After a number of inquiries regarding the variance in performance between vehicles fitted with DPF, removed DPF and cleaned DPF we thought it was necessary to carry out some specific testing so we could back up our predictions with data.

The vehicle of choice was a 2012 1.6 VW Caddy Engine code CAYE, This vehicle had covered 150,000 miles on the original DPF and had a custom tune to ~139bhp.

This was an ideal test vehicle as most start to suffer DPF & EGR issues around this mileage / age.

We logged the following data with DPF present, removed and cleaned.

• BHP
• Torque
• AFR (Air : Fuel Ratio)
• DPF Pressure Differential
• EGT (exhaust gas temperatures)

The results are presented below.

Pressure

This graph shows the difference in pressure recorded throughout the rev range.

Peaking at 651 Milibar (9.4 psi) with original DPF in place compared with 251 Milibar (3.6 psi) after the DPF was cleaned. Removing the DPF eliminates back pressure completely:

Power and Torque

Although there is minimal difference in power between pre and post cleaning of the DPF, there is a clear difference in turbo spool.

The increase in power and torque from removing the DPF is noticeable throughout the rev range with gains of almost 10bhp and 15Ft/Lb, this shows exactly how restrictive the DPF can be when it comes to tuning, especially on VAG Common Rail Diesel engines.

Red - DPF Present   |   Green - DPF Removed   |   Blue - DPF Cleaned

AFR (Air - Fuel Ratio)

We also monitored AFR between stock DPF and Cleaned DPF. Less restriction with the DPF cleaned resulted in a leaner AFR Ratio, cleaner than with the DPF removed.

Red - DPF Present   |   Green - DPF Removed   |   Blue - DPF Cleaned

EGT's (Exhaust Gas Temperatures)

EGT's were not massively effected by any of the tests we carried out, all staying within 14°C of each other at max temperature:

Max EGT (Dyno):

Blocked DPF - 798°C
Cleaned DPF - 808°C
Removed DPF - 794°C

Summary

In conclusion this has proven our initial thoughts to be correct. To eliminate any restriction, the DPF must be removed however given the current laws we do not advise this for a road vehicle.

If you are looking to achieve maximum power whilst remaining legal we recommend installing a new DPF or ensuring the DPF back pressure is ~200mb or less.

For those of you with a blocked DPF, please Contact Us and we will advise on the options available