http://www.gmhightechperformance.com/te ... otor_test/
Baseline on their dyno was 417hp, about 7hp more than expected after SAE correction.
They added long tube headers and not much happened.
http://www.gmhightechperformance.com/te ... to_07.html
Then they recalibrated the PCM and got some nice gains after 4800rpm. As much as 25hp on the top end (up to 442hp and 425lb-ft now). I don't quite understand this part, but overall I would have liked to see these results with the stock manifolds.
http://www.gmhightechperformance.com/te ... to_08.html
Next they modified the throttle body (an aftermarket shop performs these mods, and the diameter stays the same). This is worth another 11hp. Up to 453hp and 430lb-ft. That's 36hp and 29lb-ft over stock.
Dave Vizard has written quite a few books on modifying the SBC: http://www.amazon.com/s?ie=UTF8&field-a ... d%20Vizard