Weird Exhaust Sound Change

[TalonJohn94]

So I have a strange exhaust sound question. So I took my car out tonight after putting it all back together and swapping to colder, BPR7ES plugs. I thought I didn't have the MBC dialed in that high but apparently I was at about 25-26 psi. Well anyway I noticed that when Im at WOT late in 2nd gear (maybe like 5k RPM, full boost) or a little earlier in 3rd gear (4.5k RPM full boost) the exhaust tone changes dramatically. It goes from a somewhat regular exhaust sound that normally starts deep and gets higher pitched until gear change - to now when it switches to a lower not such as a blown muffler for a few thousand rpm before gear change. What could this clearly audible exhaust tone change be?

I know its kind of an abstract question but I don't think its normal. The only thing I can think of is an exhaust gasket although I just inspected those this weekend when installing my WB O2.

Any thoughts?

 

[fonzi90Tsi]

Are you catted?

 

[TalonJohn94]

No. Test pipe.

 

[Diamond Star Werks]

This is normal. you should know. its your v-tec coming on! rocket speed

 

[BurrowZ]

It's your wastegate opening fully. The turbo acts as a silencer. With the wastegate open, the "noise" bypasses the turbine and successfully changes the exhaust tone.

 

[Diamond Star Werks]

It's your wastegate opening fully. The turbo acts as a silencer. With the wastegate open, the "noise" bypasses the turbine and successfully changes the exhaust tone.

^
+1 you are correct Sir

 

[LOLVTEC]

You get an open dump for your wastegate. I call mine my vtec. Cracks louder than any vtec in the world.

 

[Ozone302]

You get an open dump for your wastegate. I call mine my vtec. Cracks louder than any vtec in the world.

How come every post I see from you has the word vtec in it

 

[TalonJohn94]

Ok, phew. I was actually kinda worried something was wrong.

You know its funny, I was going to describe it as VTEC-like but thought I might get flamed a bit.

That's good to know, but I think I'm going to dial the boost back to about 20 psi until I can get a Palm Pilot that doesn't lose the Datalogger program everytime the AAA batteries die and I can properly monitor it. Although my factory boost gauge (Keydiver) never moved indicating no counts of knock.

 

[TalonJohn94]

Just curious. Is that sound change around the same airflow/psi/hertz for everyone using an E3 16G?

Does an external WG always sound like that at WOT?

 

[Archer Fabrications]

Just curious. Is that sound change around the same airflow/psi/hertz for everyone using an E3 16G?

Does an external WG always sound like that at WOT?

youtube external WG it sounds like your engine is a fkcn angry bear. i love my screamer pipe you should also check for exhaust leaks if you havent already.

 

[TalonJohn94]

The only exhaust leak I would be worried about would be between the O2 sensor housing and downpipe because the nuts are super close to the pipe making it difficult to really torque down with a socket.

 

[Archer Fabrications]

The only exhaust leak I would be worried about would be between the O2 sensor housing and downpipe because the nuts are super close to the pipe making it difficult to really torque down with a socket.

loosen both bolts so you can shift it around the welds. i have a megan DP and it does the same thing. id check for manifold cracks, leaks, and turbo to manifold and turbo to o2 housing leaks as well.

 

[TalonJohn94]

Thanks for the tip.

Yeah, one of my turbo-to-manifold bolts is suspect because I think it is stripped. Otherwise the exhaust mani studs are good and O-2 housing bolts should be good. And I think I'll only have time to address the downpipe bolts before Shootout.

I kind of have a BEFORE SHOOTOUT and AFTER SHOOTOUT list of little fixes just because I don't want to run out of time on anything.