im plannin a 400 build. i'd like 500hp out of the setup. so i need a bottom end that can put up with it. i can get any of the three main 400 castings. i want a siamese 2-bolt block... right? i just dont kow which casting number is the good one. also, i hear that some 400's came with stock forged cranks. is this true? and if so, which ones?

 

A 2 bolt block is preferred for the 400's. You can always install main studs to make it stronger. All 400 blocks are siamese cylinders.

All factory 400 cranks are cast.

There are a few castings available. The 509 casting is probably the most common. If you don't already have one, good luck trying to find one that isn't damaged or worn out. The last factory 400 block was made in 1980. Even then, the casting is thin and can barely support a .030" overbore. Most of the production 400's have been made into and broken as race engines so they're getting very hard to find.

For high HP applications, you're going to want an aftermarket crank and block although many people have made factory parts survive for a while.

 

thanks for the info. i've already got a line on an original 509 block that was just pulled from it's original vehicle still running. so that shouldnt be a problem. what about the 511 castings? what's different about them?

 

Very little. One of those casting may only have 2 frost plugs on the side of it which makes it difficult to determine if it's a 400 block just by glancing at the block. Out of all the production 400 blocks, there isn't really one casting that's better than another although as previously mentioned, the 2 bolt casting is more preferred.

 

For all the machine work you will have to put into that block you might be better off looking into the new Dart SHP block.

 

so you're saying i should expect $2K in machine work?

 

You can find the Dart SHP block for a whole lot less than that. I think the list at Summit is around $1500 and with shopping less than that. Choices, choices and more choices.

 

Take it from a guy who has hauled many a 400 block to the crusher because it broke,if you've got your heart set on one,GO WITH AN AFTERMARKET BLOCK.I've had cylinder walls split,main webbing break,and line bore troubles out of the stock blocks.I never had a single crankshaft failure out of a stock cast 400 crank,I always ran a lightweight piston/rod combo,and sprayed 200 HP of nitrous many times.But everything has a limit,I was lucky in that respect.If I were to buy an aftermarket block,I'd buy a quality forged crank,and for little more money you can go with a 421 or 434.A new block is a huge cash outlay at once,but I could have bought a Dart block and a better rotating assembly for what I spent buying and machining stock blocks.If your looking at power levels below 400hp,I'd do a 383,they are cheaper,more durable,and you can put a bullet proof shortblock together that will withstand future upgrades for considerably less cash outlay,and the GM 350 blocks are much more durable than the 400 blocks are.Not trying to be a party pooper or spend money for you,just hoping to save you a bunch that I've already spent learning that lesson.

 

To follow up on what Irockz said here is a story from Joe Sherman. He had built up a vintage 400 motor using the factory block. On the dyno the motor was making around 600hp. Anyways after a couple of dyno pulls one of the cylinders cracked.

He had it resleeved and back on the dyno. Well after a couple of more dyno pulls another cylinder cracked. At that point he and the owner threw in the towel and went with an after market block. Well surprise, surprise on the first dyno pull the power was up to around 650hp just from changing the block. Those cylinder walls must have really been flexing and allowing pressure to slip by.

The Dart SHP block comes fully machined and the only thing left is the final bore and hone. Comes in two sizes. One with a nominal 4" bore and the other with a 4.125" bore. You would want the latter.

 

Not to beat a dead horse,but I had block failures one after another,just like this.The last block chose to split between an oil galley and a water jacket,milky oil anybody?I've been told that you can sleeve all 8 cylinders and add a main girdle and get durability,but by then you've paid for a new block,and neither one of the machinasts I use will sleeve a 400 block,because those are prone to fail as well.

$1500-$2000 is looking cheaper and cheaper,now.

 

I wish I had gone with an aftermarket block. It is on the list for the next motor...

 

I don't know enough about the Dart SBC blocks but my Big M block has fantastic castings. The bare block was also $3000. The cylinder walls on the Big M are thick. I can have my blocked bored out .125" over and still have 1/4" thick (.250") cylinder walls.

On a factory 400 block, a .040" overbore is really pushing it. A .060" overbore will probably hit a water jacket so you can get an idea on how thin the casting is.

When racers used the factory 400 block, they commonly had the water jackets in the block filled. This stabilized the weak cylinders and there was no coolant going around the cylinders. The coolant just flowed through the heads. The block filler is similar to cement so it also made the blocks very heavy.

 

I had asked Kevin McClelland (of Chevy High Performance ) his opinion of stock 400 blocks after my machine shop said they wouldn't work on them anymore because of cylinder walls cracking. It seems that the cylinder bolt holes are so close to the bore that even during torque plate honing or bolting on cylinder heads, the bolt holes will split and ruin the block.
His advice ( the letter was printed in CHP ) was to purchase an aftermarket block. After all the prep for an OEM block ( sonic checking, boring, align bore, decking, etc) you've approached two thirds the cost of an aftermarket block. It was convincing enough for me to sell my original 400 and build a 350 instead.