Join Date Oct 2003 Posts 377 Re: Northstar 4.0 mods? 1st, a autobahn pcm would also make the car think you would have 3.71 gears, and mess all kinds of stuff up i remember this TB vs highflow cat discussion on edmunds, lol, you are scewing the numbers some there. they are $250, but you need the matched mount plate, $100 more. so $350, plus the cost of a new TB, unless you can have your car down for 1-2