DragStuff

i hear that there is a problem with the 4-bolt 400 SBC what is it? thanks.

The GM 4-bolt 400 blocks are weaker than the 2-bolt blocks because of there being less "meat" for the main cap bolts to thread into.

Well, from what I've heard, one of the problems with them is the main webs. They have been known to crack. A lot of guys will get a 2 bolt block at fit 4-bolt caps to it.

CoMax Racing wrote:Well, from what I've heard, one of the problems with them is the main webs. They have been known to crack. A lot of guys will get a 2 bolt block at fit 4-bolt caps to it.

I heard the samething

Im getting ready to build a 2 bolt 400 Im probably gonna stud it or just use some good ARP bolts but Im only looking to make about 500 HP Ive built one before so Im hoping it will work again. We built a 421 with a stock 4 bolt block and caps and made around 700 hp never had a lower end problem but it was N/A maybe a power adder would hurt it.

I had a 4bolt 400 in a street car making around 425hp it performed flawlessly as a daily driver, things might have been differant if it was a bracket car? Ive just always heard a factory 2bolt was stronger then a factory 4bolt

I can't remember the numbers but some castings have a lot better grade if iron than others.

speedracer119 wrote:i hear that there is a problem with the 4-bolt 400 SBC what is it? thanks.

The 509 casting block is the better of the castings, I would advise installing steel splayed four bolt caps and a steel two bolt front cap ( you would have pan clearance problems with a 4 bolt front cap), Also after line boring the block I recommend finish sizing the main bores with a line hone, The main bearing heat transfer is greater with the smoother finishbores. Hope this helps.

yep the 509 casting has more nickel than other castings. We run a 2 bolt 442 (and others) CI block with splayed caps, cemented with 800 hp for 3 seasons with no problems yet.

Like it has been said the 509 has more nickel. I have seen many 4-bolts with the the crank removed with some of the cap still torked and in place because the block broke. I would suggest not running it with nitrous or high compression seems when both are involved that is when we have seen the cylinders cracked or the mains broke.I know a guy a while back that thought he came on to the mother load while buying a machine shop out he got a bunch of untouched 400s and all had cracked cylinders.Just don't get all down if you have problems. We look at it as; if it last a season you did good. Just my 2 cents.Jason

We ran the 421 for 4 years without a rebuild, when we did just new rings, brgs, etc no big hard parts. I dont know which casting # it was .Its got about 3 more seasons on this rebuild but it really doesnt see a lot of street or track time.Its got stock caps and no hardblock.

which ever you get drill out the steam holes as large as you can, this will help cool the block and help stop cracking at the web.