I searched but did not find (I'm sure it is there somewhere) My Miltek header and cat-back drone. It feels like a pressure builds up in the car at highway speeds. It is not that the "loud" bothers me but the pressure does. In the twisties where the rpm changes no problem but at constant hgwy RPM it would be nice to lower it. The Borla street was no problem. I love the performance. Any Ideas?

 

You're just hearing the lower frequency drone, it sounds like.

My first step would be to try extending or retracting the mid-pipe to
change frequency and see if that helps.


shorter, higher frequency drone.
longer, lower frequency drone.

 

Have you checked the clearance at the valance when the car is hot? The vibrating valance can produce an aural sensation much like having your head inside a drum. If this is the cause then a box cutter will easily fix it.

If you suspect something on a grander scale, sound-deadening material placed strategically or completely throughout the interior can alter the cabin’s resonating frequency. In my case, I gutted the interior and applied materials (including stuffing cavities) over several weeks until the uncomfortable tone/sensation was reduced.

 

I have the Milltek header and catback. During trackdays, road trips and canyon runs, I've had no drone. Having the rear seats down increases cabin volume of exhaust, but only under load. That's why I bought the Milltek in the first place. Civilized at cruise, but throaty under acceleration.

I'd check your car for spots where your exhaust might be contacting the chassis or bodywork. Then try changing midpipe lengths.

Good luck and please post results.

 

Thanks to you and k-huevo for some great tips......I will experiment. I know the valence IS touching.

 

k-huevo- would you please explain which 'valance' you are referring to?
Are you talking about the exhaust tip hitting the rear bumper valance?
If so, you cut your rear bumper?!

 

I just got back from RSPeed and Hector is goping to put some spacers in to separate the tip fronm the bumper. They are touching now. He can't get the car in until next Thursday when he puts the AP RAcing BBK on. Then except for some do dads here and there I'm done. The $ is way out of hand but the fun keeps going up. I am having an experienced suspension guy do some tuning as well next week.

 

Do you have the Aero bumper? My Milltek was hitting it completely so just
got 4 longer hangers at Autozone. #17219 $3 each? It's an easy fix.
You can use spacers, but new hangers are much easier to do imo.

If you have a ramp, you can do it in 5min.

 

Great tip $12 will bring those to Hector Thanks

 

The tip touching the bumper isn't the problem - you need to "pull out" your tips from the bumper surface, so they stick out. This will de-baffle the tips and thus reduce interior amplitude.

OR

Take off your cat-back and run with an open header for about a week. Then, put the cat-back back on, and you'll never hear your exhaust again

 

OR ANYTHING ELSE!

They are exposed about an inch to 11/2 inches. We are going to rehang, pull them out some more, maybe some Dynamat

 

Yes kenchan, it is “valance” not that atomic term “valence”. Sorry about the spelling folks. The rear trim has a ridge that can be shaved or the valance relieved further without showing at eye level.

The exhaust tips are tilted downward and may clear the plastic trim when cold, but when the exhaust becomes extended, the elevated entry portion of the tips gets closer to making contact. Compound that with the exhaust can hangers inserted completely to get more extension. After the exhaust heats up, it causes the rubber hangers to travel upward in an arc and the tips will become elevated further. The entire exhaust train gets placed under tension with the hangers at their limit, and the whole thing vibrates like a plucked string. Of course there are many who don’t have this issue. Then there are those that get the poorly executed build requiring many “adjustments”.

The issue I found with longer rubber hangers and shimming, was more lateral movement. The can hangers would knock left and right

 

k-huevo- I wasn't trying to be a smartass...didn't even notice you mispelled.. Just thought cutting the bumper was a little extreme, but if it works.

Here's how far mine's sticking out when heated. I get no drone.

 

Mine touch while cold. They clearly need work and it drones like crazy. Thanks for all the help

 

be careful pulling out the tips further. the first day i put the system on i was getting a loud drone when the car warmed up. when i installed the system originally, the tips stuck out about one inch (maybe a little more) when cold. after i put it up on the lift i saw an indentation on the back side of the battery box. apparently this system increases in length over an inch, because that's about how much clearance i had when it was cold. right past the Y-pipe the two smaller pipes curve around the batt box, thats where it was hitting. after readjusting for clearance, the tips stick out less than 1/2 inch when cold, that's the most i could get. when hot they go to about 1 1/2in. (stock rear valance). i also have very little clearance at the tips, and this does cause a bit of noise, more like a buzzing at idle from the tips hitting the valance. i like the longer hangers idea, i'm going to try that...

 

I left about a little less than 2 inches clearance before the battery
tray by the Y piping. I checked the system a few times while
checking the torque on the mid-pipe clamp while it was hot.
I still had a good inch of clearance on the Y from the battery
tray area... (I only drive the car on the streets where exhaust
temps are much lower than on the track)

On my system, the flange was hitting the heat shield where
the midpipe meets the rear section, so I pushed the shield
upward about 1/2" for clearance before I took it out for its
first spin.

 

i also had to push that same heat shield out of the way. and a correction to my earlier post, my tips stick out almost an inch (measured from the top of the tip) when cold and about 2 inches when hot.

 

re-hung the Miltek dropped about 1/4 to maybe 1/2 inch (no longer touching)and the problem is solved. Thanks to all for your help.

 

Sounds great! A nice finish to 2004 and a great way to start 2005!