for the records, just came back from Powerzone yesterday and learnt its 4-2-1 extractor ISN'T a plug & play replacement for our Wira 1.5 Carburettor model, ie. has to cut and reposition the front silencer (mid box) slighthly to the rear....
finally, gave up on the Powerzone & Hotbits extractor product and went for the Marco 4-2-1 extractor which is a fully plug & play mod for a Wira 1.5 (M) Carbie..
as for bro zac, i remember reading somewhere that an auto car runs best on a S-flow centre pipe while for manual, a straight flow is more appropriate...but not sure whether this is true or not...