14 replies to this topic

[Newsoobowner]

Anyone have advice to leave in or cut out the factory catalitic converter. I'm interested in performance to increase economy/MPG. I'm currently in the middle of a valve job and while at it am upgrading the factory carb. to a Weber 32/36. I saw some advice on removing the factory muffler and replacing it with a "turbo" for some gains in performance but it only covers the "cat-back".

[hooziewhatsit]

A couple years ago the cat element at the junction of the Y pipe in my 88 GL came loose and tried to squeeze itself out the back of the car. Needless to say, it didn't work and killed my power (35mph+? ha)

Anywho, I cut open that cat, took the element out, and welded it shut again. I still have the second cat a little farther back.

I used to get ~30mpg. I still get ~30mpg. Power is pretty much the same also.

YMMV

[mikeshoup]

Take one cat out, and leave one cat in.

My XT Turbo came with no cats in it, but came with a downpipe that had a cat in it. The engine is much more torquey with one cat in it then not.

[Newsoobowner]

Take one cat out, and leave one cat in.

My XT Turbo came with no cats in it, but came with a downpipe that had a cat in it. The engine is much more torquey with one cat in it then not.

I don't have two cats. Just one after the Y under the passenger seat and then the factory muffler at the rear. I'm contemplating cutting out the catalytic converter and replacing it with a pipe w/two clamps then cutting out the muffler and replacing it with a high-flow "turbo" muffler. Any reason this would be a bad thing? Also, I don't have to pass emissions in my county so all smog equipment up under the hood is coming off as well.

[scrap487]

I don't have two cats. Just one after the Y under the passenger seat and then the factory muffler at the rear. I'm contemplating cutting out the catalytic converter and replacing it with a pipe w/two clamps then cutting out the muffler and replacing it with a high-flow "turbo" muffler. Any reason this would be a bad thing?

If you're gonna do that, I'd just do straight pipes

How much do you care about noise? If you take the cat out your exhaust will be a bit louder. As to how it affects torque I'm not sure, I've seen several claims about how not enough back pressure will cause poorer engine performance in the lower rpm range, but I've also seen an equal amount of claims that that is a myth. I have a universal 2-1/2" cat and a cherry bomb, its pretty loud, but the clacking from my engine still drowns everything else out.

[mikeshoup]

I don't have two cats. Just one after the Y under the passenger seat and then the factory muffler at the rear. I'm contemplating cutting out the catalytic converter and replacing it with a pipe w/two clamps then cutting out the muffler and replacing it with a high-flow "turbo" muffler. Any reason this would be a bad thing?

(I thought most subarus had two cats? One at the y-pipe, then one in the mid pipe)

Removing the cat completely would of course void its emissions passing-ness. Other reasons I can think against it would be you'd lose some low-end torque, and the high-end gains may be only marginal. Of course it'd be louder.

Probably won't gain any mpg either...

If not for your ears' sakes, leave the cat in for the environment. This is another reason why I'm contemplating putting one back in. Denver has a pollution problem during the winter, and my tie-dye shirt and long hair are disagreeing with my catless car.

[Newsoobowner]

I don't have two cats. Just one after the Y under the passenger seat and then the factory muffler at the rear. I'm contemplating cutting out the catalytic converter and replacing it with a pipe w/two clamps then cutting out the muffler and replacing it with a high-flow "turbo" muffler. Any reason this would be a bad thing? Also, I don't have to pass emissions in my county so all smog equipment up under the hood is coming off as well.

Check out this info on performance enhancing and see what you guys think.
http://www.ultimates...erformance.html

[jeffast]

If you're gonna do that, I'd just do straight pipes

How much do you care about noise? If you take the cat out your exhaust will be a bit louder. As to how it affects torque I'm not sure, I've seen several claims about how not enough back pressure will cause poorer engine performance in the lower rpm range, but I've also seen an equal amount of claims that that is a myth. I have a universal 2-1/2" cat and a cherry bomb, its pretty loud, but the clacking from my engine still drowns everything else out.

i did that you lose all power before 3k and i mean all. my car performs way better with the 2.5 exhaust system and high flow 2.5 cat with magna flow muffler

[grossgary]

don't know if you have an EA81 or EA82. what is good for one person isn't good for everyone. i've found that opening up the exhaust a little gives 1-3 mpg better on all highway trips. the less highway driving you do the less i'd expect to see. i've taken a long highway trip, swapped exhausts on my XT6 and then taken another trip and seen an immediate jump in mpg. but i drive alot (used to drive alot) and mostly highway. i noticed the best improvement by just replacing the stock muffler. i've always used dynomax, i'm sure there are many other choices. i've removed the cat in place of straight pipe and also installed a high flow converter and noticed no difference in these two changes. like jeff said, open the exhaust up too much and you will loose significant low end power which is annoying if you drive up hills or stay in the low RPM range often as the car will want (AT) or need (MT) to downshift to keep speed. i've gone to straight pipe or no cat and just a muffler and that was too much low end loss for the kind of driving i do. this is all on the XT6, same motor as the EA82 with two more cyilnders slapped on.

[calebz]

Removing the cat completely would of course void its emissions passing-ness.

Not at all. I have owned 3 cars That have passed emissions catless (all three came with factory cats).

Especially on older carb'd cars, cats are a bandaid for people's inability to keep their car in tune.

[grossgary]

wonder if states have different regulations? i've heard this before and tried to get my XT6 through without a cat, it didn't pass.

[Dylan86GL10]

Virginia has visaul inspection so you could spew as much emissions as a tractor trailer but as long as you have the right equipment (performing improperly) your goldedn. Pretty stupid in my opinion.

Now for a really dumb question, why does Subaru have two cats from the factory? Every car I've ever owned came with one cat. I even think the newer WRX has three cats!!!!!!!!!! :-\

Turbo shmurbo, the SRT-4 has one cat, my ancient turbo Charger had one cat, Ford turbo one cat, etc....

[grossgary]

i actually had a converter "shell" on mine so i guess i would have passed in VA?

the main converter is designed to work at a high temperature and so is inefficient at start up (if the exhaust is cold). the pre-converter at the y-pipe is designed to work when cold.

[mikeshoup]

Not at all. I have owned 3 cars That have passed emissions catless (all three came with factory cats).

Especially on older carb'd cars, cats are a bandaid for people's inability to keep their car in tune.

I guess it depends what state you're in. I really doubt my Turbo would have passed emmissions being catless. It might pass if I drive it around and get it super hot before driving in, but I usually get stuck in line 20 minutes or so before I get to pull my car up.

[calebz]

I guess it depends what state you're in. I really doubt my Turbo would have passed emmissions being catless. It might pass if I drive it around and get it super hot before driving in, but I usually get stuck in line 20 minutes or so before I get to pull my car up.

I agree.. The turbos are harder to custom tune than the carb cars are. My turbo wagon has never passed emissions since I got it. I think it is well beyond the point of really worrying about that now. Its all about the fun