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De-stroke a 400 to a 377 for a boat?


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BRAAP. PPARASKA, & Grumpyvette; Thanks for the good feedback – that’s the type of discussion I was looking for. Based on what you’ve seen in the past, here are a couple questions you might be able to help me answer:

1)Is cylinder wall flex with a 400 block a real or imagined problem under sustained high loads? I’ve got no experience to know if this is more rumor (like the over-heating rap the 400 gets labeled with), or a valid concern?

2)If cylinder wall flex IS an issue, is it mainly the result of piston side loads against the cylinder wall, or is it the result of extended operation under high cylinder pressure conditions?

Thoughts? Thanks again.

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The rod/stroke ratio of the engine, in my opinion (based on reading things from Vizard, and many other tech writers) is only an issue at the extremes. The difference in rod/stroke ratio has been seen worthy by many writers only as it pertains to what you are looking at - reliability in terms of piston side loading. I've seen articles where "experts" think that once you get to 1.6:1 or below rod/stroke ratio, then you need to be concerned about the side loading issue. Here's one example: http://www.musclemustangfastfords.co...ld/piston.html

 

However, other net-wisdom is pointing to a 1.7:1 ish or above ratio as

"good" for piston side loading, etc.:

http://www.victorylibrary.com/mopar/rod-tech-c.htm

 

The stock 400 had 5.56" rods, 3.75" stroke - that's a 1.48:1 rod/stroke ratio. This has been deemed as "not good" by many, as a "too short rod" setup.

 

And "The 350 Chevy should have built" has a 6.209" rod, 3.25" stoke has a 1.91:1 ratio.

 

From what I've seen, the kind of power and torque you are talking about will be a bit of a stretch for a 377. You'll need to have optimum everything to get it out of the 377 in my opinion. It's going to be easier to do with the 400. Just another reason I'd not worry so much bout the slight difference in the rod/stroke ratio difference between the 1 or so degree difference in rod angle between a 377 and 400 with 6" rods.

 

Thanks for the detailed response – I’d previously read those (or very similar) articles on rod:stroke ratio. The majority of the published builds I’ve seen to date for the 406 have used the 5.7” rods (rod:stroke ratio of 1.52), while most of the 377 builds have used 6” rods (giving a rod:stroke ratio of 1.72), so the difference between those two (which equates to about 2 ½ degrees difference in rod angle) were the numbers I was playing with. A more accurate comparison is probably one assuming a 6” rod for the 406 and a 6.125” rod for the 377 (gives a pretty comparable piston compression height for each) yielding rod:stroke ratios of 1.6 and 1.76, respectively. Probably a moot point since the general consensus seems to be that the effect on engine durability is nil when comparing the 406 to the 377. (As an aside, the article “The 350 Chevy should have built” was one of the big things that made me take a second look at the 377. Once I saw that the 352 in the article made 440 ft-lbs with a very broad torque curve, it made me think that 475 ft-lbs (my min torque goal) was probably attainable with the same block in a 377 configuration.)

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if your concerned about cylinder wall flex in any sbc Id strongly suggest an aftermarket BLOCK which has FAR thicker cylinder walls, webs and decks and bolt anchor points and a much stronger main cap support than any stock block has for any sbc factory production block, in any displacement and larger coolant passages, but unless your boring the cylinders over .030 over bore I don,t think its a valid concern, and you can always short fill the block jacket up to the lower freeze plugs to add about an inch or two more cylinder wall support.

with very little if any effect on cooling

 

BTW theres TWO comon types of block filler

one MOROSO sells is basically CONCRETE

theres also an EPOXY/METALIC SLURRY product available (can,t remember the name at the moment but its much better and anti freeze has zero effect on it once it hardens)

 

http://www.alvinproducts.com/Products/Products.asp?id=1

 

http://www.whitecapdirect.com/products/220885

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maverick2

I've been reading this thread without comment since I know absolutely nothing about boats, but I thought I'd lob a completely different option at you to see if its been done before. You stated that you want high torque at relatively low to mid-range RPM with high reliability and low weight.

 

It may sound off the wall, but have you considered a 472-500 CID Cadillac engine of 1968-73 vintage. They make gobs of torque (400-600 Lbft), weigh only 50 lb. more than a SBC due to thin wall block castings made possible by high nickel content iron, and no core shift diue to better tooling. And the more cubes you have to play with, the easier it is to make that much power, so reliability goes way up. Those engines were made to run 200k miles and the torque curve is as flat as a table from just above idle to about 4800 RPM. Add aluminum heads from Bulldog, and an Edelbrock 2115 alunimum intake, and the weight is about the same as an iron headed SBC. The completely stock 1970 10:1 compression 500 CID engine will make 500 lbft. at 4000 RPM all day without breathing hard. They have a 10.815" deck height (taller than a Merlin BBC) and long rods so the rod angle is very low compared to anything else out there. Offset grind the crank .300" for 2.5" journal BBC 6.8 " rods, add some forged or hypereutectic pistons with a 1.511" pin height, and an lightweight flywheel and harmonic balancer you can shave over 800 grams per cylinder out of the reciprocating weight while increasing displacement ot 540 CID without an overbore. That nets you a torque monster that revs quickly like a SBC rather than slowly like a Caddy land-yacht cruiser to about 600 lbft. It has the GM BPO bell housing bolt pattern to I'm sure adapters are available to bolt up your impeller drive. MTS in Delevan, Wisconsin makes one, and there are at least a few others. Check out MTS, The Cad Company, and Potter Automotive web sites if your interested.

 

I know it's not a 377 CID SBC, but it seems to meet a lot of the criterion you've been shooting for, and you have to admit that it's different. If not, then I'd go with the 406 for similar reasons.

Steve

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It may sound off the wall, but have you considered a 472-500 CID Cadillac engine of 1968-73 vintage. They make gobs of torque (400-600 Lbft), weigh only 50 lb. more than a SBC due to thin wall block castings made possible by high nickel content iron, and no core shift diue to better tooling. And the more cubes you have to play with, the easier it is to make that much power, so reliability goes way up. Those engines were made to run 200k miles and the torque curve is as flat as a table from just above idle to about 4800 RPM. Add aluminum heads from Bulldog, and an Edelbrock 2115 alunimum intake, and the weight is about the same as an iron headed SBC. The completely stock 1970 10:1 compression 500 CID engine will make 500 lbft. at 4000 RPM all day without breathing hard. They have a 10.815" deck height (taller than a Merlin BBC) and long rods so the rod angle is very low compared to anything else out there. Offset grind the crank .300" for 2.5" journal BBC 6.8 " rods, add some forged or hypereutectic pistons with a 1.511" pin height, and an lightweight flywheel and harmonic balancer you can shave over 800 grams per cylinder out of the reciprocating weight while increasing displacement ot 540 CID without an overbore. That nets you a torque monster that revs quickly like a SBC rather than slowly like a Caddy land-yacht cruiser to about 600 lbft. It has the GM BPO bell housing bolt pattern to I'm sure adapters are available to bolt up your impeller drive. MTS in Delevan, Wisconsin makes one, and there are at least a few others. Check out MTS, The Cad Company, and Potter Automotive web sites if your interested.

 

Thanks for the different idea. Actually ran across a thread on a jet boat forum from a builder that specializes in builds with those blocks -- their performance characteristics looked great for this application, but if I remember correctly, he was struggling to find an outlet for the various "bolt-ons" it takes to "marinize" an engine for safe use in a boat. It seems like there are multiple options available for any Chev block and a lot of Ford blocks, but it's pretty limited beyond that? Will track that thread down and see where it takes me. Thanks!

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It was mentioned before, this is a "jet" boat, and at any given rpm you will only be able to pump just so much water. It wouldn't matter if you ran a blown 572 at any given rpm it will only pump the same amount of water. It might get there quicker but it really use a lot of fuel. So build as much cid and you can get for the torqe(406). Given this is a marine application, and cool water is readily available, I would probably fill the water jackets to just below the water pump ports on each side. This would eliminate core shift in the cylinder walls. I would also look for a 2 bolt main block and have it machined for 4 bolt billet main caps. I never had much luck with the stock 4 bolt main blocks. I also would throw the little short stock rods away or weld them all together to make a nice little anchor. Use at least 5.7's or 6 inch rods. This will lessen side pressure on the pistons and walls. Some say a longer rod will make more hp at higher rpms. I'm still in debate on that, but the advantages of longer rods will out weigh any thought you may have on short stock rods.

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