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+--- Thread: Big exhaust on your Mercs! PICS (/showthread.php?tid=7176)
Big exhaust on your Mercs! PICS - -Mackan- - 04-24-2016
Hello!
Im going to start building my exhaust, what is the biggest exhaust you have managed to fit?
I think ill be using 3.5" all the way from the turbo?
Feel free to post pics on your exhaust systems!
RE: Big exhaust on your Mercs! PICS - barrote - 04-24-2016
i personaly use a 70mm, 1.5 thick wall.
that is close to 3inch, in my build there´s no need for wider, conservation of flow caracteristics.
sorry i dont have a pic of it.
RE: Big exhaust on your Mercs! PICS - MartinB - 04-24-2016
3" (76mm) downpipe -> 2.36" (60mm)
Garrett GT2359V
RE: Big exhaust on your Mercs! PICS - Sultzi - 04-24-2016
4" downpipe to 2x3"
Overkill? Yes, very much for the 2x3" section, downpipe better to be big enough than too small..![[Image: _medium.jpg]](http://sultzi.kuvat.fi/kuvat/MB+W123+-81/IMG_0239.JPG/_medium.jpg)
![[Image: _medium.jpg]](http://sultzi.kuvat.fi/kuvat/MB+W123+-81/IMG_0241.JPG/_medium.jpg)
RE: Big exhaust on your Mercs! PICS - Dark Hawk - 04-25-2016
not a picture but very purist sacrilege
https://www.youtube.com/watch?v=zXd7NtqnKHA
RE: Big exhaust on your Mercs! PICS - seanyt - 04-26-2016
ive gone with 3" all the way as 3.5" was hard to get from a supplier and then ran a 16" piece of 4" out of the exhaust.
No problems with power as of yet. dyno time in a month.
depends what your power goals are also
RE: Big exhaust on your Mercs! PICS - ross - 04-27-2016
Exhaust diameter will play a big part in the performance. Its a balance between getting it big enough for the flow.... but equally going too big will slow the gasses as they expand to fill the space.
RE: Big exhaust on your Mercs! PICS - Turbo - 04-29-2016
(04-27-2016, 06:45 AM)but equally going too big will slow the gasses as they expand to fill the space !? Exhaust diameter will play a big part in the performance. Its a balance between getting it big enough for the flow.... but equally going too big will slow the gasses as they expand to fill the space.
RE: Big exhaust on your Mercs! PICS - ross - 04-29-2016
You've almost quoted me but not said anything?
RE: Big exhaust on your Mercs! PICS - Turbo - 04-29-2016
Roos Can you please develop what you wrote, I m specially thinking of the last part _" but equally going too big will slow the gasses as they expand to fill the space."
RE: Big exhaust on your Mercs! PICS - ross - 04-30-2016
For best performance the exhaust needs to be matched to the engine. Too small and it can't flow enough. But going too big is also harmful due to exhaust velocity. You want the exhaust gasses to get away as quickly as possible, and by going too large a diameter you're actually slowing them down. It's all to do with what's called the 'ideal gas law'. To keep the energy and heat up in the exhaust you need to keep it moving, and going into too large an exhaust will slow it down and cool it as it expands.
Think about it a bit like this.... You can breath out at a certain rate but you have to blow down a pipe. Blowing into an empty bic pen is hard, breathing into a drain pipe means the air is going to be slow out of the other end but breathing out brought something like a large garden hose isn't hard to do and keeps the air speed up.
Hope that makes sense
RE: Big exhaust on your Mercs! PICS - raysorenson - 04-30-2016
Ross, I would agree if you were talking about pre-turbo exhaust sizing. Manifold tubing can get too big and reduce velocity. But after the turbo, the best exhaust is no exhaust. Corky Bell said the ideal exhaust post-turbo is a bellmouth.
RE: Big exhaust on your Mercs! PICS - ross - 04-30-2016
Well yes because no exhaust is no restriction and the exhaust gas is out of the system.
It still applies post turbo as well, you want the exhaust gas to keep moving otherwise the gasses that are still coming out of the turbo will be slowed.
RE: Big exhaust on your Mercs! PICS - Tito - 05-01-2016
The bigger the exhaust, the lower the pressure in the exhaust (after turbo of course). So the pressure difference is higher. Higher pressure difference means more flow. It's not that the higher the gas velocity equals more flow. Higher gas velocity is only achieveable by restricting flow.
The only place you want higher gas velocity is after the exhaust valve. The higher gas velocity of course helps spool the turbo, but can also suck remaining exhaust gas from the cylinders for better scavenging.
This only works when you have gas pulses. Not with continuous flow. It just doesn't make sense.
The ideal situation would be no gas flow after the turbo (no dp or anything) because this leads to a bigger pressure difference. this is not possible but is it at a minimum with nothing after the turbo.
So I'm wondering why would you want speedy exhaust gasses after the turbo?
RE: Big exhaust on your Mercs! PICS - ross - 05-01-2016
If the gases can expand into too large an exhaust they become cooler and have less energy, so are harder to shift on out of the exhaust. If the gasses aren't moving quickly after the turbo, then how are the gasses coming out of he turbo going to do so quickly!
RE: Big exhaust on your Mercs! PICS - Tito - 05-01-2016
You're saying that the size of the exhaust diameter determines after turbo temperature and that you want to keep exhaust gases as hot as possible by reducing exhaust diameter?
RE: Big exhaust on your Mercs! PICS - ross - 05-01-2016
Yes it will have an effect. Keep the gasses hot and they'll not slow up.
RE: Big exhaust on your Mercs! PICS - ross - 05-01-2016
It's getting the balance between too big and too small.
RE: Big exhaust on your Mercs! PICS - don - 05-02-2016
Not big by any means but the I redid the downpipe on my as the stock MB DP was hitting the bulkhead.
I took pieces of the stock DP (turbo flange and flex section) and added 2.5" SS 90° bends. The rest of my exhaust is 2.5" mandrel bent stainless with V-Clamps.
Maybe down the road I will do 3" but even the 2.5" is close to the bulkhead and the front driveshaft.