given that germany has the strictest standards regarding noise, i would imagine they did quite a lot about that
adding an afpr can help with the lean mixture, but you will need to tune with an a/f meter to know where to set it, and it would help to do it on a dyno - having done that very thing, i can tell you that 2lbs too much can mean a pretty serious dip in power - i also found that how much i needed depended on the other things done (i.e. different cat-backs)
while it is possible to get 30-35hp out of bolt ons, it's not about the horsepower numbers on the street - it's about mid range torque - peak hp numbers are for bragging rights only, and can really only be made use of on the track
the first thing to do is define what the car will be used for - then you can decide what things to do to it to get what you want - there is always a bit of give and take though, so be prepared for that
a lot of work has been done in this area - i'd read up a bit here before jumping in - you may find the answers you are looking for
94 Midnight Metallic Blue Cab Porsche 968 w/deviating cashmere/black interior and WAY too many mods to list - thanks to eric for creating
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