We've already mentioned that a whole lot less throttle is needed to move the car. The other obvious part-throttle difference is the crisper shifts of the tranny, which are firm and occasionally hard enough to yield a little squeak underhood (presumably from gently rocking the engine/trans assembly on its mounts). But Hahn did a good job with the calibration of this electronically controlled slushbox, whose running parameters were halfway decent from the factory (typical of most GM 4-speeds). Shift points are basically unchanged at part-throttle, which is great, as the rpms stay low to take full advantage of the turbo torque. It's not kickdown-happy either, so you can, say, remain in 4th and build some boost up steep highway inclines (whilst enjoying the easily audible turbo whistle, mind you). At full throttle, shifts are instantaneous but definitely not neck-snapping. Driving pleasure, as with all cars, must be greatly improved with a manual (remember, this kit works on 5-speed cars as well), but there's nothing inherently bad about the 4T45-heck, it's even stout enough to have survived well in heavy, 3800 V-6-powered, full-size FWD GMs. Bill says the reliability results from Cobalts in the field thus far have been "stunning:" zero reports of tranny slippage or failure, and none expected at these power levels. In fact, the manufacturer's torque rating is actually higher for the 4T45 than it is for the Getrag manual; and for those who are stick-inclined, Hahn has taken those trannies into the low-11s in the quarter with zero attrition-that's with 600hp engines and slicks!
Worried about turbo lag? Forget about it. At part throttle, sure, you can roll into it gradually and let the turbo spool-but anything more than, say, half pedal movement gives instant gratification, with the kind of instantaneous go-power you might find in an N/A or supercharged engine. This has to do with the highly appropriate sizing of the turbocharger. "The GT2860RS is a great middle-of-the-road choice, which at its outer limit can support about 400 engine hp," says Hahn. "It has outstanding low-speed response, and begins to spool up hard in the 2,500-rpm range on these cars. It's a testament to modern turbo and turbo system design, in that there really is no lag-that's an outdated misnomer, born of an era of inefficient designs, when the body of knowledge and capability was not there. These days, I like to say that turbos give you 'continuously variable' power-it's like having a variable-displacement engine that's infinitely adjustable based on the position of your right foot!"
As to other driving dynamics, the traction control still works, and kicks output a good bit when in full activation (it is, after all, closing the throttle for you). But if you roll into it on a slippery surface, it functions pretty well with you to accelerate the car. And as typical of a high-powered FWD'er, torque steer is definitely present, but it's by no means uncontrollable-just be ready for it when you stab the throttle. As long as you're prepared to make slight corrections to the wheel, you're in business (my advice: give whoever's going to borrow your ride a heads-up about this, along with the more general concern that this is no longer your typical sub-180hp econo-car!)
 We're done under the car,...  We're done under the car, so the exhaust system can be reinstalled to the back of the turbo's O2 housing. The stock nuts (and gasket) are reused, as is the entirety of the stock downpipe, as mentioned earlier. When attempting to fit the downpipe, we find that its inlet flange now sits about an inch down and rearward from stock (a fairly minor amount, considering an entire turbo system now sits in place of the stock exhaust manifold!). To compensate, a small amount is cut from one of the slip-fit connections in our GMPP cat-back. The exhaust then fit well, with the downpipe hanging just a bit lower under the car than before. |  The heart of the fuel system:...  The heart of the fuel system: the BoostFueler unit. Here we've installed all included fittings into it. The AN fitting on the right connects to the return line running to the tank; the AN fitting on the left connects to the fuel rail atop the engine. Some turning of this latter fitting will be required to get the angle of the line right, as will some bending of the bracket (bottom of photo) for optimum underhood placement. |  The Schrader valve must be...  The Schrader valve must be removed from the fuel rail. A short piece of braided line (which will be the beginning of the return line) then connects from here to the BoostFueler unit. Again, by controlling how much fuel can exit through this port at any given time, the BoostFueler thus controls the fuel pressure in the rail (and hence, the rate of fuel flow during each injector pulse) at any given time. |