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Everything You Want To Know About The GM Gen V / LT Engine

By: Jeff Smith | 12/14/2020 < Back to Motor Life Home
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By now everybody knows about how big a role the LS family of engines has played in making horsepower. While the Gen III/IV engines are impressive, GM raised the stakes with an upgrade as a fifth generation small-block called the LT1 that appeared in 2014. If you thought the LS was complex, the Gen V ratchets this up a notch or so. There’s plenty to cover so let’s hit it.


Introduction


2020 Chevrolet LT2 V8

The most recent addition to the Gen V engine lineup is the 2020 C8 Corvette LT2 engine. Note the factory header and the relocated ignition coils. The large plastic cover on the driver side front is the integrated dry sump tank, placing it on the engine to minimize external plumbing. Because the intake ports are symmetrical, note that the intake manifold is oriented toward the rear of the engine.


The whole reason for the Gen V was to introduce gasoline direct injection (GDI) to meet increased emissions standards. The 6.2L LT1 and its followers all employ a high pressure fuel system operating at over 2,100 psi to shoot the fuel directly into the combustion chamber. This required a mechanically-driven high pressure pump that is driven off the rear of the camshaft.


The whole point of GDI is to improve combustion efficiency. The best way to make a gallon of gasoline go farther is by squeezing it harder with more static compression. The new LT1 bumped the compression ratio to a GM unprecedented 11.5:1. The last time a small-block came anywhere near that number was in 1970 with the first generation LT-1, but that engine is crude in comparison. A 2016 6.2L LT1 Corvette makes 460 horsepower and with an automatic transmission earns an EPA highway fuel economy rating of 29 mpg. You’d be Tuner of the Decade to achieve that with a 370 horse 1970 carbureted LT1.


GM also used this new injected technology across the V8 car and truck lineup by spec’ing this same engine package for trucks and other larger vehicles. The truck engines are offered in two V8 versions – the L83/L84 5.3L and the 6.2L L86/L87. There’s even a 4.3L 90-degree GDI V6 base truck engine. Note that the Gen V did not offer a 4.8L version as with previous generations. The 6.2L L86 is very similar to the passenger car LT1 with the only real changes to the intake and exhaust. The truck engine employs a longer-runner intake manifold and deeper oil pan, but beneath the skin, the two engines are identical.


There’s also an RPO LB9 5.3L that is spec’d with a different RPO code but it is essentially the same as the L86. The reason for the different code is that the LB9 engines employ an electric-assist powertrain combining an electric motor that initially accelerates the vehicle away from a dead stop and then the gasoline engine takes over.


Finally, there are two variations on the LT1 GDI engine. Knowing that Corvettes would be subjected to higher lateral g-forces, those engines are fitted with a modified dry sump oiling system while the Camaro-bound engines retain the more traditional wet sump lubrication system.


It’s also important to note that GM has stuffed superchargers on two of its Gen V variants – labeled the LT4 and LT5 engines. The LT4 uses a smaller, 1.7L supercharger while the big daddy LT5 spins a massive 2.65L high helix, four-lobe blower making 755 horsepower. With the major points covered, let’s dive into the Gen V’s internals.

The Three Faces of LT-1

When the Regular Production Option (RPO) code LT1 is mentioned, it’s important to note that this RPO has been used on three completely different versions of the small-block Chevy. The first LT-1 was created for 1970 Corvettes and Camaros. This engine was a 350ci, rated at 370 horsepower with a single four-barrel carburetor. It came with a solid lifter camshaft and 11:1 compression. The second version of the LT1 appeared 22 years later in 1992 as the Gen II small-block, with a reverse cooling system and an ignition distributor located on the front of the engine driven by the camshaft. The ignition was called as the Optispark system. This Gen II engine was factory rated between 275 and 305 horsepower and used a hydraulic roller camshaft and a multi-point EFI system. The second LT1 and was used in the Chevrolet Camaro, Pontiac Firebird, Chevrolet Corvette, Chevrolet Caprice/Impala SS, Cadillac Fleetwood and Buick Roadmaster. An upgrade to this second version LT1 appeared in 1994 as the 330 hp LT4. This engine enjoyed larger intake port heads and more aggressive cam timing but was rare, only being found in the in the 1996 Chevrolet Corvette with a six-speed or the Grand Sport package, the SLP-modified Chevrolet Camaro SS, and the SLP-modified Pontiac Firehawk. It was eventually supplanted in 1998 by the Gen III LS1. The current LT1 first appeared in 2014 as the Gen V small-block. Following close behind was the second iteration of the LT4, this time as a supercharged upgrade to the LT1.

Cylinder Block


GM Gen V bare block mains

There are many changes to the GEN V block over the Gen IV - we’ll hit just a few here. The motor mount pattern has changed and there is a single bolt hole change at the top of the bellhousing pattern to accommodate the mechanical fuel pump.


The Gen V engine is a combination of carry-over and all-new components starting with the cylinder block. The original small-block Chevy’s 4.400-inch bore spacing and 90-degree V8 layout are retained (just like the Gen III/IV), but the details will amplify the story. Direct injection required provisions for the mechanical fuel pump that is driven off the back of the camshaft with a tri-lobe eccentric. The pump location required moving the 12 o’clock bellhousing bolt location slightly to the passenger side to clear the fuel pump.


In terms of external changes, the external four-bolt block mounting lug spacing was also changed, so new motor mount adapters for engine swapping will be necessary. The oil pan rail is different as well. Other than these minor alterations, the Gen V block is a carryover although it does not appear that this block could be interchanged with Gen IV components.

Crankshafts


GM Gen V crankshaft flange

All Gen V engines also include an 8-bolt crankshaft flange, which is an upgrade over the Gen III and some IV engines with 6 bolts.


Again, here is more commonality with the Gen IV engines. The smaller, 5.3L truck engines sport a cast crankshaft while the 6.2L L86 truck and LT1 and LT2 Camaro and Corvette engines use a forged steel crank. The layout is also the same with the thrust located in the center main as with the Gen III /IV engines and both rod and main journal sizes also remain the same. Stroke is the same for all these engines at 3.622-inches including the 5.3L version and the 58x crank trigger wheel is also the same.


A change that GM retained that began with the Gen IV supercharged engines is an 8-bolt crankshaft flange. Earlier normally aspirated Gen III/IV engines used a 6-bolt pattern but all Gen V engines now employ 8 fasteners. The 8-bolt pattern was originally used on the supercharged LSA Gen IV engine.


There are actually two different LT1 crankshafts. The more traditional configuration is for the wet sump Camaro engine version while dry sump engines require a two-stage (scavenge and pressure) pump assembly which, like the Gen IV LS7 dry sump predecessor, requires a longer front snout to accommodate the more complex and deeper oil pump assembly. We’ll have more details on the dry sump portion in the lubrication section

Connecting Rods


Another carry-over component from the Gen IV is the connecting rods. The LT1 and its Gen V cousins all share the same 6.098-inch forged powdered metal connecting rods that were used in the previous generation GM engines. The center-to-center length is significantly longer than the traditional 5.70-inch small-block Chevy rod with a center-to-center length of 6.098-inches. The pin diameter also differs from the small-block Chevy’s 0.927-inch, now larger at 0.943-inch. All Gen V factory rods use a 9mm rod bolt

.

These rods are constructed using what is called fractured cap technology. Instead of the traditional process of cutting the cap from the rod after initial forging, the powdered metal rod caps are removed by fracturing the cap. This produces a rough texture between the cap and the rod which helps to accurately retain the rod cap under load. Unfortunately, this also eliminates the ability to rebuild the rod’s big end by traditional methods. While perfectly acceptable for use in mild performance applications, under high rpm and/or high horsepower use, the recommendation is to upgrade with a traditional forged 4340 steel rod as inexpensive insurance.

Cylinder Heads


Of course, the first major change incorporated into these heads is the direct port injection into completely new head castings. The port of entry for the fuel is between the intake and exhaust valves directly across from the spark plug. In terms of chamber design, the idea is to minimize the volume and surface area to maximize efficiency, which the Gen V does very well.


Way back in 1955, the original small-block Chevy’s valve angle was 23 degrees. This angle is referenced against a line parallel to the bore, making the valve angle 23 degrees from vertical. As knowledge of airflow progressed, these angles have progressively moved toward vertical. The ‘60s big-block Chevy introduced a canted angle to tilt the valve head away from the cylinder wall to improve flow. By the late ‘90s, the Gen III engine pushed the angle to 15 degrees and the LS7 bumped that to 12 degrees.


The Gen V engine combined the advantages of a taller intake valve angle of 12.5 degrees with a splayed or tilted angle of 2.6 degrees similar to the Rat motor. The exhaust valve also moved to 12 degrees with a 2.4-degree tilt. All of this is aimed at improving airflow from what were already large rectangular intake ports.


On top of everything else, GM engineers also re-oriented the valve layout. Gen III/IV engines organized the LS into a symmetrical port configuration similar to the traditional small-block Ford. This eliminated the siamesed pairing of the small-block’s center exhaust ports. The Gen V places the exhaust port on the leading edge of the front cylinder whereas the Gen III/IV placed the intake port at the front. This re-orientation was performed to allow a more direct path between the intake manifold and the cylinder. Of course, the Gen V camshaft lobe layout also had to change to mimic the heads.


Another change that is more obvious is the extremely large intake port configuration that is closer to a square with a wider base compared to the Gen IV’s vertical rectangle orientation. Comparing volume numbers can often be deceiving, so be wary of direct comparisons between the LT1’s intake runner at 297cc with the previous rec port LS3 at 257cc. The LT1’s intake valve is actually slightly smaller than the Gen IV LS3 heads with the Gen V at 2.13 / 1.59-inches while the earlier LS3 sported the same size exhaust but a larger 2.165-inch intake. The 5.3L engines with smaller bores breathe through smaller valves. Advancements in chamber design now spec increasingly tighter chambers so the LT1/LT2 measure barely 59cc’s while the supercharged LT5 is slightly larger at 65cc’s to compensate for the added boost pressure.


The exhaust ports are still space symmetrically and exit in roughly the same relationship to the Gen III/IV heads, but the Gen V bolt holes are in a completely different location. This means that headers or manifolds for a Gen IV will not bolt up to the LT or any of its immediate family members. We can expect that Gen V headers should be fairly quick in forthcoming since manufacturers will only need to re-orient their exhaust flanges and drill new bolt holes.

Pistons


GM Gen V Piston

All of GM’s gasoline direct injection (GDI) engines feature a computer-designed reservoir in the piston crown where the fuel is injected. This creates a pre-chamber to expedite the combustion process. The LT1 static compression ratio is an amazing 11.5:1. Also note the coated rod bearing that is OE on both the LT1 and LT4.

GM Gen V oil squirters

Increased power means more heat in the pistons, so all Gen V engines now use oil squirters aimed at the back side of the piston to control crown temperatures.


Gen V pistons can be immediately identified by the “sugar scoop” or small depression in the middle of the piston crown. This scoop area is designed as a pre-chamber area intended to enhance initial combustion. The flame front is then aimed in the direction of the exhaust side of the chamber. There is talk that this pre-chamber area may not be necessary for a high rpm competition engines and some direct injection pistons are now being made without the sugar scoop area.


The pistons are cast hypereutectic aluminum with a factory anti-friction coating on the skirts. The wrist pin diameter is a carry-over from Gen IV at 0.943-inch and the pistons are of a full floating configuration.


The ring package is also new and thinner. Gen III engines started with a 1.5mm top and 2nd ring with a 3.0 mm oil ring .Some later engines used a 1.2mm / 1.5mm / 2.5mm package. There has been a lot of misinformation out there about the new Gen V engines using thinner rings, so we asked our friends at Scoggin-Dickey Performance Center to measure the rings on the LT1 and they found the ring package at 1.2mm / 1.5mm / 2.5mm, which is the same as the earlier Gen IV engines. Thanks to Nicky Fowler, Kurt Urban, and Keith Wilson at Scoggin-Dickey for clearing up this misinformation.

Camshafts


GM Gen V Camshaft

The Gen V camshaft is significantly changed with its new tri-lobe mechanical fuel pump lobe at the rear (arrow). The VVT drive at the front of the cam is similar to the Gen IV’s orientation.


Valve timing on early Gen III engines was relatively conservative and has gradually become more aggressive. But with the inherent advantages of variable valve timing (VVT) standard on all Gen V engines, the designers can add a little more duration to even mild truck engine applications. VVT allows the freedom to advance the camshaft at lower engine speeds to regain what may have otherwise been lost with longer intake or exhaust duration specs. VVT can then retard the position of the camshaft by several degrees and add even more power at the top end.


In a recent dyno test at Westech Performance Group in California, moving the VVT numbers in an attempt to change power only resulted in lost power with no ultimate improvements. The obvious conclusion from this initial attempt was that with stock cam timing, it is best to leave the VVT alone as any change will likely result in a loss of either low-speed torque or top-end power.


We’ve included a chart with some Gen V cam specs that reveal how impressive these engines are even with conservative cam timing. The LT1’s 200/207 degrees of duration at 0.050-inch tappet lift generates over 0.550-inch of intake valve lift using the factory 1.8:1 rocker ratio. Recent Chevrolet numbers released on the C8 Corvette’s LT2 engine added 18 degrees of duration on the exhaust side along with a 4-degree increase in duration on the intake side. Lift did not significantly change compared to the LT1 specs but the added duration is certainly a big reason for the increase in the LT2’s peak horsepower to 495 (with the tubular exhaust). All the specs are listed in the cam specs chart. We did not list the duration at 0.050 numbers for the LT2 camshaft as they are not officially listed in the data that Chevrolet released but you can assume they will be slightly longer in duration than the LT1 specs.

Valvetrain


GM Gen V valvetrain

There are lots of Gen V details here that are different. With the valve layout reordered, the 1.8:1 rockers are now all the same as opposed to offset intake rockers with the Gen IV rectangle port heads. The exhaust port flange pattern has also changed so Gen IV headers won’t interchange with Gen V. Also note the return to a perimeter valve cover bolt arrangement.

GM Gen V Active Fuel Management cutaway

All LT1, LT4, L83, and L86 engines include AFM technology. AFM controls the lifters for four cylinders (identified by the springs on top of the lifters) that deactivate valve action through ECU control. The LT5 is not fitted with AFM components. Also, there are minor cam timing differences between AFM lobes and non-AFM lobes. All Chevrolet Performance LT crate engines retain the production lifters but AFM is deactivated in the matching Chevrolet Performance Controller.


There’s plenty to talk about with the Gen V valvetrain since GM has elected (in certain engines) to make this system much more complicated. Most Gen V’s are now equipped with Active Fuel Management (AFM). This was originally a system created for the Gen IV engines that is often referred to either as cylinder deactivation or displacement on demand. Gen IV engines used what is called a Lifter Oil Manifold Assembly (LOMA) that, when triggered by the ECM, would apply oil pressure to disable four pairs of hydraulic lifters. The lifters then became essentially lost motion devices where the lifter body still moved up and down following the cam lobe, while the pushrod remained stationary. Cam lobe lift was absorbed by the small piston inside the hydraulic lifter body.


AFM system has been retained with the LT1 but in 2019 was enhanced with the development of Dynamic Fuel Management (DFM). Dynamic takes control of all eight cylinders and 16 lifters and has the capacity to offer 17 different configurations of cylinder deactivation. The earliest offering came in 2019 and is mostly aimed at light duty 5.3L and 6.2L Silverado trucks. The LT1 retains AFM but has evolved away from the LOMA to four oil control valves (OCV) managed by the ECM. Full DFM employs eight OCV’s working all 16 lifters.


Use of both AFM and DFM varies with vehicle application. The new LT4 engine for example incorporates AFM and controls cylinders 2, 3, 5 and 8. The AFM and DFM lifters can be quickly identified as they are taller, using a large coil spring situated on top of the lifter. Conversely, the higher output LT5 supercharged engine is not fitted with AFM.

GM LT1 Oil Control Valve lifter valley cover

012 The LT1 incorporates AFM but does not use a Lifter Oil Manifold Assembly (LOMA) but instead a redesigned lifter valley cover with four oil control valves (OCV) mounted on the valley side of the cover. This image includes the AFM style lifter that is easily identified by the coil spring located on the top of the lifter.


Another of the dizzying array of alphabet soup abbreviations and acronyms is variable valve timing (VVT), which has also been carried over from the Gen IV family branch. The system is pretty much a carry-over so if you are already familiar with its function, we need not duplicate that effort here.


Another small yet significant change to the Gen V valvetrain is the upgrade from the Gen III/IV 1.7:1 rocker ratio to a steeper 1.8:1.With valve lift numbers hovering around 0.550-inch on both the intake and exhaust sides, this additional ratio creates a much more aggressive valve action even with somewhat similar cam timing numbers. This also demands a much stiffer valvetrain and better valvesprings to withstand the increased valve acceleration rate created by the additional ratio. The pushrods have also been upgraded. Gen V engines use an 8.7mm (0.342-inch) vs. smaller 7.9mm (0.311-inch) used on earlier LS engines which is almost identical to the standard small-block 5/16-inch pushrod diameter.

Lubrication System


GM’s made it a bit confusing on this side of the ledger since the Gen V engine has been fitted both as a wet and a dry sump engine. The wet sump engines were bolted into Camaros while the Corvettes enjoy the dry sump configuration. Wet sump engines use a variable-vane style pump while dry sump engines use a gerotor for the scavenge side and a variable vane pump for pressure. The wet sump orientation is similar in layout to the Gen IV versions with its crank-mounted pump pulling oil from the cast aluminum pan. The filter is located on the left or driver rear side of the engine. The oil pan is also a different bolt pattern compared to the Gen IV engines, so they are not interchangeable.


Because the LT1 and L86 engines are fitted with both VVT and AFM, these engines require a different oil pump compared to Gen IV engines. This is mainly due to the higher volume required for valvetrain control. Adding to the complexity is the dry sump application where GM stacked a gerotor pump in front of the original pump. This operates the scavenge side that evacuates oil from the oil pan and pushes it to the external dry sump tank. The pressure side pulls oil from the dry sump tank and pumps it through the engine. A third pump on the LT2 engine was added in the lifter valley to pull oil from this area that has been blocked off to prevent oil from splashing down onto the cam and crankshaft thus improving windage.


Another minor issue that the dry sump eliminates is the long pickup tube extending from the front-mounted oil pump to the rear on wet sump engines. On startup, the pump requires a moment or two for it to pull oil from the sump into the pump to create pressure. This tends to exacerbate bearing wear since a large portion of wear occurs during initial startup before oil pressure is created and separates the crank from the bearing. With dry sump engines, the oil pump is constantly primed by the oil reservoir that is located above the inlet to the pump, so pressure builds almost instantly. It’s a small point, but worthy of mention.


If you purchase an LT4 crate engine, the instructions list minimum hot oil pressure specs that are somewhat surprising. The instructions offer a minimum acceptable oil pressure at idle of 6 psi at 1,000, 18 psi at 2,000, and 24 psi at 4,000 rpm. Keep in mind that these are minimums running the 5w30 Dexos 2 oil. 15w50 Mobil 1 is also published as acceptable.


There is a large finned aluminum rectangle fitted to the LT4 engines on the lower driver side that is a liquid-to-oil cooler. Unfortunately for engine swappers, this will almost always need to be eliminated or relocated in order to fit the engine in an earlier chassis.

Induction


GM Gen V injector layout

Direct Injection requires a large, mechanical fuel pump at the back of the engine with hard line plumbing used to accommodate the over 2,000 psi fuel pressures required to inject at high engine speeds. Also note that the fuel pump required a slight relocation of the upper bellhousing bolt hole (arrow).

GM LS vs LT spark plug comparison

In addition to the major changes, the LT family also uses a longer thread reach spark plug (right) compared to a typical LS plug (left). This moves the plug even closer to the center of the combustion chamber.


The switch to direct injection means that the injector has moved from the intake manifold port to the cylinder head. Plus, with a much larger intake port opening, this demanded revisions to the Gen V intakes. We mentioned this at the beginning of the story but it’s worth noting again that the L86/L87 6.2L truck engines use a completely different intake manifold, front accessory drive, and oil pan compared to the passenger car LT1. However, internally these engines are the same, which means compression, cam timing, and cylinder heads have not changed from the LT1. So if there is a Gen V engine in your future, consider looking for an L86 truck version as potential engine swap material.


As you might expect, the truck intake manifolds feature longer runners to enhance low-speed and mid-range torque compared to the Corvette or Camaro intakes that emphasize peak horsepower. As mentioned, these intakes completely interchange. Both the L86 and LT1 engines employ an 87mm throttle body.


In terms of aftermarket upgrades, MSD now has a very nice, two-piece polymer material intake that offers a 103mm throttle bore opening for a larger throttle body although the stock unit will work. Testing has show up to a 20 horsepower improvement over the factory LT1 intake. This would make a fantastic upgrade for the L86 truck engine as a swap candidate into an older muscle car.


The 2020 LT2 Corvette engine offers an updated manifold that is 3 inches taller than the LT1 version but still retains its 87mm drive-by-wire throttle body. Chevrolet claims the manifold adds three percent power to the LT2 engine with significantly improved port-to-port air distribution compared to the LT1. The LT2 runners are all equal length at 210mm (8.26-inches) in length while the LT1 runners vary a bit. This runner equality may be one of the reasons (along with a larger plenum) for the power gains above 5,200 rpm. While it appears the LT2 manifold will interchange with previous Gen V engines, this has yet to be confirmed.


The LT2 in-cylinder fuel injectors are dramatically larger in flow capacity and operate at exaggerated pressures compared to electronic port fuel injectors. LT1 injectors are rated at 114 lbs/hr at 2,205 psi maximum operating pressure while the LT4 supercharged engines employ a larger 143 lbs/hr injector. These output numbers may seem extremely high but keep in mind that direct injection engines are limited to extremely short injection duration periods, so the injector output volume must be very high along with the injection pressure. A typical multi-point factory fuel injector located in the intake manifold of a Gen IV 6.2L LS3 for example is 42 lbs/hr, but this injector has far more time to inject fuel than in-cylinder injectors.


Remaining on the topic of injectors, The LT5 supercharged engine that we will discussion in the next section employs both the same in-cylinder direct injection but then adds port fuel injectors to supply the additional fuel required to make the LT5’s added horsepower. The LT4 and LT5 engines use the same injector, verified through Scoggin-Dickey.

Factory Superchargers


GM LT4 cutaway by Kimble

The LT4 was GM’s first shot at LT supercharging. This David Kimble cutaway offers an x-ray view of the internals. Inside the supercharger, note the small butterfly connected to a vacuum canister. At part throttle, this valve opens and bypasses the supercharger, reducing pumping losses and improving mileage. This engine also sports VVT.


Having set the precedent with superchargers on the Gen IV engines, it’s not surprising that GM would follow that success with the Gen V engines. The initial Gen V effort used a smaller 1.7L blower on what was essentially an LT1 with less compression called the LT4. The idea was to employ a smaller 1.7L (down from the previous 2.3L) supercharger but spin it faster to improve responsiveness.


In all these Roots style blowers, GM uses a small bypass valve that at part throttle redirects airflow around the supercharger and the intercooler to aim it directly into the engine’s inlet ports. At the appropriate rpm and manifold pressure, this valve closes and all the air is directed through the supercharger. Even with the smaller blower, the LT4 cranked out 650 horsepower and 650 lb-ft of torque pushed by 9.7 psi of boost using a vacuum-controlled bypass valve. Given the conservative nature of the current OE correction factor, this engine is likely closer to 680 horsepower if run on an aftermarket dyno using the older standard correction for temperature and pressure.


Of course in today’s escalating horsepower wars, it didn’t take long for GM to respond to the Mopar shots across the bow with its supercharged late-model Hemi. The GM response was the current LT5. This raised the stakes on the LT4 by using a larger R2650 (2.65L) Eaton supercharger placed on a similar 6.2L long block. The larger blower demanded a wider 11-rib belt compared to the LT4’s 8-rib drive but feeds as much as 13.9 psi through a 95mm throttle body using an electronically-controlled bypass valve. All this is worth a substantial amount of power, generating a 755 horsepower rating at 6,400 with 715 lb-ft of torque.


Besides the LT5 52 percent larger blower size is the addition of a second set of multi-point injectors located in the supercharger manifold. At partial boost, the engine continues to operate in full direct injection mode but at a predetermined point, the upstream injectors kick in supplying additional fuel to achieve the 755 horsepower rating.


We also found some interesting specs in an SAE report that indicates it requires a full 110 horsepower to spin this larger supercharger compared to 94 horsepower for the 1.7L version at maximum boost. This means that the actual power generated at the crankshaft is much closer to 865 horsepower with 110 lost to spinning the blower.

The New 6.6L L8T

GM L8T V8

The latest addition to the Gen V family is a brand new gasoline direct-injection 6.6L engine that will be used in heavy-duty GM trucks. L8T is the RPO code for this engine and is based on the Gen V LT1 architecture but sports a longer stroke at 3.858-inches versus the LT1’s 3.62-inches. The engine is intended to build useful torque at low engine speeds and the easiest way to do that is by adding displacement. The forged steel crankshaft adds the necessary stroke while compression is limited to 10.8:1 since this engine is intended to operate on 87 octane fuel. There is limited information on this engine which is why there are only limited details listed in the accompanying chart. The block is siamesed but engineers did place passages to improve cooling and the block deck surface would appear to require a different head gasket but that information is not confirmed. The block will also share the Gen V bellhousing pattern. This engine uses a very tall, long-runner intake manifold with equal runner length that helps make the required low-speed torque. We can also assume that the cam timing will be very conservative as that also tends to enhance torque. The engine also uses a traditional wet sump oiling system and the oil filter is still located in the conventional Gen V location. This engine also uses a very heavy-duty water pump with a larger, 1-inch diameter shaft to support the engine-drive fan that is stock on these engines. The added displacement will likely make this 400ci Gen V a popular engine swap candidate in the coming years. More compression, a longer-duration camshaft, improved intake (assuming the intake is interchangeable with the LT1) and headers would clearly pump the power up on this engine. A mild performance version of this engine could easily make well over 500 hp and 500 lb-ft of torque. That mark is already achievable with 400ci LS Gen III/IV engines and increasing the compression with a DI engine only promises to add more potential to this latest branch on the GM small-block family tree. L8T Specs Displacement: 6.6L - 400ci Power: 401HP at 5,200 rpm, 464 lb-ft Torque at 4,000 rpm Bore and Stroke: 4.065 x 3.858 inches Compression Ratio: 10.8:1 Fuel: 87 octane Block Material: Gray iron Head Material: Aluminum Crankshaft: Forged Steel Pistons: Hypereutectic VVT Yes AFM No

Conclusion


The level of sophistication in the current generation of the small-block Chevy is certainly escalating. But so is the power this engine produces. Combine that with increased fuel efficiency from higher compression ratios that are a big part of direct injection along with a wider torque band thanks to VVT and what we have is an ultra-sophisticated pushrod V8 that shows no signs of retiring. A couple of decades ago, GM made the decision to stick with the pushrod V8 in response to Ford’s move to the overhead cam Modular engine. It would appear that the horsepower generated by these latest Gen V engines clearly overcomes the early criticism that the pushrod V8 was ancient technology. It would appear that GM engineers did indeed make the right choice at the right time. High performance GM fans are now enjoying the fruits of that momentous decision. The only question that might remain is what future surprises GM may have in store for the small-block of the future. It would appear that the new 6.6L engine offers plenty of promise!


Atomic p/n 2700

If you’re like most guys, you’re already looking for ways to make more power with the LT1 or upgrade an L86. MSD’s Atomic AirForce polymer two-piece intake is worth a solid 20 horsepower over the stock LT1 intake. It features a 103mm throttle bore that’s perfect for a larger bore throttle body.

Atomic P/N 2700 Opened

A peek inside the Atomic AirForce intake reveals the computational fluid dynamics (CFD)-perfected ports that offer serious airflow opportunities.


Firing Order1-8-7-2-6-5-4-3
#1 cylinder left bank, forward
Block319-T7 aluminum deep skirt block, cross-bolted mains, except:
L8T: gray iron
Bore LT1 / LT4 / L86 / LT5/L8T: 4.065
 L83 5.3L: 3.78
Stroke3.622, except:
L8T: 3.858
Engine WeightLT1: 550 lbs.
LT4: 570 lbs. (weights are approximate)
Bore Spacing4.40 inches
Deck Height9.240 inches
Bank Angle45°
Cylinder Offset0.949 inches, left bank forward
Main Journals5, thrust at #3
Main Journal Housing Dia.2.751
BalanceInternal
CrankshaftL83: Cast iron
L86, LT1, LT2: Forged Steel
LT4: Hardened Forged
LT5: Hardened Forged (higher heat treatment than LT4)
Crankshaft reluctor58x
Crankshaft main journal dia.2.559 nominal
Crankshaft rod journal dia.2.0995 nominal
Flywheel bolt patternLT1 - 8 bolt
Connecting Rod Length6.098 inches
Camshaft journal dia.55mm (2.163")
(Gen 1: 1.868")
Camshaft attachmentOne bolt
Cam gear poles4x
LiftersHydraulic roller, 0.842 inch dia.
Rocker arm ratio1.8:1
Hydraulic lash adj.Net lash design - lifter preload set by pushrod length
PistonCast hypereutectic aluminum
LT4 and LT5: forged aluminum w/ graphite coating floating wrist pin
Piston compression HeightLT1: 1.340
Piston ring packageLT1: 1.2mm / 1.5mm / 2.5mm
LT4 and LT5: 1.2mm / 1.2mm / 2.5mm
Piston pin dia.0.943, full-floating
Oil pump Wet sump: Crankshaft mounted, variable vane
Dry sump: Variable vane pump for pressure, gerotor scavenger
Cylinder head materialAluminum 356 T6, except:
L83 and L86: 319-T7
LT4 and LT5: A356T6 Rotocast
Cylinder head port styleRectangle
Valve sizesL83: 1.93 / 1.55
LT1 and LT2: 2.13 / 1.59
LT4 and LT5: 2.13 / 1.59 titanium intake valves
Valve angleIntake: 12.0°, 2.6° splay
Exhaust: 12.0°, 2.4° splay
Combustion chamberL83: 57.5cc
L86, LT1: 59cc
LT4, LT5: 65.47cc
Intake runner volumeL83: 248cc 
L86, LT1: 297cc
Exhaust runner volumeL83: 102cc
LT1: 107cc
Spark plugIridium-tipped
Intake manifoldOne-piece composite
ThrottleElectronic drive-by-wire
Throttle body dia.87mm, except:
LT5: 95mm
Fuel pressureLT1: 2,205 PSI
LT2: 2,175 PSI
Engine oil5w30 Dexos 2 or 15w50 Mobil 1 
EngineDisplacement
(CID)
BoreStrokeCompression
Ratio
Horsepower/
Torque
5.3L L83 and L843253.7803.6211.0:1355 / 383
6.2L L86 and L873764.0653.6211.5:1420 / 460
6.2L LT13764.0653.6211.5:1460 / 465
6.2L LT23764.0653.6211.5:1495 / 470
6.2L LT43764.0653.6210.0:1650 / 650
6.2L LT53764.0653.6210.0:1755 / 715
6.6L L8T4004.0653.85810.8:1401 / 464
EngineDuration @ 0.050
(degrees)
Valve Lift
(inches)
LSA
L86 Intake
2000.551116.5
L86 Exhaust2070.522
LT1 Intake2000.551116.5
LT1 Exhaust2070.522
LT2 Intaken/a0.551n/a
LT2 Exhaustn/a0.551
LT4 Intake1880.502120
LT4 Exhaust2230.561
LT5 Intake1890.492120
LT5 Exhaust2230.551
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