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Old 09-11-2005, 04:03 PM   #1
Silver on Blacks
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Default catted downpipe vs. un-catted downpipe

I was wondering what downpipe will create more power and what is better for the car.

I am looking for the turbo spooling noise and I heard you cant get that sound when you have a catted DP. Is this true?

I also dont want CEL and I have to pass emissions since Im in california.

If I did go with a catted DP can I go catless the rest of the way back and be fine with no CEL or boost creep and still pass smog?

Im not sure what company I want to go with but I want a good sounding downpipe and a good sounding catback thats not a big mellon shooter. Any suggestions?

Is there anyway I can get an aftermarket DP, keep the stock midpipe with resinator in it and have a catback bolt to that??
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Old 09-11-2005, 07:42 PM   #2
Silver on Blacks
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buummpp
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Old 09-11-2005, 08:08 PM   #3
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screw emissions register it somewhere else and get a perrin cl dp
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Old 09-13-2005, 04:42 AM   #4
Silver on Blacks
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anyone have advice?!?
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Old 09-13-2005, 11:21 AM   #5
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First off a catted DP or non catted DP you will still fail emissions. Unless your state does not do a visual check, but I see you live in Cali, so you FAIL. Got to love California.

If you get a AP stage 2 it will eliminate the CEL codes for the DP. If not you will have to do the mechanical fix or use the resistor.

Other then that have fun breaking the law. I will be there soon, hopefully.
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Old 09-13-2005, 01:07 PM   #6
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Quote:
Originally Posted by Silver on Blacks
I was wondering what downpipe will create more power and what is better for the car.

I am looking for the turbo spooling noise and I heard you cant get that sound when you have a catted DP. Is this true?

I also dont want CEL and I have to pass emissions since Im in california.

If I did go with a catted DP can I go catless the rest of the way back and be fine with no CEL or boost creep and still pass smog?

Im not sure what company I want to go with but I want a good sounding downpipe and a good sounding catback thats not a big mellon shooter. Any suggestions?

Is there anyway I can get an aftermarket DP, keep the stock midpipe with resinator in it and have a catback bolt to that??
A lot of DPs will help you get more power, there is not 1 specific brand that does. There is a lot of info on personal opinions/impressions on DPs/UPs/etc. here on the board. You really should do a search on downpipes and read thru the 10,000,000 hits you'll get. I think there is also a DP FAQ here on the board you can look over for a more unbiased viewpoint. And check the Vendors Forum for DP suppliers. Daddy's is a good one but opinions vary.

You will hear more noise w/no cat in the downpipe than w/a cat in the downpipe.

You pull all those cats and you will almost definately fail emissions. Some on the board have removed all of them and have passed. You may fail a visual check, but failing a visual check is not failing emissions. But, in either case, emissions or visual, you have failed.

Yes, you can get an aftermarket DP, keep the stock midpipe and resonator and get an aftermarket axleback, not a catback. A catback means from the cat back, which would replace the stock midpipe and resonator.
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Old 09-13-2005, 01:29 PM   #7
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PDE makes a DP that does both but its expensive..the cat can be bolted on and off

i have there regular catted dp with stock mid section..and a ti axleback..combined with AP
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Old 09-13-2005, 02:47 PM   #8
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Cobb says they have seen the same power with a high flow cat!
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Old 09-13-2005, 03:04 PM   #9
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{flame suit on}
All you emmissions haters and republic of california grumblers should count your blessings and relatively clear skies. Spend some time in toilets like Moscow or Nairobi and you will be swearing by catalytic converters - you'll want to put three on your car. For the minimal loss incurred (5-10 hp in most cases) it is an excellent exchange and one that any decent and mature citizen should be able to live with.

Sign me, catted and proud of it but not a dolphin hugger or a granola eating freak.
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Old 09-13-2005, 07:10 PM   #10
Driving_Miss_Daisy
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Quote:
Originally Posted by GeorgeRex
{flame suit on}
All you emmissions haters and republic of california grumblers should count your blessings and relatively clear skies. Spend some time in toilets like Moscow or Nairobi and you will be swearing by catalytic converters - you'll want to put three on your car. For the minimal loss incurred (5-10 hp in most cases) it is an excellent exchange and one that any decent and mature citizen should be able to live with.

Sign me, catted and proud of it but not a dolphin hugger or a granola eating freak.
I have been to Enviromental class and saw why they have smog laws in Cali. In the 60's and 70's you could not even walk outside because you where choking from fumes.

There is a point where the law is just stupid. If I have a car that runs cleaner and passes emisions but fails visual, why is it illegal? That is the question everyone is asking over here. If a car is a gross polluter then fail it but if it farts out clean air then what is the problem.
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Old 09-13-2005, 07:26 PM   #11
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Quote:
Originally Posted by Driving_Miss_Daisy
I have been to Enviromental class and saw why they have smog laws in Cali. In the 60's and 70's you could not even walk outside because you where choking from fumes.

There is a point where the law is just stupid. If I have a car that runs cleaner and passes emisions but fails visual, why is it illegal? That is the question everyone is asking over here. If a car is a gross polluter then fail it but if it farts out clean air then what is the problem.
I lived in California in the 70s and 80s. I remember sitting in my brother's convertible in traffic with my eyes stinging from the smog. Look at Cali now . Point taken on the visual and the absurdity of the implementation of law but if you have ever been inside a bureaucracy you will understand that this is the best you can hope for.

By the way for the spoolup noise fan, with my catted downpipe and JIC titanium catback, I can clearly hear my VF-39 spoolup, just revving it in neutral.
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Old 09-14-2005, 01:56 PM   #12
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Quote:
Cobb says they have seen the same power with a high flow cat!
If I read the numbers right, a good high flow cat will flow twice the volume, or more, as compared to a stock cat.
Quote:
Originally Posted by GeorgeRex
{flame suit on}
Sign me, catted and proud of it but not a dolphin hugger or a granola eating freak.
I'm all for at least 1 cat.
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Old 09-14-2005, 02:26 PM   #13
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Quote:
Originally Posted by Silver on Blacks
I am looking for the turbo spooling noise and I heard you cant get that sound when you have a catted DP. Is this true?
Not true.

Turbo-spooling noise from a DP is more of a function of the material the DP is made of, and also the method of manufacturer (cast bellmouth vs. "formed" bellmouth). The cast bellmouth (as found on a COBB DP) will be a bit quieter as there is physically more material in the bellmouth area versus a bellmouth that was formed by manipulating the metal to form the bellmouth shape. The process of manipulating the metal to form the bellmouth (think "stretching") results in thinner metal in the bellmouth area which often equals more exhaust noise (& turbo-spooling noise) eminating from the DP area.

COBB has some interesting DP info here:
http://cobbtuning.com/sti/power-i.html#s-downpipe

Make sure to click on the "Click here to view Pictures and more in-depth information" link for more info.
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Old 09-14-2005, 06:03 PM   #14
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i can hear the spooling noise just by replacing the intake.
(shiiiiiiiiii................shaaaaaa) those types.....

oh wait... those are actual noise from the air compression but not the actual spooling noise like my S4 (weeeeee)

oh well maybe i am wrong ... I hate noise anyway....
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Old 09-14-2005, 06:16 PM   #15
STI_FFY
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Quote:
Originally Posted by Syms-STI
I hate noise anyway....
...and you drive an STi?

I still enjoy all the strange sounds that come from this car.
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Old 09-15-2005, 01:12 PM   #16
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[quote=WinglessSTi]PDE makes a DP that does both but its expensive..the cat can be bolted on and off

We don't make that downpipe anymore - they're just too damned expensive to manufacture. Just sold the last one last week.

As far as HP numbers between catted and cat-less, it really depends on the cat being used. When it comes to aftermarket cats it seems you definitley get what you pay for in terms of flow numbers. Some aftermarket cats flow WAY better than others - the cat we use flows close to 600CFM @ 28" of H20 (when tested by itself), but they're not cheap for us to purchase - and that's reflected in the $559.00 price of the downpipe compared to $295.00 for the cat-less version.

As an indicator of potential HP loss from a catted downpipe, our flow numbers are as follows. These numbers were created on our Superflow 1020 flowbench.

Stock WRX Downpipe (Two Cats) ~ 260.4 CFM @ 28" of H2O
PDE Catted Downpipe (One 400cpsi Cat) ~ 414.1 CFM @ 28" of H2O
PDE Cat-less Downpipe ~ 475.8 CFM @ 28" of H2O

HP gains / losses between these different exhausts are directly relevant to the amount of boost / mods on the individual vehicle. An engine running 20psi will lose more running a cat than and engine running 16psi for obvious reasons. Surprisingly, with a good quality aftermarket cat, the WHP numbers between catted and cat-less are often minimal on the dyno unless some serious boost is being added.

I'd personally like to see everyone running a cat but we all have our own opinions and I respect that.

Hope this gives a little insight...

Regards,

Ian Stewart.
PDE Inc.
www.pde-usa.com
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Old 09-15-2005, 01:16 PM   #17
STI_FFY
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Quote:
Originally Posted by PDE
Hope this gives a little insight...

Regards,

Ian Stewart.
PDE Inc.
www.pde-usa.com
It does indeed. Nice post.
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Old 09-15-2005, 01:28 PM   #18
titsataki
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but isn't the case that by removing the cats you get flow more so you can raise the boost? So you will pretty much gain flow and that would be enhanced by the added boost?

example: running the catted downpipe you can tune for 16psi.
running the catless downpipe you can tune for 17psi
(random boost numbers). So the measured flow difference is even more procounced.

Is that true?

Nick
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