What would be the benifits from building a sbc 400
bored .30 over and stuffed with a 3.875 crank and 6.0" rods? Would I loose lots of low-end torque by going with a stroker? Im looking at one for a resonable price.What machining would be required?Can't decide if i want to use this or the stock crank. What are the pros/cons of running this?

Thanks,
bobo

Quite the contrary, more cubes, and longer stroke = more low end tire fryin torque!! Basically the downside is cost. You'll need all of the normal machine work, in addition to some possible clearancing, custom pistons depending upon your target CR, a good balance job, ect.... I know I'm missing something, what is it guys?
Best of luck with your beast!

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Can a factory 400 swallow a 3.875" crank that easily?

How much grinding is needed to clearence everything?

When I built my 408 I had to grind the block just to clear the 5.7 Eagle H beam rods. I hate to think about what it would take for a longer crank.

I'm sure it is possible and has been done.

Bobo,
I have built one of these---------it's in my jet boat. EXCELLENT motor! I built mine the the budget way, based on articles that I had read years ago in performance magazines such as HOTROD.
Here is how its done.
Bore it your choice-----------.020, .030, .040, whatever. Offset grind the rod journals of the crank down to the early small journal size (2in vs 2.1in of the SB400). If you want to gain even more stroke, then offset grind the journals an additional .020 or .030 and use .020/.030 undersize rod bearings. This will give you between 218 and 224 cubic inches. I went with a set of early 327 rods (which are 5.7in), resized with ARP Wavloc bolts (supposedly about the strongest). The typical clearancing of the bolt heads for the cam was done, plus, the lower end of the block had to be slightly clearanced for only 3 rod nuts to clear. Everything else gets built just as would be done to suit your needs for a SB400. This is the poor boy's way of building a 420SB. There are aftermarket cranks available with a 3.875-4.0 stroke for the SB400. Heads? Again, your choice. I will say this about heads, 400+ healthy cubic inches needs to breathe. So, a set of aftermarket big valve/big port heads are going to allow it to work to its potential. Its only money!!!

KEEP THIS ONE THOUGHT IN MIND AT ALL TIMES!!!
When investing in a killer SB400, you can put more money into it, REAL QUICK, than what a very nice 454 would cost! A VERY nicely built SB400 can very easily be built for LESS than $100 more than what it would cost to do the same thing to a 350, and virtually the same price to build a 383. If you are REAL good at parts shopping, maybe even $50 less. ALLLLLLLLLLLLL the machine work will be the same for a 350-383-400, with the exception of additional crank grinding. I find it very difficult to justify spending an additional $1000-2000 (above a regular rebuild) on a SB400 when that amount (or maybe less) could be invested in building a 454-------------that will devour a SB400.
Yes, there are 4 SB400s in my family. They're very healthy, but also built on a budget. Just one example, when buying a cam (this is for a street/performance motor, not a thoroughbred race motor), I buy a "house" brand cam, such as from Summit. Their in-house cams are all the same price, with a large range to choose from. So, whether it is a stock profile cam or a thumper, same price. Also, some applications are not practical for installing a BB, thus a SB is the obvious answer. My 56 Vette was not designed to accept a BB, so it has a very healthy SB400. It is literally a drop-in bolt-in fit. Same situation with ChevyIIs. But Chevelles, Camaros, Impalas, trucks, they're designed for a BB.
So, be careful about how you spend your money on a SB400. Yep, a BB is heavier, but it doesn't take much for a BB to overcome that added weight handicap!