Exhaust Emissions

Catalytic Converters
Why do GGR recommend the removal of the first cat on a modified car?
I have been told that if I remove the catalysts, the Lambda will not work, is this true?
CATALYTIC CONVERTERS
If an engine was able to burn 100% of the fuel used, the only by products of combustion would be carbon dioxide and water. Unfortunately, there is never complete combustion, so a further number of gasses are produced. Throughout The World, a number of steps have been made to try to reduce the most harmful of these gasses. Initially, by encouraging more efficient engine design, and controlling the chemical additives used in the fuel itself. Although this has brought about significant improvements, a further reduction of harmful exhaust gasses was sought. The decision was taken that it would be easier to remove these components from the exhaust fumes after combustion, instead of preventing their creation in the first place. This is why we now have catalytic converters in our exhaust systems.
As most people will remember from school chemistry lessons, the word catalyst is used to describe an agent that provokes or speeds change, without any change in its own state. Catalytic converters (known as cats) were fitted into the exhaust of the 4x4 Sapphire Cosworth with 'Green Top' engines, and all Escort Cosworth models. There are three cats used on these cars, the first (pre cat) is fitted in the exhaust downpipe, directly after the turbocharger, and the second pair of cats are sited in the next section of exhaust, near to the gearbox. Catalytic converters can only function efficiently if the air to fuel ratio is tightly controlled at the correct mixture, and if they are up to their optimum operating temperature of 600 to 800°C. The temperature of the cat is initially provided by the hot exhaust gasses, but when it starts to function, a thermal reaction takes place that provides the additional temperature. As explained elsewhere, cars fitted with catalytic converters also use an exhaust Lambda sensor to enable the engine management system, to monitor exhaust gas quality. Both the Lambda sensor and catalytic converter will become damaged if used with leaded petrol. The lead will leave a coating on both items, and prevent contact with the exhaust gas, so it is essential that unleaded fuel is always used in these vehicles.
The important materials used in catalytic converters are the precious metals Platinum and Rhodium, and these are clearly expensive. Platinum and Rhodium are carried inside the standard exhaust system coated onto a honeycomb of ceramic material. As explained above, extremely high temperatures are experienced within the catalyst, and its component parts must be able to withstand these. If you were to cut through a standard catalyst, you would see that the honeycomb creates thousands of small channels for the exhaust gas to pass through. The sports catalyst that GGR use in their own exhaust systems is of a superior design. The catalyst chemicals are carried on a finely corrugated metal foil that is would into a spiral shape. The metal foil is very fine, (it is only 0.05mm thick), and because of this, more channels can be accommodated into the same area, offering less resistance to the passing of the exhaust gasses. Due to its metal construction, it is also more durable than the ceramic type.
Why do GGR recommend the removal of the first cat on a modified car?
When an engine produces an increase in horsepower, it also produces an increase in exhaust gas volume and temperature. This increase in volume and temperature would overload the restrictive ceramic catalyst, and may cause it to disintegrate. The particles from this would then block the second cats and this restriction would then lead to a loss of engine power. The second pair of catalysts are less restrictive, but are capable of maintaining the required exhaust emissions.
I have been told that if I remove the catalysts, the Lambda will not work, is this true?
No! The Lambda sensor is fitted to the Cosworth turbocharger, before the exhaust system even starts, so any alterations a carried out after this cannot affect the Lambda sensor.
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	Catalytic Converters Why do GGR recommend the removal of the first cat on a modified car? I have been told that if I remove the catalysts, the Lambda will not work, is this true?

CATALYTIC CONVERTERS
	If an engine was able to burn 100% of the fuel used, the only by products of combustion would be carbon dioxide and water. Unfortunately, there is never complete combustion, so a further number of gasses are produced. Throughout The World, a number of steps have been made to try to reduce the most harmful of these gasses. Initially, by encouraging more efficient engine design, and controlling the chemical additives used in the fuel itself. Although this has brought about significant improvements, a further reduction of harmful exhaust gasses was sought. The decision was taken that it would be easier to remove these components from the exhaust fumes after combustion, instead of preventing their creation in the first place. This is why we now have catalytic converters in our exhaust systems. As most people will remember from school chemistry lessons, the word catalyst is used to describe an agent that provokes or speeds change, without any change in its own state. Catalytic converters (known as cats) were fitted into the exhaust of the 4x4 Sapphire Cosworth with 'Green Top' engines, and all Escort Cosworth models. There are three cats used on these cars, the first (pre cat) is fitted in the exhaust downpipe, directly after the turbocharger, and the second pair of cats are sited in the next section of exhaust, near to the gearbox. Catalytic converters can only function efficiently if the air to fuel ratio is tightly controlled at the correct mixture, and if they are up to their optimum operating temperature of 600 to 800°C. The temperature of the cat is initially provided by the hot exhaust gasses, but when it starts to function, a thermal reaction takes place that provides the additional temperature. As explained elsewhere, cars fitted with catalytic converters also use an exhaust Lambda sensor to enable the engine management system, to monitor exhaust gas quality. Both the Lambda sensor and catalytic converter will become damaged if used with leaded petrol. The lead will leave a coating on both items, and prevent contact with the exhaust gas, so it is essential that unleaded fuel is always used in these vehicles. The important materials used in catalytic converters are the precious metals Platinum and Rhodium, and these are clearly expensive. Platinum and Rhodium are carried inside the standard exhaust system coated onto a honeycomb of ceramic material. As explained above, extremely high temperatures are experienced within the catalyst, and its component parts must be able to withstand these. If you were to cut through a standard catalyst, you would see that the honeycomb creates thousands of small channels for the exhaust gas to pass through. The sports catalyst that GGR use in their own exhaust systems is of a superior design. The catalyst chemicals are carried on a finely corrugated metal foil that is would into a spiral shape. The metal foil is very fine, (it is only 0.05mm thick), and because of this, more channels can be accommodated into the same area, offering less resistance to the passing of the exhaust gasses. Due to its metal construction, it is also more durable than the ceramic type.

Why do GGR recommend the removal of the first cat on a modified car?
	When an engine produces an increase in horsepower, it also produces an increase in exhaust gas volume and temperature. This increase in volume and temperature would overload the restrictive ceramic catalyst, and may cause it to disintegrate. The particles from this would then block the second cats and this restriction would then lead to a loss of engine power. The second pair of catalysts are less restrictive, but are capable of maintaining the required exhaust emissions.

I have been told that if I remove the catalysts, the Lambda will not work, is this true?
	No! The Lambda sensor is fitted to the Cosworth turbocharger, before the exhaust system even starts, so any alterations a carried out after this cannot affect the Lambda sensor.

Back to FAQs & Features · GGR Home
Correspondence/Requests Sales Enquiries: sales@grahamgoode.com Technical Enquiries: tech@grahamgoode.com Tel: (+44) 0116 244 0080 Fax: (+44) 0116 244 0140