123quattro

The cat I just pulled out of Robert's car was totally shot. It wasn't melted, but the case was totally rotten, the tubes were really shot, and the monolith was cracked all over the place. That car is much better off for not having it.

SharkSkin

John, my cat is in excellent shape. The pipes and casing are solid with no sign of anything beyond surface rust. I think I should be able to find at least a core in similar condition. I'll talk to the guys that modified the Borla cat-back to fit my '78 and see what they say about the project, whether they have flanges in stock that will fit and what their thoughts are on starting with a cat vs starting from scratch. They do nice work.

I may be able to find a used cat that doesn't rattle, which is another option I'd consider. I've heard the Random Tech cats are good for maybe ~10K miles, hardly seems worth it. I know I could just get a core and knock the guts out of it, keeping what I have now for inspection time, but if I'm going to run without a cat I'd rather have a Y-pipe for however many ponies that's worth.

Jim bailey - 928 International

A gutted cat becomes a resonance chamber and at certain RPMS can really make a droning sound.

SharkSkin

Jim, I was wondering about that. When I was checking my car over after my latest wrenching adventure I thought sure I had an exhaust leak where the rear pipe attaches behind the resonator. When I held my gloved hand near the joint I could swear I felt pulses of exhaust gas. Then I noticed I felt the same thing directly under the resonator and near where it was welded to the front pipe. Turns out it was just the pressure waves coming off the outside of the resonator. It did cross my mind that an empty cat housing might be a bit "boomy" with nothing in there to break up the pulses, aside from the obvious point that the exhaust flow through there would not be especially smooth.