In short, the BoostFueler is one of the main showpieces of ingenuity that allows the Garrett turbo kit on which this system is based to play with the 2.4L engine. So why exactly is the LE5 such a PITA to tune? In essence, it's the Variable Valve Timing (which is not used on any other Ecotec engine save the new 2.0L factory-turbo LNF). Hahn explains that GM's VVT is a closed-loop feedback system analogous to the O2-controlled fueling schemes we know so well. It continuously monitors cam positions and alters oil flow from the control solenoids to achieve the cam phasing it is programmed for. "It adds two magnitudes of complexity to the calibration because it adds two more axes to the fuel modeling that takes place in the ECM," says Hahn. In other words, take that pretty 3D fuel map from your custom Camaro tune and instead draw it up in five dimensions-needless to say, it's impossible for humans to even visualize, and the calculated airflow through the engine at any given time becomes extremely mathematically complex. Talented as your local LS tuner may be, this is a whole different ball game, and many a shop has been handed a boosted LE5-equipped car only to send the customer packing shortly thereafter. Hahn deserves major props for cracking this-so let's see how it turned out!
Nearly two weeks had passed since first dropping the car off at the Hahn facility (the kit install can be completed in a matter of hours; the added time spent here was for development and tuning on this pre-production kit). Now it was finally time for some behind-the-wheel action. The first thing I noticed when driving the car (other than the exhaust note being much quieter, which is a definite plus) was that a lot less throttle input was required to get the car moving. Talk about a change in response! Initial drives with Bill riding shotgun doing some laptop tweaks on ice-cold Illinois roads showed a huge lack of traction below 50 mph, thanks to the combo of FWD, skinny tires, and some serious newfound cojones under the hood.
Just how serious? Back in New Jersey, I headed to TT Performance Parts (Passaic, New Jersey) to get a solid comparison to our pre-install baseline. If you look at the accompanying dyno graph, you'll note almost 222 whp-73 more than our previous intake/exhaust combo (and just shy of 80 more against the exhaust-only situation-equating to 100 hp at the flywheel!). Obviously, values like these can be dyno-dependent, so the real world was the only way to get some true numbers-and that means hitting the 1320.
Quarter mile results were had on an early April day at Raceway Park (Englishtown, New Jersey). Two sets of back-to-back runs were performed. For the first pair, the tire pressures were a bit high, yet I was still able to nail a best pass of 13.59 at 103.8, on a 2.25 60-foot. This pretty much surprised everyone in attendance-including some magazine editors who shall remain nameless-and was only a few ticks off from the e.t.'s being turned during grudge races between a near-stock Pontiac G8 and Mustang GT! After the car cooled a while (during which time I dropped the tires to 30 psi), I did a second set of back-to-back passes, and the last was the best: 13.57 at 102.7. Clearly, I had nailed the launch better than before (2.19 to the 60-foot mark), but the air apparently just wasn't there by that time of day to support the same mph or a significant improvement in e.t. Considering a race weight of 3,090 pounds, this Cobalt is not a featherweight, and I can imagine what a stickier set of tires and/or some sort of a burnout would do to those timeslips. Low 13s anyone?
Driving Impressions
My experiences have revealed that there's much more to a Hahn-equipped Cobalt than just straight-line smackdowns. We want readers to know that Hahn Racecraft put very extensive development time into its final product, and the result, simply put, is about as close to OEM reliability and mannerisms as a turbo system can be.
 The only modification needed...  The only modification needed to the module involves this little check valve. (To gain access here, simply unclip the gray plastic cover; the Hahn instructions say a nylon tie must be cut to do this, but ours didn't have one.) The lever is pried up and the metal ball and its seat removed. We hang onto them in a small plastic bag-remember, the Hahn turbo install is 100% reversible should the desire ever arise to go back to stock. The lever is left to rest against a now-empty hole where fuel from Hahn's return system will reenter the tank, and the gray plastic cover replaced. |  With the simple in-tank mods...  With the simple in-tank mods complete, the tank is reassembled and reinstalled into the car. Everything is reconnected save for the smaller of the two lines (5/16) running from the fuel pump module. It now connects, via a couple of special provided fittings, to the braided return line seen in hand. This line had originally connected to one of the ports on the silver so-called accumulator (which looks a heck of a lot like a fuel filter). So, this port is now plugged with the blue-hose-and-fitting-array shown. Make sure you hear this sucker clip in place! |  The braided return line is...  The braided return line is run under the car alongside the factory fuel lines, being securely tie-wrapped along the way. Care must be used when entering the engine compartment, as this bad boy needs to stay clear of hot exhaust parts and the steering system. |