which 400sbc is better the 2bolt or 4bolt(with or without steam holes). A engin shop told me i wouldnt get that much more power with the 400sbc compared to the 350sbc.

 

The engine shop was lying. I think they have a 350 laying around that the customer didn't pay for, that they would love to trade you even for your 400 block and put the 400 in their dirt-track car.

If you supply the flow capability (very big IF!!!) a 400 will make approximately 400/350 as much power as a 350, or about 14%. That's significant in my book.

All 400 blocks have steam holes.

The 2-bolt block is a stronger casting. The first couple of years of 400 production they made the 4-bolt ones, then switched to the 2-bolt in 73. In their stock configuration (8.5:1 2-barrel) the extra 2 main bolts were basically useless added weight. They did however add some more metal in the webbing area around the main journals. The strongest configuration therefore is a later 2-bolt block with aftermarket 4-bolt splayed caps installed in it.

However, this does not mean that you should run right out and do that. My 400 has the stock 2-bolt caps, cast crank, stock 5.56 rods, and puts Mustangs to mortal shame on the street. Unless you're building a really brutal motor (which if you're asking this question, I would tend to doubt) it's a matter of mostly theoretical concern to you. I'd estimate that until you get past 500 HP, or 6000 RPM on a regular basis, you won't need anything more than the stock bottom end; your money would be better spent on induction components like heads.

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"So many Mustangs, so little time..."
ICON Motorsports

 

Thanks , will the access. switch over from the 305.(alt,starter,ac,etc.)