Breathing Easier...MAF and CAT Feedback

[guruerror]

I'm currently running my '05 with a K&N CIA, Gibson shortly headers, and a Flowmaster exhaust and am now considering replacing the stock Mass Air Flow sensor and going with a high-flow CAT or catless down-pipe to get the big boy breathing even easier.

I'm looking for input from folks on their results with either or both...(i.e., changes in throttle response, general performance, mpg, etc.)

Thanks in advance.

[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.

[Scarsman]

Well, that sounds right to me. When I did the exhaust on a 93 Suburban I used to have I talked to Flowmaster and I was told the same thing. They said my Suburban had the older style cat, which was HIGHLY restrictive, but that later in the 1990's their design was completely changed, and the new ones now flow very well with very little restriction. To the point where there is no point in eliminating them on a street vehicle. I also called and talked to someone at Catco, and was told pretty much the same thing. I used a Catco hi-flo cat on my Suburban with a 3" catback system from Flowmaster.

If you look through a modern cat you can see right through it. They have a sort of honeycomb structure inside instead of the old ones that looked like styrofoam inside with. The old ones actually had to force the exhaust through the catylist substance.

I would stay with the stock one unless you are changing exhaust size or going true dual. And then I would still just use a good modern cat. Or two.

[IRA51]

you can run no cats with downstream sims with no problem or check engine light .A flowmaster muffler has bafles and produces back preasurs . you will have no problem if you have a good stock mass air flow sensor and a good (un restricted cat,or no cat with a downstream sim . How ever it is a fed law that you have a cat . I recomend Carsound/Magnaflow hp cats .