400 4bolt or 2bolt

[kanuck]

Not that I was looking for them, but I ended up with 2 400 SB engines.
The first is a 74-77 approx 2 bolt short block with standard bore in need of a rebuild ($50). The second is a 70-73 4 bolt short block also in standard bore ($100).
Looking at the valley of the 4 bolt block it has the heavier casting, as pointed out to me by an engine builder, of the high nickel early blocks. (Have a 1970 350 4 bolt from a heavy tow truck with the same casting).
Wondering which to build as a street motor and which to keep for a more street/strip. I was told in the 400 SB that the 2 bolt was stronger than the 4 bolt unlike in the 350 SB.

I ended up finding 2 sets of hyperutectic pistons at our last swap meet, both for .30 over 400 sbc. Both sets of pistons are flat top with the 4 valve reliefs, but one set uses stock 400 rods and the other uses the longer 5.7inch 350 rods and has the anti-friction coating on the skirts. Both sets of pistons are like new and have no more than 1000 miles on them.
Would like to use the ones with the 400 rods for the street motor and upgrade the other set to H beam 350 pistons for the street/strip.

So opinions on which block to use??

Thanks

[Marv D]

Flip the block over and take a look at the outer bolt holes on the 4bolt block. Now look at how the main webs are scalloped and where those outer bolts go. How's that for a Halloween scare! The 4bolt casting is prone to cracks in the main webs. In fact all 400's are real susceptible to main web cracking and cracks across the deck. Once the deck is surfaces you can see the spiderweb cracks radiating from the bolt holes over to the edge of the bores. It's a real common deal. Some leak, some don't. So no matter WHICH you choose to use, first step if to have it baked clean, then pressure checked, then magnafluxed for cracks.

The last thing you want to do is invest the $ to short fill, add splayed mains, align bore, cylinder bore, deck, dress this thing up like a 'real' serious block. The machine work will be just darn near as much as a new Dart SHP block. (go ahead,, ask me how I know that!!!!, Spent $1600 at the machine shop putting a dress on a 509 2bolt casting)

Oh,, the most favored is the 3951509 casting in 2bolt configuration from 74 through 80. the better metallurgy, thicker main webs, and is 2bolt only after 74. In 74 even GM realized the 4bolt issue and discontinued making ANY 400 as a 4bolt.

Second favored is the 3951511 casting in 2bolt configuration

Then the 509 or 511 casting in 4bolt configuration.

And finishing dead last and the least favored 400 casting ,, affectionately termed 'soft as butter' by more than a few reputable machinists is the 330817 casting.

These days a GM 400 casting is not nearly as desirable as they once were. Not with Dart releasing that SHP block in 4.125 bore configuration. It just doesn't make sense to invest in a high dollar rotating assembly and stuff it in a questionable block. But for a near stock build / driver motor.. what do you have to loose!

[kanuck]

I checked out the 2 blocks that I have. I see what you mean on the outside holes on the 4 bolt mains. You can see the bottom of the threads as it is not a blind hole as on the 350 block.

The 4 bolt block is a 3951511 block.

The 2 bolt block is a 330817 block.

Thanks for the info.

[Rodms]

I have seen them crack half into and also down the sides where the freeze plugs kinda run from front to back.

[Ticker]

2-bolt blocks are considered stronger due to the thin casting for the outer bolts on a 4-bolt stock cap as noted.

No 400 block is a good casting, but if you have $$$ have the 2-bolt block fitted with 4-bolt aftermarket steel caps - figure on $750+ to get it done. Generally not a good investment for a HP block.

[kanuck]

So if I want to use up what I have which as suggested then is the 2 bolt block, a stock cast crank, the .30 hyperutectic flat tops which use the longer 5.7 inch rods, a set of 63cc iron double bumps (since I have them and they will give some compression), and a single plane holley strip dominator and keep it in the 6500 rpm range, Will this get me anywhere as a motor for the track???
Will it last a while??

Thanks

[chevybuldr]

yea unless you want some real high compression I dont think you want to use those flat tops. You would get a static of about 11.5:1. Good if you want race gas but not so for the street. Just some things to keep in mind.

[kanuck]

OK, sounds like I'd be better off to use a larger CC head. I have a set of basic 1.94 truck heads at 96cc or up grade to a set of RHS aluminum 2.02 heads with 92CC and springs set up for a max lift of .5 lift that I ordered for another motor I have planned.