S-mann Exhaust Fitting

Mid way between MOT’s I had the emissions checked on my 2011 fortwo 451 turbo and it looked like it would fail when the MOT came around. It was a 2nd hand Brabus exhaust that I had put on in 2012 so it had lasted OK.

I didn’t really want to put the standard exhaust back on as I already had the Brabus valance  to suit a twin centre exit exhaust, so really, I needed another twin centre exit exhaust. Having had S-Mann exhausts previously on a Roadster and a 450, it was a no-brainer. I contacted Imro at S-Mann, threw money at him and he made me exhaust in no time at all.

Really! Another Exhaust Fitting Guide?

I know what you are thinking. Do we really need another exhaust fitting guide? Obviously, there is a guide for fitting the Brabus exhaust that I’m removing, however, fitting the  S-Mann exhaust isn’t as simple as the Brabus exhaust. So I thought I’d show you what I did.

What’s So Different About The S-Mann Exhaust?

When the package turned up, I didn’t think I’d been sent the right thing. The box is much smaller than a smart exhaust.

It all became clear when I opened the box. It’s a 3 piece jigsaw.

This guide shows you how to easily construct and adjust the exhaust to suit your car.

Fitting The S-Mann Exhaust

Remove the rear panels, remove the rear crash bar, open the engine cover, look over to the right by the oil cap. That’s the upstream lambda sensor connector. Disconnect it…

…and pull it through.

The downstream lambda sensor is in the main can of the exhaust, follow the wires back…

…until you find the connector. Disconnect it as well…

…and pull the wiring through.

Remove the 2x 14mm bolts.

Spray a bit of lube onto the exhaust rubbers…

…put your foot on the rubber and pull the exhaust out. Repeat the other side and the exhaust is free.

You will need a proper 22mm lambda sensor removal tool. Either a spanner or a socket.

Spray the sensors with penetrating lubricant, leave them a while and then remove them.

Take your 3 pieces of exhaust.

Push the CAT into the silencer and fit one of the supplied pipe clamps. Tighten it a bit.

The existing manifold has a sealing gasket to stop the exhaust from leaking. Because the S-Mann has a much wider inside diameter, it needs a bigger sealing gasket. The old scabby bum-hole looking gasket on the left. New gasket on the right.

Because the new gasket is larger, it has a larger inside diameter. So you get an adapter to make it fit.

Slide the adapter into the back of the new gasket…

…and slide the assembly onto the car’s manifold. You’ll have to hold it in place until the exhaust is fitted.

Slide the rods into the exhaust rubbers and replace the 14mm bolts so everything is held in place correctly.

Fit the twin center exit outlet and hold it in place with another clamp.

If you think you are done, you are wrong. Due to the amount of adjustment, you don’t want to just tighten up the 2 exhaust clamps and put the rear panels back on the car. The reason is that the exhaust tips might be off centre or facing the wrong direction. The 3 sections need a little adjustment just to make them perfect.

However, if you put the rear panels on, it makes adjustment and tightening of the clamps tricky. So, put the crash bar back on with 1 bolt each side. Tighten it up properly.

You can now attach the valance to the crash bar but still get to everything for adjusting and tightening.

Adjust the silencer angle and the tips position until they sit where you want them.

You have 2 options now, you can either just tighten up the 2 exhaust clamps and reassemble the car, or you can do the job properly and also add a bit of security to your new exhaust. OK, you decided to do it the proper way. Good job.

Remove the valance and the crash bar again, making sure not to move the perfectly adjusted exhaust. Take a pen or a scribe and make a registration mark where the parts connect. This gives depth and angle.

Remove the exhaust from the car and break out the exhaust putty. This stops any leaks between the connections which is a really good idea if you want to pass the MOT without any issues. It also glues the sections together.

Disassemble the exhaust and place a bead of exhaust putty around the outside of the tube’s mating face. Don’t put it inside the opposite piece as assembling it can push the paste into the exhaust.

Push the parts together, making sure to line up the registration marks. Fit the hose clamp over it and tighten it right down to stop any movement.

The CAT and the silencer will stay together as they are restricted by the exhaust rubbers once fitted. However, I was a bit concerned about the exhaust tips falling off because I hadn’t tightened it enough. I was also worried the the tips might droop down if someone stepped on it. So I decided to permanently hold the tips in place by drilling a 5mm hole through both pieces…

…and then setting a 5mm stainless steel rivet through the hole. You MUST use a stainless steel rivet. If you use other metals, it could cause bi-metal corrosion between the 2.

Once the rivet was set with a rivet pop gun, the tips were held in place securely. No chance of me seeing them fall off as I’m driving.

Place the supplied pipe clamp over the joint and tighten it up. The base of the clamp hides the rivet head.

Fit the lambda sensors into the new exhaust, connect them up and reassemble the car.

Job done, looks awesome.

What Adjustment Is There?

If you adjust the silencer, you adjust how far the exhaust tips protrude from the valance. The adjustment for the tips can set the angle of the outlets. I angled mine up slightly.

How Does It Compare To The Brabus?

I measured the volume in decibels using an app on my iPad. The microphone was 140cm away from the tips and sitting 40cm higher than the exhaust exits. I didn’t want the exhaust blowing straight into the microphone.

Standard Brabus Exhaust

On tick over, the Brabus exhaust created 80.3dB. Blipping the throttle to the red line and releasing created 89.4dB.

S-Mann Exhaust

On tick over, the S-Mann exhaust created 88.1dB. Blipping the throttle to the red line and releasing created 91.6dB.

So, the S-Mann exhaust is a bit louder than the Brabus which is to be expected. The Brabus exhaust has a lower note than the S-Mann, which is a little bit more raspy.

Is It Annoying On Long Journeys?

It depends on you.

I think it sounds good but I generally have my stereo volume up fairly loud so I don’t hear the exhaust over the music. It sounds good when you turn the stereo down, open the windows and drive through a tunnel.

Does It Pass Emissions Tests?

In the UK, an emissions test is performed during an MOT (yearly Government inspection). I fitted this exhaust in 2017 and had 7 MOT’s in the time I owned the car (sold in 2023). Emissions were never an issue mentioned on the test.