A few months ago, we got our hands on an L8T crate engine from Chevrolet Performance and teamed up with Brian Tooley Racing to see what the hubbub was about with GM’s 6.6-liter Gen  V LT truck engine. From 500 horsepower with a completely stock engine on E85 to 723 horsepower with a perfected heads, cam, and intake combo on the stock bottom end, it’s finally time to see how much the stock block and crank in our ProCharged L8T can handle with all the boost we can throw at it.

Short-Block Recap

Things are about to get real in BTR’s engine dyno. In our last article, we rebuilt our L8T crate engine to handle the long four-digit-horsepower road ahead. We chose to keep the L8T cast iron block and forged steel crankshaft in their stock form. These two pieces have already proven themselves to be more than just tough and robust for heavy-duty fleet trucks, but the rods and pistons needed to be exchanged.

The cast iron block and steel forged crankshaft that come stock in all L8T engines are designed to handle fleet-duty, but can those parts hold more than four times the stock horsepower rating?

For pistons, we turned to Diamond Pistons for its forged 2618 LT2K pistons. The “2K” in the name means these can handle more than a typical 1,000-horsepower forged pistons. The area under the crown has thicker material for the wrist pin and extra support behind the skirt.

The L8T’s stock crankshaft features forged steel construction and a 3.858-inch stroke. It remained unmodified during our testing.

This area is also fully CNC machined to eliminate stress risers for maximum strength. Diamond supplies upgraded wrist pins to handle the extreme force transferred from the pistons to the connecting rods that are made from H-13 tool steel and utilize a 0.250-inch wall thickness.

These MGP aluminum connecting rods are tough enough for 2,000-plus horsepower.

The OEM L8T connecting rods are surprisingly skinny, they have less material than a stock LT1 rod and a smaller-diameter wrist pin. At the end of the max effort naturally aspirated dyno testing, our L8T was pushing over 700 horsepower, and Brian Tooley advised that this was the upper limit for the stock connecting rods. Since we’re aiming to triple that power, we turned to MGP Connecting Rods for a set of Pro 2500 series aluminum rods.

Diamond Pistons forged LT2K pistons. The “2K” in the name means these pistons can handle more than typical 1,000-horsepower forged pistons.

Aluminum connecting rods are the perfect combination of strong and light. MGP’s Pro 2500 series aluminum rods feature full radial serrations where the cap meets the body of the rod and custom-made ARP 7/16-inch rod bolts to ensure zero cap movement. The small end does not have a typical bronze bushing for the wrist pin, but a proprietary MGP “Hard Bore” process that provides a hardened surface of the aluminum in the bore for reduced wear and bore deformation. The piston and rod combo, combined with the L8T crankshaft in the stock block, will handle more than 250 horsepower per cylinder.

Heads and Valvetrain

To finish off a short-block that tough, we need a pair of cylinder heads and valvetrain to help reach our 2,000-horsepower goals. We ended our last dyno runs aiming for max effort naturally aspirated with a pair of CNC ported CID heads and BTR’s 230 camshaft. But for our new goal, we need to change it up (more on that in a second).

Now that we are adding boost, there were other considerations that made Chevrolet Performance’s CNC-ported LT1 heads a better fit. The LT1 castings are the same as the L8T castings, and while Chevrolet Performance does not advertise CFM ratings, the CNC port job increases flow on the intake and exhaust to fill the chamber with as much air and fuel as possible.

Our ProCharged L8T is still running a hydraulic roller valvetrain and stock style rocker arms.

The advantage of  this head change is that the Chevrolet Performance heads feature provisions for PLEX sensors in the combustion chamber. PLEX sensors allow the team at BTR to data log, in real-time, combustion chamber temperature, knock intensity, and combustion chamber pressure. When pushing eight cylinders to their limit, we need to monitor everything we can to help our ProCharged L8T live on BTR’s engine dyno.

Collecting the cylinder pressure data with the PLEX software is very interesting. We were able to see the valve opening and closing events as they relate to cylinder pressure, power production, and our cam lobe designs. That data is extremely valuable and gave us insights into where the engine was bottlenecked once we added boost. — Brian Tooley

These heads received a valve spring swap to match the BTR Gen V 4.00-inch Stroke Supercharger Cam installed in the block. This cam has an intake duration of 233 degrees on the intake and 25x degrees on the exhaust at 0.050-inch lift with 0.648-inch lift on both. The 115-degree lobe separation angle and 38 percent fuel pump lobe match the needs of a supercharged LT. This ProCharged L8T is still running a hydraulic roller valvetrain with Johnson Lifters 2126LSR link-bar roller lifters.

Oil Control For The Strip

The oil system is just as important as camshaft and cylinder head selection, especially at the power levels we’re shooting for. Oil control is about supplying internal moving parts with the proper volume and pressure of engine oil and controlling horsepower-robbing windage

The Moroso COPO oil pan houses a trap door baffle, anti-slosh baffle, and removable windage tray for superior oil control.

The future of our ProCharged L8T has yet to be written, but whatever chassis it ends up in will be destined for the quarter mile. To handle pumping the oil, we went to Katech for one of its Gen V LT wet sump oil pumps that replaces the factory powdered metal internal gear with a 4140 billet steel single gear.

The factory oil pan that came on our Chevrolet Performance L8T was designed for a 3/4-ton truck. The cast aluminum construction is designed to last a lifetime, but not designed to properly handle the engine oil when it’s subjected to the g-forces generated by hard acceleration. So we went to the biggest name in the business for oil control: Moroso.

This fabricated oil pan features a 7.5-inch deep sump with a seven-quart capacity.

Moroso makes fabricated aluminum pans for street builds, off-road, road race, and drag racing. Since we know we will be tackling the quarter-mile in a chassis that needs a rear sump design, we went with Moroso’s COPO Camaro drag race oil pan. This pan was originally designed for the 2016 and up COPO Camaros running a Gen V LT engine.

This drag race oil pan features a billet pan rail and front cap with a fabricated aluminum sump. The billet front cap design houses the integrated pickup and O-ring pickup pass-thru to the oil pump for a sealed installation. To handle hard acceleration racing from a dig, the rear sump houses a trap door baffle, anti-slosh baffle, and removable windage tray for superior oil control. The shape of the pan and baffle system keep the pickup tube slurping fresh oil at all times, which is important when you are on the ragged edge like our L8T.

ProCharger’s F-3R-121

For our lofty power goals, we went with a ProCharger F-3R-121 centrifugal supercharger and skipped over the belt drive options for ProCharger’s CrankDrive kit. The CrankDrive mounts a billet aluminum gear reduction box to the front of the block to drive the ProCharger head unit directly off the crankshaft snout. The CrankDrive eliminates side loading that can happen with big-boost belt-drive setups and also eliminates belt slip. This means that hopefully our stock crank will live longer and we’ll have less potential failure points for our test.To change the boost like you would swapping pulleys in a belt drive setup, you swap the gears inside the CrankDrive.

The ProCharger F-3R-121 is rated at 3,100 cfm, a max boost pressure of 40 psi, and a max horsepower rating of 2,400 horsepower. The F-3 series offers a CNC machined 7075 aluminum billet impeller measuring 4.4 inches at the inducer and 6.75 inches at the exducer. The F-3 transmission has a 5.63:1 step-up ratio and is built with heavy-duty 9310 steel shafts and gears with a patented high-speed compound bearing design that can handle the high speed and excess loads a racing supercharger churns out.

Dyno Run 1

With our refreshed ProCharged L8T strapped down to BTR’s engine dyno, we’re ready to see if we will end the day victorious or with our guts all over the dyno room floor. The CNC-ported BTR Trinity intake and Granatelli 112-millimeter throttle body from the naturally aspirated dyno testing was reused and methanol was run in both the direct injection and port fuel systems.

In addition to the CrankDrive running the supercharger, it also drives the mechanical fuel pump for the port-injection side of the fuel system.

The tune-up for the first dyno run was really soft as far as ignition timing and air/fuel ratio to play things safe. This run was with the slowest gear set for the CrankDrive BTR had on hand — a 1.40:1 overdrive. The result was 1,435.6 horsepower at 7,800 rpm and 1,055.5 pound-feet of torque at 6,400 rpm with a peak boost pressure of 29.5 psi.

BTR started conservatively with tuning and still managed 1,435.6 horsepower at 7,800 rpm and 1,055.5 pound-feet of torque at 6,400 rpm with a peak boost pressure of 29.5 psi.

Dyno Run 2

Now that the BTR team was comfortable tuning the stock ECU with a BP Automotive harness for the direct injection along with the Holley Dominator ECU for the supplemental port injection, it was time to swap in the overdrive gear set in the CrankDrive to turn up the impeller speed and boost. After all, the bottom-end was built to handle a lot more and so far the ProCharged L8T hadn’t even broken a sweat yet.

The air-to-water intercooler looks like overkill, but when you’re doing back-to-back dyno runs over 30 times, you need it at this power level.

Going from the 1.40:1 gear set to 1.50:1 pushed the boost from 29.5 psi to 36.0 psi which allowed the 6.6 to make 1,537.4 horsepower at 7,800 rpm and 1,067.7 pound-feet of torque at 7,100 rpm. The L8T could live all season long at the dragstrip at this power level, but the team at BTR was now getting comfortable with tuning and was hungry for more boost and power.

A gear set swap in the CrankDrive from 1.40:1 to 1.50:1 pushed the boost from 29.5 psi to 36.0 psi which resulted in 1,537.4 horsepower at 7,800 rpm and 1,067.7 pound-feet of torque at 7,100 rpm.

Dyno Run 3

If one step up with the CrankDrive gear set resulted in 6.5 psi more boost and 101.8 horsepower, another change should add another 100 horsepower, right? Well, going to a 1.60:1 gear set resulted in a 4.8 psi increase to 40.8 psi at peak, but a bigger jump to 1,792.0 horsepower at 8,150 rpm and 1,195.7 pound-feet of torque at 7,400 rpm.

Going to a 1.60:1 gear set resulted in 40.8 psi and a jump to 1,792.0 horsepower at 8,150 rpm and 1,195.7 pound-feet of torque at 7,400 rpm.

The ProCharged L8T was still trucking along at almost a very impressive 1,800 horsepower and over 8,000 rpm, but this run surpassed the max boost pressure ProCharger rates the F-3R head unit at. While the engine is proving how tough it can be, even when still using stock parts, we started to wonder if we could push past the 2,000-horsepower mark.

Overlay of horsepower and torque from the first three dyno runs.

The Final Run

BTR made over 32 pulls with the ProCharger on the L8T, with nine of those pulls over 1,750 horsepower. This ProCharged L8T is proving to be bulletproof, but it was time to make the leap to see if it could reach our goal. Now that the BTR team was more comfortable increasing the timing and mapping both fuel systems to work in sync, they crammed 45.0 psi of boost into the L8T to make a colossal 2,046.1 horsepower at 8,200 rpm and 1,357.5 pound-feet of torque at 7,750 rpm. This final dyno run jumped a whopping 254.1 horsepower and 161.8 pound-feet of torque over the previous run.

We made over 32 pulls with the ProCharger on the L8T with nine of those pulls over 1,750 horsepower, all on a stock block and crankshaft. – Jeremy Nichols, BTR

The massive ProCharger F-3R-121 head unit and CrankDrive don’t do any favors for room under the hood.

We did it, we achieved our horsepower goal! Over 2,000 horsepower and 8,200 rpm with an F-3R-121 ProCharger and the stock L8T block and crank. But we had to really dial up the boost to reach this achievement, way past the max boost ProCharger rates this head unit for. Is this because of a restriction from the off-the-shelf camshaft or the cylinder heads or both?

45.0 psi resulted in 2,046.1 horsepower at 8,200 rpm and 1,357.5 pound-feet of torque at 7,750 rpm. More than quadruple the L8T’s stock factory rating.

We think the answer might actually be a real-world lesson in choosing a properly sized supercharger to match your build and meet your performance goals. The 40 psi max rating ProCharger assigns their F-3R-121 head unit is not because that’s the most it can physically handle and produce, but the most it can produce before becoming inefficient.

This L8T has come a long way from just a simple stock replacement truck engine in a wooden crate to a 2,000-plus horsepower, 8,200 rpm, methanol-chugging drag racing engine. Most impressive of all is that we more than quadrupled the factory power output to achieve our goal while still using the stock cylinder head castings, cast block, and crankshaft. Stay tuned, we have other plans for this L8T that are bound to raise a few eyebrows