Resonance improvement
 

While I had my transmission out this winter, I decided to do a couple of things to get rid of some of the exhaust drone in the cabin. I removed the heat shield from beneath the rear trunk and lined the sheet metal with black Hushmat. It molded well around all the curves, etc. and the heat shield went right back on. I also removed all of the stock sound deadening from around the engine compartment and replaced with more of the Hushmat. Finally, I put a layer of Hushmat in the engine cover between its heat shield and the inside plastic.
Bingo! Yeah, since it's pretty much an open exhaust, it's still loud, but the 2800 RPM drone is gone. My wife and I can actually have a conversation on the highway. And the hushmat came in a few pounds lighter than the stock stuff I pulled out.

What kind of exhaust do you have ?

Chinese headers, Fabspeed bypass pipes and a Borla muffler.

Did you get a free Pu Pu Platter with those headers ? Just kidding . :) I'm surprised that it caused that much drone .

So you think the trick is to add more to the engine cover? I have a stainless exhaust I got off some guy on craigslist for $150 that drones in the 24-2600 rpm range. I make due cause it sounds better than stock.

When he came by to bring the exhaust, he also gave me a fuel filter, another set of tail lights, a boxster bra, and another factory exhaust. Not a bad deal for $150 I didn't think

J, thanks for the post, I didn't know about this stuff. I'll keep it in mind when I dump some cash on a new exhaust system.

IMHO, the most improvement came from lining the underside of the trunk. Stock, the trunk has nothing, yet it is one of the largest single metal panels. As well, it is only separated from the exhaust by the heat shield, which itself is another large, undampened panel. Take the carpet out of the trunk and tap on it. It reverberates.

Since I had the trans out, I decided to put the dampening material on the underside of the trunk. I figure if I can deaden the vibrations before they get to the metal, I'm better off. If I had had the engine out, I would have put the material inside there as well. The engine stayed in the car, so the material is on the outside of the firewall and engine compartment.