Well, then the pipes of those $300 Godspeed Audi 1.8T kits (all are 2.5") are good for 500+ whp.

rb12: don't worry, the 2.5" pipes of the kit work well for what you have in mind. Just no sense going bigger (will only cause further spool up delay, since all the air in the system (from turbo to throttle plate, i.e. pipes and intercooler) needs to be compressed first.

And pressure drop (i.e. losses - they go with the square of the air speed in the system) is not a major issue (lower hp, lower airflow, lower airspeed, lower losses).

 

Really? Id be afraid to run 2" on a franken k04
I thought 2" was good for the k03

 

My point is that you dont want to run 2.5" on something making way less power, that large of a pipe on a smaller turbo is just going to decrease velocity and thats going to increase lag. This is why the kits that are designed for our cars use 2" pipes for a K03/K04/GT28r setup and the ones designed for a BT use a 2.25" hot side pipe and a 2.5" cold pipe. 2.5" cold pipe isn't needed till running a GT30r/GT35r. Just look at the outlets on the turbo.


Why? It is basically the same flow as a GT28r and people have been running 2" pipes on the stage 3 kits and PES T28 kits for the last 10 years. If you want to run something larger keep then go 2.25" pipe.

Sure 2.5" might work, but your not going to get the most from the turbo. It just isn't going to flow enough to take full advantage of a 2.5" pipe.