If you're running a tune I would say the charge pipe that goes from the turbo to the throttle body. I would upgrade the bov as well.

 

1300 miles running stage 3 (19psi) or custom e85 (20 psi) still on stock tubes... I did upgrade the BOV tho

 

I don't think it's possible for a tube to gain hp. However there might be some restrictions where new tubes would benefit better air flow for the system.

It seems like many change the charge tube when they do tuning/ upgrades

 

the tubes by themselves don't really provide any real hp gains, what they do is allow you to run a tune with higher boost levels without having the plastic pipes blow apart. The tune is where you will see hp gains, that's pretty much how any of the upgrade parts for the turbo motor are going to be, you are technically only upgrading to support the tune level you want to run. If you don't upgrade these parts and try to run a tune that is too much boost the stock parts will not hold up to it and/or create too much heat, limiting reliability and power gains.

 

This, I can say do to the smoother inside and no flex sections and larger diameter. when you start running some files on the ECU you will likely get an increase in flow...I know my intakes talked more when mine were upgraded vs the stock ones.

 

thx for the info

should have been more precise in my line of questioning, however the replies do give ample info

thx again