[gumby79]

I know an old Jag mechanic that figured out the size hole to drill in the cat. He would open the cat enough to see the performance gain you got. But leave most of the cat in place. He worked in a emissions compliance stateback in the 90's AKA California so the cat was mandatory for smog testing by only removing part of the cat, enough of it was still there too cause it to heat up(read still working but to lesser degree) allowing it to pass emissions temperature testing, some of his customers were race use 90%, street 10% . Race use will kill a cat quick . With his mod a 1" hole through the honeycomb the cats stoped melting.
At WOT the engine will go rich trying to cool the cat, this loads up

As to ,emission equipment forces an engine to run cleaner I call BS on anything pre fule injection

On my old 79 3/4t 4x4 Chevy 7.5mpg up hill, down hill, always (with 1 exception with a car trailer loaded with 10,000lbd of cinder blocks +1000 in the truck 17000gross ofer a mountain pass droped me to 7.0mpg). Pushing about 400hp it almost failed smog exam for being too clean. 2years later the almighty CARB decided to hit smog teck personally for a car failing a random roadside inspections (this was later thrown out by the courts too late for me but I got test data). My truck had been rebodied aka Salvage Title, before I got it. So had none of the stickers telling them what was required. So I went from 49 state heavy duty emissions that only required 3 things pvc, factory air cleaner , and heat riser(self adjusting warm air intake) all gear I'd run required or not, even as an 18 yo kid. Over $1000 in USED parts and $500 in new parts . I passed the visual inspection, all there bs in place. The gas test was on the high side almost a fail . There smog gear cost a full mpg 14%loss(there equipment cost 2X the fuel towing 10k . Shortly after Enlisted in the Army. And moved to Kansas and left there crap in Ca (with a gain to 14.5mpg going from CA to KS and an average of 9.5mpg) added msd complete system , probillit distributor, MSD 6 digital control box and an Edelbrock RPM Air Gap intake.and 1406 carb(600cfm ) And a custom built Th400/Np205 with low stall tork converter 700rpm lockup. Idle was 450rpm by 800 all 4 tires were turning wether or not the truck was moving.

Now dont get me wrong epa has done something good, air is breathable in LA agen.