My guess would be that the Primera engine would not make the current BTCC limits. It might not actually produce more CO2 but I think there would be plenty of other nasties in the exhaust fumes. All the 1999 videos seem to show large plumes of black smoke on the brakes/overrun. The modern Honda and Seat engines still do that a bit and the Chevy can create huge exhaust flame outs, but not to the same extent. Flames may actually be a sign of better emissions than smoke because of the combustion.