TVR Forum

Abschnitt Emission compliant (catalysts) mode

All production cars post August 1992  (UK) have to run in this way with a catalyst fitted in the exhaust system.  Here the air fuel ratio is clamped at 14.7:1 under normal running conditions (up to 3400 rpm or 3/4 throttle) as this is the point chosen for the Rover V8 engine, to be  near to the ideal  14.7:1 air fuel  ratio that is considered the best point for a complete fuel burn and minimum exhaust pollutants. (referred to as lambda 1 .) Due to the old design of the engine it wont run nicely that lean, so this compromise was reached. Due to the way the emission regulations where written in the 1990's the catalysts fuel mapping and lambda feedback is disregarded above 3400 rpm or 3/4 throttle to allow the engine to give best performance, at a point when emissions are not measured.

Abschnitt Catalyst Mode, closed loop
 
The ECU only tries to maintain the emissions up to 3400 rpm, or about 3/4 throttle, and beyond these points it simply fuels the engine dependent on the fuel map data, so the performance is the same as a non catalysts open loop setup.