Intake And Cylinder Heads
Both of these parts had to flow better if the designers were going to meet their 300hp goal. The engineers were successful on both counts. Not only did the LT1 intake flow better than the Tuned Port Ignition manifold, it was shorter and lighter, which aided in packaging it to fit the new cars' low-profile hoods. Also, its one-piece design eliminated the labor associated with fitting the three-piece TPI manifold on the assembly line.
GM has discontinued the LT1 manifold, but Edelbrock makes a replacement. It accepts all emissions equipment and is machined to accept a 52- or 55mm throttle body as well as the stock 48mm one. Its Air-Gap design will help cool the intake charge, too.
The LT1 cylinder-head design was one of Chevrolet's best. It outflowed the legendary Bow Tie heads and was the basis for the Vortec head, one of the best bargain performance cylinder heads on the market for the small-block Chevy. Much work was done to improve airflow into and out of the combustion chamber. The intake parts were redesigned to flow as a continuation of the intake runner, and the exhaust ports were reshaped to move more air at higher engine speeds. The shape of the combustion chambers was updated, and the valves and seats got three-angle valve jobs where the previous L98 engines had two-angle jobs. It's interesting to note that all LT1s came with aluminum cylinder heads except the B/D car applications. Apparently, the law enforcement community was concerned about heat soak and the longevity of aluminum heads in police service.
Trick Flow, Airflow Research, and Edelbrock each manufacture aluminum heads to fit most people's budgets. The builders we spoke to also emphasized the option of porting the stock heads. Since they are a good design to begin with, they respond very well to porting.
LT4
The LT4 was the last hurrah of the Gen II small-block, and did it go out with a bang. Though its torque rating was the same and it only made 30 more horsepower than the LT1, it was loaded with high-tech parts. The crankshaft was stronger, the valvetrain was lighter, and the heads flowed even better. The accompanying chart lists the specifics, but putting the valvetrain on a serious diet shed enough weight to allow the LT4 to rev to 6,300 rpm. Bigger intake runners moved more air in a more direct path into the engine. LT4s were standard in '96 Corvettes with manual transmissions and also came in a select few special-edition '97 F-body cars. There are some interchangeability issues to be aware of, though. LT4 intake runners are raised 0.100 inch higher than the LT1. They will bolt onto an LT1 block but require an LT4 intake manifold (Edelbrock PN 7109).
You can still buy LT4 cylinder heads from GM. "We have them on the shelf right now," say the guys at Scoggin-Dickey Chevrolet. At a little over $1,000 each, they're not cheap, but they're a viable option for the guy who already has a good block. Scoggin-Dickey also has a killer-sounding, race-spec CNC-ported LT4 head with 64cc chambers, 205cc intake, and 77cc exhaust runners that flow 262 cfm at 0.050-inch lift. Don't have a good block? Scoggin-Dickey sells those, too. A new LT1 long-block with four-bolt mains can be purchased for just under $5,000. If you want to go all out, Scoggin-Dickey also sells a race-prepped 383 short-block for almost the same amount of money. It comes with Milodon splayed four-bolt main bearing caps, a forged Lunati crank, Pro Mod 5.850-inch rods, SRP flat-top pistons, and JE rings.
Potential
All the builders we spoke to agreed that 450 hp is easy to get out of an LT1. Chad Golen built his business on LT1s and was the guy everyone told us to talk to. Golen Engine Service moves about 200 LT1s a year and offers a variety of packages to choose from, including a 460hp package that will pass California emissions. The most popular package Golen sells is the 440hp 383, but he can put together a 396 that will crank out 520 naturally aspirated horsepower.