Starting with GMHTP's July issue, we've been slowly feeding our readership (or, at least the open-minded portion thereof) details of a turbo system installation on our non-factory-supercharged 2007 Cobalt SS. Well, ladies and gentlemen, hunger no longer: this month, it's finally time to finish off the installation and put this little blue 4-banger through its paces!
For those who may have missed our prior installments on this FWD alt-hotrod in the making, here's what we've been up to. Not satisfied with a bolt-on-enhanced 148 whp and accompanying mid-15-second timeslips, we decided that to get anywhere near V-8 territory with a 2.4L engine, we'd need to go boosted. Enter Hahn Racecraft's "Stage 2" turbocharger system (Part No. H TS-2910, MSRP $4,199), a kit designed for 2006 and later manual- and automatic-equipped Cobalts and Pontiac G5s with the LE5 engine. Don't get us wrong: we are in no way attempting to duplicate the fantastic all-around performance of the LS/LT/SBC-powered RWD GMs to which this magazine owes its dedicated fan base. Instead, we're toying with an alternative, relatively low-dollar route to high-performance-and one that should make for a very sensible, economical, worry-free daily driven ride. We'd more or less polished off the turbo kit install at the Hahn facility last time, save for fuel system modifications.
So first and foremost, let's get Hahn's BoostFueler on the car before moving on to the really good stuff (i.e., power and performance results). We've mentioned this component in our previous installments, but never went into the details of how it works. (As a side note, Hahn Racecraft had used the BoostFueler on its Solstice and Sky turbo products-they use the LE5 mill as well-so by the time the Cobalt project rolled around, it was a proven setup.) As the name implies, the BoostFueler allows boost-proportional fueling in a form that works well with the ultra-sensitive ECM of the LE5 engine (we'll delve into that can of worms in a moment). But there's more to it than just that, as it also allows some end-user tuneability. According to company proprietor Bill Hahn Jr., "The field adjustability is a very strong value-added feature because it gives folks the ability to make adjustments that suit their particular condition-climate, equipment combinations such as different exhaust systems or boost pressures, etc.-that are hard to achieve in a solid fashion that suits every possible customer with just a single reflash approach." The installation of the BoostFueler is very straightforward, and the gist of it is this: as with most vehicles manufactured in the past few years, the stock Cobalt fuel system is returnless (primarily a concession to cost savings), so Hahn Racecraft converts it to a return-style setup that can vary the flow of fuel that is permitted to exit the fuel rail, thereby modifying fuel pressure at the rail as a function of manifold vacuum or boost. See our photo captions for more info on how the BoostFueler works and how easy it is to adjust.
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Step one in getting the BoostFueler system in: under the car, the gas tank must drop out. Two straps hold it in, and taking it out fortunately does not require messing with the rear axle, just unhooking a bunch of plugs, tubes, and hoses (along with the remainder of the exhaust system, save for the tailpipe-factory units are one-piece, so be ready for a little extra work here if you're retaining the stock exhaust). | 
After tapping its retaining ring counter-clockwise using a punch that can't spark, the fuel pump module lifts out the top of the tank. Because we're dealing with volatile fuel here, it's in one's best interest to run the gas tank as low as possible before the turbo system install. |