Exhaust Write-Up
Headers
There are 3 main different types of headers: shorty, mid-length, and long tube. Each have their advantages and disadvantages.
Shorty
GOOD- Price, Size, Ease of fitment
BAD- flows less, Compact design can cause plug wire clearance problems
Mid-length
GOOD- Flow slightly better then shortys, Fitment easier then long tubes
BAD- Less flow then long tubes, bit more expensive
Long tubes
GOOD- Extremely high flow
BAD- Expensive, tougher to install
Headers should be an important part of anyone’s MOD plans. Stock manifolds on the 3.4's and the early 3.8's are very restrictive. In 2000 tubular manifolds were added. While they are an improvement, there is still much to be gained with headers. No matter what mods you have to help increase the air flow into your engine, if you can't get that air out it will do you no good. Headers are the first and most important way of doing this.
Your headers flow is determined by 3 main things: primary size, primary length, and collector size. The rule of thumb here is bigger is better, but that’s only to a certain extent. Having larger primaries and collectors decreases backpressure. By doing this it increases horsepower, but moves your torque higher in the rpm range. This is good to a certain point. If you get to large you will have a serious loss of torque due to low backpressure. All the headers made for the f-bodes have large enough primaries to help with power, without giving up torque on the low end.
Another important part of headers is the material they are made of, as well as any coating that is applied to them. Their are many different metals that headers are constructed out of, including mild steel and 304 stainless. While mild steel helps to make a more cost effective header, stainless is the best for quality and durability. Once your material is chosen, the next step is to determine if you want a coating on them. Some opt just to paint them with a high temp paint (which will bake off fairly quickly). While this is again the most cost effective, this does little to protect the metal. If your headers are made of mild steel and merely painted, they are more apt to rust though. The next option is to wrap the header in exhaust wrap. This has been around forever and is effective in keeping the heat in the header, and out of the engine bay. The only problem with wrap is that it can hold moisture against the header, and cause some rusting problems. The last, and best option is to have the headers ceramic coated. Their are different temperature coats that can be applied. The good thing about ceramic is that it holds heat inside the header, and provides protection for the metal.
Basically your choice should come down to what your goals are. If you just want a bolt on car that’s fun to daily drive and might see a little track time, then shorty or mids are your answer (pacesetter, Clear Image, RK Sports). If your going all out with it and want max power (using FI of some sort, stroker, or other big N/A build) the long tubes are for you.
Catalytic Converter (cat)
A catalytic converter is a device that uses a catalyst to convert three harmful compounds in car exhaust into harmless compounds.
The three harmful compounds are:
· Hydrocarbons (in the form of unburned gasoline)
· Carbon monoxide (formed by the combustion of gasoline)
· Nitrogen oxides (created when the heat in the engine forces nitrogen in the air to combine with oxygen)
Carbon monoxide is a poison for any air-breathing animal. Nitrogen oxides lead to smog and acid rain, and hydrocarbons produce smog.
In a catalytic converter, the catalyst (in the form of platinum and palladium) is coated onto a ceramic honeycomb or ceramic beads that are housed in a muffler-like package attached to the exhaust pipe. The catalyst helps to convert carbon monoxide into carbon dioxide. It converts the hydrocarbons into carbon dioxide and water. It also converts the nitrogen oxides back into nitrogen and oxygen.
Once headers are done, the cat is the next most restrictive part of the exhaust. It’s very common for our cats to become clogged, causing a loss of power as well as mpg’s. Even if they are not clogged, however, they are a bottleneck for the exhaust. If the blockage does occur, it can simply be replaced with any universal cat that has in and out diameters that match your current exhaust size.
For the performance aspect, there are many high flow options available. The trade off with a high flow cat is that it allows more of the harmful compounds into the air. This can cause you to throw ODB2 codes, and even fail emissions test that your state may have. These codes can be corrected with an O2 simulator, or by having the codes deleted via HP Tuners. This will allow certain people that only have and ODB2 emissions test to pass; however if you have to do a sniffer test you can still fail. Another option is to completely remove the cat, and replace it with a piece of pipe. **Warning: its illegal in any state to modify the emissions part of vehicle. So do this at you own risk. V6f-body.com does not condone doing this. While this will provide the best flow there are two downsides. This allows all the harmful compounds the engine produces to be released into the air, it causes even more rasp in the exhaust, and can have a horrible smell as well.
Cat-back Systems
They are what the name implies…a full exhaust system from the catalytic converter(s) back. Since it is unlawful to remove cats before 50,000 miles (or unless they’re damaged…in most states…check local laws), most exhaust companies offer such systems.
There are many advantages to choosing this route. For one thing, the tubing diameter of most aftermarket exhaust systems is usually larger and this configuration, usually offers more horsepower. Of course, not all manufacturers test and build their systems the same way.
Material used is a big part of selecting your exhaust. The cheaper cat backs will use aluminized metal. While this is cheaper, it is more apt to rust out after a couple years of use. The more expensive exhaust will use stainless steel. This is a much more durable metal, that will hold tough for many years to come.
With today’s engines and exhaust tracts being offered as highly efficient right from the factory, extensive testing is required to actually gain horsepower. There are many companies that simply offer a bigger pipe and a muffler that is freer flowing and while the vehicle is louder, they can not quantify any horsepower gain.
**It is recommended to have any cat back system completely welded instead of clamped together. This helps to prevent leaks, and keep the performance gains where they should be.
Shop-Built Systems
Another option for a cat back is to have a local shop custom build for your application. Most shops now have a mandrel bender that can accomplish the same smooth bends you will get from a pre bent system. You will usually pay a bit more since this is a one-off build that is labor intensive. A small downside here is loosing all the research the big exhaust companies have in dyno testing their systems.
Universal Mufflers
If you are just looking for that rumble and do not care about the performance aspect, simply adding a muffler is probably for you. Nearly all major suppliers that offer cat backs will have the mufflers available for individual sale. You can even usually find these mufflers with the in and out diameters matching your stock, so they are a simple clamp on application. Just like with cat backs however, it is suggested to have it fully welded to prevent leaks.
Which should you buy?
It depends upon your budget and goals for the vehicle. If you want it done right, a properly engineered, dyno tested cat back system is the best choice, hands down. In situations where lack of availability of such a system or associated costs are prohibitive, consider some of the alternatives we’ve presented here.
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Originally Posted by sweetv6camaroguy
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