High Flow Cat

[pissedoffgokart]

I was considering 5the purchase of an Xtreme Flow Cat on my GT, but I have never replaced a Cat before and do not know what to expect. The one thing I do not want to happen is to lose what little low end torque I have! Also I know that the cat reduces much of the exhaust sound even before it reaches the muffler. Will the cat make it a little louder or will it sound like a NASCAR racer with the muffler (thinking flowmaster, as I do not care for the giant bumble bee sound of many of the other's)? Any info will be much appreciated!

[d_m_kolb]

The free flowing cat will reduce back pressure and you might lose a little low end torque but I think you'll be very happy with your top end power. Installing a 60 series flowmaster and I don't think you'd lose any low RPM torque and you'd gain some high RPM power.Let us know how it goes. I did this mod on a 97 Chevy Lumina but that car had a 3.4 Liter in it so the results wont be the same but I was very pleased with the performance.

[MadBill]

A cat does have some backpressure as well as muffling effect, but depending on whether the vehicle manufacturer relied on the latter or tuned the rest of the system to do the job on its own, you might or might not notice the difference. If you were going to/have chang(ed) the main muffler, the characteristics of the replacement would make a far bigger difference to both than a cat swap. Also, most/all cats these days (ours included) are welded into place and you would need someone with good skills to cut out the stock cat and stainless weld-in the replacement. Further, in many jurisdictions it is technically illegal to swap out a functional cat. Another point: It appears the GT and base exhaust systems are identical. (I could be wrong) The base system has TWO cats, a welded-in resonator and a bolt-on rear pipe/muffler, so changing one cat might have very little overall effect. Ideally, someone would check the exhaust backpressure upstream of each component, then we would all know where to look for the bottleneck(s)! (My money's on the main muffler.)I put in a pressure tap between the the cats on my base 5 speed and found the system, excluding the first cat, has 4 psi BP at ~6,300 RPM. The rule of thumb is that BP goes up as the square of HP, so if the GT system IS the same, it should hit ~ 8 psi @ 8,000! A good factory system should be As far as needing BP for low end torque, this depends a lot on the engine charateristics, but, especially with a high RPM engine, the cam timing usually makes it very sensitive to any BP, and the loss of top end power due to BP is much greater than any possible slight gain at low revs.Hope this helps!

[d_m_kolb]

On small dispacement engines as in the Vibe back pressure is key to low end grunt. To much and you might gain some in the low RPMs but hurt yourself in the upper RPM. To little and you will feel it in the ((removed) dyno) and the car will feel sluggish down low. You'll have to find the right combo.In my opinion the free flow cat talked about here and a 60 series muffler would give great results. Since the Vibe has a pre cat, (small cat before the larger cat) the pre cat would also need to be replaced. Most aftermarket CAT manufacturers don't make high flow pre cats so you'd have to install two full size cats.As for it being illegal to replace a working CAT, this is correct. The way to get around this is to replace it and say it wasn't working. Could be clogged, wont heat to the proper temp anything that would warrent replacing it and you'd be fine.It doesn't take much if any skill to cut a CAT out of the exhaust piping. It does of course take someone who can weld somewhat to install one back in.For all exhaust welding type things I use a very farm boy type approach. My uncle who is a farmer taught me this and it all ways works great. If you happen to have a cutting torch. You can take a medal coat hanger and melt the coat hanger around the two peices of exhaust pipe your wanting to weld together. It works great and actually will hold just as long as if it were welded.I would suggest most people just let your local speed shop or muffler shop do this work for you. If you have the parts, it wouldn't be over $50 to have 2 cats cut out and replaced with your new ones and a muffler removed and replaced with a new one.

[Flip-Side]

quote:It wouldn't be over $50 to have 2 cats cut out and replaced with your new ones and a muffler removed and replaced with a new one.So I have to install 2 NEW cats! Thats expensive for the high flows! I mught as well cut them off and weld a glasspack there instead for better sound and to fill the gap. 2 decent high flows are pretty expensive...now you got me thinkin....