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Old 05-21-2004, 01:18 PM   #1
zoomfactor
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Default STX Drivers: Factory third cat or high flow third cat

For those STX guys who replaced their factory third cat with a high flow cat, did how would you rate the modification?

I've read multiple opinions on some of the technical forums, but wanted some feedback from STX auto-xers.
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Old 05-21-2004, 01:34 PM   #2
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i dynoed with before and after i made a custom 3" downpipe with high flow cat and saw no difference in power. this was already with 3" catback and headers. it might have brought my spool time a little closer to stock but not very noticable.
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Old 05-21-2004, 05:14 PM   #3
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Quote:
Originally posted by zoomfactor
For those STX guys who replaced their factory third cat with a high flow cat, did how would you rate the modification?

I've read multiple opinions on some of the technical forums, but wanted some feedback from STX auto-xers.
What seems to be the general concensus?
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Old 05-21-2004, 05:37 PM   #4
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The general consensus seems to be that unless you are pushing high HP levels the factory third isn't a significant restriction...

However, if that is the case, why do I see so many high flow CATs on the STX cars. My uninformed opinion is that every little bit helps. As several of you have noted in the past, it's a game of tenths and hundreths of a second. There may be a flow benefit or weight benefit.

Until someone comes out to a National event with a Hydrocarbon organic vapor analyzer and a CO meter, it's all window dressing.
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Old 05-21-2004, 05:58 PM   #5
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turbo lag is always reduced the more open the exauhst.


i strongly reccomend minimizing exauhst restriction in ANY way you can, as turbo lag is one of the huge downsides of WRX autocrossing.
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Old 05-21-2004, 06:21 PM   #6
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Quote:
Originally posted by jmott
turbo lag is always reduced the more open the exauhst.


i strongly reccomend minimizing exauhst restriction in ANY way you can, as turbo lag is one of the huge downsides of WRX autocrossing.
I agree.
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Old 05-22-2004, 02:05 AM   #7
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Hi flow cat all the way.

Quote:
Originally posted by jmott
turbo lag is always reduced the more open the exauhst.


i strongly reccomend minimizing exauhst restriction in ANY way you can, as turbo lag is one of the huge downsides of WRX autocrossing.
yup...
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Old 05-22-2004, 02:38 AM   #8
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I think for those of us that compete locally/regionally a hi-flow cat is not necessecary. I run the stock 3rd cat.

You guys can keep your 4hp you gained.

tcc
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Old 05-22-2004, 02:54 AM   #9
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Quote:
Originally posted by thechickencow
I think for those of us that compete locally/regionally a hi-flow cat is not necessecary. I run the stock 3rd cat.

You guys can keep your 4hp you gained.

tcc
Did you piece together an exhaust system or buy a complete matched system? A lot of folks buy a matched system and with it comes a high-flow cat. Does it help? Who knows, but it doesn't hurt. If you have something you like...go with it! That's all that matters.
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Old 05-22-2004, 05:23 AM   #10
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I've pieced all together.

Catless uppipe, borla headers, scoobysport downpipe, and straightpipe (when I feel annoying).
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Old 05-22-2004, 01:43 PM   #11
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thechickencow - did you lose any bottom end with the Borla headers? The only thing holding me back from the headers is the talk I hear about losing some bottom end. I'd rather have a little less HP on top if I can gain torque through the mid- to bottom.
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Old 05-22-2004, 01:52 PM   #12
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Quote:
Originally posted by thechickencow
I've pieced all together.

Catless uppipe, borla headers, scoobysport downpipe, and straightpipe (when I feel annoying).
after last night's swap that's almost exactly what I've got.
i took off the stone racing header and replaced it with a Borla and TurboXS UP.

i haven't noticed and major low to mid range changes just yet, but i'll update after tomorrow's event.
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Old 05-22-2004, 06:51 PM   #13
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The car with the headers is faster than the car without. I haven't noticed spool/low end differences.

I figure for the $100 I paid there isn't much downside to running them, even if they're only 5hp.

Jay
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Old 05-23-2004, 03:16 AM   #14
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In STX you can replace all the cats with one high flow cat, depending on 02 sensor location I would get rid of every cat you can!

In my SM turbo Matrix(don't laugh, a very fast car I replaced the dual factory cats and original(first real turbo street matrix) 2.25" downpipe with a 3" downpipe and 3" high flow cat and saw a huge overall improvement in bottom end response, sooner and smoother, improved my times tremedously!

Rick
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Old 05-23-2004, 08:44 PM   #15
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Quote:
Originally posted by raamaudio
In my SM turbo Matrix(don't laugh, a very fast car I replaced the dual factory cats and original(first real turbo street matrix) 2.25" downpipe with a 3" downpipe and 3" high flow cat and saw a huge overall improvement in bottom end response, sooner and smoother, improved my times tremedously!

Rick
That sounds like it would be fast...but really weren't they asking about a STX legal car? You can do all manner of things in SM that you cannot in STX. I believe that you also have to have the high-flow cat within 6" of the original primary cat.
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Old 05-23-2004, 11:51 PM   #16
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Quote:
Originally posted by DrBiggly
I believe that you also have to have the high-flow cat within 6" of the original primary cat.
How do you prove which is primary? The one in the downpipe or midpipe?
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Old 05-24-2004, 12:03 AM   #17
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The rule commitee ruled that the last cat in the system is considered the primary one.
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Old 05-24-2004, 12:03 AM   #18
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Quote:
Originally posted by afpdl
How do you prove which is primary? The one in the downpipe or midpipe?
I have no idea. Whichever one is the largest? The other two I know are considered pre-cats. Granted since the factory service manuals are usually what gets referenced by SCCA for protests then I would guess go by which one is considered primary by the Subaru Service Manual.
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Old 05-24-2004, 12:03 AM   #19
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Quote:
Originally posted by forced4
The rule commitee ruled that the last cat in the system is considered the primary one.
Doh! Simulateous posting. Was that in a Fastrak?
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Old 05-24-2004, 07:29 AM   #20
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Quote:
Originally posted by raamaudio
In STX you can replace all the cats with one high flow cat, depending on 02 sensor location I would get rid of every cat you can!

In my SM turbo Matrix(don't laugh, a very fast car I replaced the dual factory cats and original(first real turbo street matrix) 2.25" downpipe with a 3" downpipe and 3" high flow cat and saw a huge overall improvement in bottom end response, sooner and smoother, improved my times tremedously!

Rick
I'm might be completely wrong here but didn't Sport Compact Car do a turbo Matrix before the Matrix was even available at dealerships? Is this that car?

Either way, the Matrix is pretty cool and a turbo matrix would be even cooler. Is yours AWD? I though about getting one before I started looking for a 2.5RS and ultimately buying my WRX.
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Old 05-24-2004, 09:16 AM   #21
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Quote:
Originally posted by forced4
The rule commitee ruled that the last cat in the system is considered the primary one.
People... 2004 rule books need to be read. the Moutons site, while great for looking up rules quick, is NOT up to date.

The rule is no longer saying 'primary' when describing the cats rule in STX. They clarified it last year to read:

Quote:
Multiple catalytic converters may be replaced by a single unit. The inlet of the single replacement converter may be located no further down stream than 6" along the piping flow path from the original exit of the final OE converter.
The whole intent of the previous wording (which was ambiguous due to 'primary') and the current wording was and is to prevent someone from running a cat as a muffler all the way at the back of the car.

--kC
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Old 05-24-2004, 12:45 PM   #22
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So KC, rules discussions aside...what do you think of your high-flow cat?
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Old 05-24-2004, 01:09 PM   #23
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My cat has no relevance in this discussion as it's on the downpipe and not in place of the factory 3rd cat (which was deleted along with the uppipe cat).

The location of my cat may offer different benefits and detriments than just having a free flow DP going to a high-flow 3rd cat.

--kC
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Old 05-24-2004, 03:18 PM   #24
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I thought you had a Random Technology cat I was sure I saw it on your web page (not currently accessible).
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Old 05-24-2004, 03:23 PM   #25
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Quote:
Originally posted by zoomfactor
I thought you had a Random Technology cat I was sure I saw it on your web page (not currently accessible).
Might be a random tech... whatever Buschur Racing uses.

My site is http://www.rallydecals.com/kccar I moved to a new server a few months ago and the URL changed a little bit (removed the /rallydecals/). I don't mention who made the cat in the listing... just that it has one in the DP.

That said.. I likes it! It does well by me.

--kC
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