However big you can make a small block, you can always make a big block way bigger using similar after market blocks. Plus, the big problem is not simply the size with the small block, it is more the fact that big block heads flow so much more air. I think the highest flowing small block heads are the Dart little Chief heads or SB 2.2 at around 450cfm (or around 330 cfm for a SBC conventional head and a stock oval port BBC head flows that with a little porting and big valves). A conventional after market ported big block head is capable of flowing almost that. If you get into exotic BBC heads, you are looking at ~600 cfm. For what it would cost to build a little chief headed 550cid motor, you could probably build a 600+ cid big block with big chief heads and probably make another 100-200 hp. Along with being more powerful the big block would most likely also be stronger due to the shear size difference of the parts.
Here is what you can expect between with a conventional Headed big block and a conventional small block in a racing application:
Big block:
http://www.shafiroff.com/sportsman/582_965.asp
Small block:
http://www.shafiroff.com/sportsman/434_685.asp
Here is a big chief combo:
http://www.eatonenterprises.com/632b...inepackage.htm
Here is what is capable with a big block and a dart big M block and pro stock heads.
http://www.sonnysracingengines.com/p...632-1320hp.htm
Or if you want to really go all out, this
http://www.sonnysracingengines.com/p...es/811hemi.htm
Sure, you are talking $75,000 but you simply cannot make this power with an N/A small block regardless of the money.
The most I have heard out of an N/A small block in any configuration is ~1100 hp
Here is a good comparison between the best of both that the small block and big block worlds have to offer as far as heads go.
Little chief heads
http://www.mbellc.com/files/Flow%20%20Lit%20Chief.pdf
Pro stock heads
http://www.sonnysracingengines.com/p...al5inDrag.html
Adam