Back pressure good or bad?

[setay]

i've been trying to gather information on this subject, and i have seen many "opinions" stating that back pressure is good. Why is this? How could back pressure be good for a turbo'd car? I ask this because i will be custom building my own exhaust soon but have had trouble deciding between 3" and 2.5". I know it will have little to do with performance, even with a GTRS, but i still would like to know the physics behind this.

But for what its worth, here is my view.
Assume a car is left in neutral, you step on the gas and the RPMS fly to redline instantly. now put the car in 1st gear, step on the gas and the RPMS fly up quick, but not nearly as fast; because of the load being applied to the engine. i figured the load (back pressure) would have the same effects on a turbo, but in this sense causing a slower spooling time, and a less efficient powerband. Where is the flaw (or flaws) in my reasoning?

I'd appreciate any responses, no matter if its based on fact or opinion.

[_audible_]

Well, the choice of words "good" or "bad" doesn't actually apply here. Turbo cars respond better to less back pressure. NA cars do not.

As for custom exhaust, why not just run a cut out?

[setay]

thats the conclusion i came to already, that less backpressure must be better for a turbo'd car. but i was asking why some believe the opposite.

and what do you mean a cut out? im planning on 3" back split to 2.25" for the mufflers. and building an exhaust isn't difficult at all, and should be no more than a saturdays worth of work. ive already completed one when me and my dad custom built a full exhaust for his '62 impala.

[2001S4NY]

with less back pressure and better manifolds you can run more timing on a car when it comes down to tuning it and squeezing out extra power.

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IIRC, smaller turbos benefit from a bit of backpressure in the exhaust system and larger turbos want to have no backpressure at all.

I'd have to search the archives to tell you why this is true.