Chevy Small Block 400 - Any Good for Boat?

[Martin Leaney]

I have a line on a 1981 400 SBC to replace my 1985 305 Mercruiser. <br />Will it work? <br />Are these a good engine for a boat (Chris Craft 26')?

 

[texomatom]

Re: Chevy Small Block 400 - Any Good for Boat?

IIRC the 400 is externally balanced with the harmonic balancer and flywheel? If this is the case I don't think the swap can be done without having the engine internally balanced.<br /><br />Tom

 

[kenimpzoom]

Re: Chevy Small Block 400 - Any Good for Boat?

Also remember the bores are siamesed. That is, there is no cooling water between the bores. Steam holes are required.<br /><br />This works fine on a car, dont know about a boat.<br /><br /><br />Ken

 

[bomar76]

Re: Chevy Small Block 400 - Any Good for Boat?

Poor choice for a marine engine.<br />As stated above, siamese bores - which in addition to needing steam holes drilled deck,head gasket, and in the heads - has other problems. There isn't much space between cylinders for the head gasket, so head gasket failures can be a PITA.<br />Also 400's were all 2 piece main seal engines.<br /><br />Not to say that all siamese blocks are bad - some racing engines use these as it adds stability to the block. It just isn't a good thing in the 400.

 

[Martin Leaney]

Re: Chevy Small Block 400 - Any Good for Boat?

Thanks all...<br /><br />One more question though - can anyone tell me EXACTLY what the diff is between an 'auto' engine & a 'marine' one. I have been getting various opinions as i shop for a rebuilt engine.<br /><br />CM

 

[kenimpzoom]

Re: Chevy Small Block 400 - Any Good for Boat?

Do you mean the short block or the entire engine?<br /><br />The short block difference is the freeze plugs. Others will say you need to swap to a marine cam. I have heard some say the pistons are different, but I dont know why.<br /><br />As for the entire engine, all the accessories are different. Have to use all marine accessories, ignition, and starter. Probably a few more things I forgot.<br /><br />Easiest solution is to use an automotive short block, change the freeze plugs to brass. Swap out to marine cam. Then take everything else off your old engine and put it on the new.<br /><br />Ken<br /><br />Ken

 

[Dunaruna]

Re: Chevy Small Block 400 - Any Good for Boat?

Marine cam so that torque kicks in at lower RPM, not essential but recommended. Other internal parts associated with temp flutuations & condensation associated with boat motors, especially with raw water cooling.<br /><br />Aldo

 

[Bondo]

Re: Chevy Small Block 400 - Any Good for Boat?

A lot of Good Rumors here.........<br />A 400 SBC will run Excellent in a boat......<br />What better to Cool a siamese block than with Gallons of relatively Cold Water.........A Whole Lake Full......<br />For reasons stated, You'll need to use the 400's own Flywheel,+ Balancer......<br /><br />A Properly Set-up 400cid will do a Super Job in a Boat.......<br />It's Truely a Torque Monster.......

 

[anesthes]

Re: Chevy Small Block 400 - Any Good for Boat?

The 400 is a great block. Many a racer have been very successful with the 400 block. <br /><br />The steam hole thing is easy. Get a 400 gasket as a template.<br /><br />-- Joe

 

[Martin Leaney]

Re: Chevy Small Block 400 - Any Good for Boat?

Great - a lot of good info - I will be getting an engine today so I'm glad to have some knowledge before I make the final decision!<br /><br />Thanks

 

[kenimpzoom]

Re: Chevy Small Block 400 - Any Good for Boat?

Originally posted by kenimpzoom:<br /> Also remember the bores are siamesed. That is, there is no cooling water between the bores. Steam holes are required.<br /><br />This works fine on a car, dont know about a boat.<br /><br /><br />Ken

I had a 400 SBC as my last race engine. It ran great.<br /><br />Some I have talked to expressed concern that the 400 has less tolerance to overheating because of the siamesed bores.<br /><br />My engine builder said otherwise, so I went with the 400.<br /><br />I wasnt sure how the experts felt about the 400 SBC in a boat so I left my previous evaluation open for discussion.<br /><br />Its just that I have never heard of a 400 SBC on a boat. I thought there might have been some reason, but the experts cleared it up.<br /><br />I agree, for the power to weight ratio, nothing beats a 400 SBC.<br /><br />Ken

 

[f_inscreenname]

Re: Chevy Small Block 400 - Any Good for Boat?

Trust me if mine was a Chevy s/b it would be the 400ci. You have to love that longer stroke. Thats why I have a 360ci Mopar and not a 318ci that came with the boat I have now and my last boat went from a 302ci to a 351W.

 

[Rainmaker]

Re: Chevy Small Block 400 - Any Good for Boat?

Due to the siamezed bores in the 400 block you should not bore the block more than .030" oversize. The metal between the cylinders gets pretty thin, giving you less margin should the engine overheat.<br /><br />If you are afraid of using the 400 block, get a 350 block and use the crank from the 400 in it (use the 350 rods). You end up with a 383 ci torque monster. There are plenty of aftermarket parts for this combination.

 

[anesthes]

Re: Chevy Small Block 400 - Any Good for Boat?

You need to machine the block before using a 400 crank. And its actually better to use 6" rods instead of the 5.7" rods.<br /><br />Even boring a 350 more than .030" isn't the best idea. I know a lot of recon places do it but I wouldn't. I had an absolutely perfect block .030 over, except one cyl that needed to go to 0.40 because of some piston slap. Junked the whole block rather than boring it to .040.<br /><br />-- Joe

 

[sculbert]

Re: Chevy Small Block 400 - Any Good for Boat?

I have 400 crank with a small spot on crank needs to be smoothed becuase of surface rust. Machine shop says it isn't a problem can take a little emery cloth to it or they can turn it down if I want. I was just going to use it as it is in my 350 but it just won't die. I have the standard pistons with 400 rods if your interested also. If you need to bore the block you will just have to use different pistons. Alluminum intake