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Dumb question: Merc 496 Mag vs. Chevy 3500HD 496 HO truck motor????

Old 11-05-2004, 04:06 PM
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Default Dumb question: Merc 496 Mag vs. Chevy 3500HD 496 HO truck motor????

Hello everyone... Ok, dumb question here...

I have have researched the 496 HO from Merc on the internet and compared it to the stock 496 found in the 2001 - 2003 Chevy 3500 trucks... and have not been able to find much difference (besides the obvious).

In your opinion(s) is it feasable to pick up a pair of truck engines and use them in a twin marine application? All of the internal parts of the truck 496 are forged... Crank, pistons, etc... very heavy duty, same as the Merc engine. The HP ratings, however, are different.

Truck 496 = 340hp
Merc 496 = 370hp
Merc 496 Mag HO = 415hp

I am sure that the marine system has a different cam set up, timing differences, etc..etc...

I am in the middle of redoing a boat that needs a good set of twins... just wondering what the major differences were...

Thanks in advance everyone and any help is appreciated!

Q
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Old 11-05-2004, 09:10 PM
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Default Re: Dumb question: Merc 496 Mag vs. Chevy 3500HD 496 HO truck motor????

You sure the crate motor is forged?

Cause the Merc 496 is NOT.
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Old 11-05-2004, 09:22 PM
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Default Re: Dumb question: Merc 496 Mag vs. Chevy 3500HD 496 HO truck motor????

TeamPSI - Not a dumb question at all.

I put a ZZ502/502 crate motor in my boat {GM says not for marine use}. Forged rotating assembly, SS valves. Some said I was nuts, others said excellent choice. It's a matter of both opinion and hands on experience. Plus, how much $ you want to spend.

I was advised by some that bearing clearence and, piston/cyl wall clearence is tighter in auto than in marine applications. Others say there's no difference. Those two items seemed to be the main "issues", other than the obvious....marine carb, ignition, etc.

I've put about 85 hours on the ZZ {no changes, right out of the box}. I change oil {synthetic} and filter every 15 to 20 hours. I've made a few 25+,- minute WOT runs with it, a bunch of 10-15 WOT runs, and a chitt load of 5-10 minute WOT runs. WOT is at 5150 and 5350 rpm's depending on temp/humidity. The rest is mainly cruising at 2800 to 4000 rpm stuff. The engine never misses a beat. Runs great.

496 might be a different animal. I don't know. But, if the specs are the same with the auto and marine versions it might be ok. The marine version likely does have a different cam. And may also have different heads. Check the torque curve, you need good torque to move a boat. Good idea to go with Inconnel's for exhaust valves too.

Wish I could give you more but my knowledge is limited. I'm sure one of the more knowledgeable guru types will chime in and provide more info.

Good luck.
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Old 11-06-2004, 08:50 AM
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Default Re: Dumb question: Merc 496 Mag vs. Chevy 3500HD 496 HO truck motor????

Thanks everyone for your help... here is a write up that I found on the Chevy 496:

The big Vortec 8100 V8 delivers 455 pounds-feet of peak torque at 3200 rpm. Torque is that force that propels the truck off the line and this 8.1-liter, 496 cubic-inch V8 has gobs of it. It generates 400 lbs.-ft. at just 1600 rpm. Introduced last year, this 8.1-liter V8 replaces GM's 7.4-liter V8. It has advanced features such as an engine oil life monitor and a limp-home mode.

Bore + Stroke = Identical 108 x 111
Compression ratio = Identical: 9.1:1

I did find that the chevy uses a forged crank which is pretty strong and I take it that the marine crack is not forged??

If you think about it... the chevy truck is built to pull 12,000lbs... + it's own weight, so I would think that a twin engine marine set up would work fine. (Twin engines pushing a 6800lb boat = 3400lbs per engine)

I am still up in the air on this one... anymore help is appreciated.

Q
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Old 11-06-2004, 09:39 AM
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Default Re: Dumb question: Merc 496 Mag vs. Chevy 3500HD 496 HO truck motor????

3400 lbs. on the water is a lot different than on wheels. What kind of boat? Just curious.
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Old 11-06-2004, 11:07 AM
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Default Re: Dumb question: Merc 496 Mag vs. Chevy 3500HD 496 HO truck motor????

Originally Posted by Kidnova
3400 lbs. on the water is a lot different than on wheels. What kind of boat? Just curious.

I have a 1987 donzi Z-33 It is at the gell coat man right now... chaning the color of the boat from TEAL to mostly white hull with Yellow/black stripes.

I have about 5 months to come up with an engine solution.... trying not to hurt the old pocket book if I can help it...
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Old 11-06-2004, 12:38 PM
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Default Re: Dumb question: Merc 496 Mag vs. Chevy 3500HD 496 HO truck motor????

Sounds like a cool project.

There are several guru's on the site that will be able to provide good feed back on your question. I'm not much of an engine guy so not much help to you. But my guess is, if the tolerances on the truck 496's are ok, and the torque and hp is enough for you, and the engines have good internals, then they would probably work out ok, for normal use.

Another option might be locating a pair of BB pull outs with low hours. Why 496's. 502's would be a good and or possibly better choice. Tons of parts available for upgrades down the road. Plus 502's have stood the test of time.

Last edited by Kidnova; 11-06-2004 at 12:42 PM.
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Old 11-06-2004, 12:44 PM
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Default Re: Dumb question: Merc 496 Mag vs. Chevy 3500HD 496 HO truck motor????

You would be better off to buy some late model, low hour take outs. Brackets, hang-ons and exhausts are expensive to buy one at a time. With the 496 engines there are not a lot of aftermarket items available yet. Some of the rigging shops on line will have access to these engines when upgrading customers boats to bigger power. Work the e-mail to them. You should be looking for some 502 Mags, as the are a good starting point for latter mods. Looking at your screen name are you in the hydraulic business?
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Old 11-06-2004, 01:02 PM
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Wink Re: Dumb question: Merc 496 Mag vs. Chevy 3500HD 496 HO truck motor????

TeamPSI:

the engines are the same except for a few minor things. First one is that you would need the marine ECM, MEFI or similar. Second the marine 496 uses a 8 qt. long deep pan, the truck pan is too deep and small for boat use. The water crossover is diffent as well as the thermostat. The injectors would have to be changed to the marine injector ( larger output). The marine duty fuel injector which is 35% bigger than the truck injector. As for crankshafts, some of the early 2001 and 2002 496's came with a forged crank that GM changed over to a newer cast unit in late 2002 that is supposedly is as strong as the forged unit. My advise, don't take any of these cranks above 575HP in a 496, our tests support this finding! If you simply wan't more power from any 496 call us or visit our website. You can bolt on our parts and with truck 496's you will have more power than stock Merc 496's. We also have a some forged cranks, crossovers,marine pans, etc. You can easily set up some nice 525HP 496's for any boat without denting your wallet.

Good Luck
Ray @ Raylar
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Old 11-06-2004, 04:09 PM
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Default Re: Dumb question: Merc 496 Mag vs. Chevy 3500HD 496 HO truck motor????

hey kid nova is that fresh or salt water you boat in?
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