I've used both the TTI and Doug's 2" tube w/3.5" collector on 440s. The Doug's seem to be a bit higher build quality and fit better at the head, but the TTI don't sit nearly as low under the car. They both sound bitchen with an x pipe and Dynomax Hemi Super Turbos. I'd sure like to see a dyno shoot out between them. Here's some pics of new TTI vs 7 year old Doug's -

TTI - Note the dent for spark plug clearance and squared off pipe at flange











Doug's D452 Not sure why Doug's does a full length weld at the flange to pipe seam and TTI does a short weld. Doug does not dent for plug clearance, but will BBQ plug caps if you don't use insulators.