Expert: Dan Liddy - 8/8/2009

Question
I have a 79 camaro hobbystock and race at stateline speedway an asphalt 1/4 mile track. i heard there is a way to tune your exhaust by marking it with a crayon and cutting off the excess. any idea how to do this or a better easier way?

Answer
That will help, though I doubt you'll notice much difference. You need to start at the cylinder head, and measure the volumn of each exhaust port, then equalize them.  Your engine builder can do this though he may not believe your request at first. You will want to ask him to "CC" the exhaust ports and make them all equal.

Next, you will want to measure each runner in each header, and make sure they are of equal length. If they are, you're close, BUT each runner should equal the volumn of one cylinder. Now then once you get to the collector of each header, expand them to accept 2 1/2" pipe and make any bends with mandrel bent "U" bends cut to the amount of arc needed and welded into the system. The muffler shop bender will RUIN any efforts at tuning an exhaust. Their bends also crimp the pipe somewhat. So finally your 2 1/2" pipe should be of a length to equal the volumn of one bank of cylinders, figure what lentgh will equal that volumn, and at that point build a 31/2"Dia. expansion chamber of about 14" length. Again using a mandrel bend, fabricate a bend to move the gasses out from under the car, or through the rear quarter panel if you can build to that extreme.

That's all I know about the subject, I learned it about 30 years ago, and it's worked well for me. I'm sure there are computer models that are more specific, some don't explain their logic and can be intimidating. The above method works and anyone who has mastered high-school math should be able to figure it out.

Good luck, and feel free to write back if you have questions

Dan Liddy
Sarasota, Florida