1. A plenum spacer or new upper plenum is supposed to give +/- 10hp at full rpm. However, I rarely drive at 6000 rpms. Other than bragging rights, would I notice any difference around 3500-5000 rpms if I installed one or the other?

2. What exactly are "test pipes"? I know what headers, Y pipes and catbacks are but I've never heard of test pipes.

 

1.You can feel a difference with the plenum in the mid-range that you are referring to. I would go plenum personally over spacer.


2.These are straight pipes that bolt in the place of the catalytic converters. They go between the exhaust manifold and the y-pipe.

 

Thanks!!!