While the rest of the automotive universe is content to LS/LT swap the world… dropping a Chevrolet Performance crate engine LT4 into a vintage Pontiac feels a bit naughty. We’re talking 50 shades naughty. Something you’d do for great satisfaction but wouldn’t tell your Mom and Dad about. They probably wouldn’t understand anyway.
Here’s the down and dirty of the deal: We’ve taken a sweet, legendary vintage muscle machine and put a modern spin on the entire idea of vehicle consummation. We started with the foundation, substituting the soft and flexible parameter-frame suspension with a purpose-built chassis from Schwartz Performance. Now we’ve gotten to the hidden personality of the build, the thing from which potential is derived, the engine and transmission.
Follow along as we walk through the drivetrain swap and discuss the features and benefits of the Chevrolet Performance LT4 crate engine Connect and Cruise kit. We promise to pull out some other goodies from our pleasure room (AKA: The garage), to complete this conversion.
The initial goal with this project build is to make a race car that can compete in autocross or street racing events. This could be done in a vast number of ways. What we didn’t want to lose in the process was the old-school flavor the Pontiac GTO was known for.
Using a pushrod GM crate engine in a chassis specifically built for a GM A-body application was the best way we could pay homage to the original GTO and still be combative with its modern peers. Submissive was not one of the 50 shades used in this monochrome built.
GM’s supercharged Gen V Small-Block LT4 is offered with either a wet-sump or dry-sump lubrication system from the factory. Speaking of factory engine, not only do you get the second most powerful engine ever offered in a regular-production Chevrolet, it comes factory-stock and fully-warrantied.
A 24-month or 50,000-mile limited factory warranty is a nice thing to have when you’re spending your own dough on some muscle. Because it is made at the factory, there are economies of scale that your local machine shop cannot take advantage of, which helps keep the base price down.
GM unleashed a new small-block engine in 1991 that featured the same configuration as the previous generation of small-blocks. The LT1 was a 90-degree 350ci V8 with a pushrod valvetrain and two valves per cylinder. The most significant difference between this generation small block and the earlier GM small blocks was the reverse-flow cooling system.
By reversing the flow in the LT1, the engine coolant ran through the cylinder heads first. This allowed the combustion chambers to run at a lower temperature, enabling the engineers to put together an engine with higher compression without fear of pre-detonation. Higher compression generally means higher power.
In 1996, a special high-performance version of the LT1 was introduced in the 1996 Corvette. This engine was dubbed the LT4, and featured several performance upgrades that were normally reserved for well-funded race teams. These improvements led to increased horsepower and overall weight reduction.
The Original LT4
The original LT4 engines were only available in the 1996 Corvette equipped with the 6-speed manual transmission (6,359 produced). However, when a few extra LT4 engines were found in the factory, someone got the bright idea to put these into special versions of the 1997 Camaro and Firebird.
Two Camaro prototypes were made, then 106 completed Camaro SLP/LT4 SS cars (100 U.S. and 6 in Canada) were rolled off the assembly line. Only 29 Pontiac Firebird SLP/LT4 Firehawks were made. Almost all of these cars were snapped up before they ever left the factory with very few, if any, actually reaching a showroom floor. Needless to say, these are very rare and hard to find.
The Modern Gen V LT4
The latest iteration of the LT4 was introduced in 2015, in the Z06 Corvette. After the rollout, there was little doubt what GM’s intention was with the LT4 platform: To build a high-performance engine that was race track compatible. The biggest addition was a 1.7L Eaton TVS Supercharger forced induction system. As the heart of the Corvette Z06, the supercharged LT4 6.2L SC is the second most powerful engine ever offered in a regular-production Chevrolet.
This version continued to use the direct fuel injection, active fuel management, and variable valve timing that was pioneered with the LT1. The original LT4 engine came with a dry-sump oil system only. The new GM crate engine versions can be purchased with either a dry- or wet-sump oiling system. New cylinder heads were also added to support the forced induction (higher cylinder pressure) in the form of Rotocast A356T6 aluminum cylinder heads.
The Rotocast method of casting requires the mold to rotate for an even distribution of the molten alloy. The principle behind this is to create a denser casting by eliminating porosity. Not only does this create a denser cylinder head, but the A356 aluminum alloy has higher strength and considerably higher ductility after the T6 heat treatment than conventional aluminum heads.
The GM LT4 offered by the factory today is similar but very different from the one that debuted in 2015 under the hood of the C7 Corvette Z06. It is even more different than the other crate engines offered by Chevrolet Performance, which means it takes some special components to make everything play nice when transplanted into a new frame.
- Displacement: 376ci (6.2L) supercharged Gen V Small-Block V8
- Part Number: 19417413 (wet sump)
- Maximum recommended RPM: 6,600
- 650hp @ 6,000 rpm
- 650 lb-ft @ 4,600 rpm
- 10.0:1 compression ratio
- Bore x Stroke (in): 4.065″ x 3.622″ (103.25 x 92mm)
- Block: Cast aluminum with 6-bolt, cross-bolted main caps
- Crankshaft: Forged steel connecting rods: forged powdered-metal steel
- Pistons: Forged aluminum
- Camshaft Type: Hydraulic roller
- Valve Lift (in): 0.492″ intake / 0.551″ exhaust
- Camshaft Duration (@0.050 in): 189° intake / 223° exhaust
- Cylinder Heads: A356T6 Rotocast aluminum; as-cast with 65.5cc chambers
- Valve Size (in): 2.130″ intake / 1.590″ exhaust
- Rocker Arms (P/N 12619829): Investment cast, roller bearing trunnion
- Rocker Arm Ratio: 1.81:1
- Recommended Fuel: Premium pump
- Reluctor Wheel: 58x
- Balanced: Internal
Getting The Crate To Play Nice With Others
While you can buy the LT4 as a crate engine, the smart move is to pick up GM’s complete LT4 Connect and Cruise Powertrain System. The crate engine does not include any electronics like the Engine Controller kit but does have the direct injection, VVT, and Active Fuel Management onboard. Making the engine, transmission, electrical, hydraulic, and mechanical parts all work together in terms of clearances and function can be a difficult proposition without a controller.
Chevrolet Performance takes away most of the confusion and frustration with the Connect and Cruise powertrain systems. All you need to do is figure out what options you want. In the case of the LT4 engine, enthusiasts can choose between the dry-sump or wet-sump options in manual or automatic transmission configurations.
LT4 Connect and Cruise Systems Offered:
- LT4 Wet-Sump Connect and Cruise Powertrain System with 4L75E automatic transmission (Part #CPSLT4W4L75E).
- LT4 Dry-Sump Connect and Cruise Powertrain System With 4L75E automatic transmission (Part #CPSLT4D4L75E).
- LT4 Wet-Sump Automatic Connect and Cruise Powertrain System W/ eight-Speed automatic transmission (Part #CPSLT48L90E).
- LT4 Wet-Sump Manual Connect and Cruise Crate Powertrain System (Part #CPSLT4WT56).
- LT4 Dry-Sump Manual Connect and Cruise Crate Powertrain System (Part #CPSLT4DT56).
We opted for the wet-sump manually shifted Connect and Cruise Powertrain System for Project Payback GTO. Initially, we wanted to go with the dry sump to aid with ground clearance and prevention of any oil starvation issues when on the autocross track. Plus, there is another layer of cool factor when sporting a dry-sump.
Unfortunately, when we went to order our kit, there were only accessory drive systems for the wet-sump engine. Not knowing how long it would take for anyone in the aftermarket to make a drive system for a dry-sump configuration, we backed away from that choice. Given the LT4 engine was originally designed for a car with electric power steering and an air conditioning compressor that mounted in close proximity to the frame rail, the wet-sump seemed like a better option to us. It’s worth noting that even today, there are substantially more accessory drive options for wet sump LT4 engines.
Installing The Connect And Cruise System
The system we ordered (Part #CPSLT4T56W) not only included the LT4 engine but also combined a Tremec T56 Super Magnum six-speed manual transmission (19352208), engine control modules with harnesses (Part #19419241), and GM’s transmission install kit (Part #19329912). These kits are mostly plug-and-play, therefore they work well together and are easy to install. In fact, the engine control module is designed to work with a 4L75E or T56 transmission. You will need a three-pin fuel pressure sensor to round out the electronics.
Because we were mounting everything to our Schwartz Performance chassis, the entire procedure was simplified by the technology engineered into the frame. Normally, the stock body bolts onto Schwartz’s chassis with no fabrication or cutting required. However, we selected an engine and transmission combination different than typical drivetrain combinations. Plus, we were using a body that was designed for a GM automatic transmission and we were shoehorning in a wicked manual transmission.
The Schwartz Performance chassis came with adjustable Gen V-specific motor mounts which help set the engine back toward the firewall for better weight distribution. The GTO’s body was originally designed for a larger engine with an automatic transmission, so changing to a small block that was moved back and a beefy manual transmission, there was going to be some cutting and massaging of the tunneling and floorboard to make it all properly fit.
Make It Hurt!
The advantage of laying out a build plan in advance is knowing what other future upgrades are coming so when the slicing and dicing start, you can fabricate to make the future upgrades easier. For instance, we knew there would be some work on the firewall and transmission tunneling due to the engine/transmission swap. While we were there, taking care of things like the pedal box and air condition evaporator box could be dealt with for future aftermarket components.
Speaking of pedals, we needed to add a clutch pedal for the automatic to manual transmission swap. From past experience, we knew that finding factory parts is easy. We relied on Silver Sport Transmission for the pedals, hydraulics, and wiring necessary to get the job done correctly.
Silver Sport provided a template for the conversion but we were using an aftermarket chassis that differed greatly from the stock factory chassis. Because of the engine setback engineered into the Schwartz Performance chassis, the provided template was not compatible and we had to go it on our own. Our skilled fabricator took out enough of the floor and bent sheetmetal like a true pro. We ended up with a perfect custom tunneling that was topped with a decorative shifter cutout from Silver Sport that replaces the factory center console. It looked great and the shifter was placed perfectly to suit our taste.
Anytime you are doing an uncommon build, you can expect to find a problem here and there. One of the problems we ran into when dropping the engine/transmission combination into the Schwartz chassis was a clearance issue with GM’s wet sump oil pan. The factory wet sump pan simply would not clear the frame. We placed a quick call to the folks at Schwartz Performance where we were guided to Holley’s LT Retrofit oil pan (PN 302-20). Talking to the tech reps at Holley, we explained our intentions to road race the GTO. They recommended we also use the company’s oil pan baffle kit (PN 302-30) to effectively keep the oil pump pickup submerged. According to Holley’s tech department, this kit helps bridge the gap between a wet and dry sump during those high-g corners.
Not Finished Yet
While the drivetrain was firmly seated in its respective place within the chassis, we are far from being done with the conversion. We will be bringing more detailed feature stories relating to the drivetrain installation. At this stage in the build, there were some obstacles we avoided and some we navigated around.
One of the challenges of the Gen V crate engines is that they do not come with power steering pumps. Factory applications all have electric power steering. What’s more, the air conditioning compressor does not fit many restomod engine compartments, so we had needed to find a solution for that problem.
One of the biggest problem-solvers for us was Holley‘s wet sump LT4 accessory-drive kit (PN 20-220). This kit is all-inclusive, containing all of the brackets and tensioners and even the A/C compressor, power steering pump, and alternator. It’s a completely plug-and-play system. Stay tuned for that installation article in the near future.
For more information on Chevrolet Performance, go to www.chevrolet.com/performance-parts. To find out more about Schwartz Performance, visit them online at www.schwartzperformance.com. Silver Sport Transmission can be researched at shiftsst.com. Holley Performance Products can be viewed online at www.holley.com.