I switch back & forth from custom down tubes with cats,
to custom down tubes without cat.
Its a little louder without the cats, inside of my SC Bird
while driving. Its not bad, but if I were going on a long trip.
I would want the cats installed.
Without the cats ,just turn the stereo up with some good
head bangin sounds.
When I run catless, I did not notice better gas mileage.
or any seat of the pants horse power gain. All though
there should be a gain in both, when tuned right.
I have a SCP exhaust system with the cats. My d
catless down tubes came from T-Bird 88.