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Witnessed two dyno runs with cars without cats completely. The one just had the cats removed along with an intake but the numbers came out the same as cars with just the intake. The other one had just installed long tube headers and there was only an 8 rwhp increase. Conclustion not worth it.
It's all relative IMO. I had gutted stock CATS and could not stand the smell of fuel and fumes.................it was sickening. I installed the Random Tech HF cats and it COMPLETELY fixed that problem. It was worth every penny for me.
My car still made 477rwhp/544rwtq. That's with a 436ci stroker.
Take a run over to LGM (in Wyle, Texas). They can provide information (stats) on their long & short header systems for you to review.
I replaced my B&B's with thier "long's" - have run with and without cats (as of now staying without). ODB II testing in the major cities of Texas, so car passes inspection without any issues.
Sound difference is much more to my liking (have Corsa Indy exhaust, and X pipe).