I normally like my cars to be stock simple but there is just something about having a ForTwo that makes me want to customize it. I ordered a Doug Thorley Headers muffler from SmarTune when they first announced their prebuy in April.

The first step was to remove the lower rear (black) valance by removing two Torx T-25 screws and two plastic rivets.

I used a putty knife to carefully lift the insert out then pull the rest of the rivet out of the body.

Looking up from under the car near the left rear whell you can see the flange that connects to old muffler to the catalytic converter. There is a heat shield that has an E-10 (external Torx) bolt connecting it to the muffler pipe (and two more screws connecting the heat shield to the top of the catalytic converter). I ordered an E-10 box wrench from Sears.com but they mysteriously cancelled my order. A 5/16" box wrench fits just fine.

The instructions say that you can reach the top of the catalytic converter from the inside of the engine compartment. But I removed the rear body panel instead (not recommended due to the extra work). Here you can see the two top E-10 bolts clearly. These must be temporarily removed in order to lift the heat shield in order to access the flange bolts.

A closer look.

Now I can finally get to the E-12 bolts using an E-12 socket with swivel adapter. Both bolts come out fairly easily once you lift the heat shield up and away from the catalytic converter. I will need to reuse the flange gasket so I carefully handle it when I take the muffler out. A generous coating of WD-40 in the rubber mounting pads helps slide the old muffler out of its pads.

The Thorley muffler is much lighter than the original.

Here you can see the E-10 bolt that was connected to the original muffler. It is not used with the new one.

Here it is installed.

With the valance back on and ready to test.

A side view.

Showing ground clearance.

And a right side view closeup.

Next I took the car for a spin. The muffler is a bit louder than OEM but has a pleasant throaty growl. The claims are that the muffler provides up to a 20% boost in low end torque. Here is their dyno test:

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Had my Doug Thorley exhaust installed yesterday and I like the sound, the system fit perfectly, and it is a quality product.

The installer had the same problem that others have had with one of the bolts on the cat flange. The bolt started out easly but seized up and the head twisted off. The remainder of the bolt was removed with vise-grips and the bolt was replaced with a bolt and nut.

Note to smart: There is a problem at smartville with the installation of the two bolts in the cat to muffler flange. The bolts are being over-torqued or cross-threaded or the lack of anti-seize compound on the bolt threads is causing the threads to gall which leads to bolt failure when it is removed. This problem has occurred on several smarts.
I am interested if after doing this after market upgrade you gain mpg? Thanks for the links they still work. I wonder if/when there'll be a cai (cool air intake) for the 4-2?
The mod does add horse-power, if you visit the Doug Thorley site they have the dyno test. The smart has a factory cool air intake it is just over the left rear wheel. I will post my MPG aain or loss when I have enough data.
Thanks for the reminder Roy. I uploaded the Dyno chart.

Some have reported a good increase in MPG using their scanguage but it it still early to have confidence in the numbers. I feel that I am seeing both better low end power and better mileage (when I drive with a light foot in 'D') in town.
This is an excellent upgrade. I am seeing approximately 2 - 3 mpg increase with the last two tanks, and it sounds awesome. No fart can sound, but more like a British sports car.
The man to call about this is Paul Bridle of the smart Center of Round Rock at (512) 244-1491 or refer to his post here:

Will wait to hear the DTH's in person at The Meet N' greet in Charlotte. Have to see if I can live the the the different exhaust node. Had some on my Jeep's and truck. Some were good and some just had a bad drone!!!
Thank you very much for your tutorial. It made the installation of mine go much more smoothly than it would have otherwise.
This is definitely a job you want to do when the car hasn't been run and the exhaust is cold. I followed the lead of others and did not remove the top bolts on the heat shield. While it did make it a tighter squeeze to get out the others, it avoided the potential problems that have been reported with over-torqued factory bolts on the heat shield that break off when you try to remove them.
Leaving the heat shield in place, I found that there wasn't enough room to get my e-sockets in there but was able to break free the bolt with the 5/16" ratchet wrench for the heat shield bolt attached to the stock muffler and the 3/8" ratchet for one of the cat/muffler bolts. For the other one cat/muffler bolt, I had to put on the box end wrench and grab the open end with my needle nose vise-grips to get enough leverage to finish breaking it loose.A switch to the regular box end wrench completed the loosening of the first one, because there wasn't room to get my particular ratchet (craftsman) to click to a new ratchet position.
The tip about using channel locks to squeeze the muffler hangers through the hanger rubbers made that a simple task after the liberal application of WD-40. (Sorry I don't remember who suggested this, they deserve a hand.)
I did use the bolts supplied by DT, liberally coated with locktight, and the 12mm socket with 1/4" drive for the new installation. (The larger drive wouldn't have fit in the space.)
I'd say it sounds a bit louder than the Mini but not offensively so and most posters say it quiets down a bit after it's broken in. The sound is definite improvement, but I can't say I really saw any performance difference on the first test drive.

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