westman

Well my old man picked up a 400sbc the other day for $150! He wants to stroke it and make it either a 415 or 421. The question we've been asking is what is the maximum you can bore out a 400? I've heard .030 is max and I've heard .100 over. Anyone have a definite answer??

Apeiron

Most blocks can take a .030 overbore with no problems, but not all. There's almost no chance you could get .100 out of it.

The only way to get a definitive answer is to have the thickness of the cylinder walls sonically measured.

westman

Interesting, might have to check that out. I really don't forsee going .100 over, but curiosity was getting the better of me.

Irockz

iTrader: (1)

As a general rule,400s will go .030.Some will go .040,and a VERY select few can go .060,but I wouldn't trust it.
I've had a couple of engines built in the stock 509 casting 400 block,and IMHO,It's pretty easy to max out what the stock block can handle.
I personally would advise an aftermarket block for this venture.I've seen more than one 400 block crack in the main webbing from making big HP #s.
At the very least I would run splayed caps.

Trevor86TA

Is this a street car or a race car? Some guys fill the water jackets with block filler.

And in my opinion, the extra 6" you'd get from .060" vs. 030" is not worth the headaches it may cost.

westman

This is actually gonna be a blower motor. He's getting the 400 to 415 all forged race kit from Speedomotive and use a weiand 177 supercharger. Using I assume around 8lbs of boost. Which works out wonderful for me cause I get the 383 out of his truck to put in my camaro now that mine is @!#$%^&.

AlkyIROC

Buy an aftermarket block.

The 400 block, as mentioned above, can go to .030 and a few, if the cylinder walls are sonic checked, can go to .040. Very, very few factory 400 castings can go beyond that. The cylinder walls are just too thin.

The majority of the magazine articles about stroking a 400 to make a 416, 434 etc, all use aftermarket blocks.

westman

Wow, I don't think he'll be happy to hear that lol.

AlkyIROC

The 400 block was GM's attempt at getting the maximum displacement from the same external dimensions of the SBC block. With the limited bore spacing, the cylinder walls between each cylinder share the same chunk of metal (siamesed). This means there isn't a lot of metal between the cylinder walls. Aftermarket blocks have heavier castings.

Stroking a 400 poses other problems. A 400 is already a stroked SBC with a slightly larger bore than the typical 4" bore blocks to get the increased displacement. To stroke it even more requires some block modifications for the crank and rods to clear the bottom of the cylinder walls and the pan rail. Too much stroke and the rods can hit the camshaft also. Some aftermaket blocks offered a raised cam position and the bottom of the cylinder walls and pan rails are notched for the increased stroke.

There's nothing wrong with building a good 406 by boring the block out .030 but don't expect to do anything really exotic with a factory block. Once you start getting into making a "big" SBC, you need to buy more expensive parts. HP is in the heads and to feed a big engine, you need good aftermarket heads. Building a "small" BBC can make the same amount of power with nothing more than factory parts.

westman

I agree with that statement totally. I tried to talk him into build a BBC but he insisted on keeping a small block. But to each his own I guess. Anyways, thanks for all the help guys.