2007 Chevy Cobalt - Practically Powerful
Now the GMPP intermediate pipe slips in above the rear axle assembly. Attach the stock rubber hanger at the rear portion to hold it, then move forward and slide the intermediate pipe onto the resonator pipe. This is going pretty easy, isn't it? Note that we have a supplied band clamp on the pipe ready to go. Like the entire system, this pipe is 2.25 inches-no larger in diameter than the stock system, but the flow (and sound) gains are in the muffler and resonator design. | 
The muffler pipe goes in. Just slide it onto the intermediate pipe (have a clamp ready here too) and pop on the two stock rubber hangers just aft of the muffler. Note again that the GMPP exhaust is supplied sans tip, so don't forget to order one up. | 
The tip slides onto the back of the muffler pipe. Although the top of this tip is stamped with a Chevrolet bowtie, the wraparound nature of the SS bumper cover means it'll be hidden. We put the tip on before final-tightening the cat-back system-align things wrong, and the tip might come too close to lower fascia, resulting in meltage. Take particular note of pipe orientation in the over-axle area, as there are fuel and brake lines running next to the exhaust. After all clamps are super tight (they are, after all, band clamps), you may wish to start the car and inspect for any leaks-while enjoying your new exhaust note of course! Tighten additionally as necessary. | 
On the dyno rollers at TT Performance Parts, our Cobalt probably confuses the Dynojet a little by spinning its rollers backward-they're used to feeling the twist of several-hundred-horsepower RWD street machines in the opposite direction! All joking aside, TTP specializes in all GM performance cars, even offering custom tuning, as well as installation of, for example, GMPP's staged packages for supercharged Cobalt SS's. Our SS had baselined at 140.7 hp and 133.6 lb-ft-not exactly LS1 territory. | 
Gains with the GMPP exhaust were modest, yielding only 1.2 hp and 1.3 lb-ft at the tires (red graph). We're not sure what to make of the richer AFR experienced after the exhaust installation and are probably more willing to chalk it up to variations in how we had our wideband 02 secured into the tailpipe (the slippery finish of our stock and GMPP tips meant that it blew out a couple of times and actually ended up being held by hand-with gloves of course). Apparently, the stock exhaust proves just about adequate for the needs of the factory 2.4L. Not all improvements are dyno-measurable, however, as the GMPP exhaust enhances sound, improves appearance, and gets us ready for flow needs we'll be growing into big time in an upcoming issue ... | 
GMPP's Performance Air Induction Kit (PN 17800653) includes everything you need to help your Ecotec fourbanger swallow more air and get down the road faster. Inclusive of all necessary clamps, ducts, and hoses, this particular item works on all 2005 and later Cobalts (Supercharged models excepted), as well as Pontiac G5/Pursuit models. MSRP is $325. | 
Ganking the plastic Ecotec-stamped engine cover reveals that a good bit of the aforementioned engine shrouding is actually done by the factory air intake's large oblong intake silencer (it surely adds plenum volume, too, of course). This item certainly must soak up some engine heat, a consequence that stands juxtaposed to the intake system's pull-cold-air-from-the fenderwell design. | 
Form and function analysis aside, the stock intake system is coming off, and it starts by disconnecting this PCV hose. Use pliers to remove the clamp and disconnect it from the fitting on the valve cover. You can actually leave the other end attached to the intake tube as this piece of hose will be discarded. But both clamps will be needed for installation of the GMPP intake, so set them aside now so they don't end up in the garbage can. After doing so, unplug the MAF and loosen the hose clamp attaching the intake tube to the airbox lid (both items in bottom left of photo). | 
Now loosen the clamp holding the silencer assembly to the throttle body. One small item that the provided GMPP instructions do not mention, though they're quite comprehensive otherwise, is this small plastic clip helping hold the silencer to the engine. A small flathead pops the top off and undoes it... |
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