Exhaust Sizing on Turbocharged Engines...??

[cjperformance]

On a turbocharged engine you can easily make way more Hp/csa than on a N/A engine.
You have a smoother exhaust flow due the the turbine acting as a pulsation dampner which makes the same pipe CSA 'look' larger to the turbo setup, you also have less reliance on scavenging post turbine than post collector in a N/A combo.
Yes pipe restriction post turbine makes a difference to spool time, boost and HP but not to the same extent as N/a Hp V pipe CSA.
In my experience even with a reletivly ineffective turbo setup you can get away with around 20+% less pipe CSA/Hp @.014"²/hp than you can N/A with a reasonably efficient pipe setup @.018"²/hp.

My experience is similar, one can make a lot of power with turbos even if the turbo-back exhaust is somewhat undersized.

Another way to think about this is weight, noise, and hp. Turbos work as mufflers, so one _can_ run a larger diameter exhaust with fewer and/or lighter mufflers while meeting the same noise requirement. This would, on the face of it, probably lead to larger tail pipes on turbo cars than NA cars at a given hp level, if one is at the corner solution at the noise limit -- not certainly but probably.

On a single turbo V8 setup ive recently done its running a 2.5" od pipe off of the turbo for around 20" including a 90* bend , steps up to 3" for around 40" then splits out to a dual 2.5" with 1 muffler per side. It has less exhaust noise at full rpm than at idle. No science in this, I did it this way simply for space reasons and to then reuse as much of the existing exhaust system as possible for $$reasons. Its a 100%streeter, driven 500+km every week work vehicle. Very very basic engine and turbo setup only making 324rwhp, but is a TQ monster due to the "on the small side turbo" , i may give it another 2lb boost at next tune/dyno. But the point is, this is maybe in the 400fwhp range and doing that happliy and easily on 9lb boost at the moment, whereas a 400hp N/A engine would not be so happy using a single 2.5" engine pipe.