Performance is Exhausting !

[Pingu]

Replaced the rear mufflers with straight through pipes.

The improvement in acceleration is impressive...

The red lines show the speed from around 18mph in 2nd up a certain hill (acceleration starts from the same point [a line across the road]). Full throttle (WOT) applied at the line at approx 1800rpm (18-20 mph).

Blue lines are RPM.
Open muffler data is solid lines. Standard muffler data is dashed lines.

Standard Muffler
Delta Time = 8.7 - 1.4 = 7.3
Delta Speed = 63 - 17 = 46
=> Acceleration = 6.3 mph/sec

Open Muffler
Delta Time = 6.5 - 1.8 = 4.7
Delta Speed = 65 - 20 = 45
=> Acceleration = 9.6 mph/sec

The data was downloaded using TestO.

 

[Brian H]

Those time differences are huge, can you still hear though ?

 

[Pingu]

Those time differences are huge, can you still hear though ?

When I gun it, it is louder than Concorde - must be close to Deano volume

 

[littlefeller]

the green line is a red Yaris going up another certain hill

 

[Pingu]

MOT Man - he say "Too loud".

Next stage is to investigate standard muffler on one side and a "track use only" bypass valve on the other.

 

[NigelM]

You could put removable baffles at the end of the tail pipes. They will cut noise and don't have to stay in all the time...

Or you could change your MOT man!

 

[Cooper]

I am thinking of putting these in x 2 just before the muffler, then use the remote to open it up for more noise, closed for other times

 

[Pingu]

Watch out for the size. The M pipes are 2.25".

I've ordered a bypass valve, a 200x200x10mm T304 stainless steel plate and an (on)-off-(on) switch, as I prefer to make as much myself as I can.

Just waiting for them to arrive before I can start annoying the neighbours with more grindin' 'n' weldin'


A point to note about the above kit - it is dangerous for the exhaust to terminate under the car.

 

[Cooper]

Where will you bring the exhaust out? Can you show us?

 

[Pingu]

The M has twin pipes. One of them will be standard, the one with the bypass will be open...

 

[Pingu]

I'm hoping to do the bypass for around £100.

£30 for steel and will have about half of it left over.
£4 for switch
£30 for valve
£15 for hole saw
£5 for wire and terminals
£20 for welding consumables

I've already spent around £100 making two straight-through mufflers, but I will only need one if I use the bypass.

£40 2x1m 60mm stainless tube (only needed 0.5m)
£20 1m 63mm stainless tube (needed it all)
£5 grinding discs
£30 welding consumables
£3 exhaust paste

I could have made a single muffler for around £50 if I hadn't bought too much tubing and used so much Argon.

 

[Brian H]

@Pingu Have you bought the switch? I think I have a OEM front and rear fog light switch here you can have, proper stealth!

 

[Pingu]

@Pingu Have you bought the switch? I think I have a OEM front and rear fog light switch here you can have, proper stealth!

I've already bought the switch. I don't think that just one "normal" switch would be enough. I did think of using the solution you are thinking of, but I don't think it would work without having to rework each of the switches.

I've not rec'd the valve yet, but I've guessed that you need to power the valve motor in one direction for a very short time to open it, and to power it in the other direction for a very short time to close it. I've bought one of these...

https://www.ebay.co.uk/itm/MULTICOM...135617?hash=item2854302e81:g:9icAAOSw0e9UtpnO

When I know the power-on time, I may include a 556-timer (or a couple of 555-timers) in the circuit - or I may just press and hope.

 

[Pingu]

The valve has arrived. I was right about how it works. It takes 2 seconds to open and two seconds to close. As I can count to two, I'm not going to bother with a timer.

The current when opening is 0.1A and the stalled current is 1.1A. As the switch is spring-loaded and returns to the off position when released a 3A fuse should be good enough.

Here's the circuit diagram for the switch...

I've tested the circuit with the switch and the valve - it works.

 

[Pingu]

Plan A was to weld some tubing to the valve frame...

It hasn't worked because the frame is too thick and I can't get enough local heat into it to create a weld pool without damaging the mechanism.

Plan B will be to make two flanges using the stainless steel plate that I bought. I'll have to see if my tools are up to the job.

 

[Pingu]

I was looking around the cabin for a place to put the switch and I thought "the roof switch is an (on)-off-(on) switch - I wonder if I could use one of them instead?"

The price is a bit steep, but affordable - £30 for a 2nd hand one.

I checked out the circuit diagram http://www.porterbility.co.uk/Files/PDF/e36z3_98_AG.pdf, p.188 and it looks like I would need two additional relays. BMW know how to make a simple solution unneccesarily complicated.

I think that I'll stick with my £5 DPDT switch.

 

[Pingu]

I used T304 stainless tube, T310 stainless wire and a MIG welding torch with 100% argon gas. Stainless steel is a much harder steel than mild steel and most of the cutting was by grinder (with cutting discs).
I was able to use my jigsaw to cut the large holes, but I wasted many cheap blades, even when I kept the blade soaked in oil. It was cheaper to use many £1.99 (for 3) blades than to buy cobalt blades at £30 for 3. It is not best practice, as the stainless steel becomes work hardened when it gets red hot. I had cobalt drill bits, so I was able to drill the 10mm holes without too much trouble.
The whole process took about 40 hours to make the bypass adaption and the straight-through muffler. A lot of work and very tiring (and noisy) due to the hardness of the stainless steel.


I've described how I made the muffler already. This is how I fitted the bypass valve...
When I cut the exhuast I found that it had a double skin. The inner tube was 57mm ID/60mm OD.

This was lucky as I still had plenty of 60mm ID stainless tube.

Originally, I planned to weld a small ring of tube directly onto the bypass valve

but I couldn't get enough heat into the bypass valve body

The butterfly is attached with screws that would have to be drilled out to remove, so I decided not to dismantle the valve, but to make adapter flanges. I was going to make the flanges from some 10mm plate that I had bought.

but, instead, I made them from some stainless that was part of an old industrial kitchen

I tack welded the 60mm ID tube to the flange, trying to keep the tube perpendicular to the flange

then I seam welded the assembly

I ground off the excess weld, filed the excess weld from the inner bore and cut the tube to a length that would allow it to fit in the cut exhaust

After fitting it and adjusting its position on the car, I welded the flange to the exhaust

I did the same for the other half of the exhaust

(the green leaf blower was used to check for leaks)

I bolted the bypass valve in place and sealed the joints with exhaust paste

The wiring was quite straight forward. The hardest part was deciding on a stealthy switch position and hiding the wires. I took a feed from the ignition wire to the radio and used a convenient earth point in the cabin. The wires go through the boot floor grommet to the bypass valve.

[Edited to add images of the completed exhaust]

 

[Pingu]

The speed comparisons...

The data doesn't agree with how it feels - no surprise there. The data suggests that the car is fastest with the bypass closed. This may be the case, but I doubt it.

The data is only from single runs of each system. I suspect that experimental error is playing a part in the results as each test should be done until standard results are obtained (at least three tests of each system is required).

More testing required - as if I need an excuse to give it the beans.

 

[Pingu]

Looks like all that work was a waste of time. Here's the results of the tests (3 runs with each system).

At medium revs (3000 - 5000), the dual open tailpipes work the best.
At 4000rpm, the standard tailpipes start to really perform. This is probably due to tuning. A good example of bigger not always being best.

At higher revs (5000-6500), the standard tailpipes continue to perform well and show no signs of choking.
The dual open tailpipes begin to show signs of choking at around 5250rpm.

At the top end of the rev range (6500-7500), the standard exhaust continues to perform well and still shows no signs of choking.
Surprisingly, the single open tailpipe out performs the dual open tailpipes at the very top of the rev range.

If the data is to be believed, the bypass system (the red and blue lines) performed poorly compared to the OEM system.

Nothing ventured...

 

[Brian H]

Really good data and info albeit not what you wanted to see, seems as if the engineers in this case knew what they were doing.