Just found this package for LS1s -- 400 RWHP with external Bolt-Ons:

http://www.speedengineeringanddyno.com/packages.htm

"400 rwhp LS1 X package (external bolt-ons)
The X package consists of a combination of components that work in harmony together with custom tuning to produce the absolute maximum power gains without the use of power adders and without heads and cam. It was first developed on an '01 Z06 Corvette in 2001. This car ran 11.44 @ 122 mph

http://www.speedengineeringanddyno.c...ackages-01.htm

when most cars with heads and cam weren't running that well. This was a daily driver with the stock gear and at full weight. The perfect combination of parts and precision tuning is the key to the X package and the X package is the key to getting the most power available from a Naturally Aspirated Stock long block. Some people like not changing heads and cam because it allows them to maintain the factory warranty. Some people just don't want the "race car" sound or give up the drivability that comes with a cam. Some people just want to have as much power as a lot of head/cam packages are providing so that when they do heads and cam they will be well ahead of the game. No matter what you want, the X package gives the absolute most power available from external bolt-ons. We can also modify this package to work on other LS1 Vehicles as well as LS6, LS2, LS3, LS4, LS7 and LS9, with each one making more power respectively. Check out the LS1 F-body X package
here - 400 RWHP - naturally aspirated - without heads/cam. The X packages are available only as in-house turnkey packages."

http://www.speedengineeringanddyno.com/records.htm