I read on here that some people make a spark killer by just having a switch for the spark wire coming form the ECU, so it carries on chucking fuel in but if you cut the spark for a brief second it will just spit the fuel in the exhaust, so as soon as you flick the switch back and it fires again there will be a big pop. Pretty dodgy though! Best bet would just be an exhaust system, nice pops on the overrun, a deep throaty sound too, these things sound amazing with a good pipe, check this out!