They will magically give you 20hp at the crank. Ad a huge ass sticker to your ride and I'll guarantee an additional 50+hp. This I know, I seen Joe Ricer down the block saying his new Mugen sticker increased his trap speed in the 1/4 to mach 2....LOL...j/k <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/biggrin.gif" border="0" valign="absmiddle" alt='
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I wouldn't do it for a daily driver car. We need a little bit of backpressure for the daily grind in traffic and such. Now, if you spend your time in the upper rpm ranges, then I would say yes. You'd probably improve high end breathing/scavaging. If you don't have an intake already with a exhaust, then I wouldn't bother.