This is all coming into better focus now.

So do you have any equation or rule of thumb to determine the max header pipe diameter before loosing scavenging and therefore torque? I assume there is a universal rule you can apply to a 3.4, 3.8, and 5.7...

 

A rough rule is that the displacement of a cylinder determines the optimum diameter of an exhaust header runner, and the speed that the engine is expected to operate at determines the length of the runner. After the exhaust is out of the runner thebigger the pipe and the less back pressure, the better. An extreme example would be a dragster, where the exhaust runner dump right into open air.
Cat back systems work because the eliminate a lot of the back pressure due to poor plumbing, and headers work because they improve cylinder scavenging over the typical exhaust manifold. You really want to get all of the exhaust gas out of a cylinder so that it can get completely filled with the incoming A/F mixture.

As for X pipes and H pipes, they require full dual exhaust. Whether they work depends on the firing order of the engine. On a V engine if the cylinders are set up to fire sequentiallyfrom alternate banks they do not accomplish much. However; as in the typical V8, where there are 2 cylinders firing sequentially from the same bank they are helpful. The side firing the two cylinders in sequence will at that time generate more exhaust pressure than the other bank which is skipping a beat while waiting for its turn to come up. The connection between the exhaust pipes allow the side with the high pressure to overflow into the side with low pressure thus reducing overall back pressure.

Cats got a bad rep becuse when they first came out they were extremely restrictive. Current high flow cats flow much better and removing them accomplishes little. Mufflers are a different story as they range all over the place.

The makers of exhaust systems have all this stuff figured out and refined with much trial and error. Just tell them what you have and how you intend to use it, and they will recommend the right set up.

The funny part is that most people buy exhaust systems according to the sound that comes out from them, and that is mainly determined by the mufflers, numbers of cylinders, and firing order. So you can have a very restrictive system that sounds really good to some individual.

 

Thanks for that detailed lesson - it really helped understanding. ;-)

So for a real-world example on a '02 3.8L V6 do you know how to compute that optimum diameter of the header runners? I am contemplating the FFF LT Headers, if CIA ever private-label USA manafactures them, and curious what the ideal is. I'm not sure off-hand what theirs are currently...

Looks like this software does the trick, anyone here own it and care to do the calculations? ;-)

http://www.maxracesoftware.com/pipemax36xp2.htm

 

Looks like they have everything covered, and if it works as advertised well worth the price. Much better to know what to look for than spending hundreds on something that does not produce results. For a 3.8 normally aspirated, 1-1/2" diameter X 24" to 30" long primary tube works well for street use. For a race version increase the diameter to 1-5/8", and shorter primaries to take advantage of the high RPM capability. Using the software work up the dimensions and then buy the closest thing to what you specked out, or if you have a big budget get them custom made. Good luck in your project.

 

Interesting perspective discussed here about V6 Camaro headers:
http://www.camarohomepage.com/project/part4.htm

Also see the making of their custom 3.8L Dawson Racing Headers (theirs have the stock EGR hookup, apparently unlike all the other brands out there):
http://www.camarohomepage.com/projec...ersequence.htm





Which leads to the question, how do you eliminate the EGR if you want to so it does not throw any SES codes? How much performance gain can be expected from this elimination?

 

If the EGR is working properly it does not affect power output. The EGR is designed to work only at part throttle operation. At idle and WOT it is closed and does nothing.

 

What if it's an older Camaro which is not subject to emissions testing and the EGR is throwing codes, but you don't feel it's worth replacing a part that provides no value, given the aforementioned? ;-)

 

You can remove the EGR and block off the opening, but you will need to get the computer tuned to delete the EGR in order to do away with the codes.

 

Ok, so does anyone know if there's a tuner that works on both a '95 3.4L & an '02 3.8L?
I assume a Tech 2 can talk to both? Any inexpensive tuners out there?

 

Never heard of one that will, one's obd1, one's obd2. Tech 2 is a scanner, not tuner.