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rush2112

  • Karma: +0/-0
454 big block
« on: February 09, 2011, 02:04:07 pm »
Hi,im new to this jet boat game..I would like some advice..Im looking for a gig block chev...I found some marine and some street......whats the deal...can i use a street motor without tearing it down replacing gaskets and some other things I was told...or just buy a used marine 4 my first motor to blow up......lol thanks   i run rivers and lakes on east coast no salt water..
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SLCKREG

  • Karma: +0/-0
Re: 454 big block
« Reply #1 on: February 09, 2011, 02:49:13 pm »
Others will probably expand or elaborate on this but basicaly a marine-ized bbc typically has looser tolerances than a street motor. If your just looking for something to drop in and run....a well used street motor may work fine.
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rush2112

  • Karma: +0/-0
Re: 454 big block
« Reply #2 on: February 09, 2011, 07:12:25 pm »
Thanks...
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SLCKREG

  • Karma: +0/-0
Re: 454 big block
« Reply #3 on: February 09, 2011, 07:33:22 pm »
Fwiw....you may want to elaborate a little. Are you talking about building a motor...and wondering what the differences are? Or wondering if you can drop a used street motor in your boat and get by with it?
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obnoxious001

  • Karma: +4/-1
Re: 454 big block
« Reply #4 on: February 09, 2011, 08:11:10 pm »
Hi,im new to this jet boat game..I would like some advice..Im looking for a gig block chev...I found some marine and some street......whats the deal...can i use a street motor without tearing it down replacing gaskets and some other things I was told...or just buy a used marine 4 my first motor to blow up......lol thanks   i run rivers and lakes on east coast no salt water..

As Kreg said the biggest difference is clearances.   I would normally use bearing clearances close to .003" on a big block, additional piston to wall clearance, since the block temperatures run cooler in a boat, and the pistons are usually going to be hotter from being run harder.  Since marine engines are typically run at double the RPM of a normal street engine (I run 80 MPH on the freeway at 2500 RPM), most engine builders would recommend forged pistons, rather than factory cast pistons.  Also, for the same reason, higher rpm range, you would normally run a larger duration camshaft.

One other big point would be to make sure to use a marine oil pan, partially due to rpm range, but also all the bouncing around a boat does, it's important to keep oil around the oil pump pickup.

You can drop a used street engine in the boat, but chances are it won't last real long, whereas a properly built and installed engine should last a long time.
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TrollerDave

  • Karma: +32/-0
Re: 454 big block
« Reply #5 on: February 09, 2011, 09:36:23 pm »
Is it just the main bearings and piston to wall would have to be different for a jet boat motor? anything else?

What ways would you change piston to wall clearance? different diameter pistons, boring the cylinder or does it have to do with the rings?

Thanks
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GT Jets

  • Karma: +192/-0
Re: 454 big block
« Reply #6 on: February 09, 2011, 10:19:24 pm »
Is it just the main bearings and piston to wall would have to be different for a jet boat motor? anything else?

What ways would you change piston to wall clearance? different diameter pistons, boring the cylinder or does it have to do with the rings?

Thanks

Over hone the cylinders larger than the pistons would be designed for.

You are trying to allow for a large temperature differential. An automotive engine will virtually never see a 110% engine load and 55*F water at the flows available on a jet boat.

The cooling water would be in a closer range of the cylinder wall and piston temp in the automotive deal...

GT
  • Boat #1: 1992 Carrera 20.5 Elite (I/O bitches)
  • Boat #2: 19' Bubble deck Jet BBC Berkeley
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If i get some free time tonight at work, ill play with it and post it for everyone to see.

Time to man up and yank it John!  :banghead:
Ray

obnoxious001

  • Karma: +4/-1
Re: 454 big block
« Reply #7 on: February 09, 2011, 10:33:50 pm »
Is it just the main bearings and piston to wall would have to be different for a jet boat motor? anything else?

What ways would you change piston to wall clearance? different diameter pistons, boring the cylinder or does it have to do with the rings?

Thanks


Both rod and main bearing clearance.  I did not mention ring gap, but that's true also, and will vary depending on the manufacture's specs and cylinder bore size.  For a typical recreational marine BBC I normally add .001"-.0015" to the bore size, which also should be determined by measuring pistons with a micrometer and then adding the manufacture's recommended cylinder to wall clearance, plus the extra for marine use. 

Note that if you were building a  forced induction engine, such as blower or turbo, you might even add a bit more. 
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rush2112

  • Karma: +0/-0
Re: 454 big block
« Reply #8 on: February 10, 2011, 04:10:32 am »
wow thanks for the info...I like this sight...This is my first jet boat..I have skies..I got boat without motor...just as time is limited at the current time .I was just looking to get the boat going 4 this season and when i get more educated on the build I will build a motor next season...I found a few gm 454 from boats like baja and some mercruiser 454 also...used but good...I think that would be my best bet...I have the oil pan from boat..also have headers...I found a gm marine 454 that i would just strip of all its junk.....thanks for the info and keep it comming...its 17 degrees here in pa but 78 in my garage lol
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