Now, this modification is for "off road use only". It is ONLY intended for race applications and severe repurcussions can result if the following piece is added to a street Miata.

Having said that, the "test pipe" can add power to the high end of a Miata while making the exhaust note MUCH more raucous. When I put on my test pipe, I immediately noticed the same sound I was used to hearing from my otherwise modified exhaust, only now the sound was much, much LOUDER! If you haven't already guessed by now, I like LOUD, as long as the exhaust note is otherwise pleasing. You don't want a loud exhaust note if your car sounds like a Ford Pinto with an exhaust leak. Alas, that is not the case with my Miata.

So what are the horsepower gains from this mod? All evidence I have seen or heard estimates 2-3 added ponies from the test pipe. But remember, the less restrictive you make your exhaust, the less torque you will have in the lower RPMs while the higher RPMs see an incremental increase in horsepower.