Although the one that started it all is already considered relatively old, no one could have predicted the impact the original Gen III LS1 would have on the hot rodding public. The LS1's greatest asset is its revolutionary 15-degree cylinder heads, which are capable of flowing over 320 cfm in the hands of a skilled porter. So good were these castings, in fact, that it took the aftermarket over five years to even attempt to top the factory design. Simply massaging the stock heads and swapping in a larger cam had LS1s easily approaching the 550hp mark in no time. Furthermore, bone stock LS1s routinely pushed F-bodies into the 12s. While LS1 F-bodies were rated at 40 hp less than their Corvette-spec brethren, they essentially produced the same power despite minute differences in cam specs. Likewise, all '01-04 LS1s were upgraded from the factory with the same valvesprings and high-flow intake manifold as found in the LS6. One of the biggest drawbacks of the LS1 are its thin iron cylinder liners that can only be bored about 0.010 over. Anything larger requires re-sleeving the block with aftermarket liners, which isn't cheap, but doing so enables displacement figures well in excess of 400 ci. Likewise, the standard 3.900-inch bore isn't compatible with the latest and greatest GM L92 cylinder heads. Nonetheless, the original LS1 provides more than enough power potential for the vast majority of hot rods, and there are still a ton of them available in salvage yards ready for plucking.
The first of the Gen IV small-blocks, the 400hp LS2 was first unveiled in the '05 Corvette. Compared to its LS1 and LS6 forbears, it boasted a larger 4.000-inch bore while retaining a 3.622-inch stroke, which bumped displacement to an even 6.0 liters. At its core, the LS2 resembles an enlarged LS6. It utilizes LS6 cylinder heads, as well as an '01-spec LS6 camshaft. Subtle differences include a larger 90mm throttle body (75mm on LS1/LS6), a higher 10.9:1 compression ratio, and a different intake manifold. Interestingly, the LS2 intake manifold features slightly greater plenum volume and recontoured runners, which actually flows less than the LS6 intake. For hot rodders, one of the key advantages the LS2 has over its smaller-bore counterparts is that it's compatible with the highly desirable rectangle-port L92 cylinder heads.