does anyone have any experience showing that changing to slightly larger diameter piping hurt lag?
it theoretically shouldn't hurt lag in terms of how quickly the turbo spools up unless you have a situation where the increased volume is _very_ large, like, in compared to the flow rate. the volume increase between 2.5 and 2" piping would certainly be significant in relative terms, but how much volume does like 5 feet of 2.5" and 2" piping take up?
the difference in volume between that much piping would be on the order of like a tenth of a cubic foot. that doesn't seem so significant when flow rates are on the order of hundreds of cubic feet per minute.
maybe the effect is more one of throttle response, or the 'lag' is because of poorer off-boost performance because of low velocity through the pipe?
but at high flow rates, smaller diameter piping and the turbulent flow that would undoubtedly result from it might offset some of those considerations. i have no idea really, i'm just guessing
i always thought it was strange that toyota used such small piping with such a big motor. many other OEM turbo set ups use much larger piping after the intercooler. volvos use ~2.5" piping, saabs, audis, ~2.375", all with much smaller engines (though they are running higher boost).
anyway, the same argument about lag has been made about using larger intercoolers. mk4 owners say they don't notice any increase in lag when they install those huge ass FMICs. *shrug*
i personally would go for something larger than 2", but worry a bit less about diameter, and more about using as few transitions as possible and making them smooth.
shiva
