Selecting long tube headers can be an intimidating task and does require some technical knowledge, but it isnít the voodoo some make it out to be. In this post I will try to arm you with as much information as I can to help you decide on the best option for you and your ride. If you have any questions after reading it feel free to send me a PM or give us a call at the phone number in my signature.
Which Manufacturer Should I Go With?
The good news here is that this is hard to get wrong. Ask around on the forums and you will hear some of the same brand names over and over again. Stick with brands like Stainless Works, Stainless Power, ARH, and Kooks and you will be fine. From a performance stand point all of these brands are pretty close, no one has a secret sauce that makes one of them produce substantially better results than any of the others. In terms of quality, again, most of them are pretty close in this area as well. If you are looking at other brands though here are some of things to pay close attention to.
Pay attention to what they are made from.
Stainless steel (particularly 304) is what you will want to look for. 304 stainless steel will not rust or discolor from exposure to the atmosphere like the cheaper 400 series stainless steel. Unlike aluminized steel, it will not rust from the inside out due to the corrosive fluids produced during combustion. 304 can discolor slightly from getting extremely hot or if you spill engine oil on them but another attribute is that it isnít permanent.
Pay attention to how they are made.
CNC mandrel bending is the best manufacturing method for producing exhaust systems and headers that flow and fit well. When this process is used in conjunction with the 304 stainless steel it allows for the use of a thinner wall tubing that will weigh less than other headers. Those weight savings will be lost, however, if you opt for ceramic coating. With 300 series stainless steel the coating isnít needed for corrosion resistance purposes (ceramic coating is often pushed because the manufacture is using inferior material) and I have never seen some of the claimed reductions in under hood temperature scientifically demonstrated in hard numbers. It looks great and they cool off quickly, that is about the sum of it.
What Primary Diameter Should I Go With?
This is the area that seems to cause the most confusion but it is fairly straight forward. Header manufacturers usually offer two or three options when is comes to primary diameters for a specific vehicle. For example, for the Camaro SS most manufacturers are offering 1 3/4 inch, 1 7/8 inch, and 2 inch primaries. Below are some pretty typical numbers for what you can expect on an otherwise stock SS:
Stock: 370 RWHP 375 RWTQ
1 3/4 headers with high flow cats: 400 RWHP 405 RWTQ
1 7/8 headers with high flow cats: 410 RWHP 410 RWTQ
2 headers with high flow cats: 415 RWHP 410 RWTQ
As you can see, simply switching from the restrictive stock manifolds to 1 3/4 long tube headers is worth approximately 30 RWHP and 30 RWTQ on a bone stock Camaro SS. The larger the primary diameter gets the more air the headers will flow and the further up the RPM range the power band is moved. The more powerful the engine is the more beneficial it is to go with a larger diameter, especially when you introduce forced induction. This means that generally the more power you make or the more race oriented your application is the bigger primary diameter you need, the closer to stock or the more street oriented the smaller primary diameter you need.
In the specific example of the 5th Gen Camaro SS, we have found that the 1 7/8 long tube headers are the best all around header for the typical bolt on modified car that is street driven regularly and occasionally taken to the track. They offer a tremendous improvement over stock with room to grow as the car is further modified. The 2 inch headers offer very similar numbers to the 1 7/8 headers up to 5000 RPM where the 2 inch headers pull ahead. They are ideal for those running forced induction or for race applications.
High Flow Cats or Cat Delete (Off Road Pipe)
With modern high flow cats there is essentially no performance advantage to a cat delete. They flow 99.9% as well as straight pipe. On a dyno you might
see 1-3 rwhp in the mid RPM range. Going with a cat delete does cost less but the biggest draw back for street driven cars in my opinion is the rotten egg smell of running without cats. Others are the potential legal issues and the inability to pass emissions testing and inspections. For track cars none of these are a concern so save the money and apply it elsewhere but if your car is used primarily on the street high flow cats are probably your best bet.