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502/450 hp gm blocks whats the mystery ?

Old 04-30-2011, 09:55 AM
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Here is a good thread on the topic. I also purchased two, and took them apart to put in Mandra valve train. They have the best of everything including VALVES.

http://www.offshoreonly.com/forums/g...se-engine.html
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Old 05-01-2011, 09:28 AM
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Thanks guys, 1BIGJIM hows your motors holding up? I can go to my local chevy dealer and get 2 part#(12568782) 502 partial engine blocks for 5100 each. I was more or less concerned about the rotating assembly being the same or not. My buddy says there the same. He also said the cam has the same specs as the HP500 motors, he had the opportunity to measure one from a HP500 and one from a new GM block and said they were identical. We were just going to put a nice set of heads. My other concern was the size of the oil pan the zz502 only comes with a 6.1 quart pan opposed to an 8.1 which comes on gm marine blocks. Do you think this will be an issue? I may just upgrade the pans. I also just got a price from a marine engine builder he can get me a brand new gm"marine" engine for 7800.00 w/ tins no intake carb or dist. with 1yr warranty. Buts thats for a 450hp 502, then we could change the cam and jets in the carb after the warranty period and get the 500 hp I'm looking for.Hopefully. My goal is to push an easy 75 in this boat and a 50 to 55 cruise. I think its gonna be hard to do with anything less then 500hp. Thanks for all the comments and feedbacks, I've been pondering over this for 2 weeks.
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Old 06-11-2017, 09:26 PM
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I am in the same dead end, bought a boat with a blown (rusty) 502ci and I am debating between buying a 496ci or a 502ci (GM or Merc). The last owner gave me a few parts such as carbs, stainless marine manifolds and custom made dry exhaust, msd ignition, msd distributior etc. By any chance nobody knows if the exhaust height of the 502ci is the same as the 496ci ?
thanks
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Old 06-11-2017, 09:35 PM
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Originally Posted by Duck Diggler
I can go to my local chevy dealer and get 2 part#(12568782) 502 partial engine blocks for 5100 each. I was more or less concerned about the rotating assembly being the same or not. My buddy says there the same. He also said the cam has the same specs as the HP500 motors, he had the opportunity to measure one from a HP500 and one from a new GM block and said they were identical.
ZZ502 and HP500 are not the same cams. Tell'm, to measure again.

Here's the real GM Marine Oil Pan : http://www.michiganmotorz.com/74l--8...an-p-4052.html
I don't have the GM# for the pump pick up though.

Last edited by SB; 06-11-2017 at 09:42 PM.
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Old 06-11-2017, 10:15 PM
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I picked up a 502 HO engine. Tag on side of engine sez not for marine use. Like there are that many guys buying these for their chevelles. ZZ502 cam. 224/234 at .050 527/544 lift. 110 lsa. Dont run with stock exhausts. Little more duration and less lift than hp500 carb crane cam. 502 HO 461 hp cam. 211/230 at 50 510/540 lift. 112 lsa. A little hotter than mag cam. Can probably get away with srock exhaust. GM Likes to keep their lift low so they can keep their springs soft so the valve train lasts the warranty.
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Old 06-12-2017, 08:01 AM
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if you look thru the GM performance parts books, ALL of the engines listed say NOT FOR MARINE USE, not to say that many have not ended up in boats, but GM does not warranty any marine engine as I said before, all warranties are left up to the marinizer who sells the engines. I got caught up in all this when 1 of the brand new GM 454's killed a crank @ 120hrs, never saw 4k, in my gibson, took apart and had a scat crank, started researching from there. If GM is selling/warranting marine engines I have never seen it and my local dealer says no. Love to see a link to marine engines sold by and warranted by GM.
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Old 06-12-2017, 09:27 AM
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My 500hp ZZ502 crate engines came with a 1 year warranty, (dealer knew they would be used as marine engines). I did change the oil pans to larger (Merc HP500 style) pans, and made a change to the oil filter base, (also found on OSO history), Sold one. The other is still running fine in my Thunder.
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Old 06-12-2017, 09:59 AM
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The dealer was looking the other way (wink, nod). If there was a warranty issue it woulda taken a song and dance. Mebbe hafta buy a trashed 75 Vette or pickup so you had a vin number, something like that.
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Old 06-13-2017, 08:02 AM
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exactly, in order to get any warranty on these engines you must provide a vehicle VIN that is ok to use that engine in..
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