obviously i would like to use my cai and charge pipe (2.25 id) because it would be easier, but my starion intercooler has the stock 1.75 id pipes. which size is better for a td04 on a d16y7? the smaller should allow it to spool quicker right? the larger will give me more hp? what are we talking about in terms of difference though 500-1000 more lag on spool? i'm trying to get around having a shop weld side in-out pipes on the fmic and stick with the stock, plus it may be easier to run smaller dia pipes in/out of the engine bay behind the bumper. so...getting back to the question instead of rambling...what pipe size should i use?

 

your spool time is dependant on your exhaust outlet size. (downpipe) 3" is great. now with your charge pipes anything below 14psi 2.5 will do just fine.

i dont think bigger charge pipes have anything to do with how fast you spool up. (not positive but i have heard otherwise)

 

If you can't fit your ******* in it, it's to small.

Seriously, for your motor, 2-2.25 charge tubes are fine. Bigger wont show any performance gain, probably a loss actually (keep velocity high), and smaller will start to restrict at high rpm. Spool up changes when you change pipe size, but not enough for you to notice it.

Turbo's love free exhaust, and although a 3" downpipe is always good, 2.5 would work great as well, and is easier to work with.

 

where can i get a 2.5" or 3" down pipe for my greddy manifold?

 

Charge piping diameter has its biggest effect on turbo lag, which is different than the boost threshold or spool up time. Turbo lag is often used to mean spool up time, but really it is the time it takes to build boost after cruising and stepping on the gas. With larger piping, it will take a little longer to feel the boost after you floor it on the freeway or wherever. Anyway, smaller charge piping is not the way to get quicker spool. Turbine size and exhaust diameter affects spool time.

 

Good man...