[guruerror]

I got an email from a fella at Flowmaster who reported, "...we certainly do not recommend removing cats, as that simply 'confuses' the vehicle's computer, which results in a (usually noticeable) power loss.

A fact that's not widely know, as well, is that your Hummer, like every vehicle sold in the US since the mid-nineties, came from the factory with state-of-the-art high-flow cats installed. There's really nothing to improve on there, with a stock-engine vehicle."

...thoughts...I'm not sure I'm a believer (but, then again, I'm no mechanic). The worst that I could see happening if you remove the CATs is that you'd throw a CEL...which you can avoid by tuning the ECM to ignore the DTCs. Right? Or am I missing something...?

And regarding his last statement, I'll give him that modern CATs may be better then the CATs of the 80's, but I find it hard to believe that they are 'high-flow' by today's standards and that there is no improvement to be seen by replacing the stock units.

NOTE: Before this turns into an emmission testing thread...I live in MD, emmissions testing is required every three years and I've always gotten OBD tests...never seen them to do a sniff test or visual inspection yet.