Sometimes the best ideas are also the easiest. When GM decided they needed more torque from the venerable 6.2L L86 Gen V direct injected truck engine, the quickest way to do this was to add a stroker crank. So that’s what they did and created what is now known as the L8T.

This is a 10.8:1 compression, direct injected engine with a longer 3.86-inch stroke coupled with a 4.065-inch bore that creates a 401ci, 6.6L engine. The stroke increase does its job boosting torque with this 87-octane rated engine at 464 lb-ft of torque at a low 4,000 rpm with a horsepower rating of 401 at 5,200 RPM, giving it exactly one horsepower per cubic inch.

Like its L86 and now DFM-triggered L87 cousins, the L8T is direct injected and does use variable valve timing (VVT) but is not encumbered with either Active or Dynamic Fuel Management which automatically makes this engine an immediate favorite with engine builders.

We will run through some interesting facts about the L8T and compare it to its smaller L86/L87 relations.

The basis for the L8T is a sturdy iron LT configured block with 4.065-inch bores and extended length cylinder liners. Note that the cylinder head dowel holes on LT engines have moved from the lower row of head bolts to the top.

Our source for much of this information comes from the guys at Scoggin-Dickey Parts Center (SDPC) where they operate neck-deep in all things pertaining to Chevrolet Performance. Let’s start deep within the bowels of this cast iron block performer and build it on paper from the foundation upwards. It’s an interesting journey.

Rather than an aluminum block, GM decided that this stroker would need the strength of cast iron for its basis. The block retains many of its gen IV/Gen V characteristics with six fasteners for the cross-bolted mains and a center-placed thrust bearing. One indicator of the strength this block delivers is that our pals at SDPC tell us this block is only 12 pounds lighter than the vaunted Chevrolet Performance LSX race block.

Since this block does not use AFM or DFM, the hydraulic circuits for the lifters are not drilled but the stands remain inside the lifter valley. This is one area where SDPC says it can remove weight. In fact, SDPC now offers a performance-modified block in which the stock main caps have been replaced with steel versions using 7/16-inch studs, the lifter stands in the valley have been removed, and the dowel pin locations for LS heads have been added. Gen V LT engines move the head dowel placement to the top of the deck surface compared to previous generation LS engines that positioned the head dowels on the lower side of the deck. The production block has steam holes much like the old 400ci small-block Chevy.

This SDPC photo shows the chamber side of the L8T head. Engine builder Kurt Urban is pointing to the steam holes present in both the head and block that vent steam that can occur at low engine speeds around the siamesed cylinders. This is a technique carried over from the old 1970s 400ci small-block Chevy production castings. Also note the hole for the direct injection nozzle directly across from the spark plug.

The L8T uses a 4.065-inch bore and it would be reasonable to assume that increasing the bore out to 4.125 would be a simple way to gain additional displacement. SDPC’s Nicky Fowler says the thrust side thickness of this block appears to support increasing the bore for normally aspirated engine out to as much as 4.145-inch but he suggests keeping the bore to 4.085 for power adder applications.

Fowler also told us that with this longer stroke, GM extended the length of the cylinder walls to accommodate the additional stroke, which makes this block that much more attractive for longer stroke packages. This is important because adding a longer stroke tends to pull the piston out of the bottom of the cylinder especially on earlier Gen III blocks.

Since the L8T is a direct injected engine, it uses heads similar to other Gen V family engines. One change with all direct injected heads is the valve order. The LS family (right) placed the exhaust valve in the leading position. The direct injection heads position the intake valve on the end.

Emphasizing strength, GM continued its use of forged steel crankshafts with the L8T enhanced with its added 3.86-inch stroke. The crank does differ from its previous smaller iterations in that it sports additional center counterweights to improve durability. Fowler added that the GM durability cycle puts this engine through an amazing 600 hours of between peak torque and peak horsepower.

Perhaps the best part of this crankshaft news is that this forging is also very affordable. At well under $800, this would be a great addition to other L86 or earlier LS engines. Fowler says the crank has some minor changes to it around the crank gear that will require some modifications for use in other engines, but Scoggin-Dickey has the expertise to make that work.

The connecting rods retain the 6.098-inch length of other LS engines, but they are not interchangeable. In order to accommodate the longer stroke with the stock 9.240-inch deck height, engineers made the wrist pin diameter smaller compared to the normal Gen V LS pin diameter of 0.927. The L8T wrist pin diameter is smaller yet at 0.863-inch. This was done to allow the standard rod length while avoiding the issues of the wrist pin intruding into the oil ring while still clearing the counterweight with the piston at bottom dead center.

For performance applications, SDPC has created several forged piston and 4340 steel connecting rod combinations that can push this engine to the next level. SDPC has already built and tested a 14:1 compression competition engine with a solid roller cam using a SDPC race version of the L8T block that makes 860 horsepower at 8,000 rpm with ported LT4 heads and port fuel injection using a Holley Hi-Ram and Dominator ECU.

This image shows the location of the arrow-shaped piston oil squirter bosses at the bottom of the bores that will aim upward so shoot cooling oil onto the back side of the pistons.

Moving on, Fowler told us that one area that is of concern for higher rpm applications is the L8T’s variable volume oil pump. In the quest for more efficiency, GM designed a pump that varies the volume and pressure with the use of a solenoid that can move the position of the center portion of the pump. At idle, low rpm, and low load situations the volume and pressure are reduced.

The problem is that above 5,500 rpm these pumps begin to suffer from cavitation, which introduces air into the oil. This is partially due to the fact that the pump is driven at crankshaft speed while older engines like small- and big-block Chevys used oil pumps driven at half crankshaft speed.

According to Fowler, SDPC’s own testing has revealed the stock pump fails to supply sufficient oil at loads above 1,200 lb-ft. Obviously this is not a problem for a typical street engine and SDPC is working on at what levels of normally aspirated power and rpm will dictate changes to the pump. This is why SDPC’s own twin-turbo engine is fed with an externally-driven oil pump.

Direct Injection intake ports are huge and designed to flow great quantities of air with nearly a direct shot to the back side of the intake valve. This is a ported LT1 version but illustrates the concept.

Direct injection also means these Gen V heads feature a fuel injection nozzle in the chamber opposite of the spark plug. The nozzles are fed from a high-pressure pump located at the back of the engine on top of the lifter valley cover in a similar fashion to the other direct injection engines. The high-pressure pump is driven off a tri-lobe arrangement at the back of the camshaft.

The L8T heads are similar to other direct injection heads. One feature of the Gen V heads that is not commonly known is that the engineers reversed the order of the valves compared to the Gen III and IV LS family of heads. The older heads placed the exhaust valve at the front of the head repeating an exhaust-intake pattern. The LT engines reverse this placing the intake valve forward repeating an intake-exhaust sequence. This of course, also changes the lobe arrangement on the camshaft.

The L8T heads offer an ever-so slightly larger combustion chamber compared to the other LT engines. A typical LT1 chamber is 59 cc while the L8T measures just over 60 cc. Since this engine was designed for 87 octane fuel use the lower compression likely involves a slightly deeper pocket in the piston. This combination drops the compression ratio to 10.8:1 compared to 11.5:1 for the LT1.

The L8T heads, like other Gen V heads, feature amazingly large intake ports with nearly a line-of-sight to the intake valves. Valve sizes are also the same as the LT1 with a 2.126-inch intake valve but SDPC engine builder Kurt Urban tells us the exhaust valve is made of Inconel, which is a material that’s stable under high temperature. This material makes it perfect for turbocharged use. The valve angle also remains the same as other Gen V engines at 12.5 degrees.

The exhaust port on all LT engines which includes the L8T, offer raised exits to drastically improve exhaust port flow, allowing hot rodders to make amazing power even with relatively short duration camshafts.

The selection of intake manifolds for the Gen V family of normally aspirated direct injected engine is substantial so there should be opportunities for swapping a more performance related intake onto the L8T engine. The intake manifold bolt pattern retains the same configuration as its smaller displacement cousins along with its 87mm drive-by-wire throttle body.

One interesting note on the L8T truck engine is that because it is used in a heavy-duty application the accessory drive employs two alternators, placed on opposite sides of the drive assembly. It’s unclear at this point if a single alternator L86 accessory drive could be used in its place. It also should be noted that all current Gen V engines do not employ a hydraulic power steering pump but there are both Chevrolet Performance and aftermarket kits available to add hydraulic power steering to a Gen V accessory drive.

To illustrate the power potential and durability of the L8T block and crank, Urban has assembled a twin-turbo version of the L8T using a SDPC race block, Callies rods, forged pistons, CNC-ported LT4 heads fed with a port fuel injection system using a Holley Hi-Ram intake and fuel rails along with a Holley Dominator ECU. To top all this off, they added a pair of Precision 7685 ball bearing turbochargers and on C-16 race gas and were able to make a reliable 2,077 horsepower.

We will follow this engine in a more in-depth story at a later date but what this information reveals is the strength of this L8T’s foundation using the stock forged steel crank. So clearly the L8T offers a wide range of opportunities from a mild normally aspirated street build to potentially 2,500 horsepower capability. How big do you want to go?

Editor's note: the author would like to thank Nicky Fowler, Keith Wilson, and Kurt Urban of Scoggin-Dickey Parts Center for their knowledgeable assistance with this story.