Tech Tuesday: C6 Exhaust

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Why Mod?

Modifying your exhaust can be inexpensive but costs can mount quickly the more changes you make. The entire exhaust system includes two exhaust manifolds (headers), two catalytic converters, two pipes, two mufflers and finally the exhaust tips. Any and all of these parts can be replaced or removed with varying degrees of power increase and changes in sound (both loudness and tonal quality). There are essentially two ways to go about modifying your exhaust system; first, just cat-back (which means changing everything after the catalytic converters) and second, headers and cat-back. However, it is possible to remove and replace any individual part, the aforementioned two are the most common.

If you’re going just going to be driving in town and on the highways, then cat-back is probably enough. Replacing the headers adds considerable time and cost to the project. It will also increase power gains, but is only really effective if you’re making major engine modifications that necessitate an exhaust system with greater flow and efficiency. If intake and exhaust is all you’re interested in, then the stock headers are probably enough.

Another possible modification if only going cat-back is the addition of an X-pipe, which helps balance the back pressure like the stock H pipe and also scavenges the exhaust to help the engine breathe a bit better. Unfortunately, exhaust modifications are usually a poor project for the novice DIY’er as welding is required. For proper results, it’s often best to find a reputable shop and have them do the work.

What are the negatives? Well, modifying the exhaust makes your car louder (which is the reason most people do it) and obviously it will require you to spend money.  This is a poor place to begin if you’re looking for power gains, unless you’re building a monster engine in which case you’ll  have to modify the exhaust. But if you want 50 hp, this is not the way to do it.

Having said all of that, check out this DIY header install (it doesn’t require welding) that CF member PowerLabs posted:

My 2006 Z51 2LT Corvette, current relevant mods are a Vararam CAI and GHL exhaust (quad 4″ tips).
The headers:
Kooks 1 3/4 Long Tube, JetHot Coated, 3″ catted X-pipe.
The tools:
Car jack, Jackstands, Torque Wrench (used 18ft-lbs for the header bolts and 45ft-lbs for the exhaust clamps), and a craftsman 165pc tool set.

I wouldn’t run uncoated headers on any car; for me the reduction in underhood temperatures (and lessened chance of melting plug wires) is the main reason; the performance gain from maintaining high exhaust gas temperatures and the improved looks and longevity are also pluses.
I went with kooks because I could get them coated from Tbyrne, and because when you add the cost of coating, other header options start to become too expensive for the power gains they provide.

I did the install myself, with the help of my neighbor; this was my second time ever working on my ‘Vette; I had no printed instructions or service manual, but I did look over similar builds beforehand.

The install took 5 hours, which included a snack break, some beers, and taking the pictures. The kooks fit PERFECTLY and I am extremely satisfied with the fit and finish.

The process:

Jacked the car up and stand it on jackstands. I needed about 15″ of ground clearance for this.



Removed the engine covers, the spark plug wires, and the oil dipstick. The dipstick pulls right out after you remove one single bolt. Also make sure you remove the battery positive; if you don’t, the headers will short out your battery on contacting the starter motor. Don’t ask me how I know. At this point, loosen all bolts. You may not want to remove them all just yet.


In retrospect, it would have been easier to remove all the above BEFORE jacking the car up.

Do not bother attempting to remove the exhaust manifold into catalytic converter nuts. They will ALL shear:


Nice view of what the stock manifold collector looks like though. Compare it with what Kooks uses:


Now that, ladies and gentlemen, is what a 4-into-1 merge collector should look like…

The proper method of removing the stock manifolds is to leave them connected to the cats and remove them at the H pipe connection. I did not have to remove the alternator, starter, or anything else in order to accomplish that.

Having removed the stock headers and cats, I moved the O2 sensors over. They were easy to remove. Don’t forget the antiseize.


Now it was time to get the new headers in. I installed them from below, but could not have done it without help. I held them up while my neighbor (thanks Les!) put the bolts on. Don’t forget the gaskets; I re-used the stock ones as they are 3 layer steel and better than the ones that come with Kooks. Just make sure to clean them up nicely beforehand. I kept all bolts lose for now:



I then installed the catted X pipe, one section at a time; I was able to push the axleback exhaust out of the way to get the rear section of the X pipe in; wasn’t easy, but just be patient…




Finally, I used aluminum tape to hold the O2 wires out of the way. Aluminum tape reflects heat, but it does not appear to be a very durable option. Still looking for a better way to do this.


So there you have it… A 5 hour install using nothing but a car jack, jackstands, and basic hand tools. It WAS laborious, but I’d do it again in a heartbeat. Actually, I am doing it again; my neighbor was so impressed that he ordered headers for his car a few days later.
But of course the question is: How does it perform?

First of all… *WOW*!!! Jesus Christ I never through a car -any car- could sound like this! Damn! It is slightly louder at idle and cruising, but when I floor it and the revs climb up towards the 3500+ range, the engine lets out a wail unlike ANYTHING I’ve ever heard before. It is unique, special and downright exotic. I absolutely love it! Other than the sound at wide-open throttle, the car feels and drives as normal, despite not having been tuned. I haven’t seen any change in fuel economy, engine bay temperature, etc. At full throttle it certainly feels faster, but I will refrain from commenting too much on the performance until I get the car tuned. I love my car, and these headers make me love it just a little bit more.

We’re not going to show a cat-back install as it requires welding and most people have neither the equipment nor training to do it properly, but most any exhaust shop can do it well.

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