In the summer of 1997, Texan Joey Thackery decided to tune up his '93 F-body, and these Dallas boys always think big: The plan was to produce the baddest daily driven, naturally aspirated stock-block LT1 on the streets. While it's true the car's a Pontiac and this is Chevy High Performance magazine, this is also an LT1, and it's doubtful that the engine cares whether it's bolted in a Pontiac or a Chevy. Think of this as cross-cultural education and you'll do fine. The real story is what it takes to coax 1.2 rear-wheel hp/ci from a pushrod EFI V-8 while maintaining driveability in a six-speed door-slammer.
To find out, we tracked down Thackery in Houston where Gallant Technical Performance (GTP) had transformed an LT4 intake and heads with custom-porting wizardry. Thackery then assembled a compatible, super-duty hydraulic valvetrain. After observing Gallant in action, we made our way to Dallas, where Thackery’s start-up company, Area 51 Performance, installed the GTP equipment on the bone-stock LT1 short-block and upgraded the 1993 to handle the power upgrades. It’s also where Team Dynotech’s Chris Harrington installed an ACCEL/DFI ECU on the car.
Thackery found 428 actual rear-wheel horses (estimated to be 500 at the flywheel), which more than justifies Gallant's fast-growing reputation as the place to go in Texas for pushing your CNC-ported or stock heads to new frontiers of heavy breathing.
Raw Material
Area 51's Very Yellow Poncho made 260 rear-wheel hp on the Dynojet, which is as good as it gets on a stock LT1. In fact, Harrington has found that low-mileage bone-stock LT1s commonly vary by as much as 25 rear-wheel hp on the Dynojet.
Thackery acquired his 1993 F-body last summer and immediately installed a chip, a cold-air intake, and an after-cat exhaust and removed the cat to run a respectable 13.62 at 104 mph at the Ennis dragstrip near Dallas. Then he got serious. In October, Area 51 Performance installed everything at once on the stock short-block.
Head Games
"Motors such as the LT1 are very efficient," begins GTP owner Craig Gallant. "With sophisticated port-EFI engine management, they can make the same power 500 to 1,000 rpm lower than analogous carbureted engines. Chevy's LT4 head is one of the meanest production castings around, but it can be improved tremendously. Air speed is everything."
GTP reworked the heads and valvetrain for Thackery's LT1 to produce not only the excellent high-end airflow needed to make maximum dyno power in the 6,000-7,000 range, but also a great area under the curve. In order to accelerate hard between 4,500 and 6,500, you have to care about more than just peak cfm airflow. You have to maximize combustion quality under all conditions. A good set of heads doesn't sacrifice low-lift airflow for big peak-lift numbers. Instead, the entire curve improves, which makes solid gains in torque as well as horsepower. "Which do you think is better," asks Gallant. "410 horsepower from 250cc runners or 400 horsepower from 200cc runners?" The answer is the smaller heads.
According to Gallant, GTP porting considerations include throat diameter (the runner size very close to the valve where the runners turn the air toward the back of the valve), bowl diameter (the geometry around the valve face inside the combustion chamber that smoothes airflow entering the cylinders), short-turn radius, overall combustion-chamber shape, runner volume, and then cfm. Valve size, lift, duration, and opening and closing speeds must perfectly match the head specs. GTP uses a flow bench, swirl meters, computer modeling, and other tricks to design the optimal heads and valvetrain for a particular application. GTP removes head material with grinding but may also add metal with welding to reconfigure the combustion chamber, ports, and intake.
"The target peak powerband on Thackery's engine was 6,000 to 7,000," says Gallant, "but the operating range was everything up to that. Again, port efficiency and air speed are so important on a street application. A street-type engine or even a Competition Eliminator motor needs a runner volume and port configuration that'll keep air speed high, and it needs the right combustion-chamber shape for really good flame propagation. On Thackery's heads, we were looking for around 300 cfm through the intake side and 220 on the exhaust at 0.650-inch lift at 28 inches depression."
The stock LT4 uses 2.00-inch intake and 1.560-inch exhaust valves, which GTP increased to 2.02 inches and 1.585 inches using stainless steel Ferrera valves. "The LT4 seat can only handle 2.02 intakes," says Gallant.
"Some people are fitting 1.600-inch valves on the exhaust side, but to do that, the seat must be removed, and really, this size is too big for a street LT1. If you're going supercharged or all-out racing, we take out the seats and put in 1.650-inch valves. But on a normally aspirated street-type car, keeping the exhaust valves a little smaller keeps the car from turning into a pig." With the GTP heads in place, the static compression ratio is 11.0:1.
Valvetrain
Area 51's LT1 valvetrain package is designed to live at over 7,000 rpm. The LT1 runs a hydraulic roller cam for driveability to avoid the maintenance of a mechanical roller cam. In fact, the requirement to simultaneously produce a good-quality idle and big power at exceptionally high rpm was the biggest challenge in building up the LT1. Area 51 Performance spec'd out the Competition Cams Extreme Energy hydraulic roller camshaft with 0.555- and 0.600-inch lift and a duration over 230 degrees at 0.050-inch lift, with lobe centers at 114 degrees and the cam installed 4 degrees advanced. The stock LT1 hydraulic roller lifters are augmented by an Air Flow Research Hydra-Rev kit to improve the top-end powerband via springs loaded against the heads that keep the lifters on the cam lobes at high rpm. Comp Cams Pro Magnum 1.6:1-ratio roller rockers support the fast valve-opening via radical cam-lobe ramps. The Pro Magnum rocker tips' reciprocating weight is actually 5 percent lighter than aluminum rocker. Comp Cams double valvesprings with dampeners, retainers, and locks keep the LT1 out of the valve float. Comp guideplates keep the TPIS hardened pushrods in place.
Externals
With the GTP heads and Area 51 package in place utilizing a GM Performance Parts extreme-duty timing set and underdrive crank pulley, Area 51 installed compatible SLP 1.75-inch primary, 2.50-inch collector headers that flow into a Borla 3-inch Cat-Back exhaust and muffler. Thackery selected this header configuration to avoid exhaust restriction. A 58mm ASM throttle body regulates airflow.
With the F-body back together, Harrington installed the DFI using an RES dual-computer wiring system that retains the stock ECM for certain functions. Area 51 installed Bosch heated O2 sensors, 30-lb/hr injectors, an ACCEL adjustable fuel-pressure regulator, and a Bosch inline auxiliary fuel pump that produces 43-psi nominal rail pressure, providing sufficient fuel to make over 500 hp. Champion No. 13 plugs with a 0.040-inch gap on TPIS wires provide the spark generated by an ACCEL coil and an MSD 6A box, while a '95 LT1 Opti-Spark unit distributes the high-tension spark.
Performance Analysis
Area 51's initial fuel and spark maps produced 386 hp and 361 lb-ft of torque at the wheels, but dyno tuning quickly yielded 406 hp at 5,800 rpm at which point power and torque fell off precipitously. Gallant and Thackery figured a set of 150-pound valvesprings would stop valve float, but Gallant consulted first with Competition Cams: "They wanted to help," says Gallant, "but Comp had no dyno results related to what we're doing." Thackery installed the new springs, and the Very Yellow Poncho gained another 500 rpm and made 20 more horses. Power now falls off fast at 6,350. Gallant and Area 51 have seen cars with Comp hydraulic grinds running 6,600-6,800 rpm, but ultimately, the solution to further increase rpm in Thackery's car may involve a mechanical roller cam and lifter package.
In the meantime, the LT1 makes a smooth power curve from 3,000 to 6,350 rpm. Power rises smoothly to 415 corrected rear-wheel horses at 6,200. The DFI redline is currently set at 6,500. With the stock hypereutectic pistons still in place in a 500hp powerplant, this engine is clearly on the ragged edge of longevity. The car has plenty of spark, but with available time for injection being very short over 6,000 rpm, the engine is almost certainly close to the limits of the 30-pound injectors.
The Rest Of The Story
The Very Yellow Poncho runs 4.10 gears, a Hurst shifter, a polyurethane trans mount, and an aluminum 1LE driveshaft. Wheels and tires are front Forgedline 17x9.5s with BFG T/A 275/40s and rear Forgedline 17x11s with BFG T/A 315x35s. Eibach springs lower the front suspension, which uses Bilstein shocks and polyurethane bushings. The rearend is suspended by custom solid-mount, fully adjustable lower control arms and a Panhard rod, with a custom-built solid-mount torque arm with fully adjustable pinion control. Eibach springs and deCarbon shocks provide ride height and dampening. The chassis is stiffened by a custom-built subframe.
If you're looking for serious F-car performance, look no further. This is definitely an LT1 with an attitude. CHP