skylar troutwine

I cut off my cats becsuse i bieved they were clogged because it was running funny, turned out that the driver side cat was fine, and passenger side was hollowed out

My question is, if i reinstall cats, will the truck run better than before, and second

Can i just get 2 regulat 2.5 inch cats and have them welded on. Or do i need the whole assembly

RPM WS6

iTrader: (3)

Cats don't make any engine run "better", they are simply an emissions control device. The engine will always make more power and attain better fuel economy if the exhaust system is optimized for the application sans cats.

However, there are certainly some high flow cat options that won't do much at all to negatively impact MPG or power. But they add expense and complexity to the exhaust system with no actual benefit other than emissions control. So, if you can pass whatever state E-test you need to pass without them (or don't have any testing in your region), then there is no operational benefit to including them when designing an exhaust system.

Lastly, without any details on the vehicle in question there is no way to be sure if universal fit units would be easy to install or if the necessary mounting location is extremely size/shape specific.

SouthernRex

I recently installed a high flow cat in the middle of my Y-pipe with long-tube headers and an electric cut out post-cat, and I didn't notice any measurable performance loss at all with my "butt dyno", and my fear of it being too quiet were also relieved. With the cut out open, it actually sounds better now than when it was just off-road Y. Still extremely mean, just less... redneck-y? 1998 WS6 A4 TransAm ~80,000 miles.

Also, I'm not an expert, but on dual cat systems, if one is flowing free and the other still has the inside, I think that's bad for the engine because you have dramatically different flow rate / velocity in the exhaust on passenger vs. driver side. That's why I did 1 cat in the middle of the Y, and they never recommend removing just one cat if you have two. This is just what I've read.

bammax

Cats help with reducing emissions which is a good thing. Cats reduce the exhaust smell which is also a good thing. Cats are expensive and can be difficult to package which are both bad things. If you need them for inspection then you don't have a choice. If you don't have inspections then you can try both ways and go with the one that you feel better about. I run no cats, but I may add some later to cut the smell down if I ever start daily driving my TA.

SouthernRex

That's because we're both in FL, lmao. No emission test. But that unfiltered exhaust is just so toxic, I finally got sick of it (especially with women and kids in my car) and went with the high-flow cats. Pretty pleased with it.

RPM WS6

iTrader: (3)

One of my first cars was a '71 Cutlass that was, of course, catless from the factory; with a stock engine the smell was barely even noticeable to me. ~25 years later, I've owned several catless, cammed/built engine vehicles which smell much stronger, but to this day I'm still not bothered by the smell as long as the car has proper tail pipes (I could see how this might be bothersome on a daily driver with dumps though). Mrs. RPM has never complained either. I guess everyone has a different level of tolerance. I think I was about 8 years old before my parents even owned a vehicle built in the cats/smog years, guess I got used to it at a young age.

IMO, the biggest subjective downside to cats is that they give any engine a more smooth, mellow sound. This significantly detracts from the traditional muscle car "cackle". But I guess the youngest generation of enthusiasts are probably used to this, and may even prefer it.

wannafbody

iTrader: (2)

Cats reduce the hollow tinny sound of an off road y pipe and reduces drone.

SouthernRex

With my cut outs open (pre-muffler, obviously) it still sounds amazing to me with high-flow cats. It did change slightly, I guess as you call it the cackle, it doesn't let some of the slight afterfire through?

But when I refer to toxic, I don't just mean the smell. I mean, don't catalytic converters help make exhaust less dangerous to the human body?

RPM WS6

iTrader: (3)

To be sure, the Y-pipe configuration changes some of the sound characteristics quite a bit. The Y-pipe setup is notorious for sounding like a Kazoo on crack after a cat delete and with certain types of mufflers (or, especially, with no muffler at all). If you've ever heard an LS1 with LTs, ORY and an SLP LM1 you know exactly the sound I'm referring to (most noticeable in the mid-2k rpm range). This is not usually a desirable sound to most folks, and having a cat (or cats) will clear this up. Another alternative is bullet mufflers in the Y-pipe and/or I-pipe in addition to a typical catback system. Getting an ORY setup to actually sound really good across the entire rpm range requires careful muffler selection at a minimum, but it can be done and the end result sounds better than a catted version IMO.

On the other hand, the original/traditional "muscle car" sound requires catless true duals with either an H-pipe or no crossover at all (even an X-pipe will cause the pitch to be higher and/or smooth the note). A couple of platforms from this era used a dual in, dual out muffler which acted as a type of crossover, but many just had independent dual systems. These true dual systems create a distinctive sort of sound (different from even an ORY) that can't be exactly replicated with cats in place. Furthermore, that undesirable "Kazoo" sound (which is typical of an ORY setup) is not something which occurs with a true dual system, regardless of cats/catless or crossover or not.

IMO, the best sound comes from no cats, true duals, H-pipe or no crossover at all, and chambered mufflers. But, of course, that's subjective.

The primary danger to humans in the pre-cat era was really from the exhaust produced by leaded fuels. Long term exposure to this is certainly not healthy, but no leaded fuels are sold as regular street gas today. Beyond that, the only other critical danger would be carbon monoxide - but as long as you're not running the engine in an enclosed space or allowing the fumes to accumulate inside a closed cabin (such as could be the case with axle dumps in certain situations), this won't be a problem.

bammax

I grew up with old cars too so I'm not really bothered by the smell. I only notice it when I'm loading or unloading the back with the engine running. After that my clothes smell sooty for a few hours. If I was driving it to work or school the smell on my clothes would be a problem after a while, but since it's only a fun car at the moment I'm not in any hurry to spend money on cats lol

Chris25

iTrader: (1)

Haven't run cats in years on any of my weekend cars, but if its your daily wouldn't hurt to put new high flow cats back on.

tacoraptor

do you have emission laws where you are? CO requires that you have cats so we all use 3" high flow cats.

landstuhltaylor

iTrader: (6)

Emissions equipment is required in every state. Just because you live in a state that doesn't check for it doesn't mean you have an excuse to be a selfish *****.

RPM WS6

iTrader: (3)

Also, just because someone implies that a you're a selfish ***** doesn't necessarily mean that everyone else will agree. Not to get too far off track, but we don't all share the same opinion on these matters.

bammax

And being ignorant of the science or reasoning behind most emissions and safety equipment on modern cars doesn't give someone the right to act like a self righteous *****.

mlee

There were some very good answers in this thread.

landstuhltaylor

iTrader: (6)

Please educate me. I'm looking forward to seeing how much garbage comes out

Chris25

iTrader: (1)

I'm super selfish I ripped it all out....... Weight reduction man every little ounce counts ya know.

bammax

First off high flow 2 way cats at the end of long tube headers are virtually useless for reducing smog no matter how much you like them. The further the cat is from the head the less heat it gets and that takes it out of its operating design parameters. Beyond that 2 way went obsolete almost 40 years ago because it doesn't reduce NOx at all. 3 way cats are used for that, but they can also create hydrogen sulfide when they start to break down. Hydrogen sulfide is a bad chemical that should be avoided when possible. So you really need to have 3 way off manifolds with a fresh air source for the full effect and you need to change them at the first sign of any loss of efficiency.

The way to reduce smog, which is the ultimate goal of all emissions equipment, is to reduce the time an engine spends running and reduce the fuel consumption while it does run. That means reducing necessary drive time, reducing pleasure driving and reducing time spent at higher rpms where more fuel is burned. These are all things that are done on a regular basis by people who spend time posting pics of their race car on a car forum. From your post history I can promise that you release more smog in a year than I do in 5.

bammax

Reducing weight will increase your fuel economy which is a good thing for lowering your environmental impact. So good job on being environmentally friendly