For those of you who have changed exhaust have you noticed a change in boost pressure.

 

As I understand it, when you add more mods like CAIs and exhausts, you'll see a drop in boost pressure which is due to the boost being used more efficently.

 

Expect a slight drop in boost with freer-flowing exhaust components installed. This is due to to more efficient cylinder evacuation by the exhaust leaving more 'space' for a complete intake charge. Expect a slight increase in top-end boost with freer-flowing intake components allowing more air to move into the engine.

I noticed a 1/2-1 psi loss of boost going from a stock exhaust to a Milltek. Car already had a 15% pulley and JCW intake with Alta hose.