Anyone with an 87 300d? May I recommend a test pipe. - PeachParts Mercedes-Benz Forum

winmutt · #1 03-03-2011, 10:54 AM

If you dont have diesel emissions you should try putting in a test pipe in place of cat and resonator. Best $75 I have spent in mods in a looooong time. The exhaust note is changed some, pleasantly. Not loud or anything. Also fixed my hunting idle........ And the power difference is there.

babymog · #2 03-03-2011, 11:18 AM

I have a couple of the CATs in the garage, found that they're worth about $150/ea, looks like I can sell the cat for more than the "test pipe" will cost.

I was going to gut one until I checked on its value.

compu_85 · #3 03-03-2011, 12:26 PM

Gutting a cat is bad for exhaust flow IMO. I'd think the pressure drop caused by the hollow chamber would not be the most efficient.

-J

compu_85 · #4 03-03-2011, 12:26 PM

Gutting a cat is bad for exhaust flow IMO. I'd think the pressure drop caused by the hollow chamber would not be the most efficient.

-J

babymog · #5 03-03-2011, 12:35 PM

Hard to say really. Many forms of exhaust tuning create decreases in pressure, the CAT certainly is worse for flow than an empty cat chamber.

winmutt · #6 03-03-2011, 01:01 PM

Quote:

Originally Posted by compu_85

Gutting a cat is bad for exhaust flow IMO. I'd think the pressure drop caused by the hollow chamber would not be the most efficient.

-J

Considering that is essentially what the muffler is on the w123 300d atleast, cant be all that bad..

compu_85 · #7 03-03-2011, 01:49 PM

Fair enough!

bigblockchev · #8 03-03-2011, 02:34 PM

If I recall correctly with a Turbocharged Diesel engine the best solution for power and efficiency is no back pressure at all. The tuning of the exhaust system of a naturally aspirated engine relies on the pulsed pressure wave which assists cylinder scavenging at certain rpms . This yields a higher volumetric efficency or more charge air being drawn into the cylinder because of the momentum of the column of leaving through the exhaust port. Since a turbo'd engine essentially has a pressurized manifold of air waiting to get into the cylinder as soon as the intake valve opens, I am of the understanding that the sooner the exhaust leaves the cylinder the better.The turbine wheel and to some extent wastegate are hopefully the only and most necessary cause of back pressure Hence no back pressure is better, it assists the turbo to spool up faster and at a lower rpm. Just my understanding of the way things work. Cheers Dan

winmutt · #9 03-03-2011, 04:56 PM

There is plenty of back pressure in a turbo diesel...

bigblockchev · #10 03-03-2011, 07:09 PM

Maybe I'm not clear on this I thought the cat was after the turbo? If so then one would believe straight pipe in place of the cat would be better to produce less backpressure? If the cat is before the turbo then it would only restrict flow if it was plugged? My bad.

Alex300DT · #11 03-03-2011, 08:02 PM

For the ones that removed your CATs, did anyone do it without a welder? if so how?

I was thinking about getting rid of mine with a sawzall and then using an expanded piece of straight pipe and clamping it in there.

good or bad idea?

vstech · #12 03-03-2011, 08:16 PM

cat is after the turbo.
trap-ox is before the turbo.
the one I replaced I used my mig.

Alex300DT · #13 03-03-2011, 08:17 PM

Quote:

Originally Posted by vstech

cat is after the turbo.
trap-ox is before the turbo.
the one I replaced I used my mig.

I wish i had a welder

jonbobshinigin · #14 03-03-2011, 11:37 PM

So you cut out the cat and resonator and welded in a solid straight pipe, and left the rearmost muffler stock? I have been thinking of doing this in my wagon for a while.

Can someone list the parts from downpipe to tip in order for me?

Is it: cat, resonator, muffler?

I kind of thought there was something in between that I am missing.

compu_85 · #15 03-03-2011, 11:45 PM

My car has just the resonator... it never had a cat and the muffler rusted off. It's not too loud, I actually rather like the exhaust note.

-J