Inside the New Chevrolet Performance 6.6

Sep 12, 2023

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You know all that talk about the death of the V-8 and the end of gasoline? Yeah, well, for the foreseeable future, that talk is bovine excrement. You see, the EV world has a problem (well, more than one, but let's stay focused) and the hurdle it has yet to clear without falling on its face is that EV trucks are awful at towing a heavy load any sort of meaningful distance. The new electric Ford Lightning, when not in a delivery freeze for "battery issues," can only manage under 90 miles when pulling a decent load. Who wants to deal with that nonsense? Nobody that wants to pull a heavy load any distance without hours spent watching a charge meter slowly tick upwards, that's who.

But what does that have to do with us? Well, for now, trucks that don't suck need internal combustion to get the job done, so companies like GM are continuing to develop new production V-8s, and that means modern crate engines and eventually salvaged engines for our hot rods.

Enter the Chevrolet L8T (PN 19433748). We're not sure why they named it this way, but it's a new V-8 so we don't really care what they call it. Developed to be the heart of the newest Silverado 2500HD and 3500HD trucks (as well as the GMC versions) this new naturally-aspirated V-8 crate was announced last year and might be an engine perfect for your next swap project!

As that knife salesman says, "But wait, there's more!" This isn't just a revamped LT1 with an iron block (more on that in a minute). Displacing 6.6 liters (that's 403 cubic inches for the countries that have been to the moon) this is the largest LT-family engine currently being offered by Chevrolet Performance! The iron block adds weight, but it also adds strength for power-adders.

Peak power is listed as 401 horsepower at 5,200 rpm and a whopping 464 lb-ft of torque at 4,000 rpm! All that torque is what you would expect from a V-8 swiped from large production trucks. The only downside is that L8T's redline is only 5,600 rpm. This is nothing a cam swap or other simple mods couldn't change and GM has hinted that they might be up to something in that regard. But in all honesty, a top rpm limit of 5,600 rpm is fine for most cruisers—just pretend you have a big-block under the hood.

Remember that iron block we mentioned? Well, let those who worship the god of boost rejoice: The L8T block is made from cast-iron and has six-bolt nodular main bearing caps! It also comes from Chevrolet Performance with a forged-steel crank, forged powdered-metal rods, and hypereutectic aluminum pistons! It also has oil-spray cooling for the pistons, which is helpful in boosted applications. Compared to the LT1, the compression was dropped from 11.5:1 to an 87-octane friendly 10.8:1. Here you can see the slightly deeper pocket of the L8T's piston that, combined with a slightly larger combustion chamber of the L8T head, gave them the compression drop. The bore of the L8T is the same as the LT1 at 4.060 inches, but the stroke increased from 3.620 inches to 3.860 inches.

Like the rest of the LT family, the L8T is a direct-injected deal, so the fuel injector enters the party in the combustion chamber opposite the spark plug. This means there's a high-pressure fuel pump, driven off a lobe on the back of the camshaft, located under the intake to the rear of the valley cover. The L8T heads, just like the other LT-family heads, have large and high-flowing intake ports with the same 2.126-inch intake valves as the LT1, and Inconel exhaust valves that can stand up the higher exhaust temps of running boost! The L8T is available fully kitted-out (minus ECU and front drive system) or as a long block (PN 19433750) for those who want to choose their own intake, pump, and injectors.

The new crate L8T engine can run any intake the LT1 can, and there's a wide array of aftermarket oil pans already on the market to make swapping the engine into your project nearly painless. Currently, the L8T ships from Chevrolet Performance without an ECU option, but we were recently at GM and got the chance to drive their Cadillac CTS-V development car, which was fielding the new L8T crate engine! Seems the engineers at Milford were working on a tune that would make this mill have better throttle manners in a lightweight car, compared to the throttle response needed in a massive truck. We have to say, the engine felt great in the Caddy and had more than enough grunt to get in all sorts of trouble with.

By the time you read this, an engine control kit (PN 19433736) will be available to purchase, and it will have the calibration we test-drove in addition to an E93 tune, fuel pump power module, fuel pressure sensor, a couple of O2 sensors, MAF Sensor, electronic throttle pedal, and the engine harness! This will make swapping an L8T into a project even easier!

As you can see, the L8T looks like it belongs in the engine bay of the Caddy, just like it would easily fit into your project car. GM is pretty tight-lipped on future anything, but word at the water cooler is that they have big-plans for their new 6.6-liter V-8, including versions with a different cam profile and other changes. All we know for now is that we have a new, larger-displacement V-8 to play with, and we're looking forward to adding a bit of boost to the mix to see what we can coax out this new 6.6-liter iron-block crate engine.

The 6.6-liter iron block has already been put to the test by Kurt Urban at Scoggin Dickey (SDPC) and with a Holley Hi-Ram, Dominator ECU, forged internals, and other mods, made over 2,000 hp with a pair of 7685 Precision turbos! Though that's far from the stock crate engine, it goes to show the capabilities of this new 6.6-liter iron block. You can read all about their max-effort build here: Scoggin Dickey Makes 2,000 hp With Gen V L8T GM LT Engine Parts.

On episode 24 of Engine Masters, the team explores one of the most-asked tech questions: What budget bolt-ons can be used on a stock small-block Chevy 5.7 to get more horsepower? Watch as David Freiburger, Steve Dulcich, and Steve Brule take the cheapest Chevy 350 crate engine you can buy and make mods that gain nearly 130 horsepower! It's a dyno-proven, easy-to-install power combo that will give you the best bang for your buck. Sign up for a free trial to MotorTrend+ today and start watching every episode of Engine Masters, plus much more!