2004 Pontiac GTO Header Installation - Back In Black Part 7

Underhood, the strut tower brace comes off, and the Vortech charge cooler and tubing is moved to provide access to the manifolds. On the passenger side, the coil bracket (including Vortech heat shield) is removed in order to better access the manifold.

The spark plugs then come out. This passenger side is pretty open and easy to work once the aforementioned bracket and coils are out of the way...

...The dipstick tube presented an obstacle and had to come out. One 15mm bolt and it's out with a slight tug.

Six 10mm hex-head bolts hold the exhaust manifold to the cylinder head; the manifold comes out the top. Don't lose the bolts, they will be reused.

On the driver side, there are a few more obstacles to contend with. First off, the coolant reservoir is in the way. By disconnecting the Vortech bypass valve from the supercharger air inlet duct, as well as the tube leading from the outlet of the supercharger, we were able to temporarily move the coolant reservoir up and forward enough to access the entire exhaust manifold--without even draining a drop of coolant! The driver side coil bracket comes off simply for ease of access to the exhaust manifold.

Access on this side is a bit tighter due to GM's poor placement of the computer and its accompanying heat shield (revised, thankfully, for 2005)...

...We opted to make quick work of these manifold bolts with an air-powered socket wrench. This manifold is then removed from the top, just like the passenger side.

Although SLP's instructions advised us to siphon power steering fluid out of the reservoir before disconnecting any power steering lines, we chose to the accept the consequences of additional leakage. Only the two large lines entering the back of the power steering mechanism (toward the front of the vehicle) need to be disconnected; you'll need a 5/8 and a 3/4 wrench. The two smaller ones seen on the right side of the photo can stay put, but we didn't realize this at the time (they are attached to the rack and will be coming out with it).

After ensuring that the steering wheel is facing slightly to the left, and is locked in place (ignition key out for good measure), remove the nut and bolt from the steering coupling...

...This nut will be discarded; SLP supplies a new one for reassembly later. The coupling then slides apart.

The steering rack is unbolted from the crossmember via two bolts. The bolts have a 19mm nut on the bottom and 18mm head up top; an 18mm open end will be needed on the driver side as a socket won't fit due to tight clearances...

...The steering rack can just hang down, no need to disconnect tie rods or anything.

Before the headers are installed, it's a good time to pop in SLP's oxygen sensor extension harnesses for the front two sensors. Otherwise, the header primaries and collectors will be in the way of your getting at the area above the transmission, where the factory wiring harness plugs are located. You can hold off on installing the extension harnesses for the rear O2s, they're easy.

The passenger side header slips in from up top with no interference whatsoever. As the header is heavy, it's useful to have a helper assist in holding it to the cylinder head while you get the bolts started.

Make sure that the supplied manifold gasket is oriented properly (there is a "down" and a "manifold side"), and use threadlock on all of the manifold bolts. Moving from the inner bolts outward, the bolts are torqued in two passes of 12 and 18 lb-ft. Here you can see the one-piece 3/8-inch flanges SLP uses on these headers, which are made of mild steel. But this isn't a cost-cutting measure on SLP's part; rather, stainless steel's thermal expansion characteristics can cause problems with bolt torque retention, and that is why SLP shies away from that material here.

We were delighted to discover, during the passenger side header installation, that there was no interference with anything on this side. Spark plug access on this side also impressed us; no cutting of special socket tools like long-tube headers of the past (L98s come to mind as particularly trying of the patience). There's plenty of clearance for not only a standard spark plug socket and wrench, but also for spark plug wires so that they'll be no worry of burnt boots. Spark plug torque on the LS1 is 11 lb-ft (except for brand new heads, for which it is 15). Don't forget to reinstall the oil dipstick!

The driver side header must go in from the bottom. This is not because of any interference with the Vortech; rather, the obstruction lies in the close proximity of the PCM to the cylinder head. During the insertion process, the hanging steering coupling gets in the way and has to be lifted to the right spot to give adequate clearance for the header to slip in. Note the rear primary's shape; its contours are designed to provide additional clearance around the steering linkage that other systems can't provide.

While clearance for tightening the header bolts on the driver side is more than adequate, one can see the computer and its heat shield needlessly cramping the area; again, the computer was moved for the 2005 model year. However, SLP is able to have the primaries come as straight off the port as possible, improving flow over other header designs, which can have the exhaust encounter sharp "shear" shapes or a cut section soon after entering the header (SLP's headers feature predominantly single piece primaries.) Don't forget to reconnect the plug for the coolant temperature sensor at the front of the header (view obstructed by a hose here); failure to do so will not only throw a warning light on the dash, but the computer will also be fooled into adding ignition timing, which is exceptionally bad!