Stock for stock their about the same. In a bolt on match the LS1 would win due to those magic flowing heads.

 

In stock Form the heads actually flow on par with each other, in fact I think the Lt4 betters it at .500-.550 and they both see around 245 CFM at .600 lift.

In a bolt on race it would still be close, but the Ls1's have better intakes to choose from, but I would slap on a LPE Super ram on a Bolt-on LT1 with some 1.7RR's and I think a Full Bolt-on LT4 would Run exaclty like a Full Bolt-on LS1

 

I've raced and modded my LT4 for around seven years...in stock form they run almost identical on the street, track, and dyno. I remember racing a local guy back in '99...we raced about a half dozen times (street & track) and were literally side-by-side through every gear, every race. With bolt-ons they also respond the same. The one advantage (which usually accounted for my kills) is that production LT4 Corvettes are usually lighter than LS1 cars, and the production LT4 cars are only M6. IMO, a M6 LT4 Corvette will almost always (should) kill a heaver A4 F-body on the street. The downside is with cam (and head) mods the LS1s really come alive and kill the LT4.