The reason that they may actually increase the popping is that headers increase a vacuum effect within the exhaust pipe, and that helps to pull the exhaust gases out, thereby, increasing horsepower.
Downside, as there are 2 air injection check valves, which do NOT allow exhaust gases into the air injection pump. However, it does NOT stop possible pulling of fresh air into the headers.
When this happens, the vacuum we talked about earlier pulls the fresh air into the header on decelleration, or off throttle. your combustion process is being continued inside the header, and therefore, the popping could be increased.
Best to you, c4c5
My popping increased. At first I didn't like it, but now I love it!! Go figure
I've got TPIS 1 3/4 " Long Tubes which flow into Random Tech's High Flow Cats(very light weight) and thru a Bassani x-pipe to the Corsa Indy's.
It's a great sounding system.....deep, powerful and exotic. As you can tell, I'm very happy with the way it turned out I get a whole lot of unsolicited rave reviews from the guys in my Corvette Club. I'm usually up front on our runs, so they get to hear it a lot. I love to downshift, and that's when the popping really starts a happning:guiness:
Now that you mention it, the Ford 5.0L, at least the carbureted models, DID have vacuum activated check valves to prevent that air from getting in on decel. When that valve failed on my '85, I had a ton of popping. Since I already had an H-pipe, I just plugged the port in each head. It probably would have been harder to hear the popping through the cats.
Since the popping doesn't have anything to do with making power, eliminating it would allow more 'stealth' (if there is such a thing in a Z). If someone wanted to, adding the valves might be pretty easy (someday my manual will come )
Though I'm not sure what that would do to the cats and O2 readings.