Intake enhancements are only as good as the exhaust allows them to be. All the air and fuel in the world on the intake side won't make more power if the exhaust system can't pump out the by-products of combustion efficiently. Though the '04 GTO's stock exhaust system performed well enough to handle light upgrades and did pretty well with the ProCharger we installed, we still felt there was a lot of power left on the table.
Since Stainless Works has a gorgeous set of long-tube headers just for the '04-plus Goat, we thought we'd try them in an effort to liberate a few more ponies. Beginning with premium stainless steel, CNC-cut 31/48-inch-thick flanges are welded to 1.75-inch primaries that flow into 3-inch collectors. These long-tubes are bound to wake up any Goat and add a musclecar tone. The kit we're installing on our '04 GTO (PN GTOHDR) retails for about $1,364 (at press time), including Random Tech catalytic converters, all the parts and hardware needed for installation, and even O2-sensor extensions!
Follow along as we install a set of Stainless Works long-tube headers for the '04-plus GTO. In Part II, we'll mount an '04-'05 bumper-conversion after-cat system and then dyno the GTO to gauge the improvement.
Stainless Works' long-tube...
Stainless Works' long-tube headers for our '04 GTO include everything needed for installation except tools.
With the factory system completely...
With the factory system completely removed from the Pontiac, you can see how restrictive the stock 2-inch-diameter system is compared to the new Stainless Works system. Note the crimps just after the catalytic converter on the old system. Now let's see what it takes to get out the old exhaust and install the new headers.
To start, raise and support...
To start, raise and support the Pontiac securely, and remove the catalytic-converter mounting nuts on each side. Spray down the O2 sensors, as well as the bolts to be removed, with some sort of penetrating oil.
Next remove the four 13mm...
Next remove the four 13mm bolts that hold the catalytic converter mid-pipes to the after-cat.
Remove the four 13mm nuts...
Remove the four 13mm nuts that hold the exhaust manifolds to the mid-pipes ...
... and remove the mid-pi...
... and remove the mid-pipes.
Gently pull the coolant-overflow...
Gently pull the coolant-overflow reservoir to one side and out of the way. Then remove all the spark plug wires and set them aside.
Loosen both 7mm PCM retaining...
Loosen both 7mm PCM retaining bolts and gently remove the connector. Since we have a ProCharger, we also took off the 12mm vacuum-booster PCM bracket nut to free the PCM. On a stock GTO, you only have to remove the plastic tray the PCM resides in.
If you have a ProCharger system,...
If you have a ProCharger system, trim the PCM heat shield as shown.
Unbolt and slide out the dipstick...
Unbolt and slide out the dipstick and dipstick tube. It may take some force to free it from the block as it uses an interference fit and an O-ring seal that tends to get stuck.
Unscrew all the 13mm bolts...
Unscrew all the 13mm bolts that attach the factory manifolds to the cylinder heads; let the engine cool down completely before backing out these bolts. Failure to let the engine cool can result in the threads coming out with the bolts.
Lift out the factory manifolds,...
Lift out the factory manifolds, and be sure to save the gaskets as they'll be reused. The passenger side comes out like butter. The driver's side? Not so easy.