Do Hollowed-Out Catalysts Make Power? - Fact Or Fiction

When searching for urban-legend power adders to test for Fact or Fiction, we need only to think back to a time when we were first starting out as broke-ass noobs, conniving ways to make our Civics go faster for the low monetary investment of $0. One of the first such methods we've all tried was to gut our cars' factory catalytic converter, to reduce exhaust back pressure, and ideally, free-up a few ponies by doing so.

Today, with ready access to test cars, OEM catalytic converters, floor jack handles, test pipes and dynamometers, we're revisiting our MacGyver power-making tactics of yesterday, to see if running that hollowed-out cat at the drags really did help us reach the traps quicker. For kicks, we'll also put it up against an OEM-spec catalyst, and a properly built test pipe, to see which comes out on top.

Run 1: Stock Catalytic Converter...        read full caption Run 1: Stock Catalytic Converter Our first order of business was to fit this universal catalyst to our Project Miata test car, strap it to the rollers of SoCal inline-four guru Mark DiBella's Dynojet dynamometer, and power through three Fourth gear pulls, to establish an average starting baseline.		Run 2: Gutted Catalytic Converter...        read full caption Run 2: Gutted Catalytic Converter Next up, we hollowed the universal cat out with a floor jack handle (much like we used to back in the day), bolted it back up to the roadster, and established new average power and torque marks.
	Run 3: Testpipe Finally,...        read full caption Run 3: Testpipe Finally, replacing the cat with a properly built, straight-through test pipe of the same diameter piping as the rest of our exhaust, we conducted three more pulls.

The Verdict:
Compared to our baseline runs, we were able to see no benefit of the hollowed-out cat versus leaving its catalyst core intact, and compared to the test pipe, there was no question; the gutted cat lost all around. Exhaust gasses became turbulent as they passed into the cat's open reservoir, actually increasing backpressure and hurting power. As we had suspected, replacing our car's cat with the test pipe cost a few low- and mid-range ponies and lbs-ft (bad for daily driving), but more than made up for it up top (good for race day). Bottom line: Keep the cat intact for the street, replace with a proper test pipe for the track.