Actor, automotive enthusiast, and co-host of the MotorTrend App’s new Top Gear America, Dax Shepard is building a Chevrolet 454 SS pickup with a supercharged LT4 engine and six-speed automatic transmission. HOT ROD Garage co-host Lucky Costa is doing the work at his personal shop and invited us to check in on his progress.
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It’s a pretty well-known fact that Dax is a dyed-in-the-wool gearhead. He hails from Detroit and grew up in the industry. We’ve featured some of his cars, like his hot-rodded Lincoln Continental and LS-swapped 1996 Buick Roadmaster wagon. He recently purchased this low-mileage 454 SS, and it’s really clean.
We drove it around the block and were impressed with its tight feel and ride quality. The throttle-body-injected (TBI) 454 definitely makes more torque and accelerates with more aplomb than Project Jake, the in-house, small-block-powered OBS (old body style) 1993 GMC C1500 from our sister publication HOT ROD. Still, an 8:1 compression big-block with peanut-port cylinder heads, a tiny cam, and hard-to-tune, airflow-limited induction and fuel-delivery systems doesn’t compare very favorably with even the standard engines in today’s pickups.
Say what you will about taking out the big-block in a 454 SS and replacing it with an LS or (in this case) LT engine, it’s hard to argue with the logic. Lucky told us he and Dax discussed several options on how to build the existing big-block for more power, but Dax decided on the LT4 E-Rod crate engine from Chevrolet Performance in an attempt to keep the pickup emissions-compliant. This engine package received an executive order (E.O.) number from the California Air Resources Board (CARB) allowing it to be installed in 1995 and older passenger cars and trucks up to 5,725 pounds GVRW.
The LT4 originally appeared in the C7 Corvette Z06 and is rated at 640 horsepower and 630 lb-ft of torque thanks to its 6.2 liters of displacement and a 1.7L Eaton R1740 TVS supercharger that generates a conservative 10 psi of boost. Even with the extra weight of the supercharger, the all-aluminum engine will be lighter than the 454, which Lucky has set aside in case Dax decides to put his pickup back to stock someday.
Is the LT4 Engine a Small-Block?
Although people refer to the LS and LT family of engines as small-blocks, the LT4 takes up a considerable amount of real estate, thanks to its extensive supercharger and accessory drive pulleys. Lucky removed the hood, grille, and front bumper assemblies because it would be much easier to perform the engine change that way.
Elevated Concepts, Inc. is a company that specializes in LS and LT engine swaps for the ’88 to ’98 Chevy and GMC pickups and SUVs. Owner Derek Parker sells LT-swap motor mounts that position the engine at an ideal location within the engine compartment. Lucky drilled access holes to reach the inside of the fasteners on the frame stands. They are otherwise inaccessible without removing the lower control arms.
As is often the case with engine swaps, the accessories can sometimes get in the way of the frame in older cars. Other accessory drive systems are available, but Lucky prefers Holley’s LS and LT systems for their high-quality fit, finish, and reliability. Unique to the LT4 because of its supercharger drive and throttle body location, the LT4 accessory drive kit puts the alternator low and on the right side of the engine. Lucky notched and reinforced the frame to clear the alternator, leaving enough room around it in case it ever needs to be removed in the future. We’ve seen frame modifications like this done on dozens of cars with no evidence of compromised structural integrity.
Dax chose the Supermatic 8L90-E eight speed automatic transmission from Chevrolet Performance to act as intermediary between the LT4 and the 12-bolt axle in the 454 SS. It’s rated to handle 650 lb-ft of torque and is offered with a choice of a 2,400-rpm or 3,000-rpm stall converter. First gear is a steep 4.02:1, and sixth is a low 0.67:1, so Dax will experience the delicious contrast of neck-snapping launches (providing he has sufficient traction) and sedate highway cruising once he lets off the gas. This thing will probably get pretty decent mileage, all things considered.
The stock transmission crossmember in these pickups is basically a stamped piece of sheetmetal that’s so straight it could double as an ironing board. The lack of complexity makes it easy to accommodate the new transmission, which seems like it takes a standard GM mount. Lucky just needed to move the crossmember back a couple of inches to its new mounting position. Stay tuned for more as work progresses, and be sure to check out the new Top Gear America when it debuts on January 29, 2021 on the MotorTrend App.
Chevrolet Performance, chevrolet.com/performance-parts
Elevated Concepts, Inc., elevatedconceptsinc.com
Holley, 270-781-9741, holley.com
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