GM is no stranger to tossing around alphanumeric nomenclature for its performance machinery. A perfect example is the LS1. Not many Vette owners are aware of the fact that the LS1 designation was first applied to a 1969 335hp 427 big-block long before it appeared as an all-aluminum 346. Most Vette enthusiasts are, however, aware that the '92-'96 LT1 small-block was named after the high-revving LT-1 from the early '70s. Note that while the two are differentiated by the use of a hyphen for the original model, GM was obviously playing the nostalgia card. Monikers aside, the real question concerns just how well the later LT1 compared with the original item. Did it really live up to its legendary muscle-car namesake?
Time and technology obviously march on, but the performance world was a much different place in 1992 than it was back in 1970. After enjoying essentially free reign during the '60s, performance took a nosedive in the mid '70s, thanks to ever-tightening emissions regulations. To meet the new standards, Chevy first cut compression ratios, then cam timing and carburetion-basically, everything a motor needs to make power. What started out as a high-compression, solid-lifter 350 rated at 370 hp in 1970 was reduced to a low-compression, hydraulic-lifter 350 rated as low as 205 hp (the "performance" L82) by 1975. Some of the difference in perceived performance can be attributed to the adoption of net (SAE) power ratings by 1972. The net rating provided more-accurate power numbers based on the engine as it was run in the car, with full accessories and the factory tune. The previous gross rating came with the motor strapped to the dyno, sans accessories and run in optimized tune. Thus, the 370-gross-hp rating of the 1970 LT-1 would be in the neighborhood of 300 net hp, right on par with the modern LT1.
The differences between the LT two small-blocks are numerous and significant. The LT1 offered a sophisticated reverse-flow cooling system, modern electronic fuel injection, and aluminum heads, compared with the 780 Holley four-barrel and cast-iron Fuelie heads on the original. The newer heads also out-flowed the originals heads by 10-15 cfm, despite running smaller valve sizes (1.94/1.50 vs. 2.02/1.60). The LT-1 did offer a higher static compression ratio (11.0:1 vs. 10.4:1), forged pistons, and a solid cam with wilder timing (0.459/0.485-inch lift and 242/254-degree duration, compared with the 0.450/0.460-inch lift and 202/207-degree duration of the injected mill). Both cams shared the same 116-degree lobe separation angle, but the hydraulic roller profile of the newer unit offered reduced friction and likely increased ramp rates, which improved average power production despite the mild duration specs.
The dual-plane, high-rise intake manifold used on the original LT-1 has proven to be a powerful design, but the LT1's short-runner EFI intake is likely just as effective. It is, after all, partly responsible for taking the small-block 350 from 245 hp in L98 guise to a solid 300 hp. Compared back-to-back, the LT1 intake would lose out to the LT-1 unit in lower- and medium-rpm ranges, but it would likely make similar, if not slightly more, peak power. The runner length in the LT1 is quite short and tuned for maximum effectiveness at higher engine speeds, this despite a relatively small cross-sectional area. In terms of driveability, fuel mileage, and reduced emissions, the modern LT1 has it all over the original.
Engine specs are all well and good, but the word "specs" sounds too much like speculation. To truly compare the '70 LT-1 to the '96 LT1, we had to run them against one another on the engine dyno. Obtaining a low-mileage LT1 was no problem, as our boys at Westech had several (of various years) just begging to be dyno tested. Testing the vintage LT-1 was another story, as this meant building one using factory specs. The boys from L&R Automotive and Demon Engines came to the rescue, as did a number other suppliers.