Street Brawler: Testing Livernois Motorsports’ L8T Crate Engine

The folks at Livernois Motorsports & Engineering have once again taken a bread-and-butter production engine and turned it into a killer street brawler. Their experts are known for extracting massive amounts of horsepower and torque and have applied this knowledge to modifying Chevy’s workhorse L8T 6.6-liter V8 truck engine.

Livernois Motorsports has turned the L8T 6.6-liter V8 truck engine into a serious contender for customers looking for an engine that produces serious performance at a reasonable price. Chevy’s L8T V8 boasts the largest displacement of any factory LT offering, yet its image is not yet as sexy as other offerings in the Chevrolet lineup.

That is changing, though. Hardcore racers and restomod car builders have slowly accepted this engine as a potent transplant alternative.

The L8T pumps out a respectable 401 net horsepower at 5,200 rpm and 464 lb-ft of torque at 4,000 rpm stock. These are very respectable numbers for a street rod or vintage truck, but not enough clout to make a statement when rolling out of a show or laying waste to the guy in the next lane.

This is where Livernois applies its decades of knowledge, turning the L8T into a Coyote and Elephant hunter that goes way beyond bolting parts on an existing engine. Livernois developed a complete package for the L8T that makes it a stout performer.

Short-Block Prep

Livernois learned a lot of power can be extracted out of L8T’s basic architecture with the production cast-iron block and aluminum cylinder heads. But before the short-block assembly began, Livernois Master Engine Builder and Shop Manager Brad Beabien got everything prepped. Before joining Livernois, Brad spent 20 years at Roush Performance doing prototype builds, cylinder head prep, and managing the company’s world-class machining facility.

“Since the Livernois L8T is a custom engine from intake to oil pan, it’s all hand assembled with care and detail and configured for the customer’s exact needs,” said Brad. “Whether it’s street/strip or going into a truck or even SUV, Livernois makes sure the compression ratio, camshaft, and other key factors are matched for the owner’s exact application.”

Livernois replaced the production main caps with billet units and pitched the stock bolts for ARP fasteners. The OEM forged crank might be sturdy enough for hauling one’s race car or boat behind their Silverado, but Livernois upgraded to a Callies Comp Star forged piece with a 4-inch stroke (moving displacement from 6.6 to 6.8L, or 402 to 416ci).

Since the rotating assembly in any engine takes the brunt of punishment, Livernois used Manley H-Beam connecting rods, Clevite rod and main bearings, and MAHLE forged pistons and File-Fit rings.

Livernois retained the factory GM oil pump and balancer on its L8T builds and has also done so in prior LS and LT builds. These production items help reduce costs and allow it to focus on other critical areas.

When it comes to the camshaft, Livernois uses its unique split-duration hydraulic roller (218/226 degrees of duration at .050, 0.646-inch lift and 114 LSA) that provides a wide powerband and works great in street applications, especially in a heavier vehicle like a pickup truck or SUV.

Cylinder Heads & Intake Manifold

The breathing on the Livernois L8T is handled by production aluminum LT1-style square port cylinder heads. Livernois uses both new castings and good used cores, and before any work is performed, Livernois pressure checks and sonic tests each cylinder head regardless of whether it’s a factory fresh casting or a used takeoff.

After passing the pressure check, the heads are then torn down and the valve seats get a close inspection along with the bolt holes. Livernois also checks the guides for wear if the heads are used cores.

Doing the cylinder head work is longtime employee Dave Kuchtyn—he’s been with Livernois for over 16 years and is considered a cylinder head guru. Dave has done thousands of not only LS and LT heads but also heads for Ford Coyote and Mopar Gen-III HEMI engines. He knows all the intricacies among the different styles and what they respond to when it comes to prep and porting.

Dave creates a port model after the heads pass quality check, and then creates a CNC program. Dave reworked the valve face angles with the bottom numbers coming in around 60-63 degrees and the second angle around 70-80 degrees.

Once the valves were ready, the valve seats get a good going over and get “tucked in” for increased airflow and less turbulence. After the head assembly is reworked and complete, it goes back on the flow bench and Dave goes old school and puts his decades of knowledge along with his sharp ears to use. He listens very closely to the sounds of the airflow from the head. If something doesn’t seem right, Dave pulls out the Velocity Probe and investigates further until he’s satisfied.

On the L8T, Dave’s focus is on mid-airflow as opposed to focusing on the stratosphere numbers .700-inch lift. The magic is the low to mid-airflow at .400- and .500-inch with an emphasis on the intake port. It’s this philosophy Dave used to make sure the engine achieves a flat torque curve which is what you want on a heavy vehicle that’ll spend 90 percent of its time on the street.

Dave tailors his porting around the camshaft specs, which in this case is a custom Livernois design. Dave noted how lopsided the airflow is on some Chevy LS/LT heads, as the intake side outperforms the exhaust side by a very disproportionate number—something to consider on your next build if you’re throwing superchargers and turbos at your LS.

Bolted on the Livernois-prepped heads are the production L8T intake and throttle body. They both work very well in this application and reduce costs to the consumer.

Dyno Test

Once the Livernois folks have thoroughly inspected all the components, the L8T is assembled and off to the dyno. After the initial break-in procedure has been completed, the L8T shows its chops by making 552.8 horsepower at 5,700 rpm and 586 lb-ft of torque at 4,400, all on 91-octane pump gas, and with great street manners. We’d expect fantastic vacuum and idle quality with those cam specs matched to such a large displacement (416ci to be exact). The Livernois L8T is a fantastic option to power any hot rod or restomod.