exhaust pipes

fyonn

Active Member
Joined
May 9, 2007
Messages
342
Location
Manchester
Car
BMW 330d
Hiya folks,

this post comes from a discussion between shude and I on Monday, walking back from the pub!

why do powerful cars have 4 exhaust pipes? is it just vanity or is there a proper reason?

Looking at something like an E55, it's a V8 engine. I can well imagine that the exhaust from each bank of cylinders has a pipe to itself, but does each bank have an exhaust to itself? even if it does, surely one pipe in, one pipe out? Is the fact that 2 pipes come out of each side just bling?

I can't imagine that each pair of cylinders have their own exhaust port and their own exhaust system to warrant 4 pipes?

the situation is even worse with the old BMW M3. that's an inline 6 engine, so there's only 1 bank and 1.5 cylinders per exhaust port.

I guess there could be a capacity issue, of how much gas can go down a pipe, but can't they make the pipes bigger, or wouldn't the gfas go faster in a smaller pipe?

so am I right, could these powerful cars easily make do with 1 or 2 exhausts and they just add mroe cos it looks good, or is there a solid engineering reason?

I'm happy to be educated :)

dave
 

wemorgan

MB Enthusiast
Joined
Apr 5, 2008
Messages
8,106
Car
A205 C220d
In the old generation Audi TT the 180PS had 1 exhaust pipe and the 225PS had 2. But like you suggest, I am sure this is just styling rather than functional, since the same 225PS engine in other VAG cars had only 1 exhaust pipe.

As far as I am aware (happy to be wrong here) the more serious end of the design is at the hot end (manifold). With lots of work going to design equal length pipes for each cylinder.

By the time the exhaust reaches the final muffler stage the pressure has significantly dropped, so whether it then exits from a single or double pipe is down to styling.
 

Howard

MB Club Veteran
Joined
Apr 23, 2004
Messages
18,624
Location
Toad Hall
Car
CLS 500 / A 150
W210 E55 and R171 SLK 55 share the same engine , but the E class has two exit pipes and the SLK has 4 ...

I would say its down to vanity ....
 

recycled

MB Enthusiast
Joined
Feb 26, 2007
Messages
4,278
w203 clk55amg has 2 exits as well but when they put the engine in the c- class it had 4 exits.
Astons with v12s have only 2 exits.
If you check most, it is actually 2 pipes running down, then the quad nozzles are stuck at then end of the last baffle box.
 

A210AMG

MB Enthusiast
Joined
Mar 15, 2007
Messages
8,475
Location
England
Lambo's only have one, albeit small animals could live in them :)
 

chriswt

MB Enthusiast
Joined
Aug 12, 2005
Messages
1,017
Location
Hertfordshire
Car
W203 C320cdi Sport, S-Max 2.0T Titanium Sport, 1974 Triumph Stag (needing restoration)
In the old generation Audi TT the 180PS had 1 exhaust pipe and the 225PS had 2. But like you suggest, I am sure this is just styling rather than functional, since the same 225PS engine in other VAG cars had only 1 exhaust pipe.

As far as I am aware (happy to be wrong here) the more serious end of the design is at the hot end (manifold). With lots of work going to design equal length pipes for each cylinder.

By the time the exhaust reaches the final muffler stage the pressure has significantly dropped, so whether it then exits from a single or double pipe is down to styling.
I may be wrong but I thought it was the 2WD 150bhp Audi TT that had one exhaust. The 180 and 225bhp quattro models both had two!!!
 

popuptoaster

Active Member
Joined
Oct 2, 2008
Messages
804
Location
Essex
Car
2000 E55 AMG Estate
Its mainly for styling reasons, but two smaller pipes will hug the car closer than 1 large one increasing ground clearance and making for easier routing, also you can tune exhaust pipes, yank V8's for example gave more top end power running one pipe per bank, but fitting a link pipe between the two gave better mpg and more low down torque.
 

Adam230K

MB Enthusiast
Joined
May 1, 2007
Messages
3,085
Car
German oil burner
styling. probably influenced by the amount of space underneath the car or just styling -period-
 

MPG

Active Member
Joined
Aug 14, 2008
Messages
320
Definitely vanity. I had a BMW 840 which had the 4.4litre V8 engine (286bhp) and quad pipes. I replaced it with a BMW 740 Sport which had the exact same engine but only two pipes.
 
OP
OP
F

fyonn

Active Member
Joined
May 9, 2007
Messages
342
Location
Manchester
Car
BMW 330d
Well, it seems that my thoughts are largely borne out by the crown. quad exhaust pipes just look cool (and they do) but serve little function over 2 or even one exhaust pipe as long as it's big enough to do the job. all the important stuff happens well before that stage and probably in one, or two pipes from the engine.

I may be wrong but I thought it was the 2WD 150bhp Audi TT that had one exhaust. The 180 and 225bhp quattro models both had two!!!
afaik, all the hardtop 1st gen TT's were 4wd in the UK, the 2wd versions were only on the continent. the 180bhp had 1 exhaust pipe and the 225 and 3.2l V6 had 2 pipes. the latter distinguished by a bigger spoiler.

the 2wd TT's in the UK arrived with the cabriolet's I think and also had 1 exhaust pipe.

I did once see a new shape TTRS with 4 pipes though...

dave
 

bouncer

Active Member
Joined
Sep 20, 2007
Messages
329
There is a proper reason. . . . It's to do with noise / sound and homologation or type approval. Length of tailpipe helps to remove or lessen certain frequencies.
More powerful cars are usually v configurations and can take two different routes under the car, two down pipes that converge into one middle box and split off into two rears or two separate systems that run down the vehicle.
The two downpipes into one central silencer are so much easier to silence. The tailpipes that you see sticking out of the box are usually quite short due to space taken up by the box, so the tailpipe is lengthened into the box thus giving the length of the tailpipe although its hidden from view. Having two tailpipes eases certain high frequencies and helps with back pressure. Backpressure and sound waves propagate down the full length of the system and back so a back box is just as important as the front end.
This could be done with one big tailpipe but the subjective noise may be too much for some people, even though it may pass the noise regs / type approval. The bigger single tailpipes are usually ok for diesel applications, but for petrol engines it does create a perceived noise that doesn't agree with everyone.
That's why some budget non type approved systems sound that much different, no care given to subjective noise. If you have a Mercedes you want it to sound like a Mercedes and if you have a VW you want it to sound like a VW.
So a twin system with 4 tailpipes is for noise / backpressure reasons as well as looks.

sTeVe
 

GH421

Active Member
Joined
Mar 2, 2009
Messages
314
Location
Bedfordshire
Car
W221 S320L Cdi
It's all down to style to give it a more aggressive look, if we put into comparison the BMW e60 Range

You can get yourself a 550i with a 4.8 V8 (my god does it sound beautiful at night) which has a dual exhaust and however the M5 which is a 5.0 V10 has the quad exhaust to differentiate it from the rest of the E60's. With the M series being the more aggressive of the whole BMW pack the quad exhaust system suits in nicely.

However there is a fine line between where cool and the plain stupid reside.

The quad exhaust being cool

This however, is plain retarded.

 

chriswt

MB Enthusiast
Joined
Aug 12, 2005
Messages
1,017
Location
Hertfordshire
Car
W203 C320cdi Sport, S-Max 2.0T Titanium Sport, 1974 Triumph Stag (needing restoration)
Well, it seems that my thoughts are largely borne out by the crown. quad exhaust pipes just look cool (and they do) but serve little function over 2 or even one exhaust pipe as long as it's big enough to do the job. all the important stuff happens well before that stage and probably in one, or two pipes from the engine.



afaik, all the hardtop 1st gen TT's were 4wd in the UK, the 2wd versions were only on the continent. the 180bhp had 1 exhaust pipe and the 225 and 3.2l V6 had 2 pipes. the latter distinguished by a bigger spoiler.

the 2wd TT's in the UK arrived with the cabriolet's I think and also had 1 exhaust pipe.

I did once see a new shape TTRS with 4 pipes though...

dave
thanks for that, I wasn't sure but just remember a 2wd 150bhp being launched with a single exhaust. :)
 

GH421

Active Member
Joined
Mar 2, 2009
Messages
314
Location
Bedfordshire
Car
W221 S320L Cdi
I believe the Audi R8 V12 TDI will be sporting the quad exhaust system?

I would love to see the cloud of smoke it leaves behind when it gets booted!
 

ackee911

Active Member
Joined
Jul 16, 2008
Messages
315
Location
London
Car
Mercedes-Benz S500L
For a Mercedes forum there's a lot of talk in this thread about BMW and Audi cars!
 

Smatt

MB Enthusiast
Joined
Jul 2, 2008
Messages
1,191
Location
Norfolk
Car
2011 E350Cdi Cab Auto, 2011 E350Cdi Estate Auto
I was under impression that fluid flow rate is faster in larger diameter tubes with the flow being faster the further the fluid is from the wall of the tube. So I understand the noise/aesthetics consideration, but for performance, 4 smaller pipes does not seem too logical...
 

Users Who Are Viewing This Thread (Users: 0, Guests: 1)

Top Bottom