to explain a bit more there are really 3 sprint or non heat riser versions available. The 1.9 is the most saught after since it uses the existing collector flange and was used primarily on the 75 EFI models. Next is the 2.0 sprint and it was not used in US models but can be had but uses a larger flange to the collector. Then there is the 2.4 that is even bigger yet and has yet another collector flange. Each one is bigger than the other and allow very free flow compared to a stock exhaust. Just as an example the 2.4 is around 1 11/16th on the output side. The effects on scavaging for each model is a very undefined area and intake and valve sizing has a big effect on each one.