12-01-2009, 08:23 PM
When I was on my first tuned 335i, I got a PM from a guy in a stock 6MT car who wanted to see how his stock 6MT car would stack up against me in a tune only 6AT car. He lost of course.
Then he called me back 2 weeks later and wanted to meet up again after he removed his axle back (no mufflers and piping from last cat to mufflers.
His car was pretty loud then (you'd have to drive like a granny around ANY law enforcement officer, or when coming home late at night if you want to stay on your neighbors good side) but I did notice his car seemed to be a bit quicker.
We did not only runs from dig, but from various starting points.
I'd pull on him sooner when he was stock.
Without the mufflers he seemed to hold with me for the first split second, and seemed to fall back slower than he did when stock.
Keep in mind this was on the first tune of a 335i (313 whp) and trap speeds of 108-109 mph in best case scenarios.
I'd say in a 40-120 mph run, he stayed 1-1.25 Car lengths closer without the axle back on (but still lost by 3-4 CL's)
Two reasons, dropping 30-40 lbs probably helped and less back pressure must be worth 8-10 hp (heck catback exhaust seem to add 6-8 hp themselves, so having NO catback, has got to be worth a couple more than that too). Combined it was enough to keep him 1+ CL closer.
But to me, it wouldn't be worth the glares you'll get from other drivers, the ticket you'll eventually get from the po-po and the "what the heck did you do to that BMW" comments from other BMW drivers you'll surely get as well.
Stay stock or go with a nice sounding catback instead. Nearly the same power gain, 10-15 less pounds in weight or stock, and no glares, no laughs, no tickets.