LS Engine, Building More Power in a 383 motor!

If you’re interested in racing, performance upgrades are inevitable, especially with a truck that has a Ls engine. Trucks need all of the help they can get when it comes to being on the track. From poor design to increased body mass, trucks are generally at a huge disadvantage over more traditional race vehicles. Unfortunately, in the pro-touring/autocross community, there will come a time when you have to compete against cars that are half the size of your truck and weigh in at a mere 1,000 pounds.

But there’s no reason to let those lightweight racers intimidate you. For anyone who isn’t in the know, autocross is an organized competition that tests your control of your vehicle as you navigate through a closed race course marked by bright orange cones.

The events are typically held in parking lots where there is little to no risk of damage to vehicles.

Autocross is not a head-to-head style of racing; instead, individual drivers take to the course and are timed to the thousandth of a second. Vehicles compete one at a time in designated classes against similar vehicles. Though there are only a handful of organizations that recognize trucks as an individual class. The number of truck participants is growing each year and has lead other racing organizations to consider offering a designated truck class.

Running With the Old LS Engine Setup

LS Engine iron block

A 5.7L LS iron block, which started life as a 5.3 LM7 truck block from an ’06 Silverado, was the initial platform used to power the C10R. The custom-built 5.7L made respectable horsepower at 443 ft-lbs of torque and 500 hp at the flywheel, which was more than enough to get the truck moving on the track.

In the past few issues, we’ve been documenting the metamorphosis of the PCH-Rods-built ’72 C10R Chevy

It’s been through a lot of changes and is a great example of how to slowly and deliberately modify a truck for autocross racing. Initially, PCH Rods emphasized dialing in the new suspension and upgrading the brakes and tires. Though the motor was fully customized, it wasn’t elaborate. PCH Rods started with a 5.3L LS engine truck block. The crew compromised by using a cast motor to keep the price low and durability strong, though it did add weight.

Recently, power upgrades became necessary to stay in step with the competition at big course events.

Racing series like Optima’s Search for the Ultimate Street Car Series left the C10R struggling to keep up in the straightaways on the track portion of races. PCH Rods did a motor swap and we’ve documented it all right here so that you can see how and why the upgrades were made in on this Ls engine.

Big power was not the main focus of the initial build, but after a year of running the 5.7L in the C10R, it was time for more power. The truck’s race schedule mainly included autocross events like those at the NMCA West Series and Goodguys Autocross Series. Several of the autocross courses were tight with k-rails just waiting to be kissed thanks to one slight mistake. So less horsepower was more manageable while PCH Rods sorted out the truck.

As the autocross tracks like NMCA West Hotchkis Autocross and the Optima Series got larger.

It was harder for the C10R to keep up with its competition. Because the truck is a 1972, it typically runs in a vintage class alongside several Camaros, Novas, Corvettes and other smaller vehicles. Many of these smaller, lighter vehicles have equal or greater horsepower than the C10R, making it extremely difficult to gain a competitive edge.

Though the truck performed smoothly throughout the turns, it lagged a little in the straights. The power band was minimal at the bottom, not making power. Until 3,000-plus rpm, which is not beneficial off the starting line or coming out of turns. The final reality check didn’t hit until the Speedtech C-10 chased it down .On the straight during the 2015 Optima Ultimate Street Car Invitational Hot Lap Challenge at Las Vegas Motor Speedway. It was unable to catch back up! This is when we knew it was time for more power.

Building the New

As the winter months settled in, we made a distress call to ATK High Performance Engines to see what could be done to gain more power. Our objective was to use the existing top end parts so we wouldn’t have to buy a whole new engine. Brandon Simkiss from ATK High Performance Engines suggested that we build the same platform we were already using. But stroke it to 383 ci (6.3L) and bump up the compression. Building a smaller stroked cubic motor helped move the power band down low. While allowing the power to continue into the higher rpms.

Building a 383 LS Engine

We received the motor last spring during the middle of race season. The goal was to swap it in during a four-week break between events. Then take it to Westech Performance Group to have the truck tuned and do a few dyno pulls. The new motor was an LM7 iron block, which has a standard bore of 3.78 inches and a stroke of 3.622 inches. In order to get 383 inches, the stroke needed to increase to 4.00 inches. We mated a K1 Technology 4340 forged crankshaft to a set of Scat Pro forged. I-beam rods equipped with ARP 8740 rod bolts. The windage tray was also modified to accommodate the crankshaft’s larger stroke. To get the windage tray to clear the crankshaft stroke, the tray was shimmed .030 inch, using a washer on each bolt. The Autokraft oil pan afforded us the space for this modification.

Cometic Gasket

The block was bored to 3.903 inches in order to get the cubic inches exact. This required a piston upgrade. Which was already accounted for in order to get a slight increase in the compression ratio. A set of Wiseco 2618 forged pistons was used with a mere 3cc dome. Though that may not seem like a lot of dome, a stock head gasket. At .051 thickness would give you a compression ratio of 12.0:1, which is a little too much for something that’s streetable. We contacted Cometic Gasket for a set of MLS custom-made .061 thickness gaskets that put our compression ratio around 11.5:1, which is a little more tolerable for pump gas.

In order to make all of these parts work together, a top end kit with good flow was needed. We already had a Trickflow Specialties GenX 225cc LS2 Top End Kit from the previous 5.7L combo, so this mod was a cinch. The kit included just about everything we could possibly need to set up the top end of an LS engine, including cylinder heads, head bolts, 1.7 aluminum roller rockers, push rods and a camshaft.

We needed a taller valve cover to prevent the rocker arms and Trick Flow Specialties camshaft exhaust lift from hitting the underside. A set of Holley Performance tall aluminum valve covers did the trick.

The GenX cylinder heads that came in the kit were CNC-machine ported out-of-the-box, bolt-on parts with really impressive flow numbers. We finished off the
heads with a set of NGK iridium TR6 sparkplugs, JDP Motorsports sparkplug wires and MSD Blaster coils.

To top off the engine, we needed an intake manifold and fuel system that would support the increased airflow demand. You could use a stock intake and injectors, but the injectors will push beyond their recommended flow duty cycle and the stock GM intake manifold is limited to a cathedral port design. Instead, we opted for the MSD Atomic Airforce manifold.

LS Engine with fuel injectors

The fuel injectors were upgraded with a set of Holley EFI
48-pound injectors to keep the fuel flowing at a comfortable rate. We used stock fuel rails with the MSD manifold. Though the manifold is capable of handling a 105mm throttle body, we opted to keep the Spectre Performance 102mm version, which accepted all of the factory IAC and TPS sensors.

While the motor was out, we took the opportunity to swap the old Centerforce clutch. The latest and greatest Centerforce DYAD dual disc featuring a new design. There was nothing wrong with our old clutch, but we had the opportunity to beta test the new clutch and we agreed. The new design is lighter, quieter and engages faster. Though the Centerforce crew was worried about acclimating to the new point of engagement,. They were impressed with its performance on track and even in Los Angeles rush-hour traffic.

ARP bolts were used throughout the motor. It’s cheaper to buy good hardware than to replace a motor damaged by cheap hardware. No one wants to experience a problem in the middle of the race that results in a Did Not Finish.

LS motor Spectre Performance air intake

A newly modified Spectre Performance air intake system was needed due to the new location of the throttle body. A 90-degree-angled tube replaced the 60-degree tube, though the design and location of the air intake remained the same.

Dialing Everything In

Holley fuel management system Ls engine

For the whole combo to function, PCH Rods needed a fuel management system that was easy to set up and install and simple to work on. The system of choice was the Holley HP EFI computer and harness. For LS1-LS2 engines with manual transmissions. The Holley system was extremely easy to set up. The C10R was up and running in no time. Next, we headed out to Westech Performance Group for the final tune. In order to squeeze as much horsepower and torque as we could from the new engine.

We weren’t expecting a massive jump in the horsepower and torque range, though we did see a notable increase in both areas. The primary concern was moving the power band down to see improvements on the track. Though the truck was fast with the old motor, it was a bit slow on the climb. It wanted to go, but you had to have patience because it took a second to get there.
During the first pull on the dyno, the difference between motors was clear as the new engine moved through the power band. Sluggishness was a thing of the past. As we pressed the throttle to the floor, the power climbed in a matter of seconds and the pull was done.

Secondly the pull was complete, the dyno screen switched over to a beautiful graph with little lines that crawled across the dyno sheet. This is what every builder hopes to see. The new motor was pushing 527 hp with 506 ft-lbs of torque at the flywheel. Which was not a dramatic difference from the last dyno session with the old motor. The power curve is what truly got us excited. It came on down low where we needed it and continued to about 6,600 rpm. At that point, it didn’t give up, but it had reached the end of the line with horsepower, and the torque started to level out. It worked really well, plus it sounded awesome. The final results on the dyno proved that it would put the power down where we wanted it, but the moment of truth awaited us on the track.

LS Engine 383 more power

Mere days after the motor swap and dyno session, the first track day arrived. The second NMCA West Hotchkis Autocross was scheduled to take place at Auto Club Dragway. The course provided higher speeds with a tricky start and several technical maneuvers. We saw remarkable improvements right off the starting line. The technical turns required hard braking in certain areas. When coming out of those turns, the lower rpm power band really made a difference.The faster acceleration meant quicker times. Overall, the motor swap was a huge success! We can’t wait to see what it can do when we get.