would it be good to make the 400 a four bolt if building for 450hp.  I have a scat balanced  crank kit.  

I've always heard the 400 two bolts are stronger than the four bolts.  I'm running a four bolt and figure to be making close to 500 at the flywheel  

I've heard the same thing about the 2-bolt 400s as well.

Brian

Short story, long:

I had a two bolt 400 in my Chevelle for several years. It was approximated at 500hp.   I raced it more than I street drove it, shifting it at 6500, going through the lights at about 6200. The rotating assembly was balanced, stock crank, eagle rods, trw forged pistons.

When I pulled the oil pan (due to a broken oil pump pick-up) and main caps after about two years of racing, I did detect signs of cap walk. There were marks in the metal where the main caps touch the block that were not there before  ( it was line bored/ honed, which is a process similar to resizing rods). I don't know if "cap walk" is a real term or one I made up, but as I see it, cap walk is the microscopic movement of the main caps during the stress and vibrations of extreme use.

I never had engine failure, even having used stock main bolts.

so, in short; 450hp with a 2 bolt ... sure, just don't try to nascar it at 6500rpm's for 500 miles.

2 bolt blocks are stronger and better candidates for installing splayed caps if you have the means/ funds.  Splayed caps installed on a 2 bolt block are far superior and stronger than "just" 2 bolt caps... and superior to stock 4 bolt blocks/ caps.

Was this a cast crank  

Yes. I've spoken to people who work in machine shops who claim to have turned a stock-cranked 400 7200 rpm's.

Yes, a forged crank will be safer and last longer.

The current motor in the chevelle is another 406. This one, I bought as a completed short block. It has 6" eagle rods, light weight dome pistons, low tension rings, (edit) factory four bolt mains (/edit) ... and a freaking stock cast crank.  It is balanced, but I was hoping for the crank to be a forged unit when I bought the short block, but it was still a good deal. I have raced this motor twice now... made about ten passes on it, and shift it at 7200. (it accidentally hit 7600 in the burnout a few times, because my rev-limiter chip was faulty, so removed).

Will this motor live as long as an identicle one, except for a high dollar crank? probably not.  Time will tell how long it lives, but it has survived so far.

I've been running a cast cranked 408 for 2 summers, runs 11.95 @ 113,  I race the crap out of this thing, but I don't get anywhere near 7 grand.  It runs the best times when shifted at 5800.  I started out shifting high and could only get 12.20's out of it, when I couldn't get any more out of it with timing/jetting I started messing with shift points and whammy 2 tenths. 

I want to start spraying it, but I think i'll get a good chunk of steel in there before i do.  I've seen a few cast cranks break when you start hitting mid to low 11s.

My most recent outing was the Super Chevy in Gainesville this past October, it went 10.97 @ 119.5, weighing about 3400lbs going down the track with a TH400 w/ a 5200 stall 8" convertor,  4.30 gears, and 10x29 goodyears.

It should go faster than that, according to a few knowlegeable people.  Traction problems aside, it seems the convertor was built wrong for the car.  After I get ladder bars (and have them installed) I may try a different convertor... or at least give the good folks at Coan a call and see what they have to say.

Use good studs on the mains and I wouldn't worry at all.I run a 496 with 700hp on 2 bolt stock caps and ARP studs.Hundreds of runs shifting at 6800+,no problems at all.