I am now turboing my 420a and have a tsudo 2.5 inch exhaust currently. My question is I know everyone does the 3 inch but that takes away from the low-end torque and give high end horsepower my car is my daily driver besides that my car is my advertising due to the fact that I own a tuner shop in Richmond, VA. So with that said will the 2.5 be to constricting or will it keep the low-end torque while the newly added turbo gives me the top end.

P.S. - I may own a tuner company but I do not claim to know everything and thus me asking the opinions of other. As always thanks for looking, replies, and god bless you all ...

No. Go 3". Roughly the same price as a 2.5" or 2.75" system. RRE has a few Espelier pieces that they are letting go for 340.

-K-

The reason for uprgrading the exhaust piping size on a turbo car is to relieve exhaust system pressure. The bigger piping allows the turbo to flow more, reducing the amount of time needed to spool. In other words, the smaller piping is basically choking the turbo and larger piping allows it to flow better. The noise level will actually probably be less with 3 inch over the 2.5 you have now because of the turbo. So 3in. will show more power AND torque. In a turbo car you essentially want no backpressure but you don't want to over do it and go too large, causing a scavenging effect. But 3in. will do great for the car.

Is it possible for me to run 8 - 12 psi and then upgrade later ...

2.5" should be alright if you currently have it on your car. I think it is a good compromise for a car going from NA to turbo. Otherwise I would go with 3" from the get go.

-K-