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Your grammar is a little tough to follow and I'm not sure what you mean about glass packs. But basically, I refuse to admit butt dyno observations. The human ass is a fine piece of engineering as far as seating is concerned. However, it is so poorly calibrated as a performance measuring device as to be unuseable. Almost every time I made a change to my car that resulted in improved performance, the difference was not discernable by butt dyno. Those little changes that I couldn't feel, or thought I felt, or that felt like losses, added up to almost 30 horsepower! If I relied on SOTP rather than actually measuring the results I would still be right where I started.
And really, unless you've actually measured the mean (average) backpressure as well as backpressure at different points throughout crankshaft rotation, you won't know how much more or less backpresure there is in the system after the collector, or at the exhaust valve throughout its opening and closing cycle. There's just no way to know until you test. Even then, there is no guarantee that you can simply apply a pressure reading to your power output and construct a reliable conclusion based on those two figures.
I don't know why the car you drove last week was faster, or felt faster, than whatever you are used to. You are comparing two entirely different cars with several different modification all applied at the same time. The only way to say for sure what made what difference is to test each mod, one at a time, on the same car, and see which ones help and which ones hinder. Anything less than that is, at best, guesswork.
There is so much more to the science of exhaust and induction than simply whether you have more or less backpressure. I can't even begin to pretend that I understand it all, but I know the basics, and one thing I do know for damn sure is that backpressure is not a goal to shoot for.
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