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.
Demon Engines supplied an 11.0:1-compression short-block consisting of a combination of a forged crank and rods from Pro Comp, along with a set of forged aluminum pistons from Probe Racing. These were used in conjunction with a set of 492 Fuelie heads featuring 64cc combustion chambers to produce the desired compression ratio. The 492 heads came from L&R Automotive and were treated to set of 2.02/1.60 valves from Pro Comp, along with minor surfacing and a factory-style valve job. We wanted the heads to represent what would have come from the factory back in 1970. They were treated to a set of valvesprings from Comp Cams, to ensure we could safely rev the motor to 6,000 rpm.
Our reproduction LT-1 solid cam and lifters came from Elgin. We also sourced an original LT-1 aluminum high-rise intake, but topped the dual-plane manifold with a Holley 750 HP carburetor in lieu of an original (and very expensive) or reproduction 780 Holley. Both the LT-1 and LT1 were run with 13/4-inch headers, and both were optimized in terms of air/fuel and timing. The EFI LT1 was run with a FAST management system, while jetting and distributor advance took care of tuning on the LT-1. The LT1 was run with the factory water pump (meaning a slight drop in power from the parasitic loses associated with driving the pump), while the LT-1 could be run with an electric unit. Neither motor was run with an air filter of any kind.
Run on the engine dyno, the LT1 produced 350 hp at 5,700 rpm and 379 lb-ft of torque eat 3,800 rpm. This compares favorably with the factory rating of 300 hp and 340 lb-ft. Torque production exceeded 350 lb-ft from 2,600 rpm to 5,100 rpm, while the horsepower curve flattened out past 5,000 rpm. Despite a factory (gross) rating of 370 hp, the LT-1 produced almost exactly the same peak power as the LT1, with a peak of 353 hp at 5,600 rpm. In the torque department, the '70 LT-1 offered 292 lb-ft at 4,100 rpm, bettering the LT1 by as much as 13 lb-ft. Torque production from the LT-1 exceeded 350 lb-ft all the way up to 5,300 rpm, but like the LT1, power output from the LT-1 fell flat past 5,000 rpm. Given the wilder cam timing, this seems unusual, but it's hard to argue with the results of direct, back-to-back testing. Despite the sizable differences in rated output and more than 20 years of technology, the two LT small-blocks are more alike than different, at least in terms of power production. From the results of this test, it's obvious that the later LT1 carried on the tradition of performance offered by the original and can proudly wear the name.
Despite the short runners used in the LT1 EFI intake, the late-model motor offered more low-speed torque than the '70 version. Some of this is due to the dramatic difference in cam timing, as the milder hydraulic roller in the LT1 no doubt improved low-speed (below 3,300 rpm) torque production. From 3,500 rpm to 6,000 rpm, the original LT-1 offered slightly more power. The peak hp numbers were nearly identical, with the original version pumping out 353 hp, and the later mill making an even 350 hp. In the torque department, the '70 LT-1 produced 392 lb-ft at 4,100 rpm, compared with 379 lb-ft at 3,800 rpm for the LT1. In the midrange, the high-compression LT-1 offered as much as 13 extra lb-ft, but the difference was just 2 hp at 6,000 rpm.