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How to Add Bolt-On Horsepower to a GM 5.3L LS

2002 GMC Sierra Buildup, Part One

Oct 9, 2020
Contributors: Anthony Soos
You may remember a while back here at Truckin when we picked up a slightly used Sierra and performed some general maintenance to the mostly stock 5.3L engine. Before hitting the unforgiving California smog station, we added in high-tech plugs, new generic wires, a K&N air and oil filter, fuel filter, and fresh oil. After we got the thumbs up from the smog man, we also put in a DiabloSport inTune tuner to add some ponies and overall drivability to the truck.
After some time behind the wheel, we decided to take the engine mods a step or two further. Our first call was to JBA to fulfill our needs in the exhaust department. We ordered up a set of Cat4ward Shorty Stainless Steel Headers in silver ceramic coating. We also opted for the JBA Stainless Steel Single Side Swept Exit Exhaust System. Because JBA is a sister company to Pertronix, we ordered another cool item that finishes off the look and performance of our 5.3L: the Pertronix Flame-Thrower heavy-duty red plug wire set. Keeping with the red theme, we asked Professional Products for a set of the company's Powerfire LSX Coils. Finally, Jet Performance sent us its Powr-Flo Mass Air Sensors.
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The plan was to take these relatively simple steps to make our well-used-but-plenty-of -life-left Sierra engine breathe a little easier, spark a little hotter, sound a little better going down the road, and look a little better under the hood and at the tailpipe. After a couple of afternoons at the TEN Tech Center, we were more than confident that we achieved all three. Now, the truck has an impressive throttle response and a surprising amount of power for a fairly high-mileage truck. Follow along to see what it takes to bring a '99 to '06 GM L59 to the next level, and check out these company websites to see what they have available for your vehicle.
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The JBA Cat4ward Shorty headers (PN 1850S-2JS) are built from stainless steel with 1 5/8-inch tubing and a 3/8-inch flange that features the company's patented Firecone collector before being ceramic coated in silver. These headers offer increased horsepower and torque, along with improved throttle response and fuel economy. They look good under the hood and through the wheelwell, too!
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JBA also supplied its 3-inch Single Side Swept Exit Stainless Steel Exhaust System (PN 40-3009). The 3-inch pipe terminates at the 3.5-inch rolled tip. The system comes ready for installation, adds a powerful exhaust note, and boosts power throughout the RPM range.
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To compliment the headers and help deliver the spark, Pertronix offers Flame-Thrower 8mm MAGx2 plug wires (PN 808423). They feature dual current paths for reliability and redundancy and a low 500ohm/foot rating to get more energy to the spark plug.
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Next on our list was Professional Products Powerfire LSX Coils (PN 30503). Professional Products Powerfire Coils have an advantage over competitive models and stock coils in that the actual duration of the spark produced is longer. Longer spark duration produces more complete combustion and more power.
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The last piece of the puzzle is the JET Performance Powr-Flo Mass Air Sensor (PN 69101). The flow-bench tested design provides airflow increases up to 45 percent and is compatible with other aftermarket upgrades, such as programmers, cold air intakes, and free flow exhaust systems, all of which we'll soon have.
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Because we were doing away with our stock exhaust system, we got the ball rolling by grabbing the Sawzall and chopping the tailpipe in half just past the muffler. It makes removal a lot easier, even when you're high in the air on a lift.
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We unbolted the flange between the cat and the muffler, and sprayed the rubber exhaust hangers to prepare to pry them off
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We easily dropped the front section down out of the truck, and fed the tailpipe out, too.
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The factory exhaust manifolds were next to go, so we buzzed off the nuts and let the mid-pipe drop down.
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Starting on the passenger side, we first removed the front wheels, inner fenders, and stock plug wires to gain easier access to the bolts.
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We gathered up a plethora of different wrenches, sockets, and extensions and began removing the six exhaust manifold bolts.
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Soon, the factory piece was ready to slip out through the wheelwell.
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We cleaned up the mounting surface with a Roloc bristle disc, along with the rest of the head.
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We set the header in place and wiggled it until we could get all of the header bolts started, once they were coated with anti-seize. Although the '99 to '07 trucks are fairly straightforward, we're making it look extremely easy. The driver side has quite a bit more interference, that's why we're shooting the photos over here!
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All that was left to do is snug down the bolts to 18lb-ft and admire how good the JBA headers looked through the wheelwell.
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We used the newly supplied bolts to connect the mid-pipe up to the new headers.
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We began installing the JBA exhaust by fitting the extension pipe into place. Everything we install at this time will remain loose until the entire system is mocked up and checked for clearance.
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Next, we hung the tailpipe extension by its hangers.
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We set the muffler in place, started the clamps, and hung the tailpipe and tip into place.
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Once the complete system was in place, we did many checks to be sure there was ample clearance. Next, we started snugging everything down at the front and working our way rearward.
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Finally, we made our last adjustment to the tailpipe and snugged it down.
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With the truck back on the ground, we popped the hood and began unbolting the coil bracket from the valve cover. But before that, we removed the stock plug wires and identified the connectors by writing on masking tape to be sure they returned to the same cylinder.
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The main connector was removed, and the bracket and coils lifted off the engine.
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There are about six different types of coils for LS engines. We made doubly sure our new Professional Products coils were a match before proceeding.
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We removed and replaced each coil along the row, cleaning the bracket up as we went, and cleaned up the rest of the valve cover at this time, too.
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With the old switcheroo completed, we bolted the coil bracket back to the valve cover.
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We plugged in our Pertronix plug wires, our coil connectors, and our main connector. Now, it's time to move on to the final component of the install.
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The Jet Performance Mass Air Flow Sensor install can be done in just minutes with only a screwdriver and Allen socket. First, we unclamped and removed the air filter.
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Then we unplugged the factory mass air flow sensor.
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Next we unclamped and removed the air intake tube.
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At this point, we could unbolt the sensor from the air box.
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We located the gaskets on either side of the air box to save for reassembly.
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Now we could install the Powr-Flo sensor back onto the air box.
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Finally, the intake tube and air filter were reinstalled with the connector.
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This old 5.3L doesn't look like a high-mileage motor, and certainly doesn't feel like one, either. Our throttle response and overall drivability is better than it's ever been and the power feels more like a later, higher-horsepower LS-powered truck. We're hoping to get a lot more miles out of this one!


JET Performance Products
Huntington Beach , CA
Professional Products
Hawthorne, CA