on certain engines and set ups these pipes can cause more turbulance than scavenging and there for rob power. on a turbo car the "pulses" are not even close, to say a small block for example. when the turbo spools it creates a consant flow rate thus virtually elinemnating any exhaust pulse. keep in mind you are talking about performance at higher rpm's and higher engine loads where scavenging can actually give you some benefit and with a turbo car scavenging is a minor point when you are trying to chose TD this or that's for high flow low backpressure.
