Continuing with the power theme, the next recommendation is to attend to the engine's intake side. An upgraded throttle body, cold-air kit, or airbox improvement all fall in this category. There are a variety of improvements going on here. The stock inlet, for example, is not overly large, and has some convoluted rubber hoses, which produce turbulence in the airflow path. Thus, a smoother tube or pipe helps raise airflow without having to grow too large and take up all the underhood real estate on the passenger side of the engine compartment.
We prefer a cold-air kit that places the air filter inside the fender. This avoids breathing hot, underhood air (less dense, less power) and fan wash, which can confuse the mass air meter and lead to maddening driveability woes.
The throttle body is a simple call. Aftermarket throttle bodies are larger and flow more air than the stocker-the large oval unit available from FRPP is appropriately sized, and there are others from Accufab, BBK, and so on, depending on your manifold. Like many other inlet improvements, a larger throttle body by itself is not the magic key to performance nirvana, but combined with the other breathing mods, it helps. An important building block, in other words.
Intake plenums, often called elbows, are recommended. These devices are reasonably priced and do produce a couple of horsepower. Testing has shown they won't quite match the power gain of a throttle body, but in conjunction with one, they will raise the power curve just a couple of points all across the tach. You'll do best cost-wise when buying the throttle body and elbow as a package.
At this point, the more drag-racing oriented tuners recommend a shifter, other tuners leave it until later.
Exhaust was the next power recommendation. Luckily, the X-pipe has the tuner's favor, as well as the customer's ear, so it seems the way to go. As for cat or non-cat X-pipes, tuners say it really is up to the customer, and in fact, sales are about evenly split on this item. We have to say the high-flow cats are our recommendation. We have a strong ethical bias when it comes to hobbies and clean air, and from a power standpoint, eliminating the cats is only worth a few horsepower anyway.
There is one bothersome exception to this, and that is if you are building an open-track car. The extended periods of full-throttle operation on a road course can seriously heat catalytic converters of any type, and in that case, not having cats can save a fire. The right way to do it, of course, would be to have cats on the street and swap to an off-road X-pipe (or a dedicated track-only exhaust system with straight-through mufflers and no tailpipes) for track days.
For street cars that occasionally go to the dragstrip for a couple of fun runs, don't sweat overheating the cats. They'll be fine. And, in fact, the same is likely true at the road course if you are not absolutely flat to the floor, but rather out to enjoy your car without traffic, police, and road hazards.
After-cat choices are as wide-open as always, but the Bassani and Magnaflow systems that are so popular seem to be doing a fine job. The reality, of course, is that on a street car where some semblance of decorum is required, there will be a small top-end power loss due to mufflers anyway, and just as likely a low-range torque gain compared to running short, open pipes. But, with the realistic bolt-on power expectation just over 300 rwhp, losses due to mufflers are not outlandish anyway. Bottom line: today's popular quality systems are likely giving all the power a street-licensed car can.