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Catalytic converter


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20 replies to this topic

#1 Newsoobowner

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Posted 09 April 2006 - 04:55 PM

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".

#2 hooziewhatsit

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Posted 09 April 2006 - 06:21 PM

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 :)

#3 mikeshoup

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Posted 09 April 2006 - 06:24 PM

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.

#4 Newsoobowner

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Posted 09 April 2006 - 08:43 PM

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.

#5 scrap487

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Posted 09 April 2006 - 08:53 PM

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 :headbang:

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.

#6 mikeshoup

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Posted 09 April 2006 - 08:53 PM

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.

#7 Newsoobowner

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Posted 09 April 2006 - 09:04 PM

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

#8 jeffast

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Posted 09 April 2006 - 11:46 PM

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

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

#9 grossgary

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Posted 10 April 2006 - 05:47 AM

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.

#10 calebz

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Posted 10 April 2006 - 07:08 AM


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.

#11 grossgary

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Posted 10 April 2006 - 07:12 AM

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.

#12 Dylan86GL10

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Posted 10 April 2006 - 08:05 AM

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....

#13 grossgary

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Posted 10 April 2006 - 08:20 AM

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.

#14 mikeshoup

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Posted 10 April 2006 - 11:24 AM

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.

#15 calebz

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Posted 10 April 2006 - 08:12 PM

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 ;)

#16 SnatchedHatch

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Posted 27 February 2014 - 11:44 AM

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.

I know this post is ancient, but I found it as I am considering doing the same thing debated here: my rear cat ( I have an EA81 MT with the factory 2 cats) has failed and I've noticed a dip in my mileage. I'm on a budget, and plan on cutting out my rear cat and using some flexible joint clamps to secure some piping in place.

 

I have an aftermarket muffler, in what I imagine is the stock style. Small diameter pipe coming out of it, and it significantly reduced noise (and I noticed a slight drop in power at the time).

I have a CEL come on once the car warms up and not the most consistent power (this maybe due to an improper carb tune, something I'm also working up to). At the peak of the rear cat failure, the front cat overheated and got the edge of the CV inner joint boot melting, and either the rubber dripped below or the the O2 sensor was smoking as well.

 

Sooo.. my plan was to cut out the rear cat, and see if my mileage (and I guess power) comes back to "normal".

This thread talks a lot about losing some significant torque from losing one or both cats?

 

How do you think my car would run with the stock front cat and stockish muffler?

Would I have more torque/power if I replaced the rear car with a "magna-flow" cat, or less? (I would consider investing in the MFcat if so).



#17 jono

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Posted 27 February 2014 - 03:34 PM

This is interesting as I have fitted up an EA82 cat Y pipe for its larger pipe diameter to my EA81 Brumby that had no cat being an 84 model, actually an 85 made in 84, and got improved fuel consumption and torque over the 2" sports exhaust system of no cat, no dog, just a noisy rear muffler.

 

Having then mated the Y pipe up to its original EA82 in the Brumby, for a lower kilometre, reco lifters, heads etc and fit new larger clutch in the ute, I have returned to not so good mileage :( Might be due to the less torque I fel I get from this engine compared to the EA81, and it breathes better being a twin port mpfi and revs a little higher - the power band feels about 3500 and above to about 5000, has seen 6000 - something my EA81 never saw !



#18 jeffrodta11

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Posted 27 February 2014 - 07:21 PM

anyone have any suggestions on a easy cheap exhaust set up for a 1979 brat? don't care if its stock or don't need emissions. just want it replaced to run better around the farm and back roads. thanks



#19 turbosubarubrat

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Posted 27 February 2014 - 09:36 PM

My ea81t wagon with a automatic transmission had no cat since it came from Yakima Washington. It had been sitting since or before 2004 with a blown head gasket then motor pulled in 2010 by a guy in hood river which sat 2 years before i got. The next year 2013 i got it running with out cat which made it run poorly. Just this month i finished making the exhaust a $38 shipped cat off ebay made by eastern catalytic welded on to the down pipe for the turbo, $20 for cherry bomb glass pack for the center, and $15 for the rear muffler out of the junkyard maybe had a 100 miles on it since it looked new and didn't show it had been ran hot my guess is its like a magniflow since a recpeit in the car said it cost $100 just for the muffler; also bought a oxygen sensor at carquest for $20 while i was at it and the turbo gasket kit $30 at napa. Car runs a lot better now with great power upon acceleration plus the boxer rumble sounds great with the turbo and cherry bomb with the new muffler.



#20 opus

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Posted 01 March 2014 - 09:37 PM

I left the converter and ditched the muffler.  Perfect.



#21 SnatchedHatch

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Posted 12 March 2014 - 01:25 PM

At this time, I'm just not able to buy those goodies: the cherry bomb mid sounds nice. Is it acting like an expansion ore resonance chamber?

 

What I'm doing next week is clearing out the rear cat and slapping it back on as a shell. My muffler was like $40 (on the bill) from a shop, I immediately noticed the rumble/power drop when it got on. BUT I no longer felt drunk from the fumes

 

I guess I'll wait til Spring and replace the muffler with something off eBay.

haha I'll go halfway between Opus's and turbosubarubrat's route and use an empty rear cat and a cherry bomb at the end.

 

Thanks for the thread resurrection! Til later






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