Our 2008 LS3 Corvette has been on the dyno practically more times than it has been driven. We were rewarded with a strong LS3 engine that made excellent power for a OEM bullet, but it was time for some upgrades as we just couldn’t call our Corvette stock any longer. We called our friends at Kooks Custom headers because we had heard that they offered a trick headers and X-pipe setup which would allow us to use a real 3-inch exhaust “Z06″ style, but not necked down to 2.5-inches like the original Z06. They did, and this is the story. We then capped off our installation on our Corvette with a Corsa 3-inch exhaust.

As we covered in our Part I Introduction the stock Corvette made excellent power, and is really an all-around world beater from Chevrolet. Of course, we needed more power, and a nasty exhaust scream to boot. Kooks Headers and Corsa Exhaust got the call to fulfill both of those desires with an upgraded Long Tube Header, X-Pipe, and full 3-inch Exhaust system which would reduce back pressure and increase horsepower and torque.

If you are lazy, and would rather watch our complete video on the installation and testing of the exhaust, you can watch it here:

Goals

Our goals for the 2008 LS3 Corvette are to make big horsepower improvements without affecting the overall creature comforts of the car. We wanted a lot of power, but like many Corvette owners, didn’t want to put together a vehicle that hummed, rattled, and shaked. We wanted to be very careful with the exhaust system because we wanted to avoid ill-fitting exhaust components, drone, and excessive pollution (gotta stay green!)

  • Significant horsepower increase of 30+ rwhp
  • Louder, More Throaty Exhaust Note
  • No Drone on Freeway
  • Good fit, finish and clean installation
  • Retains Cats so we can not contribute to Global warming.

The Parts & Tools

There are a number of excellent choices for headers and mufflers for C6 Corvettes, and we chose Kooks Custom Headers out of Bayshore, New York, and Corsa Performance for Mufflers from Ohio. Kooks has been building custom exhaust and headers since the 1960’s when “Papa Kook”, George Kook Sr. starting building his own exhaust for his drag racing projects. Ever since then, the Kooks family has been making a great product, and this is no exception.

Here are the parts that we chose for the build, and we’ll explain why:

Vehicle: 2008 LS3 Corvette 6-Speed
Headers: Kooks 1-7/8-inch LS3 Long Tube Headers w/3-inch Collectors
X-Pipe: Kooks Catted X-Crossover System, 3-inch x 3-inch
Mufflers: Corsa Performance 3-inch Z06, Dual Rear Exit Quad 4.0″ Pro-Series Tips

Kooks 1-7/8-inch LS3 Long Tube Headers w/3-inch Collectors

Kooks headers are made from 304 stainless steel, and are available for any C6 (’05-’07 LS2, ’08-’09 LS3, ’06-’09 Z06) in a few difference configurations. We chose to utilize the larger 1-7/8-inch headers, with 3-inch merge collectors, that feature 02 sensor bungs pre-welded into the collector. Also, the headers feature a 3/8-inch steel flange (super beefy) that won’t warp, as well as hand-ground welds on the inside of the header flanges for maximum flow. Other items you’ll need for the install are included:

  • O2 Extenders
  • Header Bolts
  • Gaskets

Note: There is a significant debate on whether the smaller 1-3/4-inch header is better than the 1-7/8-inch, but we’ll get into that below.

All headers tubes are 1-7/8-inch diameter and are fully mandrel bent. Kooks also offers LS2/LS3 headers in 1-3/4-inch sizes. There have been many a debate about the correct size headers for maximum power and torque.

Which Header Size Should you Choose?

Most of the debates on header selection have centered around the LS2 engine found in the earlier variations of the C6 (’05-’07). For the LS2, the 1-3/4-inch headers are the better choice unless you are planning on a stroker engine, a serious set of heads and camshaft, or boost. The smaller cubic inch LS2 cannot take advantage of the larger 1-7/8 inch header and will loose torque and exhaust port velocity.

However, if you have an LS3 with the larger displacement engine, the 1-7/8-inch header is by far the better choice, even if only doing the basic intake/exhaust modifications. It will produce slightly more power than the 1-3/4-inch header, and give you room to grow if you decide to add a camshaft or ported cylinder heads to your engine combination.

Headers feature hand-finishing on the inside of the header flange area to provide maximum exhaust flow. Non-ground headers here will have a visible weld-line and will not flow as high as headers such as these.

Merge collector is 3-inches and features a ball-and-socket flange system.

Kooks Catted X-Crossover System, 3-inch x 3-inch

There are a number of different choices with the Kooks X-Crossover systems, and we want to review them here with you in detail so you can select the correct system for your intended needs. We chose the Catted system with a 3-inch x 3-inch intermediate section.

Here are the four options from Kooks:

  1. Kooks Off-Road w/3-inch to 2.5-inch
  2. Kooks Off-Road w/3-inch to 3-inch
  3. Kooks Catted w/3-inch to 2.5-inch
  4. Kooks Catted w/3-inch to 3-inch

The difference between the Kooks Off-Road and Catted pipes is not legality. In California, neither is a formally acceptable token to the Smog Nazi’s. However, that is due to CARB certification and not due to the ability of the Kooks cats to reduce smog pollution. We chose the Catalytic-equipped X-Crossover because we want to be responsible to the environment and we do street-drive our Corvette. We recommend you do the same.

The second decision that needs to be made is whether you are going to choose to utilize a standard 2.5-inch C6 “cat-back” exhaust system, or if you would like to upgrade to a larger 3-inch Z06-style exhaust such as offered by Corsa and a few other companies.

Corsa Performance 3-inch Z06, w/Dual Rear Exit Quad 4.0″ Pro-Series Tips

We chose the 3-inch Z06-style at the recommendation of Corsa exhaust. “The 3-inch system is your best choice for a good mix between maximum horsepower and great sound,” said Ed Burgy, Corsa’s Product Manager. “Since you mentioned that you didn’t want a system that too loud, our 2.5-inch Extreme system really wouldn’t be a great choice. The 3-inch Z06 Street Track system is really hot for us right now.”

We couldn’t agree more. As you’ll see at the end of the story, we not only made great horsepower, but the sound and lack of drone was superior. Speaking of drone, that has really been Corsa’s calling card over the last few years, which is that they build an exhaust system using what they call “RSC” or Reflective Sound Cancellation.

In laymen’s terms, the entire purpose of the Corsa RSC muffler technology is to eliminate the drone/interior noise that can be common with some aftermarket mufflers. The RSC system uses noise-suppresion technology that reflects the sound waves inside the muffler case cancelling out the drone. You can check out the graphic above from Corsa’s web site.

With the 3-inch Z06 Track/Street system, you’ll get a very aggressive “Race Car Like” sound at full throttle, but still a relatively quiet cruising experience. Corsa says it’s worth 10 horsepower and 14-lb/lb at the rear wheels, and provides a 171% increase over the NPP exhuast closed, and 22% increase in flow with the NPP valve open. If you have a non-NPP exhaust, it’s a huge increase, but those numbers weren’t availab.e

Also, Corsa has an excellent web page on their different C6 exhaust systems. We especially like the sound system where you can pick which Corsa system you want to review and you can listen to it in a variety of different environments. Corsa’s exhaust are all stainless steel, and made in the USA. They also say they have a limited lifetime warranty as long as you own your C6. Not bad, we say.

Once you select whether you want a 3-inch or 2.5-inch system, plan on thinking about tip selection. We chose the Quad 4.0-inch Pro-Series tips, but depending on which system you choose you will get to pick from the 4 exhaust pipes or the 2 exhaust pipes. There really is no performance or difference, it’s just a choice of preference and looks.

The Install

We installed the Kooks and Corsa exhaust on our 2008 LS3 in the powerTV Garage. Freshly outfitted with tools from Cornwell, we were ready to start wrenching like mad men. We used our Bendpak lift to get our Corvette up in the air for the swap. We highly recommend that this job be done on a lift. Can it be done on a shop floor with jackstands? Yes. Poorly, and it will be a pain in the ass. Sorry, just being honest.

The stock exhaust in our LS3 was not a NPP system. It was a base system, meaning 2.5-inches and none of that nasty growl that we crave so much.

Here you can see the stock catalytic converters. They are installed by GM as close to the exhaust valve as possible.

powerTV Project Manager BJ removes the stock catalytic assembly and stock X-pipe from our Corvette.

You’ll need to remove the intake covers, and disconnect the coil wires in order to get clean access to the header bolts. Be careful here and don’t break anything. These just remove easily.

See the fresh plug. We dropped one. If you drop a plug, never reuse it. Get a fresh one and save yourself the potential trouble shooting down the road.

Removing the factory cast-iron header was easy. Here you can see us pulling the header off the car and the factory metal MLS-style shim gasket.

We removed the 02 sensors from the stock headers.

The Kooks 1-7/8-inch headers next to the stock manifolds/cat combination.

The Kooks headers go in from the bottom. We worked as a two-person team, with one person working from the underside, and then someone grabbing the headers on the top side and positioning them correctly.

The fit with the Kooks X-Crossover pipe and headers tucked away nicely.

O2 sensor extensions are provided by Kooks, and we removed one of the belly pan bolts in order to secure the extension to the body.

Routing of the Kooks X-pipe and headers in the C6 tunnel. We did have to clearance slightly the metal heat shield as there was a small area which was contacting the Kooks headers when the headers were warm and expanded. Once we did this we had no fitment issues!

The completed exhaust with the Corsa 3-inch Z06 Track Street system.

The Sound & Driving

As soon as we twisted the key on the C6, an immediate smile came to our faces. Between the Kooks long-tube headers, the 3-inch x-pipe, and the Corsa Z06 3-inch exhaust, something magical was happening. Throating and menacing at idle, open-headers sounding at full throttle, yet someone completely civilized and peaceful during cruising. And an immediate seat of the pants improvement, even without tuning.

One word: Amazing

Check out the video below for some sound clips.

Performance

With the stock exhaust, we were consistently dyno testing in the 385-387 rear wheel horsepower range. With the Kooks/Corsa system, power increased to 421 rear wheel horsepower with no tuning. This is a gain of over 30 rear wheel horsepower, and we were running a very fat 11.0-11.25:1 air fuel ratio.