Staying With OEM 3" Exhaust System

[Tractorman]

A while back I posted some concerns about how long an OEM muffler would last on the OEM exhaust system.  I was mainly concerned if back pressure could be an issue as the muffler aged.  I never really did get a definitive answer, probably because most people had moved up to 4" and 5" exhaust systems from the turbo back with either an aftermarket muffler, or no muffler at all.  

 

So, I decided to do a little research on my own.  I found a general statement that indicates Cummins does not want to see any exhaust back pressure above 3 psi.  I connected a gauge to the 1/8" port on the exhaust elbow and strapped the gauge onto my windshield wipers and then went on a test drive.  I made a few tests in which the engine was under full power (30 psi boost) at 2,000 rpm.  The back pressure averaged 3.5 psi - not terribly high, but higher than the 3 psi limit.  So, I knew I was going to get a new muffler - but which one?

 

This was back in November when I was contemplating all of this.  What muffler to buy?  Should I go to a 4 inch exhaust?  What about the resonator?  I really wanted to keep the truck exhaust system quiet.  Then I ran across a Black Friday special where PacBrake was offering a 4" in-line PRXB exhaust brake complete with an air compressor kit for $850.  They never had sales like that before. 

 

I already had a vacuum operated PacBrake that has logged over 460,000 miles - 70,000 miles on my previously owned '99 truck and the rest on my current truck.  But, the PRXB exhaust brake has much better performance below 1500 rpm due to a design change.  Well, I bought it. 

 

Now – what to do with the exhaust system?   One thing for sure, I wanted the system to be quiet.  I finally decided to remove my vacuum operated exhaust brake, keep the three inch OEM exhaust system, remove the resonator permanently, install the PRXB 4 inch in-line exhaust brake, and replace the muffler.  The decision as to which muffler to install was made easy through a fellow Turbo Diesel Register member who installed a Walker SoundFX 18853 Direct Fit Exhaust Muffler on his ’99 truck with high mileage.  It turned out to be an excellent choice.

 

Since the OEM exhaust system runs a short piece of 4” exhaust pipe between the removed resonator and the muffler, this is where I installed the in-line PRXB – just upstream of the muffler.

 

 

The end result…, even quieter inside the cab under all engine rpms (with or without use of exhaust brake), much better exhaust braking below 1500 rpm, and 2 psi exhaust back pressure compared to the previous 3.5 psi.  Plus, the turbo now spools about 100 rpm earlier in the rpm range.  I am glad that I stayed with the OEM 3 inch exhaust and an OEM style muffler.

 

I am hoping that this post may help anyone who wants to stay with the OEM exhaust system, but still get a little better performance without the additional noise.

 

- John

Edited yesterday at 04:48 PM by Tractorman

[Mopar1973Man]

I'd love to do a in line exhaust brake but after seeing 2 exhaust systems fail quickly at about 5 years because of salt on the highways. 

 

This limits me to turbo mounted exhaust brakes and very limited choices of turbos.

 

4 inch diamond eye last about 5 years and falls apart being all the clamps and hangers are steal. All just rust away.

 

Performance muffled or open is basically the same. Muffled just quieter and no drone. No resonator needed. Even open it was fairly quiet till I jumped on the throttle. I'm back to muffled system a d plenty happy.

 

Do you mind if I turn this into an article? 

Edited 20 hours ago by Mopar1973Man

[Threadzy]

My exhaust system has a drone around 2000-2200 RPM  while towing.  I need to see if they make one of those in 4X4”

in and out.