Originally posted by CalgarySVT:
What I am saying is that it is likely not "the" bottle neck, or in other words, not the single most restrictive portion of the stock exhaust system. Meaning there can only be one bottle neck in the system at one given time.

For example, if 50 widgets of gas can pass through the cats in one second, and 60 widgets can pass through the resonator in one second, removing the resonator will still only allow 50 widgets a second to exit the exhaust system...


That is extremely incorrect thinking though.

EVERY time you change the diameter of the piping, add a restriction (resonator, muffler, cat), or have a bend it affects the exhaust flow.

You can't say because the Y-pipe crush flange is the biggest restriction then adding a cat-back will have ZERO effect because it is not the "single most restrictive" part. (which you just stated in the part I quoted btw)
That is completely wrong in thinking and in plain fact!


Even after the crush flange...

The cat slows down velocity and adds turbulence to the exhaust. This uses up exhaust energy.
Then the same thing happens to a factor of about 2 in the ~1.8" I.D. resonator. More velocity and energy is lost and turbulence is generated.

Then comes the rear bends. Since they are mandrel the loss in piping size is fairly negligible so the corresponding velocity loss is as well. However "technically" it is still a loss.

Then the rear y split. This is actually pretty well built (I've had mine apart) However you will always get a loss because you are forcing the exhaust flow to divide.

Then it's the stock BAFFLED mufflers. Again a significant loss because of the multiple 180 degree short radius bends and open sectioning.

All loss is CUMULATIVE! YOU CAN NEVER REGAIN THAT ENERGY!
The more loss the less power produced because of the lower efficiency.


So YES loss does continue to occur after the Single Most Restrictive part. (and before it for that matter)


The very simple proof to this is dyno gains from a cat-back system. That's been done ad nauseam.


Now a well built cat-back system on a car WITH an optimized Y-pipe would shower a higher NET gain then one without. It's all about overall efficiency as you alluded to with the well known fact about maximum flow being limited by the smallest/most restrictive area.
However either one will still show a gain.

2000 SVT #674 13.47 @ 102 - All Motor! It was not broke; Yet I fixed it anyway.