whats the best place to get 4" pipe for a custom downpipe?????

 

burns stainless?¿?¿? google or the thread at the top of this forum would help

 

what car is this going on? 4" is huge

 

Vibrant offers 4" diameter mandrel J/U bends

 

so does atp

 

thanxs guys

 

Keep in mind that by going too large on this part, you can decrease the exhaust velocity...and cause your turbo to run hotter...which can greatly affect the efficiency of it.

Oh...and you probably want TUBING, not pipe.

 

Exhaust velocity at this end of the game is not important, a smooth transition from whatever size you have at the turbo to 4" would be a good idea, but you really can't go too big here to loose power. I actually read that old turbo f1 cars used to make this transition very rough, a big step to create turbulance and help create a vacuum on the backside of the turbo. I've yet to try is this way, but I don't see why it wouldn't work. Keep in mind, you want the exhaust side as hot as possible, and the pressure differential from the inlet to the outlet of the turbine as big as possible. Obviously you don't want to increase exhaust backpressure before the turbo, so the only way to increaase the pressure differential is to decrease backpressure after the turbine...

 

4" downpipe with a "4 to "3.5 megaphone from burns will be alright for drag racing.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by tony1 &raquo;</TD></TR><TR><TD CLASS="quote">Exhaust velocity at this end of the game is not important, a smooth transition from whatever size you have at the turbo to 4" would be a good idea, but you really can't go too big here to loose power. I actually read that old turbo f1 cars used to make this transition very rough, a big step to create turbulance and help create a vacuum on the backside of the turbo. I've yet to try is this way, but I don't see why it wouldn't work. Keep in mind, you want the exhaust side as hot as possible, and the pressure differential from the inlet to the outlet of the turbine as big as possible. Obviously you don't want to increase exhaust backpressure before the turbo, so the only way to increaase the pressure differential is to decrease backpressure after the turbine...</TD></TR></TABLE>


agreed

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 1.83Tc &raquo;</TD></TR><TR><TD CLASS="quote">4" downpipe with a "4 to "3.5 megaphone from burns will be alright for drag racing.</TD></TR></TABLE>

id go from 3 to 4 or i would transition up to at a 1/2 larger size garrett has been recommending this for quite some time and even on some of the larger GT like the 40 + turbos they are casting it into the turbine housing

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by eLusive ek4 &raquo;</TD></TR><TR><TD CLASS="quote">


agreed

id go from 3 to 4 or i would transition up to at a 1/2 larger size garrett has been recommending this for quite some time and even on some of the larger GT like the 40 + turbos they are casting it into the turbine housing</TD></TR></TABLE>


what i mean is from the turbo 3" to 4" all the way down to a 4" to 3.5" megaphone transition into a 3.5 exsuhast system with a 3.5 inlet+ outlet borla oval muffler.

 

i would stay with 4 all the way and not use a borla muff

of course i like ours but Es oval our somehting

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by tony1 &raquo;</TD></TR><TR><TD CLASS="quote">Exhaust velocity at this end of the game is not important, a smooth transition from whatever size you have at the turbo to 4" would be a good idea, but you really can't go too big here to loose power.</TD></TR></TABLE>So, at what point is exhaust velocity important?
Try pulling your header off the car and run it with on manifold or header...which is essentially like opening up to a really big area, slowing velocity down. Watch and see how long the engine runs. An exhaust serves more than to get exhaust to the back of the car...it is there to take HEAT away from the engine. By slowing the exhaust down too much, more heat soaks into other areas.
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by tony1 &raquo;</TD></TR><TR><TD CLASS="quote">
Keep in mind, you want the exhaust side as hot as possible, and the pressure differential from the inlet to the outlet of the turbine as big as possible. </TD></TR></TABLE>
Can you explain this? It seems a bit contradictory to your statement that velocity is not important...because by slowing the velocity, you will increase the heat soaking effects. If all this is true, why not go with 2.5" runners on the manifold?
(keep in mind that I'm not arguing here, I just want to hear your explanation of these statements.)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by eLusive ek4 &raquo;</TD></TR><TR><TD CLASS="quote">id go from 3 to 4 or i would transition up to at a 1/2 larger size garrett has been recommending this for quite some time and even on some of the larger GT like the 40 + turbos they are casting it into the turbine housing</TD></TR></TABLE>
I think that the best thing is if you can have a very small reduction of size within the first couple inches after the turbo, then open up about 1/2" larger than the turbo outlet. This will speed the velocity leaving the turbo, but then open up soon thereafter so that it will reduce backpressure. I really don't know what size turbo outlet he's got so I don't want to get too specific on the sizes.

Take a look at some of the performance motorcycle headers. They reduce down just after the head, to speed velocity and increase scavenging, then they increase in diameter to reduce backpressure. This is how many are made.

Aside from this specific issue in this thread, I'm interested in what testing process and equipment they have to test flowrates and other performances of exhaust parts...Casey, can you tell me about this? It seems that everybody likes to judge parts by appearance, but I want to know what means you guys use to know what works and what doesn't.

 

ok

Well to begin when we are doing R & D we have a specific outline of goals we want to accomplish. For each one of these goals there will be a certain # of tasks to complete. for each task we know there is specific data we are going to need to look at, such as pressure readings (in multiple places) egt. readins of course, and mutiple other things such as A/f.

From here we take a very methodical approach to ensuring that our environment is controlled as possiblle. We make our test runs chnages etc. go throught the entire process. After that we sit around look at the data and gather ideas of what could be happening and what is happening.

With R & D you know as long as you make a chnage and get a result (good or bad, more power or less) you are heading in the right direction. It's when you see no change i start to get worried.


I guess what im saying is we are very very methodical and thorough with our dat accquisition.

oh yeah we are doing a quite large R & D project coming really soon guess they downpipe idea is going on the list of things to test.

Thanks Casey


Modified by eLusive ek4 at 4:42 PM 12/17/2004

 

Engloid,

I don't think we can quite compare a header and a turbine downpipe.

The reason you want a larger downpipe, is because a higher pressure differential reduces backpressure on the turbine wheel. This allows it to spin easier and more efficiently. More Efficiency = More Horsepower. This is sort of the same scenario as stepping up to a .82AR from a .63 AR for example. Basically with going to a larger downpipe...You gain the 'pros' without the consequences of stepping up turbine wheel size or A\R. You worry about velocity and heat on the feed side of the turbine, not the exit...You just want the exhaust to evacuate as fast, or faster than the manifold is feeding the turbine.

Inversely, when speaking of motorcycle headers and all-motor cars...you are only dealing with the 'feed' side of the system...there is no turbine impeading flow. The thing you have to remember about a turbo system...is that the exhaust flow is pressurized. The Turbine is almost like a valve...you have to beable to flow as much out of the valve as you are flowing into it.

Then we get into mismatching compressor and turbine sizes...This is why if you put a 91mm Compressor Wheel on a T3 Housing, it would suck *****...The 'Feed' is outflowing the Exhaust and choking it. If 'velocity' made power on the exhaust side...that combo would be killer. I think i'm making sense here...

 

im pretty sure its a law of fluid dynamics that with an increase in velocity, there will be a decrease in pressure, and vice versa.

that said, i think we all agree that a larger downpipe will decrease velocity. physics says that will increase pressure. fluids travel from area of greatest concentration to area of least concentration, or in other words, exhaust gas likes to go where the lowest pressure is. if the velocity after the turbine is lower (due to larger DP) then the pressure is higher, and that makes me pretty sure that the pulses will be less encouraged to exit the turbine housing.

unfortunately, i dont have a clear understanding of what pieces a turbine adds to the exhaust gas puzzle, but i will eventually test pressure on my own with varying diameters and transitions.

burns stainless guy- have you guys ever experimented with critical flow venturis after the turbine?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by mike_belben@yahoo.com &raquo;</TD></TR><TR><TD CLASS="quote">that said, i think we all agree that a larger downpipe will decrease velocity. physics says that will increase pressure. </TD></TR></TABLE>
So you're saying that by putting a larger pipe on, it INCREASES backpressure? Cause I don't agree with that.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Engloid &raquo;</TD></TR><TR><TD CLASS="quote">So you're saying that by putting a larger pipe on, it INCREASES backpressure? Cause I don't agree with that.</TD></TR></TABLE>

i think he got the two confused ? . im no expert .. but ..
larger diam .. more flow/velocity .... less backpresure. .

 

im sorry friends, but i didnt stutter. it wont cost me anything if you have already made up your minds not to believe this. i just spent about two hours finding scientific proof and have an example youre all familiar with.

carburetor venturis. the float bowls are open to atmospheric pressure of 14.7 psiAbsolute. when the intake valve opens and chamber volume grows it creates a pressure depression. atmosphere attempts to fill the void and air flows through the carb. velocity through the carbs venturis increases. increasing velocity causes pressure to decrease, and therefore the 14.7 psiA on the float bowl forces fuel through the nozzle.

bernoulli equation and continuity equation can be used to show that pressure/velocity vary inversely.

scroll to the end of #3, last 2 paragraphs.

http://www.efm.leeds.ac.uk/CIV...i.htm

if thats not enough, heres a critical flow venturi simulator. after it loads read the directions to change the second portion diameter with the yellow box and watch the pressure and velocity numbers vary inversely.

http://www.ce.utexas.edu/prof/....html

"backpressure" is simply a term car guys use. there is only pressure. 5 psi in an exhaust manifold is called backpressure, while in an intake tract its called boost. theyre still just 5 pounds per square inch of air.

i think this pretty well shows that increasing velocity decreases pressure. i DID NOT say anything about what size is better than what, im only arguing the relationship of gas dynamics. if a 5" downpipe works better than a 4" downpipe in reality (which i do not claim to know) there is something else at play, as yet, i do not entirely understand what the turbine does to the harmonic pulses of compression and rarefraction.

im waiting for the burns guy to chime in. take a look at their collectors or at the hytech B series turbo manifolds where the turbo is up above the tranny.. tell me why there is a choke point acting as a convergent-divergent nozzle at the merge of the collector? could it be to increase velocity, thereby decreasing pressure and encouraging pulses to travel out the merge pipe to the exhaust rather than travel back up another runners primary? this might be called "scavenging" or i guess, strategically placing low pressure points in areas where the exhaust flow has a choice of directions to take, such as the collector.