Exhaust Gas Recirculation (E.G.R) System - 1974 TR-6 and Spitfire 1500

The NOx (Nitrogen Oxides) content of the exhaust gases can be reduced by recirculating a controlled amount of exhaust gas through the combustion cycle, thereby lowering the peak combustion temperature; the overall effect being that the reduced combustion temperature will reduce the NOx gases developed during the combustion process and subsequently lead to a reduction in the harmful gases emitted by the exhaust system.

The E.G.R. Valve (Part No. TKC 284) is mounted on the cylinder Head on the TR-6 and on the Exhaust Manifold on the Spitfire. In both cases, a control signal taken via tubing and vapor traps from a throttle edge tapping in the carburetor gives no recirculation at idle or full throttle but does allow varying amounts of recirculation under part load conditions depending on the vacuum signal controlling a metering valve.

Incorporated in the system is a cut-off valve actuated by the Choke Cam. This has the effect of destroying the vacuum and rendering the system inoperative when the choke control is in use; Nitrogen Oxides being minimal during starting rich mixture.

The system can be checked by running the engine to normal temperature ensuring that the Choke control is fully off. The E.G.R. Valve can be felt to operate by placing a finger on the underside of the diaphragm when the throttle is opened and closed rapidly; the valve itself, opening and closing, as the engine speed changes.

Servicing - A functional check of the operation of the system and the cleaning of the pipe work and manifold connections should be carried out at the specified servicing period; Servicing 12,000 miles or 12 month interval. The operation of the E.G.R. Valve can be tested with a hand vacuum pump when the unit is removed from the vehicle.

Both systems are illustrated overleaf.