2004 Pontiac GTO Header Installation - Back In Black Part 7

Getting the steering linkage to slide back together in its now-more-cramped space takes a little patience. Basically, it must be lined up simultaneously with the rack being put back on to its mounts. Take your time; don't force it. Although this space is more restricted than before, SLP says that "a competitor's header we tested was so tight in this area that it was like poking a donut hole through a donut. Besides looking really amateur and hokey, this isn't safe. With our design, the clearance around the steering mechanism is as big as we could possibly make it. There is room to make long tube headers work properly on these cars without boiling up the steering rack, despite some people's doubt."

Use SLP's provided nut on the steering linkage; torque to 20 lb-ft. Access will be hindered slightly if one did not turn the steering wheel to the left enough before taking the linkage apart. This was the case with us, but fortunately some extensions and a swivel let us get to the nut just fine.

The next challenge is to reconnect the power steering lines behind the pump (the ones visible didn't have to come off, remember!). Access to them was much more difficult than during their removal, with the long tube primaries interfering with getting a full-size wrench behind. Line wrenches were no longer an option and we actually ended up fabricating a stubby 5/8 open end. Make sure the lines are fully in place in the pump before attempting to tighten them; even if the nut threads, it doesn't mean the flare inside has seated properly!

The stock front oxygen sensors are now installed in the header collectors. Use some anti-seize on the threads. Zip ties will be needed to hold their wiring away from the header primaries.

Intermediate pipes run from the header collectors; the catalytic converters will be installed onto the back of them. These pipes are a full 3 inches in diameter. SLP provides very nice Torca exhaust clamps for all of the pipe junctions. Just install them loose for now and wait until the entire exhaust is assembled to fully tighten everything.

The high-flow catalytic converters are then slid onto the back of the intermediate pipes. Make sure the heat shields face upward toward the car underbody (no point in shielding the asphalt from heat, is there?).

The two pipes joining the catalytic converters to the Cat-Back system differ slightly. The one up top has a slightly tighter bend and is a bit stubbier; it goes on the passenger side. The rear oxygen sensors will also install into these pipes.

SLP provides new gaskets and bolts for the junction between the aft-cat pipes and the Cat-Back system. We tightened these bolts before tightening any of the Torca clamps; it helped things line up better. With these pipes in, the rear oxygen sensors can be installed into them.

The rear oxygen sensor extension harnesses provided by SLP snap right in and are zip-tied out of the way. The driver side sensor definitely needed an extension while the passenger side barely needed one at all.

One can now adjust the entire header system as needed and fully tighten all of the Torca clamps; hit them with an impact gun if you have one. We should point out that while other header systems for these cars have required "adjustments," like grinding of heat shield studs, the only adjustment we made was a slight grind to the extreme passenger side of the BMR driveshaft loop for a bit more clearance. Other than this, we didn't experience any interference at all anywhere around these headers.

Up top, all brackets and tubing are reinstalled and the power steering reservoir is refilled. With the Vortech supercharger system in place, it's hard to catch a peek at the headers, but the shimmer of aluminum-ceramic coating can be seen from certain angles.

With the car outside, we took a peek underneath to check out the ground clearance and were surprised to note that it was excellent! Unlike long-tubes installed on some other GMs, there'll be no rubbing of speed bumps with these babies; both the collectors and the cats are tucked up there quite well.

Back on the Dynojet 248 at East Coast Supercharging in Cream Ridge, N. J., we had our fingers crossed for a good power increase--but ended up getting more than we'd planned for! Plus, ECS didn't have to do any tuning on the car whatsoever; they left the program exactly the same as it had been before the headers were installed. Sounds strange, but different cars behave differently after headers are installed, and ours just didn't happen to need it.

The results--with the same rock-steady 11.6:1 air-fuel ratio as before--were 521 rwhp and 460 lb-ft. This is a staggering 50 rwhp gain with just the SLP headers! This number was also achieved with the torque converter unlocked, so really figure about 551 at the wheels, which translates to about 688 at the flywheel. All on 93-octane ExxonMobil Jurassic juice to boot!