Header Installation

We're in the midst of a quest for Z06-like performance out of an LS2-equipped 2006 Corvette, and though we've made progress thus far, the gains have not always been easy to measure. While our actual dyno horsepower has increased 17 or so over stock, that figure is deceptively low. Back in the November 2006 issue ("Locked On Target"), we added over 13 rwhp through the addition of a 3-inch CORSA Performance RSC Cat-Back exhaust system--a substantial upgrade over the super-quiet factory 2.5-inch unit. In the second installment of our project buildup ("Ethereal Rush," Mar. `07), induction equipment from Vararam Industries only resulted in a few extra horses on the rollers; however, a 3-mph gain in the quarter proved the ram air system's worth.

Notwithstanding the mismatch of dyno chart numbers and on-track performance, we've reached a point in the build where it's time to add a part which traditionally delivers one of the most significant, measurable power-increases of any bolt-on. Long-tube headers have been enhancing musclecar power for as long as there have been musclecars, and we are determined find out if a C6's LS2 engine can similarly benefit. The criteria in our search for a suitable header set were simple: find a company that makes them from top-quality material and has a reputation for stellar power increases.

A poll of top New Jersey-area Corvette tuners resulted in resounding nods to American Racing Headers (ARH). And while ARH hasn't been around for all that long, it's quickly become one of the most talked-about companies when it comes to header systems for late-model 'Vettes. After contacting the Long Island, New York-based shop, we found that ARH's staff was more than willing to discuss each and every one of our needs. As the company's C6 systems are available in both 1 3/4-inch and 1 7/8-inch primary sizes, we were unsure which version was most appropriate. Based primarily on our desire to continue with a loud-and-proud, dual 3-inch exhaust, ARH recommended we stick with the smaller tubing size to better fit our 364-ci mill's application.

This brought up another issue raised by our existing CORSA Cat-Back: we wanted our new header system to match up without cutting, welding, or any other hacking. We knew the added length of long-tube headers made retention of the CORSA system's forward portion impossible; but we wanted to make sure any new x-pipe would match up with our system's rear portion. Research revealed that the CORSA system's overaxle pipes are virtually identical to the kit it sells for Z06s, which retains the stock system forward of the axle. In other words, all we had to do was order the ARH header system with a Z06-spec x-pipe and connection pipes, and we were in business. (We should also note that the helpful folks at ARH will work with you to ensure your header system is built to mate up with stock or other 2.5-inch catback systems, if that's your gig.)

Just a few weeks later, a package from ARH arrived at the GMHTP offices and it was time to get going on the install. Follow along in the photos for a full technical evaluation of our ARH system, as well as tips and tricks. Those who pick up their own ARH headers will find the latter helpful, especially during removal of the Cat-Back, as the information provided by ARH lacks detail (experienced mechanics will be able to sort things out, but a little clarification never hurts). With that said, let's get to it, get through it, and get set to hit the dyno!

Results
The addition of our ARH headers immediately bumped up driving pleasure. A noticeably improved exhaust note was apparent as soon as the key was turned (or should we say, when our C6's "run" button was pushed), and light-throttle driving produced a rumble only slightly overpowering with the windows closed, and under certain conditions of engine load. Police-patrol-free daily commuting is still quite possible if you keep the revs down, but send the tach over 3,000-rpm, and you experience a wail not unlike a C6R turning 7,000 down the backstretch at Le Mans. Exhaust noise will always be fairly substantial whenever running long-tubes and an exhaust as big as ours. The catted ARH header/CORSA Cat-Back combination hits a sweet spot livable on a daily basis, and you can still provide exhaust-howl-induced adrenaline rushes when you feel the urge.Weather conditions in New Jersey's winter season prevented any track-testing of our newfound power, but a little salt and snow won't stop us from getting to a dyno. As you follow along with the testing and tuning performed at TT Performance Parts, keep in mind that thanks to our existing Vararam air induction, real-world performance will eclipse these dyno totals, as it adds substantial power at speed.

WHERE ARE WE AT?
Our to-date totals of 376.8hp and 378.9 lb-ft are up over 16hp and 21 lb-ft from what we left off with last time, so we have shown that sizeable gains in C6 power and torque are possible through the addition of long-tube headers and a bit of tuning. (ARH also believes that horsepower and torque would have been higher here if we had been using a 2.5-inch x-pipe and exhaust, a better match for our internally stock engine. But remember that our ARH headers and full 3-inch exhaust set the stage for tackling additional exhaust flow needs from which future mods will benefit.) The final dyno graph also probably could have been a little better had we avoided false knock issues, not uncommon on C5s and C6s with modified exhaust systems. We will do our best to remedy this problem next time, but for now, TTP had to cap things at around 24 degrees of timing, in order to delay excessive power-robbing retard until past the power peak.Improved though it may be, 376hp is still a good bit shy of the 450 rwhp typically produced by LS7-powered Corvettes. Including the CORSA Cat-Back, Vararam induction products, and ARH headers, we have spent just under $4,155 so far (not including labor and tuning-related costs). Add this to our sticker price of $46,535, and we are currently roasting tires in a $50,690 Vette. This is still much less than $70,000 for a Z06, and with about 33 rwhp gained so far, we have already made significant headway into the factory difference between the standard Corvette and its 7.0L big brother.

The rest will come in good time, as we are sticking with natural enhancement only--no forced induction, and no spray. So what will it take to make up the rest of the ground while staying N/A? We already know, but we will keep you guessing. Stay tuned!

Two nuts hold each factory cat pipe to studs in the stock manifolds. But do not get overambitious here--there are rear O2 sensors in each, which need unplugging (though the sensors can be left in their respective pipes until they are out). For now, just loosen the nuts so that each pipe hangs a little lower, providing enough room to reach the sensor plugs near the engine. Be patient, as they can be a bit difficult.	With the rear O2s now unplugged, remove the aforementioned nuts and the cat pipes come out. We are done with system removal underneath and can shift our focus upward.	Under the hood, the plastic engine covers are popped from their rubberized mounts and removed, exposing the ignition coils. We will need to start disconnecting items on and about the cylinder heads, and the covers obstruct access to everything--and hide a substantial portion of the LS2's electromechanical majesty. (Dare to be different? Sell your engine covers on eBay.)
Atop each valve cover, a front O2 is wired in via a plug assembly affixed to the coil bracket. Unplug it and unsnap the black plastic female connector; its wire leads to the sensor mounted in the manifold below. Repeat for the other side.	The next step is to disconnect all of the ignition wires. This function-unknown piece of black plastic on the passenger side obstructs removal of the number 8 wire from its spark plug. An upward yank pops it out; we will see if it can be reinstalled after the long-tubes are put in place. (For those who cannot stand the suspense, the answer is yes).The next step is to disconnect all of the ignition wires. This function-unknown piece of black plastic on the passenger side obstructs removal of the number 8 wire from its spark plug. An upward yank pops it out; we will see if it can be reinstalled after the long-tubes are put in place. (For those who cannot stand the suspense, the answer is yes).	With all ignition wires removed, the spark plugs come out and are placed to the side for later use. These are the last ignition-related items to be extracted; fortunately, the coils can stay in place as the ARH headers will install from underneath.
On the passenger side, a 15mm bolt holds the dipstick tube to the head. Unlike some press-fit designs of past GM V-8s, an o-ring seals it to the block and so it easily pops out and up.	The final step in system-removal is stripping the stock manifolds from the engine. Six 13mm bolts on each side hold the manifolds in, and will have to be wrenched out because they are clogged with factory GM sealant. Note that there are multiple bolts on each manifold which do not need to come out; shinier bolts hold the manifold heat shield and can stay in place for now.	Take care while removing the manifolds, as they can now easily drop straight to the floor. While still up top, orient them in order to get them temporarily stuck between the engine and fenderwell. This way, they will not fall as you venture underneath. Remember, there is still a delicate O2 sensor in each one.