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1990 Pontiac Trans Am - 12 Seconds and 25 MPG

Don Lorentzen's '90 Pontiac Trans Am

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Tech Notes
Who: Don Lorentzen

What: Don's '90 Pontiac Trans Am is slightly heavier, otherwise it is a body kit away from being a Firebird Formula like the one Car Craft has. Don's car is faster.

Engine: Don found a ZZ4 four-bolt block that was a takeoff from a Chevrolet dealership and fitted it with a steel crank and powdered-metal rods. All '96-and-later truck engines have one-piece rear seals. Don used 0.030-over Speed-Pro flat-top pistons with two 3.4cc eyebrow reliefs to get 10.5:1 compression and used a mild TPIS ZZ-9 street-legal roller cam that has 212/226 degrees of duration 0.050 and .483/.520 lift using a 1.5 rocker arm on the exhaust and 1.6 on the intake.

Intake: The upper plenum is port matched to the runners that Don cut about 3 inches from the base and rewelded so everything above the cut line is open plenum. The base is from Edelbrock and is marketed through Scoggin-Dickey Chevrolet for Vortec heads. Coincidentally, the base also fits Don's unported Edelbrock ETEC 200 heads with the same raised port and bolt pattern. The car makes 300 hp at the wheels at 5,700 rpm and 405 lb-ft at 3,800.

Exhaust: He's an exhaust guy, remember? He made his own 1 3/4-inch headers, fixing some problems that occur on other aftermarket designs, and connected them to a 2 1/2-inch Y-pipe, dual cats, and a 3-inch after-cat with Flowmaster American Thunder mufflers.

Fuel system: Everyone knows the Tuned Port engine responds to fuel-pressure changes. Don uses a Crane adjustable fuel-pressure regulator set to 45 psi at wide-open throttle and a GM Typhoon in-tank pump that produces 55 psi at 41 gpm.

Transmission: The factory T5 is mounted at an angle to the crankshaft centerline, and the T56 is not. The adapter that comes with the Tremec kit fixes this problem and moves everything back about 2 inches. Don had Driveline Specialties in Garden Grove, California, make a new aluminum shaft that is 3 inches shorter than stock. Another cool thing about the Tremec is the 2.97 First-gear ratio and the 40 percent overdrive. This allows you to have a regular 3.55 or 3.70 gear ratio and still get out of the hole at the track. The '93-and-later Camaro T56 has a 2.66 ratio in First. The OE speedometer uses a square wave that you have to convert to a sine wave; the aftermarket six-speed uses a standard, cable-driven speedometer.

Clutch: The fourth-gen Camaro uses a pull-type clutch that rides on a splined hub. As the clutch wears low, the hub can touch the pressure plate and keep the clutch from engaging all the way. That's bad. Another problem with an LT1-style T56 is that the clutch does not engage until the pedal is nearly all the way out. At the strip, this prevents a good reaction time and allows the car to roll through the lights as the clutch drags before full engagement. The aftermarket kit switches the clutch engagement to a push type, and McLeod offers an 11-inch clutch disc in a 10-inch housing that eliminates both problems at once. That's the difference between engineered pieces and cobbled-together stuff.

9-bolt: The rear is the '89 IROC (or GTA) 9-bolt with 3.70 gears that is purported to be slightly stronger than the 7.625 10-bolt in other Camaros. Don welded up some brackets to get a set of fourth-gen LS1 rear brakes to bolt on. Every Camaro from '89-'92 uses the same master cylinder, so that will be retained when he swaps the front brakes as well.

Tricks: Don uses an aftermarket Wonderbar from Top-Down Solutions so named by the GM engineers that were describing the brace that bolts just below the front antisway bar to stiffen the front structure during high-g maneuvers.

Differences between the Trans Am and the Firebird Formula: The Firebird Formula is lighter, has no ground effects, and has a hood bubble.

Mileage: Don averaged 25.3 mpg on a run from Santa Barbara, California, to Anaheim, California. The rpm was 2,000 at 65 mph, and the best e.t. is 12.80 at 108 mph with a 1.76 60-foot.

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