It still depends on how much HP the engine is making and the size of the turbo. If i had an A15 turbo producing say, 150hp, 2.5" mandrel would flow the hp easy. 3" would flow the HP just as
easy therefore no real point. But if i had an A15 turbo producing 300hp (dreaming) a 2.5" system just couldnt cope. But, if i had a 3L V6 Turbo that only produced 150hp, a 2.5" would be
fine. 3" is only really nessesary in big HP engines so that it can flow the HP. When we did Croydon Autosports Civic drag car, its engines has over 1000hp and 4" pipe was needed to flow the
HP.

Then again, if i had an A15 turbo with 160hp and no dumppipe, just straight from the turbo, would the engine run more efficient than with a 2.5" system? I dont really know. I've never really
looked into it before. I supose your right because no pipe could flow alot of HP! Im assuming turbos need a little bit of back pressure tho. I mean, if Croydon Auto wanted the best out of
there drag car, would they have had no pipes right? Im stumped. Theres probably alot of room for discusion on this subject cause im not 100% sure. Im pretty sure 3" is just way too big for
an A15 turbo tho.

Scott
Davo