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O2 Housing Recirculation Entry Angle Discussion

Muskrat

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Jun 13, 2004
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With my plans for a turbo upgrade, and going to an external recirulated 02 housing setup, I've been thinking about this a bit. (AKA trying to decide between MAP [thinner 3/8" flange - direct flow] or PR O2 housings [thicker 1/2" flange - 90* flow])

What, in the end, is the ultimate effect on performance with a 90* re-entry angle? Obviously both will work, but is there a distinct advantage of a more direct re-entry angle? I'm relating back to my college fluids class from three years ago, so I may be a bit rusty. Hopefully someone with more expirience with fluid dynamics can chime in.

The exhaust comming out of the turbine is already very turbulant, so any dirruption to flow shouldn't really affect this.

It also takes energy from the main exhaust stream to redirect the exhaust particles from the wastegate, and the exhaust particles from the wastegate lose energy as they collide with the tube wall. What would be the affect of this? Would it create a higher pressure zone immediately after the wastegate re-entry?

This would cause higher back pressue in the exhaust (would it be significant, in the grand scheme of things?) possibly causing increased spool time. This could also have an effect on boost control response. More backpressure at the re-entry means less air can be diverted and you'll have a tendancy to spike to higher boost levels at lower target pressures. The question is, is the backpressure significant enough to affect this in the real world? Or is it just bench racing?

What's your opinion?
 

PJGross

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Everyone neglects orders of magnitude when considering things like this.
It really depends on the build.
Sort of like a discussion about whether a rear mount turbo is good or bad on a V8 application.

If you are building a pump gas setup then I'd say effects of the recirc on turbo efficiency is negligible.
If you're squeezing every last bit of efficiency out of a turbo at 30+ psi then maybe it might have an effect.

Think of it this way, the wastegate only opens once manifold pressure hits its target (or close). At that point you are purposely bleeding energy from the system so who cares how efficient it is in the exhaust stream?

I do recall that by design you want a smooth wall and gentle bend in the O2 housing to have nice flow away from the turbine wheel, but again, unless you're squeezing out that last bit of performance from a very large hp application, there are plenty of more important areas to address.

(my .02 of bench racing input)

-PJ

(I located my recirc re-entry on the mid point of the ninety degree bend on my setup, but my car has been jack-standing for about 8 years now so I don't think it matters) /ubbthreads/images/graemlins/smile.gif
 

Muskrat

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Quote:
Everyone neglects orders of magnitude when considering things like this.
It really depends on the build.



This is what I'm trying to get at. You read online about these and everyone makes a fuss over the re-entry angle. At the very least there is a perceived difference, but I'm wondering if it really matters in anything but a balls to the walls race set-up. My guess is no, but I don't really have anything to go on besides my own reasoning.

I agree with what you're saying, it's not ideal but it will work. The question really is, what affect does it actually have?

The devil is in the details when building a car. I know in spec series the guy who runs the fastest is usually the guy who paid the most attention to making sure his dimensions were perfect, and paying attention to small details like this. Again, full race car vs. weekend toy. But I'm wondering if anyone know's what the effect would really be, as where ever you read about it, people always hammer the point home of direct re-entry angle.
 

Andy_S

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Shithole Wisconsin
Corky Bell states that it should be plumbed back in somewhere beyond 12in past the turbine oulet. Anything closer creates turbulence. I might be wrong on the number, but its somewhere around there. I'll check my book when I get home. Also, this is from "Maximum Boost".
 

belize1334

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Nov 18, 2003
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Bozeman, MT
Quote:
This is what I'm trying to get at. You read online about these and everyone makes a fuss over the re-entry angle. At the very least there is a perceived difference, but I'm wondering if it really matters in anything but a balls to the walls race set-up. My guess is no, but I don't really have anything to go on besides my own reasoning.



The question of whether it matters on a street car vs. a race car depends entirely on what your purpose is in installing the external waste-gate. For a race-car you're planning on running high boost and you just want the waste-gate to control that boost (not hard at higher levels) and to not be a power limiter. That means you want the re-entry to be efficient so that the exhaust back-pressure is low. On the other hand, if you're talking about a street car then the external waste-gate may be to solve boost creep which is the main selling point of the o2-housing externals that are sold by MAP and PR. In that case you want the back pressure through the waste-gate passage to be as low as possible and in which case the re-entry angle may still make a big difference. But, since the aim of these setups are different, you may decide that the re-entry angle that is ideal for a street car is different from that of a race-car.

I would think that a street car would benefit from a more severe angle as this exploits the venturi effect to greatest advantage and the main exhaust passage actually draws exhaust from the waste-gate passage. On the other hand if efficiency is your main goal then I'd think having a more subtle angle would allow for less turbulence at the merge point and thus less back-pressure to the exhaust wheel.

But again, orders of magnitude...it may be that the measurable difference between the two is so low that neither application could possibly distinguish one setup from another.
 
Last edited:

curtis

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My buddy Issac still has my old fluid power book from last semester so no numbers but the air in the turbine isn't turbulent actually it is in a venturi effect and there is a dead spot in the center of the pipe this is why 3.5 or 4 inch downpipes help. As the air comes out of the high pressure turbine to a low pressure pipe yes there is turbulence but going to even a larger lower pressure area helps even more the fast your air can get mixed back up and into a laminar flow out the back the better. as for connecting the wastegate back in I would have it enter into the exhaust at the 72 degree angle at the ground and have it aimed at the center of the exhaust pipe. Also you could run the smaller pipe into the exhaust to the air is sucked out of the tube.


Now as for whats perfect without a flow bench who knows but a trick is to use a leaf blower connected and sealed tight where the turbo will be then you could use a small pipe and have a large hole in the bottom elbow sealed with duct tape. Start having it in the center and in 6 inches or so then push it in further and and pull it out shorter. Also by doing it this way you can push it down towards the bottom or cut angles in the pipe and rotate it as well. If you hear the leaf blower bog down your blocking flow if the sound doesn't change your good but while doing all this use you hand or a piece of string to see if the smaller tube has a vacuum effect. A vacuum effect is what your after. I did the same test on a x pipe I build for a friends v8 exhaust and after 4 or 5 different design changes (size of the oval where there welded together ) I found the point where with the leaf blower blowing in had no sound change and the other side felt like a vacuum cleaner. Another exhaust I built was a large x pipe design and the internal design of the x was like a spin tech muffler. the 2 3 inch pipes come out of the long tube headers and into a H that is about 10 inches wide then it v's down to an oval that is just a hair smaller than the total area of two 3 inch pipes total. Then at that point leads to 2 3 inch flowmasters with dump tubes. Screams at top end and down low has a a super low drone that sounds like no other mustang I've ever messed with I can here him coming from about a mile away if I'm outside.



Airflow is rather silly, sometimes the way it looks may look like it will kick ass but ends up hurting more than it helps.

Real world stuff. I had a .48 turbine a .63 and a bullseye all on the same tO4B V1 50lbs a minute. The .48 was with a 3 inch then the .63 I installed with the same 3 inch then removed the 5 bolt flange and the first two bends I cut the 5 bolt flange up and welded on a 3.5 inch weld bend/weldel sch40 piece and then the second bend had a swelled inlet 3 inch normal exhaust pipe. Car really picked up then I bought a bullseye housing and spool picked up but top end suffered because I replaced it with a ss autochrome 3 inch O2 housing.

Future turbo has a large v band from that I'm welding two 4 inch weld bend caps together then setting those caps onto a 5 inch to 3.5 reducer I'll have to notch both pieces but in reality will look like a giant banjo fitting. Reason for this is space but by all the air going straight to a chamber it will go super turbulent because of high to low pressure then be compressed into the cone of the reducer and then on to the exhaust which may go out the side or to the back. Alot has to do with the fuel safe pumps surge tank and the separate meth tank that's going beside the fuel safe. May not have room back there for a muffler. Want it dumped out the side anyway. /ubbthreads/images/graemlins/devil.gif



When I get my book back it has a section of flow number multipliers for different kinds of outlets squared off, slash cut, protruding nipples (were talking serious don't turn this into he said nipples) venturi cones, radiused ve stacks etc. I'll post them up when I get the book.

read this parts apply here
 
Last edited:

Barnes

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Feb 9, 2003
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Richland, WA
:facepalm:

Here is the only thing that matters: Will the o2 housing and wastegate you are looking to purchase control your boost down to the level you want. Yes or no. Reducing restrictions where the wastegate gas comes back into the exhaust ONLY matters if you are not able to flow enough, I.E. boost creep. You will not gain horsepower by making a fancy entrance back into the exhaust. There may be some peculiar fludics reasons for doing this to give the flow in the exhaust particular characteristics. However the likelihood of making any measurable power is slim.

And if anyone is SOOO convinced that it makes a difference, dyno the two so we can have some empirical data versus all this mental masturbation.

And Curtis, no offense, but what the f*** are you talking about? What the f*** does "but the air in the turbine isn't turbulent actually it is in a venturi effect " mean??? The venturi effect has NOTHING to do with whether or not the flow is turbulent or laminar. The venturi effect is only due to a pressure reduction from increased flow velocity which decreases dynamic pressure. You make it sounds like the venturi effect describes the flow. As for the venturi effect having any measurable effect on increasing flow from the wastegate outlet into the exhaust, I'm doubtful. The gas coming out of the wastegate is already at a much higher pressure then the gas already in there that has just come from the turbo. That's why it is even going through the wastegate in the first place. The venturi effect relies on creating a LOCALIZED low pressure area. It also relies on the static pressure being the SAME at both locations. This is why carburetors work. The carburetor and the air flowing through it are at the same static pressure. Therefore when you air passes though the carb venturi and increases in velocity, the dynamic pressure decreases, you have a pressure depression, and fuel flows into it.

And this: "there is a dead spot in the center of the pipe this is why 3.5 or 4 inch downpipes help." Dead spot?!!? What are you talking about?? The center of a pipe where a fluid is flowing has the GREATEST velocity, and thus highest flow in the entire pipe?? Larger downpipes help when the downpipe itself is TOO small and therefore induces LARGE pumping losses. You lose horsepower when you are expending horsepower to pump the exhaust gas out of the exhaust system.

"mixed back up and into a laminar flow out the back the better." I don't now if this is actually possible. I only vaguely remember the discussion, but I remember the question being raised in class as to whether or not a turbulent flow could become laminar again. My fluids prof said it could, but that it takes a tremendous amount of pipe. I would bet that the exhaust gas is a turbulent flow before it exits out the back of the car.

No one on this board should ever post about fluid dynamics ever again. EVER. I know absolutely dick about fluid dynamics because I took one class. At most I see that other people have taken one class. This also means you know dick about fluid dynamics. The people that have never taken a class know even more dick about it. However I can recognize incorrect sh*t. The mangling of fluidics is finally getting on my nerves. I should have responded to Broxma's extreme mangling of fluids, but I didn't have the energy.

At MOST the people here can talk about A)Actual measured horsepower difference or B)Actual measured pressure drops in something (read: FMIC & piping argument threads)

Curtis, this isn't a stab at you. This happens all the time. I just happen to respond to this thread. I *should* have done this back on the BOV placement thread where Broxma was blathering on about elbows and sh*t.
 

PJGross

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Dec 5, 2002
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Lake Orion, MI
^^^ I concur.
I did the calcs for intake piping and the Re was turbulent for most usable rpm range (over 2000rpm IIRC) in 2-4" pipe (straight pipe assumed). my post w/ calcs is back 4 or 5 years somewhere in this forum.
As a ChemE, I've had 2 fluids classes and a few design classes where distillation trays were optimized on fluid flow, heat exchangers were optimized on fluid flow, etc....
...and I still don't know dick. /ubbthreads/images/graemlins/smile.gif My buddy is a ChemE prof now in fluids, and he doesn't even know that much, but he can integrate and derive like a madman, which is all anyone really "knows" about theoretical fluids anyway....formulas and models, baby! In reality, there's always compromise over costs to build vs optimization and cost to build almost always wins.

In a turbo system, you're bypassing so much kinetic energy that unless you are flow restricted, nothing post turbine is going to do dick on output. Hence 18" pipes or so to get the exhaust out of the engine bay and to mount an O2 sensor. Turbines work on pressure differential, so its best to maximize that pressure differential, as in, nothing on the exhaust side.
 

curtis

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May 4, 2003
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Clarksville TN
^ exactly zero back pressure exhaust works. When in doubt go bigger. If it sounded rambled this morning ain't going to get much better now. neck has been jacked up for 3 days and pills don't facilitate good grammar....Shut up KC, Terry and you to JOHN

Now as for the venturi effect I mentioned I used it as an example when there's a rapid change in size from one pipe to another through a fixed orifice heat and pressure will rise. As the boundary layers of atoms enter the smaller zone a tumbling effect happens and the center of the pipe actually reduces even smaller than the actually hole this works in reverse as well when a high pressure zone of air/fuild etc enters a larger zone with out having a taper angle etc. Thinking square off shoulder hole. The term for this is vena contracta I think.(spelling) Ever time the professor would say it someone would always mumbled out reverse penis pump.


Now as for the dead spot its there.....Myself and 3 or 4 more ex aviation types along with the professor had a 2 hour bitch session on the subject against the rest of the class. This is why certain turbine engines have a nose cone as well as an exhaust cone. The physicists are trying to create thrust and keep all the atoms as uniform as they can. Now think big ass shop fan or a cyclonic designed dust collection system or a few inches of water in a big glass spinning. If the fan spinning on high hold a piece of thread or just tie a piece to the middle and others all over the grid. The ones in the middle want move as much as the pieces out to the far edge of the fan also the ones in the middle will just flop around like a fish compaired to the ones out to the edge that are standing straight out perpendicular

Now if you want to test some of this and or just play bolt up your exhaust to a turbine housing Use some clear packing tape over the hole where the turbo center section is and hook your shop vac to the tail pipe /end of exhaust. Now with the vacuum running drop in a hand full of metal shavings some will flow on down but some will get in the turbine housing and not leave. Really cool to watch /ubbthreads/images/graemlins/grin.gif

The pictures below is of a holset I ported before christmas for a northern mid west guy /ubbthreads/images/graemlins/wink.gif. The particles of aluminum stayed in there for at least 2 or 3 minutes before they all vanished down into the vacuum.


I'll get my old fluid power book back tomorrow and throw up some k values of different bends and orifices, I do remember a globe valve (water facet outside) is super high like 400 where a throttle body butterfly is like 50 or 60 or a ball valve is like 10 or so dependent on how smooth the seals are etc inside. The day after that class I replaced the globe valves in the house water supply to ball valves and it made a huge difference in the house water ....hint for all you older home owners with a water shut off in the basement.

Pictures of highly accelerated chips

 

prove_it

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It's because of these threads that this site purely kicks a**. A question like "What O2 housing is best?" got turned into air/fluid dynamics bitch lecture that is simply amazing. /ubbthreads/images/graemlins/applause.gif

I really have only a clue to what has been discussed. I love it!
 

PJGross

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Dec 5, 2002
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Lake Orion, MI
Here's my buddy, Brent Maranzano, just so I back up my BS:
abstract for one of Brents doctoral papers
which was part of his thesis work. I kind of chuckle when I read abstracts like that. I've been away from the technical side of things a long time. /ubbthreads/images/graemlins/smile.gif

There is no reason to think about the recirc tube angle or location. Put it where it fits and worry about other more important things. /ubbthreads/images/graemlins/smile.gif

-PJ
 

ercp98

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Aug 5, 2003
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northlake in illinois
^ i feel dumb or numb, not sure yet, after reading all this. where is that dingle-banger video when you need it. that would really settle this fluid dynamic debate.
 

curtis

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Clarksville TN
Not all the info as my other book but found all this in my old fluid mechanics book

K values
K =(equivalence length ratio)(friction factor)
K =(length /dia of the same size pipe)(constant number derived from the reynolds number for relative roughness of the pipe)


Table didn't give dia's or Reynolds number of test pieces

Globe valve open 340
butterfly valve ....throttle body open 45
poppet valve....external gate .....420
foot valve hinged ...factory wastegate......75 /ubbthreads/images/graemlins/dunno.gif I guess internal gates do flow better just going larger is what helps them.
90 degree standard elbow 30
90 long elbow 20
90 street elbow tight radius 50
45 standard 16
45 tight elbow 26
180 bend tight radius 50
t fitting 20 for flow through and 60 for branching off


I'll add more later time to eat
 

boostin4door

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Oct 7, 2006
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Chicago, Il.
Quoting curtis:

"The pictures below is of a holset I ported before christmas for a northern mid west guy /ubbthreads/images/graemlins/wink.gif. The particles of aluminum stayed in there for at least 2 or 3 minutes before they all vanished down into the vacuum."


Pictures of highly accelerated chips





Curtis, the port work was perfect!! /ubbthreads/images/graemlins/applause.gif
 
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