Exhaust note changes and car surges at 3k rpm?

Hi all, Logged about 900 miles on my car so far (almost 33k) and it has a Tubi exhaust. It sounds phenomenal. Like really good, I finally got to drive it under an overpass on Saturday, downshifted and put my foot down and it sounded like a damn F1 race! You should�ve seen the smile that put on my face. I have noticed under light load it sounds nearly stock, then when you dig in it really opens up. However, if you keep your foot light, creep up to and then past 3k, when you hit about 3200-3400 (still not adding any additional pressure to throttle), it almost sounds like a valve has opened up and now I get that beautiful exhaust note. It�s like someone flips a switch. I assumed this was just normal because I had read lots of exhausts on these cars sound stock until you open it up�.until I noticed that there�s also a slight surge or jump in power when this happens. When I say slight I mean slight. Surge/jump is too strong a word, but there is something there, that should not be happening unless I have more throttle, that�s for sure. It feels Like the car is being choked down, and then at/around 3200rpm there�s enough air being moved it �open it up�? Is this possible? More recently I noticed that one day it was louder from idle to light throttle, but heavy pedal was the same as before. There was no surging or Change in exhaust note like the above. Everything felt right. Hmm�feels like it�s SUPPOSED to be like this! My own conclusion is that there is probably an issue with either the mufflers and/cats restricting a certain amount of airflow, and this is fixed by applying more throttle, or getting rpms up to the point where this proposed restriction actually clears up. Sorry for the long winded post. TLDR - exhaust seems choked under light throttle, jumps at 3200rpm, possible cat/muffler issue?

There's a resonance flap in the intake that changes state at about 3200 rpm. It sounds like that's what's happening. The resonance flap is to optimize low end torque and high end torque at the same time, which requires different intake manifold geometry.

JP, Get a copy of "the 996 essential companion". Great book that will tell you everything about the 996, things to be aware of, recommended replacements, etc. Worth the money. You can find it on Amazon. Look under Variocam in the book and it will tell you about what's happening at 3k rpm. Had no idea what it was when I first experienced it. add edit: looks like thePrf gave you a good technical explanation.

Woah, guess I should�ve done a search! Thanks guys. also, is this resonance flap what I see people deleting on the stock air box? With the elbow and the plug? Or is this something with the manifold itself? so now how does this explain the one morning where it wasn�t working as such??

JP, can't answer that one but maybe theprf can. Unless you knew the word Variocam, tough to search. Don't worry about it. Keep asking questions. The more questions you ask the more you will know about your car, and the more you will like it.

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The resonance flap's in the connecting pipe between the two manifold halves, the pipe that's hiding behind the throttle body plenum. You want to leave it in place. As GC said there's also variocam and variocam plus, one shifts the intake camshaft timing and one increases the lift of the intake valves. So there are three systems affecting the engine performance. At light throttle it can be quite noticeable when these shifts happen. I remember my E36 M3 with the VANOS intake camshaft timing adjuster, you could hear it toggle if you listened carefully - it made a kind of "zing" sound. Surprised me the first time I noticed it!

Very interesting stuff, thank you for the info!