With many thanks to Roger-Cheshire i now have a K&N air filter installed. More fiddly to fit than i imagined due to a hidden air-box lid screw - double joined fingers would help!
Result? Its difficult to determine exactly what improvement it gives - not that much i suspect, however the already keen to rev Sigma seems even more responsive - i suspect the gains are greater when revs are high.
Having followed Rogers advice by also fitting the lebrands side exit exhaust at the same time i must agree 100% that for less than £100 these small, easily reversed, additions add greatly to the car.
I have the K&N fitted since last sunday. As the K&N was no improvement on my former Roadster, it is well matched with the Sigma engine. Allows it to rev much easier and stronger. A note, after such a change as the air filter was, this Sigma engine needs at least 30 miles to drive before you can fully value the swap of the filter. The ECU has to adapt the new K&N filter.
