Open Downpipe

[SpoolinTalon2]

Hey I have a couple questions about running open downpipe.
-What are the benefits and drawbacks of it?
-If you run open downpipe, will your o2 sensors be reading check engine?

thanks guys.

 

[nightspeed87]

you loose torque not horsepower

 

[dsmsucks]

I noticed that when I ran open downpipe!
Why does low end suffer
rep points!!!!!

 

[jayman77]

open downpipes sound awesome. you can hear the turbo spoolin at idle. friggin sweet

 

[Wicked96GS-T]

I've found you can get an awesome sound, but keep some low end with straight 3" exhaust from the turbo back, no catalytic converter, and a 3" in/out Dynomax bullit muffler.

 

[nightspeed87]

I noticed that when I ran open downpipe!
Why does low end suffer
rep points!!!!!

because back pressure actually makes torque with no back pressure you
loose a little torque on the low end, but it wont hurt your actual horsepower any.

Think of it like this pretend were talking about gas flow our your exhaust
and not actual water in terms of how gas flows im just using water as example...
Now You have a regular sized water hose shooting water...
Its coming out decent speed.... Decrease that hose size and now its coming out
faster right?.... Why because its trying to squeeze the same amount out and needs to come out faster from pressure building behind it( because it cant back up too much
or theres problems ) so its just the same amount coming out faster.
( but means you cant add any more either on the small hose, because its already inefficent)

Make that water hose thicker then the same amount will take a little longer to
come out because theres not as much pressure in the hose saying hurry up come out
therefore it can take its time to come out.... ( Therefore you can add more water
to make more pressure to make it come out faster once again ( in our terms that means adding more boost ).... )

When you cut the downpipe open its like taking away the entire water hose and just
having the water dump out the faucet.... Now say when the waters running slow
( low rpm ) theres no pressure no hurry to come out .
When you blast the water full blast out the faucet (high rpm )
then it loves it because theres no restriction other than the faucet opening from the wall... ( downpipe. )
But why with a open downpipe ( faucet) that you loose power when it has less to travel right....
Well that were you get something called the ram effect.... You need some pressure, not all pressure is bad pressure
.... For instance why do you think ( an n/t engine for example ) cant just hook their
air filters to their throttle bodies ( take cold air out the picture)... Yea less distance the air has to move therefore
quicker entry... True on high rpm.. But false on low rpm, because the pipeing makes a velocity effect
which makes the air move faster from other air gaining pressure behind it and pressure makes things move faster.
thats why you gain power on high rpm running no downpipe but feel like you loose low end. Lose of pressure..

Thats why water pipes are displaced according to how much water they need to move...
And that goes for engines exhaust systems displaced for how much gas they need to move...
For instance a V8s pipeing would naturally be much bigger than a 4 cylinders piping...
In a turbo application Idont think there really is a too big, because you want the open downpipe effect so that the turbo wont have to work as hard to push the same amount of mixture out faster...(smaller pipe) But when your open pipe and your at low rpm theres less pressure(no or little boost) so less torque made..

Did that make any sense to you...?
That wasnt completely accurate because water and exhaust gas are two different substances
and gas flows differenly than water does, but it can at least give you an idea....
If anyone disagrees with my theory feel free to put your opinion on the matter to give me adifferent way to look at it.

 

[dsmsucks]

because back pressure actually makes torque with no back pressure you
loose a little torque on the low end, but it wont hurt your actual horsepower any.

Think of it like this pretend were talking about gas flow our your exhaust
and not actual water in terms of how gas flows im just using water as example...
Now You have a regular sized water hose shooting water...
Its coming out decent speed.... Decrease that hose size and now its coming out
faster right?.... Why because its trying to squeeze the same amount out and needs to come out faster from pressure building behind it( because it cant back up too much
or theres problems ) so its just the same amount coming out faster.
( but means you cant add any more either on the small hose, because its already inefficent)

Make that water hose thicker then the same amount will take a little longer to
come out because theres not as much pressure in the hose saying hurry up come out
therefore it can take its time to come out.... ( Therefore you can add more water
to make more pressure to make it come out faster once again ( in our terms that means adding more boost ).... )

When you cut the downpipe open its like taking away the entire water hose and just
having the water dump out the faucet.... Now say when the waters running slow
( low rpm ) theres no pressure no hurry to come out .
When you blast the water full blast out the faucet (high rpm )
then it loves it because theres no restriction other than the faucet opening from the wall... ( downpipe. )
But why with a open downpipe ( faucet) that you loose power when it has less to travel right....
Well that were you get something called the ram effect.... You need some pressure, not all pressure is bad pressure
.... For instance why do you think ( an n/t engine for example ) cant just hook their
air filters to their throttle bodies ( take cold air out the picture)... Yea less distance the air has to move therefore
quicker entry... True on high rpm.. But false on low rpm, because the pipeing makes a velocity effect
which makes the air move faster from other air gaining pressure behind it and pressure makes things move faster.
thats why you gain power on high rpm running no downpipe but feel like you loose low end. Lose of pressure..

Thats why water pipes are displaced according to how much water they need to move...
And that goes for engines exhaust systems displaced for how much gas they need to move...
For instance a V8s pipeing would naturally be much bigger than a 4 cylinders piping...
In a turbo application Idont think there really is a too big, because you want the open downpipe effect so that the turbo wont have to work as hard to push the same amount of mixture out faster...(smaller pipe) But when your open pipe and your at low rpm theres less pressure(no or little boost) so less torque made..

Did that make any sense to you...?
That wasnt completely accurate because water and exhaust gas are two different substances
and gas flows differenly than water does, but it can at least give you an idea....
If anyone disagrees with my theory feel free to put your opinion on the matter to give me adifferent way to look at it.

Thanks(rep points)

 

[nightspeed87]

http://dsmtuners.com/forums/showthread.php?t=168578


i just found this site try it out....

 

[jtxtrmboost]

Just thought I'd throw in my experience with the open downpipe. I (had) an Apexi N-1 downpipe that was shipped before the catback came - so I thought WTH, why not just run the downpipe. It was one of the worst noises I have ever heard, sounded like a rustic bass fishing boat motor running out of the water Once I put the rest of the Apexi pipes on it sounded amazing. Of course it is personal opinion tho -> it is LOUD

 

[nightspeed87]

Just thought I'd throw in my experience with the open downpipe. I (had) an Apexi N-1 downpipe that was shipped before the catback came - so I thought WTH, why not just run the downpipe. It was one of the worst noises I have ever heard, sounded like a rustic bass fishing boat motor running out of the water Once I put the rest of the Apexi pipes on it sounded amazing. Of course it is personal opinion tho -> it is LOUD

Ive heard different opinions on dislikes and likes of the sound, ive never done if myself but I was considering doin it till my 3 in comes... I had a thread bout it a while back actually, but I do hear its horribly loud, and I dont need attention from the cops... Id only recommend it at the track if its as loud as everyone says it is....
How did your power band feel with it open dp though....

 

[jtxtrmboost]

, well honestly I couldn't tell how the 4G was pullin b/c of the FKN noise pollution, it was ungodly loud and I didn't drive it until the rest of the back pipes came in b/c of fear of a ticket from the county brownies. I would say it pulled pretty well, seemed like it took too long to hit full boost (and that was with the T too slow) - but it pulled the same when I put the rest of the exhaust on anyway so I don't even bother to drop the pipes at the track. And yes pulling the back part of the exhaust (or running the open downpipe) will throw a code on you (rear o2), the check engine light was on until I pulled the plug on it ---> no more annoying little orange light

It does come down to personal opinion though, I have local guys who love that noise and the noise of an external wastegate farting so its really up to you, if you don't watch it though the pigs will have you on the side of the road real quick like for the racket coming from under the car

 

[DOHCAccord]

I have to agree. It really comes down to personal preference. If you dont mind cops looking at you around town or a loud idle, then go for it. if you like the ability to hide under the cops radar then go with a exhaust cut out. My mechanics 99 trans am, yes i know, runs a stock exhaust with two electric cut outs. at the track or when he may have a random light to ligth run he opens them up, around town and in his neighborhood he has then closed and cruises around without any excess noise.
just my two cents

 

[PieEyedPiper]

While a nice anaolgy and all, I'm gonna have to go ahead and disagree with most of what you said. The link I've provided discounts your water hose theory because exhaust systems are actually much different than a plumbing system of any kind.

Running an open o2 is the ideal exhaust for our cars (despite completely impractical). Get this back pressure thing out of your heads. It is never good to have backpressure, N/A or turbo. Whats important is scavenging. But it's only really important for N/A cars anyways because the turbing blades/compressor in our turbos more or less negate any scavenging effect we might have had with any kind of full exhaust, 2.25" or 3.5".
Running an open o2 provides the most flow and the least amount of resistance, that much is clear. But there may still be some kind of percieved torque loss (I'm not a believer though) since there is now no longer any exhaust piping to create any kind of scavenging effect - thus pulling/sucking/propelling or creating any kind of pressure difference to increase power is now totally lost - not that there was much if any to begin with.

Read this.
http://dsmtuners.com/forums/showthread.php?t=168578

because back pressure actually makes torque with no back pressure you
loose a little torque on the low end, but it wont hurt your actual horsepower any.

Think of it like this pretend were talking about gas flow our your exhaust
and not actual water in terms of how gas flows im just using water as example...
Now You have a regular sized water hose shooting water...
Its coming out decent speed.... Decrease that hose size and now its coming out
faster right?.... Why because its trying to squeeze the same amount out and needs to come out faster from pressure building behind it( because it cant back up too much
or theres problems ) so its just the same amount coming out faster.
( but means you cant add any more either on the small hose, because its already inefficent)

Make that water hose thicker then the same amount will take a little longer to
come out because theres not as much pressure in the hose saying hurry up come out
therefore it can take its time to come out.... ( Therefore you can add more water
to make more pressure to make it come out faster once again ( in our terms that means adding more boost ).... )

When you cut the downpipe open its like taking away the entire water hose and just
having the water dump out the faucet.... Now say when the waters running slow
( low rpm ) theres no pressure no hurry to come out .
When you blast the water full blast out the faucet (high rpm )
then it loves it because theres no restriction other than the faucet opening from the wall... ( downpipe. )
But why with a open downpipe ( faucet) that you loose power when it has less to travel right....
Well that were you get something called the ram effect.... You need some pressure, not all pressure is bad pressure
.... For instance why do you think ( an n/t engine for example ) cant just hook their
air filters to their throttle bodies ( take cold air out the picture)... Yea less distance the air has to move therefore
quicker entry... True on high rpm.. But false on low rpm, because the pipeing makes a velocity effect
which makes the air move faster from other air gaining pressure behind it and pressure makes things move faster.
thats why you gain power on high rpm running no downpipe but feel like you loose low end. Lose of pressure..

Thats why water pipes are displaced according to how much water they need to move...
And that goes for engines exhaust systems displaced for how much gas they need to move...
For instance a V8s pipeing would naturally be much bigger than a 4 cylinders piping...
In a turbo application Idont think there really is a too big, because you want the open downpipe effect so that the turbo wont have to work as hard to push the same amount of mixture out faster...(smaller pipe) But when your open pipe and your at low rpm theres less pressure(no or little boost) so less torque made..

Did that make any sense to you...?
That wasnt completely accurate because water and exhaust gas are two different substances
and gas flows differenly than water does, but it can at least give you an idea....
If anyone disagrees with my theory feel free to put your opinion on the matter to give me adifferent way to look at it.

 

[kspharris]

If I am not mistaken (which I may be, and anyone correct me if I am wrong). The turbo should create back pressure. Let me know if I am wrong, which I know you guys will.

 

[PieEyedPiper]

If I am not mistaken (which I may be, and anyone correct me if I am wrong). The turbo should create back pressure. Let me know if I am wrong, which I know you guys will.

You're right it does, being in the direct path of the combined exhaust from all four cylinders. However, this backpressure is localized to only the exhaust manifold. But this is not really important at all because having a turbo greatly overcomes any drawback this restriction in the exhaust flow might have.

 

[nightspeed87]

While a nice anaolgy and all, I'm gonna have to go ahead and disagree with most of what you said. The link I've provided discounts your water hose theory because exhaust systems are actually much different than a plumbing system of any kind.

Running an open o2 is the ideal exhaust for our cars (despite completely impractical). Get this back pressure thing out of your heads. It is never good to have backpressure, N/A or turbo. Whats important is scavenging. But it's only really important for N/A cars anyways because the turbing blades/compressor in our turbos more or less negate any scavenging effect we might have had with any kind of full exhaust, 2.25" or 3.5".
Running an open o2 provides the most flow and the least amount of resistance, that much is clear. But there may still be some kind of percieved torque loss (I'm not a believer though) since there is now no longer any exhaust piping to create any kind of scavenging effect - thus pulling/sucking/propelling or creating any kind of pressure difference to increase power is now totally lost - not that there was much if any to begin with.

Read this.
http://dsmtuners.com/forums/showthread.php?t=168578

thats why on my thread i said pretend were talking about exhaust flow but it allowed me to use a faucet as an example... I said that water and exhaust gas are completely different in the thread, and a big pressure lose does cause lose of torque, and yea theres no scavenging on a turbo and I said myself i dont realy think there is a too big on a turboed car, I was just explaining why the other guy thnks he feels power lose on low rpm with open dp. and back pressure isnt good especially on turbo cars, but you still want a slight bit of pressure because it keeps things moving faster, but the slight bit im talking about is the fact of whether 3in pipeing or not its still through pipe so its pressured.
But I agree the turbo itself already is a backpressure for your cylinders and thats why I didnt disagree with running open dp. or not even on a n/t i wouldnt disagree, I just believe it wont pick up as fast in the low rpm areas (Mainly speaking on a n/t ) but theres always a sacrific, if you want all high top end power youll compromise some low end, if you want good low end and mid range you wont have as much high end, and thats with almost any major mod you do to your car, but if were talking all high rpm then yea you dont want no backpressure because a cars torque band usually falls off way before high rpms anyways( which in my eyes is torque comes from pressure) but a all out drag car wouldnt care about low end so your 02 theory would be better. For instance a factory cars smaller pipes helps keep moderate power in the low rpm band....

 

[nismo4life]

my friend got a ticket for his exhaust, "Improper Exhaust", the funny part is he had the stock exhaust on , just open o2

 

[yfz4fittydsm]

Running an open downpipe is good for power, but not good if cops are right behind you. Such as the case with me getting a ticket tonght.

 

[xveganxcowboyx]

I suggest making the car emmissions legal. DP and 3" cat is a good choice. I don't want my grandkids sucking in noxious fumes when they are born.

Like I posted earlier... you won't boost creep with a stock turbo or a larger turbo with proper porting. For more info about creep, do a search.

I have to disagree. You can still creep on a stock turbo. I ran open O2 and open DP for a while. I creeped on open O2, not so much with the DP on. Both yielded at least some creep. Neither were enough that I would recomend against open DP because of it, but they did creep.

 

[xveganxcowboyx]

because back pressure actually makes torque with no back pressure you
loose a little torque on the low end, but it wont hurt your actual horsepower any.

You are wrong. It's been explained a million times, especially on this forum, back-pressure does NOT increase torque. Do a search on scavenging. There is plenty of info to be had so I won't bother repeating it all.

Also, my butt dyno sais no exhaust makes better power at all engine speeds.