European Exhaust and Catalyst
European Exhaust and Catalyst
Do you have back pressure?
Published on: 10/10/2011

Our technical co-ordinator Stuart Still shares some correspondence from a customer in Italy, helping to diagnose a common issue:       
“Dear Sir, I know that you are the specialist in Catalytic Converters and so I need your help in order to find the right product for me.

I have an Opel Tigra 1.6 16v year 1998 engine type X16XE., and about a week ago I made the following changes:
– Sports exhaust manifolds in stainless
– Central Sports
– Terminal Sports
After this intervention the car run great.

Then I bought a Sports 200 cells metallic catalyst converter and installed as a replace of the original. And that’s where I started to have problems in fact I lost a lot of power at the low RPM. The store where I bought it told me to not worry about it because after remapping the chip the car will go much better.

I honestly don’t believe in that and I think that:
– With a good starting base and remapping the chip you can get a lot more
– With a bad starting base you can get what you had originally

After a consultation with the Opel company they told me that the engine X16XE is very sensitive to the backpressure and a 200 cells metal catalyst converter can only make things worse. Many manufacturers argue no, and I would like to know also your opinion.
In this particular case which product would you recommend since you sell many of them? Sport, universal, or is better to put one with the exact characteristics of the original? So please give me a good advice because I don’t want to buy a wrong product again.

I am attaching the photo of the original catalyst with exact measurements and photos of the Sports catalyst converter that I put on.

The shape and the measures are important in order to not have space problems under the car. (If the diameter is more than 13cm will not fit).

Eventually do you ship to Rome Italy?
I await for your feedback.
Yours sincerely,
***** ****”
Dear ***** ****,
Thank you for your inquiry. Please let me explain.
The overall performance (MPG, sound reduction, emissions) which is produced from a four stroke engine depends directly on the accuracy of the back pressure levels from which the exhaust system has been designed.

A sports exhaust is fitted to a car to reduce the back pressure; this is needed to extract the extra exhaust gas pressure generated when improving the engines performance; extra BHP.
By fitting a sport’s exhaust system to a standard car will not improve its performance. It will change the correct back pressure which has been set for maximum performance + fuel consumption by the manufacturer (Opel).

By replacing the standard silencer with a sport box the vehicle will use more fuel, make more noise and actually go slower.
Your major problem has arisen when you replaced the original catalytic converter with a sports cat, as this has had the greatest impact on reducing the back pressure.

By keeping the OE cat on you have lessened the impact of the sports exhaust system.

You have two options, increase the performance/BHP of the engine, or refit the correct cat and exhaust system.

To check your back pressure on a standard vehicle, (not sports/high performance) test the emissions using a four gas analyser.

The emission values, if the engine is running correctly are:
CO <0.2, CO2 13.5>, HC <15 PPM, O2 <0.2.

If there is a back pressure problem, positive (less noise blocked exhaust) or negative (more noise) the emissions values will range will be:
CO > 0.3, CO2 < 13.5, HC between 25PPM and 125PPM, O2 > 0.2.
The emissions test should be done with the engine running at 2500 RPM, as this is when the back pressure has been set at neutral.  
I hope this has helped.
Kind regards,
Stuart Still
EEC Tec support.
EEC have embarked on a full emissions training program to include catalytic converters, DPF’s, lambda sensors, exhaust systems, and how to read and understand 4 gas analyser values. These training programs can be arranged through the day or in the evening.

For more information please contact Duncan Richards or Stuart Still at EEC.