On a turbo Integra,

is the backpressure lower on a 2-way 2" exhaust system (example below)

than a complete 3" exhaust system ?

 

no

 

why ?

 

assuming both systems have the same wall thickness and the mufflers provide the same flow as the plain pipe for their respective systems... the Cross Sectional Area of the 3" system is greater than the double 2" system.

two 2.5" pipes have more CSA than one 3" pipe... but they weigh more, cost more, take up more space... not very practical.