One thing to consider, the GMPP is 2.25" diameter - the perfect size for a stock or slightly modded 2.4l n/a engine.

The Corsa is 2.5" dia for minimum exhaust restriction to spin that turbo! It is the exhaust pressure differential (the difference in pressure before the turbo vs after the turbo) that makes it spool quicker and spin faster producing more hp.

Less exhaust gas back pressure makes the exhaust ports more efficient too. So if you are planning on a wild n/a build with a big cam, you could benefit from the extra .25" as well.

It all depends what your future plans are for your engine. If you don't know what your future plans are, the extra .25" won't reduce exhaust gas velocity enough to hurt performance on a stocker.

 

Yea i know they are real big with the flowmaster at this exhaust shop down the street, on my truck I put the flow master dual exhaust and it was only 200. the guy is good and pretty cheap, but ill have to see what the man has