With an A6 my personal preference is the Procharger hands down. Add a nice stall converter to the equation and we are really cooking with fire!!!
Am I biased? Maybe a little since I run a procharger on my personal setup, but I have installed them all and I really believe the Procharger cannot be beat. Plus you get room to grow, where MOST of the postitve displacement superchargers run out of breath. Look at the tvs2300+Rear Belt Conversions+Nitrous setups that are and still not making the numbers of the F1D Procharger for less money. Talk about things that make you go Hmmm
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Just my .02
Sam