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confucious240sx
07-25-2001, 04:38 PM
what is it? what does it do?

AceInHole
07-25-2001, 07:18 PM
frees up exhaust flow.

'97 S14 SE Turbo
07-25-2001, 07:19 PM
I've got one for my car...

07-25-2001, 09:25 PM
The downpipe is the pipe coming off of a turbo to connect it to the catalytic converter. If you don't have a turbo, you don't need one. If you have a turbo, a larger downpipe should help spool the turbo quicker and produce more power.

Asad

<BLOCKQUOTE><font size="1" face="Verdana, Arial[/img]quote:</font><HR>Originally posted by confucious240sx:
what is it? what does it do?

<HR></BLOCKQUOTE>

Ant240
07-25-2001, 10:16 PM
it acts like a header, it connects to the single outlet of the exhaust manifold. I forget tho, I think it has a Y configuration, 2 pipes to 1. One goes to the exhaust manifold and the other to the turbo. then the two pipes become one and attach to the catalytic converter.

**DONOTDELETE**
07-25-2001, 11:24 PM
no, the downpipe is just one pipe. No splits in it. just goes from the turbo manifold to the cat. and for turbo cars, you should get rid of the cat. So i guess you can say its just a pipe that goes from the turbo manifold to the test pipe

**DONOTDELETE**
07-26-2001, 01:59 AM
<BLOCKQUOTE><font size="1" face="Verdana, Arial[/img]quote:</font><HR>Originally posted by blee256:
no, the downpipe is just one pipe. No splits in it. just goes from the turbo manifold to the cat. and for turbo cars, you should get rid of the cat.<HR></BLOCKQUOTE>

You should no more get rid of the cat in a turbo car than you should in an NA car. I think the pressure drop across Random Tech. cats has been measured as 2 psi, so it's not like getting rid of the cat is turbo nirvana or anything. Also, you could theoretically plumb the external wastegate dump into the downpipe to make sure all the exhaust was "washed" by the cat, whether driving the turbine or not. I think this has been done on some NSX setups.

ADAM HUTCHINSON
07-26-2001, 06:12 AM
the down pipe is very important...bigger ones create a larger pressure differential across the turbine...thus turbo spools up quicker...that is its sole purpose(also takes the exhaust away http://www.freshalloy.com/ )

97 S14
07-26-2001, 06:25 AM
<BLOCKQUOTE><font size="1" face="Verdana, Arial[/img]quote:</font><HR>Originally posted by qzp:
You should no more get rid of the cat in a turbo car than you should in an NA car. I think the pressure drop across Random Tech. cats has been measured as 2 psi, so it's not like getting rid of the cat is turbo nirvana or anything. Also, you could theoretically plumb the external wastegate dump into the downpipe to make sure all the exhaust was "washed" by the cat, whether driving the turbine or not. I think this has been done on some NSX setups.<HR></BLOCKQUOTE>


I totally disagree. All cars need backpressure to operate properly. However in a turbo car, the turbo itself provides more than enough backpressure that is needed, so big free flowing exhausts with no cats are benefits to turbo cars, whereas they would not be with NA cars.

ADAM HUTCHINSON
07-26-2001, 07:49 AM
i totally disagree...the best exhaust is an open exhaust...ever see an NHRA dragster..straight open pipes...spewing out exhaust...ahhh wonderfull..

no resistance is the best resistance...for peak horsepower any way....torque is another issue...but we are not concerned about low rpm torque

on street machines you need something..otherwise you would be eating fumes...and could not stand the noise...

the greater the pressure differential across the engine...the better it will work..

Mav1178
07-26-2001, 07:55 AM
<BLOCKQUOTE><font size="1" face="Verdana, Arial[/img]quote:</font><HR>Originally posted by 97 S14:

I totally disagree. All cars need backpressure to operate properly. However in a turbo car, the turbo itself provides more than enough backpressure that is needed, so big free flowing exhausts with no cats are benefits to turbo cars, whereas they would not be with NA cars.<HR></BLOCKQUOTE>

Yes, but if this is for a street car then leave it on!

What exactly is the point if one goes on the streets and pollutes everywhere with his/her car? Not only does it pollute, it also can net you a $2500 federal fine for having no catalytic converter.

If you want to smell more of your own exhaust, go do it in your own garage. Yes, no cat. yields slightly better power from a turbo car, but it's done so at the expense of the environment.

-alex

Ant240
07-26-2001, 10:58 AM
what about a high-flow cat? Those that come in 3" to 4" in diameter?

**DONOTDELETE**
07-26-2001, 12:51 PM
I dont want to hear crap about polluting our environment. If thats the case then everyone needs to put their car back to stock trim. I just say do it, cuz you aint gonna pass emissions with an SR20DET anyways, so just go all out. I dont know if the turbo'd KA passes emissions. i am pretty sure it wont pass visuals. But as far as emssion's numbers wise, does it pass? well thats just my 2 cents. People can do what they want.

-Brian

**DONOTDELETE**
07-26-2001, 01:03 PM
I'm going to but the HKS front pipe for mine, it has a 2.5 inch bore from the turbo back and joining to my HKS Hiper Muffler, thus getting rid of most of the exhaust backpressure, this is fine for a turbo car but for a NA car you need backpressure for the car to run right, I have taken the cat of of mine and I noticed less lag and better mid-range torque. Another factor is what will happen to you if your caught, here in the UK even though my car had a cat as standard because its made before 1993 I can remove it.

I know the law on such things varies from state to state in the U.S., but here its a 200 fine.

Mav1178
07-26-2001, 01:47 PM
<BLOCKQUOTE><font size="1" face="Verdana, Arial[/img]quote:</font><HR>Originally posted by blee256:
I dont want to hear crap about polluting our environment. <HR></BLOCKQUOTE>

If you don't want to hear crap about it, don't read it then! I'm just simply stating a negative side of running without a catalytic converter... Plus, just because you have added performance doesn't mean it pollutes! With all the modifications I have to my car, my catalytic converter still helps to reduce the emissions that I am putting out. Most of the work done by a catalytic converter is done at cold-startup...

I don't hope to persuade you to think that you must have one, but the fact of the matter is that a car puts out toxic emissions. If you really want to pump more of that into the atmosphere, that's your choice, only the cops can stop you.

-alex

**DONOTDELETE**
07-26-2001, 03:34 PM
<BLOCKQUOTE><font size="1" face="Verdana, Arial[/img]quote:</font><HR>Originally posted by 97 S14:

I totally disagree. All cars need backpressure to operate properly.<HR></BLOCKQUOTE>

The topic of whether cars "need" backpressure or not has been utterly beaten to death in a previous thread, like a month ago. The truth is that for maximum power in an NA configuration, you want to maximize the scavenging effect, which only occurs if you maintain flow velocity. You can only keep flow velocity high if the exhaust piping cross-section is small (relative to a turbo-sized large cross section). The result is backpressure. We eat the backpressure as a pumping loss because we want the scavenging effect. That the turbo provides backpressure is a _downside_; ideally, we'd want 0 backpressure and complete scavenging (which would correspond to suction, so that would be "negative backpressure" if you will).

**DONOTDELETE**
07-26-2001, 03:36 PM
<BLOCKQUOTE><font size="1" face="Verdana, Arial[/img]quote:</font><HR>Originally posted by blee256:
you aint gonna pass emissions with an SR20DET anyways, so just go all out<HR></BLOCKQUOTE>

Nonsense. If you tune it properly (i.e. expend the time, effort, and money and not try to just get away with a quick, cheap, and dirty setup) then an SR20DET configuration could easily beat any emissions requirement currently imposed. Whether it could pass visuals and all that kinda crap I couldn't say, I never owned a car when I was in Cali.

[This message has been edited by qzp (edited 07-26-2001).]

**DONOTDELETE**
07-26-2001, 04:23 PM
<BLOCKQUOTE><font size="1" face="Verdana, Arial[/img]quote:</font><HR>Originally posted by qzp:
Nonsense. If you tune it properly (i.e. expend the time, effort, and money and not try to just get away with a quick, cheap, and dirty setup) then an SR20DET configuration could easily beat any emissions requirement currently imposed. Whether it could pass visuals and all that kinda crap I couldn't say, I never owned a car when I was in Cali.

[This message has been edited by qzp (edited 07-26-2001).]<HR></BLOCKQUOTE>

A relatively stock SR20DET with a cat will pass the emissions sniffer test with flying colors, on the rev test. At idle it will be a few points over the limit. A brand new cat and a little fuel and timing tweaks may get it to pass the sniffer at idle, but haven't tried that yet...
Keep in mind that this is still cleaner than a lot of other cars with "smog legal" motors that are in a poor state of tune.

Demon

BensonLovesDrifting
07-26-2001, 04:33 PM
<BLOCKQUOTE><font size="1" face="Verdana, Arial[/img]quote:</font><HR>Originally posted by Demon:
A relatively stock SR20DET with a cat will pass the emissions sniffer test with flying colors, on the rev test. At idle it will be a few points over the limit. A brand new cat and a little fuel and timing tweaks may get it to pass the sniffer at idle, but haven't tried that yet...
Keep in mind that this is still cleaner than a lot of other cars with "smog legal" motors that are in a poor state of tune.

Demon<HR></BLOCKQUOTE>


i think if i had a sniffer test done on my car, the guy's nose would fall off.

nismos13silvia
07-26-2001, 07:20 PM
I love my 3" downpipe!!! I just love my whole 3" exhaust system. 3" dump pipe and 3" Apexi N1 exhaust. My SR20DET turbo spools up pretty fast. Don't matter what other people think.

**DONOTDELETE**
07-26-2001, 10:29 PM
<BLOCKQUOTE><font size="1" face="Verdana, Arial[/img]quote:</font><HR>Originally posted by SileightyManiaSPL:

i think if i had a sniffer test done on my car, the guy's nose would fall off.<HR></BLOCKQUOTE>

Hmm yes.. I believe you must hook me up with your man with no nose

Demon

StealthmodeS14
07-26-2001, 11:04 PM
High-Flow cats, depending on the make come in various sizes. I believe some companies like Random Tech. will make them to your specs if you call and specify.

As for the performance issue of a cat, again going with the Random Tech. High-flow cat...on SCCs' project 240sx in which they installed one, there was very little if any power loss due to its' addition. I'd put one on just due to the pollution issue...just my two cents.

97 S14
07-26-2001, 11:39 PM
Guys... ANY car in GOOD RUNNING CONDITION can pass an emmissions test... even without a cat(s)... even an SR20DET. My friend William's SR20DET passed the emmissions test with FLYING COLORS and he has NO CAT. He has a GReddy 3" downpipe and Blitz 3" exhaust system. There were NO fuel additives or any type of tricks used... if a motor is running in good shape it shouldn't have any problems passing any type of sniffer test. I had 2 previous 300ZX TT's pass the same test with no cats at all and I didnt use any tricks/fuel additives either. Now I dont want to hear any boo hoo'ing about the environment... if the car passes the emmissions testing then who cares if it has a cat or not? It's still within the legal limit, and I know that there are cars out there with cats that put out more smog than 10 SR20DET's put togeather.

Mav1178
07-27-2001, 12:03 AM
<BLOCKQUOTE><font size="1" face="Verdana, Arial[/img]quote:</font><HR>Originally posted by 97 S14:
Now I dont want to hear any boo hoo'ing about the environment... if the car passes the emmissions testing then who cares if it has a cat or not? <HR></BLOCKQUOTE>

Most of the work done by a catalytic converter is done at cold-startup...

Put a sniffler test probe up your exhaust when you start the car up in the morning, and let's see if you can pass smog... It's true that well-tuned cars pass smog, but at cold startup you put out so much emissions you might as well dump gasoline on the sidewalk...

-alex

**DONOTDELETE**
07-27-2001, 10:27 AM
<BLOCKQUOTE><font size="1" face="Verdana, Arial[/img]quote:</font><HR>Originally posted by Mav1178:
It's true that well-tuned cars pass smog, but at cold startup you put out so much emissions you might as well dump gasoline on the sidewalk...

-alex<HR></BLOCKQUOTE>

Been there, done that. And lit it on fire too... much fun. It's even more fun when it's "varnished" fuel that's been sitting for 12-15 years. The fire is then almost uncontrollable. MUCH FUN!
TY: Did your friend's car pass sniffer at idle? And was this in AZ or CA? Car we tested was tuned quite a bit to try and get it to run clean. The only thing we didn't do was put a new cat on. But even put an extra set of splitfire japan coil pack upgrade kit on it and that actually helped quite a bit too! I mean, the car runs exceptionally clean for the rev test... just a little over at idle.

Demon

**DONOTDELETE**
07-28-2001, 08:40 PM
<BLOCKQUOTE><font size="1" face="Verdana, Arial[/img]quote:</font><HR>Originally posted by blee256:
no, the downpipe is just one pipe. No splits in it. just goes from the turbo manifold to the cat. and for turbo cars, you should get rid of the cat. So i guess you can say its just a pipe that goes from the turbo manifold to the test pipe<HR></BLOCKQUOTE>

This bothered me because nobody corrected it. A downpipe on a turbo car connects to the turbo itself, not to the manifold. The manifold only serves to direct exhaust gases from the motor to the turbo (and external wastegate if there is one). The downpipe comes only off the turbo (with a pipe into it from the wastegate, if it is external and is plumbed back into the exhaust.)

Dennis

**DONOTDELETE**
07-28-2001, 08:49 PM
FYI, a ka24det with the EGR connected, both O2 sensors connected, with the wastegate piped back into the downpipe, and running with the JWT retuned ECU and 370cc injectors passes emmissions.

'97 S14 SE Turbo
07-29-2001, 01:02 AM
Yes, FastAz240 pass Az emission. Az emission involves under hood inspection, idle test, and rolling dyno where you follow a moniter telling you want speeds to go to.

<BLOCKQUOTE><font size="1" face="Verdana, Arial[/img]quote:</font><HR>Originally posted by Demon:
Been there, done that. And lit it on fire too... much fun. It's even more fun when it's "varnished" fuel that's been sitting for 12-15 years. The fire is then almost uncontrollable. MUCH FUN!
TY: Did your friend's car pass sniffer at idle? And was this in AZ or CA? Car we tested was tuned quite a bit to try and get it to run clean. The only thing we didn't do was put a new cat on. But even put an extra set of splitfire japan coil pack upgrade kit on it and that actually helped quite a bit too! I mean, the car runs exceptionally clean for the rev test... just a little over at idle.

Demon<HR></BLOCKQUOTE>

NY S13 SR
07-29-2001, 08:53 AM
<BLOCKQUOTE><font size="1" face="Verdana, Arial[/img]quote:</font><HR>Originally posted by d240t:
The downpipe comes only off the turbo (with a pipe into it from the wastegate, if it is external and is plumbed back into the exhaust.)

Dennis

<HR></BLOCKQUOTE>

And on the SR20DET there is a small downpipe extension between the turbo outlet and the downpipe. You can see it here with the O2 sensor sticking out of it.

http://srswap.com/pics/sr_turbo.jpg

__________________________
Jeff Holden
Heavy Throttle Performance
www.heavythrottle.com (http://www.heavythrottle.com)



[This message has been edited by NY S13 SR (edited 07-29-2001).]