As you probably know, the Gen III and Gen IV small block engines are part of the insanely popular LS engine family. We’ve discussed the GM LS engine in-depth in previous articles and what makes them so popular.
The Gen V small block, codename LT, has been out for quite a while now and GM uses it in a ton of different vehicles, and the LT is starting to become popular for engine swaps.
The LT Family
Being that the LT engine is the next generation of the GM small-block engine, it shares a lot of similarities with the previous Gen III and Gen IV engines, however, there are almost no parts which interchange from LS to LT. The Gen V LT was originally introduced in the 2012 Corvette C7.
Like the LS engine it was replacing, the LT features an all-aluminum design and coil near plug ignition. One of the biggest differences between the LT and the LS it was replacing, is the LT’s direct injection fuel systems.
The LT V8 engine family currently includes the LT1, LT2, LT4, LT5, L83, L86, L8T, and a few others. All of these engines feature the previously mentioned direct injection fuel system, variable valve timing, active fuel management, electronic throttle control, and other advanced features.
It should be noted that the L8T uses an iron block, but is otherwise the same as other LT engines.
Another design feature which was taken from the Gen III and Gen IV engines is the Y-block design. The Y-block design helps increase rigidity in the main cap area by using 6 bolt main caps on the crankshaft.
Four bolts are facing vertically, and two bolts horizontally that clamp the block wall to the main cap. This design provides great crankshaft and block rigidity.
Cast-in-place cylinder liners result in an all-aluminum deck face with induction liner heating utilized for dimensional control. This results in an exact placing of every cylinder in every block. Nodular iron main caps, retained with six cross-bolts, replace previous efforts where powder metal was the norm.
Just like the LS, the camshaft of the Gen V is up and far away from the crankshaft, allowing for the use of a 4” crankshaft, however, there currently isn’t any LT engines which use a 4” throw crank from the factory.
In addition to the redesigned main caps, every cylinder features oil-spray piston cooling, where eight oil-spraying jets in the block drench the underside of each piston and the surrounding cylinder wall with an extra layer of cooling, fiction-reducing oil. This reduces piston temperature, promoting extreme output and durability.
The Gen V aluminum block maintains the bore spacing and main dimensions, but makes minor changes to items like the motor mount bolt pattern as well as moving the top’s bell housing bolt location.
The Gen V camshaft is unlike its predecessors, using a front-mounted variable valve timing control mechanism while at the rear employing three lobes to drive the mechanical fuel pump.
All Gen V engines are built with variable valve timing that offers an enormous swing of over 60 degrees of authority over the camshaft position. This is carefully engineered to improve low-speed torque and top-end power so it’s not necessarily a bad thing.
It should be noted, that unlike previous GM small-block engines, installing an aftermarket camshaft is more complicated than it used to be. In the LT1, can’t simply drop a new camshaft in without removing the oil pump, which now means you also have to drop the oil pan.
In the case of the C7 Corvette, dropping the oil pan requires dropping the subframes, making a simple cam install a lengthy process.
For the intake manifold, GM used an all-new design, allowing air to get the combustion chamber easier. More impressively, the imbalance of airflow is reduced 50% compared to the outgoing small block.
What GM is calling a “runners in a box” design, the intake manifold is composed of composite material which keeps the weight low while maintaining a high thermal tolerance, while air is fed through an 87 mm-wide throttle body.
Electronic Power Steering
One thing you might notice on most Gen V LT engines is the lack of a hydraulic power steering pump. Cars that use the LT engine offer electric power steering and have no need for the hydraulic pump. Gen V trucks, however, do have a hydraulic power steering pump.
Direct Injection Fuel
As mentioned earlier, one of the biggest changes from the LS to the LT is the direct injection fuel system. At the back of the engine underneath the intake manifold, the LT1 features a high-pressure fuel pump.
Hard lines are used to transfer the fuel to the in-cylinder injectors because the fuel pressure can exceed 2,200 psi. The direct injection system is what allows the LT to use very high compression ratios, even with forced induction like the LT4 and LT5.
Looking at the combustion chamber, you can see the position of the mechanical fuel injector nozzle opposite the spark plug. It’s hard to see but each nozzle contains six smaller holes that help the transition from liquid fuel to vapor, which burns much more completely.
GM is said to have spent more than 6 million hours on computational analysis to design the direct injection combustion system.
At first glance, when it comes to the LT1 cylinder heads, the reversed valves and their splayed relation are one of the most noticeable differences when compared to the LS series.
The reality is that every square inch of the LT1 head has been redesigned to support the direct-injection fuel system, from the piston topography to the combustion chamber to the valve locations to the intake and exhaust ports to the spark plug and fuel injector location, all allowing for a higher than ever compression ratio across all Gen V engines
The high compression ratio, direct injection system, variable valve timing, and superb head flow allow the LT to output impressive power in naturally aspirated and boosted applications. In the case of new LT2 used in the C8 Corvette, power output is around 490 horsepower.
Everything we’ve talked about so far relates to the stock Gen V engines, but like previous small-blocks, the Gen V comes alive with modifications.
It didn’t take long from the Gen V’s release in 2013 for tuners to get their hands on it and start developing parts. From basic bolt-ons up to stroker kits and superchargers, anything you want for the LT is already on the market. In the case of the LT1, naturally aspirated builds push over 700hp with a 7.0L stroker.
Size and Weight
Just like previous GM small-block engines, the LT is very small for the displacement it offers. The pushrod design allows the Gen V engines to be significantly smaller than competitor’s engines which pretty much all use a dual-over-head-cam design which is superior on paper but takes up a lot of space than an over-head-valve design.
Thanks to the all-aluminum design of most Gen V LT engines, they weight nearly as much as a cast-iron 4-cylinder engine.
Displacement options for the LT engines currently include the 5.3L L82, L82, and L84, the 6.2L LT1, LT2, L86, LT4, and LT5, and the 6.6L L8T. We may see other displacement options in the future, but as of right it’s just 5.3L, 6.2L and 6.6L.