back pressure tones down the pulsing of air over the exhaust valves and keeps the temperature more consistent resulting in longer valve life. the stock sodium filled valves are shitty. if he had solid inconnel valves, it wouldnt matter as much. back pressure in the manifold evens out the pulsing between cylinders which smooths out the engine and actually gives slightly better low range tq.

 

Well, I did it. (Its only a two minute procedure, so I didn't waste THAT much time) You were all right, it was COMPLETELY stupid. I've done this before with the cat on, but with the test pipe it was outright deafening. The idle was louder than my friend's V8 'Stang with a hole before the mufflers. I mostly did it to **** him off, he prides himself in winning any and every revving contest (which I know not to participate in ) and he was so angry that he lost so some German 4 cylinder. But the car was so loud I would shift into 4th at 25 mph to keep it quiet. It was just mind boggling. I've since reversed it and welcomed back my low end torque.

 

Good. The only way to truly learn is to actually do it.

 

my cat separated at the turbo flange last winter so exhaust just dumped out after the turbo, and I drove it like that for about 3-4 weeks until my test pipe came in and I could put it on, and it was terrible. It was loud and smelled like exhaust in the car all the time, if I could have that A4 back i'd take it in a second even with no exhaust, I miss that car and the sport cloth seats.

 

So in my job (lowly peon bagger at Albertson's) I have plenty of time to conjure up wild modifications to my car whilst pulling in carts or mopping floors. One recent mod I dreamed up was a downward turnout pipe welded to the downpipe that would shoot exhaust gasses straight down, making the car straight piped. This could be run with a bolt on block-off plate just like the old hot rodders, but in my neat-o world I envisioned a motorized valve, controlled by a pneumatic or electric motor. Hooked to a sweet toggle switch in cabin, this enabled the owner to switch from ***** out loud to stealthy stocker exhausts. It would be grand. Then I stumbled upon a classified on the Zine today. A test pipe with a Y welded on and on the end of that Y an electric motor controlled valve. A momentary two way switch ran the operation. I was stunned haha. Unfortunately, I own a test pipe already and this design would vent the ehaust gasses (and or backfires/flames) straight into the engine bay, presumable onto the tranny or firewall. Bad idea much? Haha, just thought I'd share that story.

 

They have those.. Google 'electric cut-outs'...

 

down in california the emissions laws are strick. So people will put an electronic louver on. It directs the airflow out the exaust when its closed, when its time to race flip the switch and it just closes the exaust and dumps the air onto the ground. Louder than crap. Easier airflow = power. no harm done