2004 GMC Sierra Engine Upgrades - 358 RWHP 4.8L With Bolt-Ons

The next step was to install these low-profile Allen-head bolts in the valley cover. These, along with small rubber stoppers under the intake, allow for clearance of the intake and valley. Each bolt was torqued to 18 lb-ft. After a quick test fitment, the factory coolant crossover tube was interfering with the front on the intake and preventing it from sealing. The instructions mentioned this may happen.

A quick trip to the GM dealer had this part in our hands. Notice the outlet (on the right side) is facing straight out now, instead of the original tube's up and at an angle. This part was for a '06 Pontiac GTO with a 6.0L LS2.

Because of the front alternator bracket interfering with the vent tube outlet, we flipped the vent tube to the rear and ran a 90-degree 5/16-inch hose around to the front of the engine.

It was now time to install the factory 24 lb-hr injectors into the new FAST billet fuel rails. FAST included new O-rings to seat properly in the intake manifold. It should also be noted that, because of the multiple applications and fitment, FAST doesn't include hoses, fittings, or adapters to make your factory fuel system work with the new fuel rails. That part is up to you and your performance needs.

As you can see, the new FAST billet fuel rails are now connected to the FAST intake and we have new fuel lines and fittings from Sweet Performance, in Placentia, California. With the intake gaskets in place, the new FAST intake was slid into place. A little tip is to apply a small amount of oil to the gaskets to help them slide over the heads and into place easier. Each intake bolt was then torqued to 45 in-lb in the recommended sequence, with a final pass of 89 in-lb.

Sweet Performance made all of the fuel fittings and hoses while we waited, and they fabbed up this adapter to plug right into our factory high-pressure fuel line. The fuel rail crossover used -8AN fittings for ultra-high fuel flow.

The FAST throttle body adapter was then secured to the intake with four counter-sunk M6 Allen bolts. Big gains can be had by using one of FAST's Big Mouth 102mm throttle bodies, but with our '04 being drive-by-wire, we had to reuse the 75mm factory unit.

We then bolted on the factory throttle body to the adapter and began reconnecting all of the sensors, vacuum lines, and hoses.

Shown here before we installed the nitrous solenoids, the intake is pretty darn sexy mounted atop our 4.8L. An added bonus, the intake even had a provision on the driver side for our massive wiring harness.

FAST includes three bolt holes for older cable-activated throttle bodies that we did not use. They did, however, provide the perfect mounting location for our nitrous solenoids for a custom look. Back on the dyno, our little 4.8L made 282 RWHP and 287 lb-ft of torque. Those numbers would be much higher if we had better heads and a bigger cam. Basically, our engine was getting too much air. Also keep in mind, the computer had a stock tune on it.

In an effort to realize our 4.8L's full potential, we ordered a complete valve train upgrade from COMP Cams, including a new Tri-Power Xtreme cam, valve springs, trunnion bearing upgrade, and the necessary installation pieces.

After removing the main and A/C serpentine belts, intake inlet tube, upper and lower radiator hoses, and alternator, the water pump was removed. With the radiator hoses removed, the coolant was drained and we also went ahead and pulled the radiator for extra clearance.

Next up, the main wire connector was unplugged for each coil pack harness and then the 10mm bolts retaining the coil bracket to the valve covers were removed.

Then, the four bolts holding the valve covers down were loosened and the valve covers removed. We then used a 10mm socket to loosen the rocker arm studs. The rocker arms are on a one-piece pedestal and can be removed individually or as one complete unit.

A key step is to keep the pushrods with the proper rocker arm. We used a large piece of cardboard to label the parts we removed. As you can see in the photo, both methods of removing the rocker arms were performed.

Using a common valve spring compressor tool, we removed each factory valve spring. A spark plug air chuck was used to keep the valves closed for easier removal and the springs were done in the proper cylinder order per the crank rotation.

To gain access to the camshaft, the crank pulley/balancer had to be removed. First, the 24mm crank bolt was removed using an air impact, and then we used a large, 7-ton three-jaw puller available for rent at most auto parts stores to remove the pulley.

With the pulley out of the way, the ten 10mm bolts were removed from the timing cover and then the timing cover was removed. Two bolts go from the bottom of the cover to the block and took a little convincing to remove.

After removing the camshaft lock plate, we inserted two 1/4-inch wooden dowels (available at most hardware stores) into the top oil galleys. This keeps the lifters from dropping back into the valley. You can also see two large bolts from the alternator screwed into the cam. We used this as a makeshift handle to pull it out.

We were able to pull the factory camshaft out with no problems. The A/C condenser did not have to be removed.

The new COMP Cams camshaft was a Tri-Power Xtreme model, with .507/.500 lift and 254/264 duration at 116 lobe center angle. This is a mild cam, but it is a good upgrade for better low-end torque and overall horsepower. It does require a computer tune. After coating the lobes in oil, we slid the new cam right in.

Four 10mm bolts secured the cam cover to the block. We then put the cam gear and chain back in place.

As the screwdriver tip is pointing out, we turned the crank gear while holding the timing chain in place until the timing marks on the cam and crank gears were perfectly lined up. Happy with the timing, we bolted the timing cover back in place and installed the crank pulley with a new GM crank bolt.