difference,brass freeze plugs,and a 8.1 oil pan versus the 6.0 on the HO. If you look at the specs in the gm performance catalog they are nearly identical. They HO even has the composite head gaskets w/stainless fire rings and brass freeze plugs . I'm more less talking the rotating assemblies and blocks. The consensus I'm getting is like 50/50 some say they are built with different tolerences and some say no difference. Somebody fill me in please. This seems to be a huge mystery in the marine world.

  2. #2
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    Hmm, The mystery continues

  3. #3
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    Quote Originally Posted by Duck Diggler View Post
    Hmm, The mystery continues
    not everything diff but the biggies are the valves, the cam, oil pan, dist, carb. do a search been covered alot

  4. #4
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    1st off GM does NOT assemble the marine engines, they are sub contracted out, and are sold with NO GM warranty, that is left up to the marine division that ultimatly sells the unit, they sell the automotive with a 3 year or so warranty thru GM dealers as long as you supply a vin thats usable. the engines them self are not that much different, camshaft, head gaskets, valves in most cases...

  5. #5
    Commercial Member Commercial Member HaxbySpeed's Avatar
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    Quote Originally Posted by ezstriper View Post
    1st off GM does NOT assemble the marine engines, they are sub contracted out, and are sold with NO GM warranty, that is left up to the marine division that ultimatly sells the unit, they sell the automotive with a 3 year or so warranty thru GM dealers as long as you supply a vin thats usable. the engines them self are not that much different, camshaft, head gaskets, valves in most cases...
    Wrong... GM Powertrain builds the marine and industrial engines and they come with a one year factory warranty.. As far as that 502, the only difference is the cam.
    The same short block gets used for all the GM performance crate engines and marine. The short block is a good deal and with a set of AFR's and a good cam (Bob M) 650-700hp is no problem.
    No matter where you go, there you are.. Buckaroo Banzai

  6. #6
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    Quote Originally Posted by HaxbySpeed View Post
    GM Powertrain builds the marine and industrial engines and they come with a one year factory warranty.. As far as that 502, the only difference is the cam.
    The same short block gets used for all the GM performance crate engines and marine.
    That is absolutely correct.

  7. #7
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    I have verified with Mercury Racing that only the blue motors are rebuilt by Merc - the black motors simply have whatever parts GM puts in them. Regular Eaton valves are used, probably not inconel, although Eaton does make an inconel valve, and I have seen it documented that GM started using inconel exhaust valves in some of their later model medium duty truck engines due to valve recession in severe duty applications. It is unclear if that was extended over to the marine engines.

  8. #8
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    Now there the answers I'm looking for. I was told by a good friend to buy a short block zz502 put a set of decent heads and he said the cam that comes in the block is identical to the HP500 cam,He suggested a set of heads from arrowhead a perfomer intake and a holley 800 and it should be real close to 500hp Now he also said the 6 quart oil pan was more than suffient for how I was going to use the boat, I don't know if I necessarily agree with that. I'm on a real tight budget for this project and we priced it out and I can build both of these motors for a hair above 15 grand

  9. #9
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    sorry but you guys are wrong..I had a issue with a new GM marine engine..talked to several people within GM with help from my local chevy dealer...ended up talking to a very good guy at GM powertrain..he told me in fact they do NOT assemble any marine engines themselves, they have a subcontractor shop that assembles ALL the complete engine and they are sold with NO warranty thru GM, was also told tghe same thing from crusader, the warrenty is up to whoever marinizes them is the warranty holder..if you do not believe me contact GM powertain, or a dealer and try to get warranty on a "marine" engine
    Last edited by ezstriper; 04-30-2011 at 08:13 AM.

  10. #10
    Commercial Member Commercial Member HaxbySpeed's Avatar
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    Quote Originally Posted by ezstriper View Post
    sorry but you guys are wrong..I had a issue with a new GM marine engine..talked to several people within GM with help from my local chevy dealer...ended up talking to a very good guy at GM powertrain..he told me in fact they do NOT assemble any marine engines themselves, they have a subcontractor shop that assembles ALL the complete engine and they are sold with NO warranty thru GM, was also told tghe same thing from crusader, the warrenty is up to whoever marinizes them is the warranty holder..if you do not believe me contact GM powertain, or a dealer and try to get warranty on a "marine" engine
    You have your facts a little confused.. The last half dozen or so marine long blocks I bought came with a 1 year GM factory warranty.. If you buy an engine fom a powertrain dealer you will have a warranty through them as they are the re-seller. The general public cannot buy directly from GM powertrain. GM does not sell complete marine engines but the base engines are all GM, some are assembled in the US and some in Mexico. If you bought a GM performance engine there is no warranty if used for marine.
    No matter where you go, there you are.. Buckaroo Banzai


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