Keep on Truckin: 4.8L LS Stroker Build

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Words and Photos By: Richard Holdener

Truth be told, this build up may have started with a 5.3L truck motor, but the result could be used for any of a number of performance applications. The idea of the build was to enhance torque production.

If you are not familiar with torque, it is that thing that shoves you back in your seat when you step firmly on the gas. We all like to brag about horsepower numbers, but torque is the thing that impresses the passenger on a spirited test drive. Whether you drive a truck, Camaro, or even street rod, enhancing torque production will yield substantial performance dividends.

It is possible to increase torque production on a typical 5.3L LM7 using basic bolt-ons, but nothing builds torque like increased displacement. When it comes to torque, bigger is always better, which is where stroker kits come in. Sure, ported heads, a cam, and the right intake will improve a 5.3L, but they will make even more power after adding the inches.

The LS engine family offers a number of different displacements, ranging from 4.8 up to 7.0 liters. As displacement increases, so does pricing, meaning a 6.0L is considerably more expensive than a 5.3L. This same sliding scale continues with the larger 6.2L up to the massive 427 LS7. For most mortals, these all-aluminum, large-displacement versions are mere pipe dreams. It is also possible to take aftermarket versions over 500 inches, but these cost even more than the factory combinations. The most common and readily available production power plants, and therefore most affordable, are the 4.8L and 5.3L variants.

The question now is, what can we do to a 4.8L or 5.3L to coax 6.0L, 6.2L, or even 7.0L power out of it? The answer is make it bigger using a stroker kit. While we can’t push displacement up to match the 7.0L, we can certainly pass the factory 6.0L (364) and 6.2L (376) motors by building an honest 383-incher.

The great thing about building a 383 stroker LS from the iron truck motor is that it doesn’t matter whether you start with a 4.8L or 5.3L, as they share the same block and bore size. The difference in the factory displacement comes from the stroke length, but since we plan to replace that anyway, either block will work.

To get the ball rolling, our 4.8L block was taken to L&R Automotive in Sante Fe Springs for machining, which included cleaning, boring, and honing to a final bore size of 3.905 (up from 3.780). To this, we added a 4.0-inch stroker crank from Speedmaster, a set of 6.125-inch rods from K1, and flat-top, forged pistons from JE. Sealing was provided by a set of Total Seal piston rings. In addition to being plenty strong, the JE pistons featured sufficient valve reliefs for our COMP hydraulic roller cam. The COMP cam offered a .617/624 lift split, a 231/239-degree duration split, and 113-degree lsa. COMP also supplied the hydraulic roller lifters, double roller timing chain, and a set of 7.35-inch hardened pushrods.

Knowing displacement and cam timing were only two parts to the performance puzzle, we chose to upgrade the cylinder heads as well. Though adequate for a 4.8L, the factory 706 castings were inadequate for our performance-oriented 383. The factory head gear was replaced with a set of Trick Flow GenX 225 heads. Why choose the GenX 225 heads, you ask? Well, for starters, they featured revised valve angles (from 15-13.5 degrees), full CNC porting, and altered spark plug locations. Need more? How about premium, high-resolution surface finish, fortified rocker-arm mounting pads, and increased rigidity for extreme horsepower applications (in case we add boost later — which we did)! The heads also featured a stainless 2.055/1.46 valve package, a dual spring package with sufficient coil bind clearance and spring rate for our .624-lift cam, and even titanium retainers to maximize rpm capability. How do they flow? How does over 330 cfm grab you (enough to support over 660 hp)? Knowing we had more cylinder head than our motor could use, the GenX 225 heads were secured to the 383 short block using a set of ARP head studs and Fel Pro MLS head gaskets.

After a thorough break-in procedure, the 383 eventually pumped out 548 hp at 6,400rpm and 503 lb-ft of torque at 4,700 rpm. Compared to the stock 4.8L, the 383 offered an additional 215 hp and 160 lb-ft.

After a thorough break-in procedure, the 383 eventually pumped out 548 hp at 6,400rpm and 503 lb-ft of torque at 4,700 rpm. Compared to the stock 4.8L, the 383 offered an additional 215 hp and 160 lb-ft.

Currently equipped with a forged short block, COMP cam, and CNC-ported heads, the only thing missing was the right induction system. While the factory truck intake is the go-to manifold for many builds, we knew there was more power to be had from the after market. Replacing the stock truck setup was a 102mm FAST LSXR intake and matching Big Mouth throttle body. The massive throttle ensured uninterrupted flow to the powerful intake design. In addition to the intake, FAST also supplied 75-pound injectors, a set of billet fuel rails, and XFI/XIM management system to properly dial in the combination.

5.3L vs 383 Stroker The power gains offered through the combination of displacement and efficiency is evident in this comparison. Run in the same manner, a stock 4.8L produced 333 hp at 5,400 rpm and 343 lb-ft of torque at 4,700 rpm. After upgrading the 383 short block with TFS heads, a COMP cam, and FAST LSXR intake, the peak numbers jumped to 548 hp at 6,400 rpm and 503 lb-ft of torque at 4,700 rpm. Note the larger 383 offered not just more peak power, but more power through the entire rev range. If you want to make big power, it’s a lot easier to start with a big motor.

5.3L vs 383 Stroker
The power gains offered through the combination of displacement and efficiency is evident in this comparison. Run in the same manner, a stock 4.8L produced 333 hp at 5,400 rpm and 343 lb-ft of torque at 4,700 rpm. After upgrading the 383 short block with TFS heads, a COMP cam, and FAST LSXR intake, the peak numbers jumped to 548 hp at 6,400 rpm and 503 lb-ft of torque at 4,700 rpm. Note the larger 383 offered not just more peak power, but more power through the entire rev range. If you want to make big power, it’s a lot easier to start with a big motor.

Finishing touches on the 383 included 1 7/8-inch Hooker headers, an ATI Super Damper, and a pan full of Lucas 5W-30 oil (synthetic after break-in). After the break-in cycles and tuning with the FAST, the 383 solidified our decision to build the stroker by producing 548 hp at 6,400 rpm. What really allowed the stroker to keep on truckin was torque production, which exceeded 500 lb-ft with a peak number of 503 lb-ft at 4,300 rpm. Compared to a stock 4.8L, the stroker was up by 215 hp and 160 lb-ft of torque.

Sources: Aeromotive, Aeromotiveinc.com; COMP Cams, compcams.com; FAST, fuelairspark.com; JE Pistons, jepistons.com; K1, k1technologies.com; Holley/Hooker, holley.com; Lucas Oil, Lucasoil.com; Speedmaster, speedmaster79.com; Trick Flow Specialties, trickflow.com

About the author

Elizabeth Puckett

Elizabeth is a seasoned writer and hardcore gearhead. She was born with motor oil in her blood and a passion for everything that goes fast.
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