In the exhuast backpressure/tuning sticky, I have a few questions regarding the length of the secondaries. It states that the length of the pipe will determine the RPM at which the exhaust will be tuned for.

My question is, I've used programs to determine the length I'd like to use. How does one achieve this? Specifically...

Does the I-pipe essentially function as a termination box making the rest of the exhaust (so long as it flows appropriately) essentially seem like the atmosphere. (The negative pressure waves start at I-pipe not at the muffler?)
Or in other words, when calculating the length of the secondaries, it would be from the collector to the beginning of the I-pipe?

X-pipes?
Does the X-pipe function similar to a termination box, again equalizing the pulses and starting the negative pressure waves at the point of the X?
Or again, when calculating secondary length would it be at the X pipe or at the muffler?

I-pipe?
When considering flow, do we then assume that the I-pipe needs to flow enough for the entire motor? It seems that a 3" I-pipe is pretty common and empirically, based on rough calculations of what pipe flows, it seems like it could quickly become a restriction on a 383 or larger motor.

I'm hoping to hook up a pressure gauge to my spare O2 bung and get some actually feedback readings. I have 3" Y-pipe to 3" I-pipe to 2.5" y-pipe. ~400hp/500tq


Thanks in advance!
Chris


David Vizard's Termination boxes
http://www.superchevy.com/technical/...exh/index.html