Turbo spool and downpipe size?

[shortbed]

i run a 4.5 inch downpipe,into a 5"y pipe with a resonator tube,no muffler,no cat then up into 5"stacks.never had a problem with spoolin up,and its only loud pullin my camper up a long grade. and i run a 100 hp chip

 

[kenholl]

I thought the rpm of the turbo would be to high with a stock DownPipe since the increase in exhaust air has to flow faster through a small area. Where as if i increase the down pipe size, the air doesn't have to move as fast to allow the same volume of air out.

Imagine if you were trying to breath through a straw. You would suffocate, even though the air is really moving fast. Now, imagine breathing through a large pipe. Therein lies the difference~

 

[MBRPCrazyford]

That butterfly valve is an ok Idea, but do they make one for a 4+" exhaust?

Shortbed, where'd you get the 4.5" DP? That's gotta be tight.