[Duffman]

Originally Posted by jpgmtech

Been there, tested that... at least in principle. Less exhaust backpressure is almost always better, with the exception of very specific circumstances, i.e. modifying the sound pressure wave tuning of the exhaust to optimize efficiency at a specific RPM. This is assuming the vehicle has equal-length headers too... and the tuner has an understanding of Helmholtz resonators.

Typically though adding backpressure effectively "throttles" the exhaust. Why not just throttle the intake, like we always do???

BTW, on a variable-vane turbocharged diesel, the vanes act as an exhaust restriction at higher vane angles. On my diesel I can pick up almost 10% highway economy by opening the VVT right up for cruising over and above the factory settings. The factory settings are there to intentionally create some backpressure for the EGR as well as making the turbo spool much quicker.

As for this "fuel economy" device - smoke and mirrors....

So does opening up the VVT result in less boost then or more?