What is classed as sensible DPF/exhaust back pressure?

Hi guys, just wondered what is classed as sensible back pressure over a DPF/exhaust etc? before you start to limit performance.
The car in question is our BMW X5 3.0d, when you are at WOT the pressure before the DPF peaks at around 480mbar.

When I do the DPF back pressure test with the just the engine running and no driving I have approx 12mbar at idle, 55mbar at 2000rpm and 100mbar at 4000rpm, these results are roughly half the BMW max recommended value.

Any advice on a driving under load exhaust back pressure would be great.

Has anyone ever measured there back pressure on there exhaust?

None of that seems unreasonable, relative to the boost pressures anyway.

With just the engine running and no driving (load) on the engine, airflow is relatively low compared to at full boost/high airflow so 100mBar at 4000 RPM with a full emissions complaint exhaust seems reasonable, along with the values being half of BMW's recommended max.

480mBar max under load seems a bit high, but remember, the exhaust pressure at the engine before the turbo is typically 1.25-1.50 times the boost pressure with no back pressure in the exhaust after the turbo. While 480mBar is not trivial, it does not sound unreasonable either.

I'm not specifically knowledgeable about the CR's or BMW's so someone more experienced than I may have me eat my words. The one datapont that I have on a VE engine with a full exhaust on it generated ~300mBar at full load with a much less complex emissions system (catalytic converter only).

That soulds like regular working but not perfect system. On BMW with a DPF in perfect condition you get roughly 350mbar back pressure with arould 300hp worth of air. Worst I have seen was 900mbar @2500rpm... The ecu starts to reduce fueling with ~400mbar and above if the function is still active in tge file.

Thanks for the replys guys, I understand the basics as I run a hybrid plus other mods on my VW T5 2.5PD and have logged EMP vs boost many times.

My last two BMW's had there DPF's removed but I am holding back on our X5 for as long as I can as our MOT test is soon going to have a DPF particle count test added.

I have added some DPF cleaner and done two forced regens and WOT back pressure has currently dropped to 350mbar.

Exhaust back pressure

I have checked it on my TDI. I welded a bung on my down pipe before the cat with a copper line running to my boost gage. In normal driving it read 2# or less. At WOT and peak RPM 4 1/2#, but at 6 1/2# there was a power loss. With out a cat, probably 3#. What reading have you got?

vwdsmguy said:

I have checked it on my TDI. I welded a bung on my down pipe before the cat with a copper line running to my boost gage. In normal driving it read 2# or less. At WOT and peak RPM 4 1/2#, but at 6 1/2# there was a power loss. With out a cat, probably 3#. What reading have you got?

Click to expand...

At WOT at about 4-4.5k the back pressure is currently peaking around 350-400mbar now I have put in some DPF cleaner and done a few regens

This is my current pressures when stationary doing the BMW workshop check at idle, 2000, 4000rpm etc.

An updated, I had a spare DPF that I had previously removed the DPF block from but left the CAT in place.
Fitted that yesterday and WOT back pressure at 4K has dropped from 350-400mbar to 150.