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Old 12-27-08, 02:33AM   #1
turbo69BIRD
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Default exhaust theory thread post up info here

http://www.nsxprime.com/FAQ/Miscella...austtheory.htm

There is also a great story from rodder and super stock on terminator boxes I want to find if anyone knows it and can find it post up.
Article may have been called no loss exhaust anyone remember it?
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Old 12-28-08, 11:15PM   #2
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I thought I would pop this in here. It's a Speedtalk topic. Turbo exhaust sizing, that goes along with some of the recent threads here. I have to paste it in here because you need a password to access this part of the forum. 3 pages. Lots of guys here with good input. Take it for what it's worth. Each post here will be each page of the thread. Watch out guys, there is some math...don't let your brains melt.

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96Mustang460cid
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Posted: Fri Nov 09, 2007 4:25 pm Post subject: Turbo exhaust sizing: primary vs collector vs merge vs turbo

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I have a 460 BBF that's getting a TV8101 turbo. Currently, the engine is N/A and ~550 hp. The engine will have new bottom end with lower compression and a milder camshaft. From my old engine, I'll be re-using my aluminum heads.

Assuming perfectly steady state conditions:
The area of (4) 1.75" primary ????? is 9.62 in^2. This leads to a crossover/collector with a diameter of 3.5 in (9.62 in^2). Next, a merge will combine the two 3.5" (total area of 19.24 in^2) to a 5" diameter tube (19.63 in^2). Now this merge goes into the T-6 turbo flange (2.3" x 4" flange = 12.6" circumference). A 5" pipe has a circumference of 15.7" which is too large for the T6 flange. The best fit for the T6 flange is a 4" pipe (12.56" circumference). This is completely ignoring any cooling/contraction of the exhaust gases. This leads to my question ---->

Has anybody taken temperature measurements at increments from the engine to headers to collector to crossover to merge to turbo? With some temperature readings, I can design for a steady velocity (my goal). I want to design the exhaust as efficiently as possible by minimizing the velocity and shape/size changes throughout the system. Because I'm building it from scratch, there is very little cost difference between "right' and "wrong" .

Discuss...

Have a good day!
Michael
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ROGUE GTS
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Posted: Fri Nov 09, 2007 8:17 pm Post subject:

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A 5" pipe that reduces to a 4 at the flange will flow more than a full length 4".

Same way a 1" garden hose with a 1/2" nozzle will flow more than a 1/2" hose.

In this case I say let it breathe and run the 5"...

What rpm and HP are you looking for? My gut feeling is your primaries are too small, I would be looking at 2" for starters.

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Warpspeed
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Posted: Fri Nov 09, 2007 8:25 pm Post subject:

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All those flow areas assume steady full flow, all the time, from each port. But that is not what actually happens.

A greatly simplified example of this effect might be to first think of a two cylinder motorcycle engine, where each cylinder fires every 360 crank degrees. If both cylinders were feeding into one turbo, there would be no problem merging say a pair of, inch and a quarter pipes into a single inch and a quarter pipe. It would not be restrictive, because each port empties in turn, there being no flow overlap between cylinders.

With half a V8 or a four cylinder engine four ports empty into one collector. But the time length of flow from each primary pipe will depend on exhaust cam duration. If an impossibly short exhaust duration of 180 degrees were to be used there would be no exhaust overlap at all from port to port.

As longer durations are used, there will obviously be some overlap, and this can be figured out. Even with an impossibly long 360 degree exhaust cam duration, only two ports will be flowing together.

If your primary ????? are 1.75 inches, they should merge into a pipe something between 1.75 inches and 2.5 inches depending on exhaust cam duration. Maybe 2.25 inches diameter might be about right ?

You certainly do not need a 3.5 inch pipe at the first merge point.

Taking this further, the second merge point will have almost steady flow from two sets of four cylinders, so double the flow area, or very slightly less might be about right.

Twice the flow area of a 2.25 inch pipe s roughly a 3.2 inch pipe, 3.0 inches should work fine. That should be more than enough, as the largest restriction is going to be the turbine housing not the pipes feeding into it.
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Dynoroom
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Posted: Fri Nov 09, 2007 8:27 pm Post subject:

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Having built a turbo system or 2 you might be worrying about alot that won't affect your system. As your only running 1 TV81 turbo all the effort you put into a well formed & merged exhaust system only to go into a T-6 flange will be of limited good. With your engine displacment you will have plenty of backpressure, lets hope its less than 2:1. What boost do plain on running? Is it going to be a race only vehicle?
As far as exhaust temp from the head to the turbo we see about 150-200 degrees higher at the turbine inlet, say 1500* @ the port exit to 1650* @ turbine inlet.

Good Luck & enjoy your project.
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96Mustang460cid
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Posted: Sat Nov 10, 2007 12:24 am Post subject:

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Guys,

Thanks for the input! Yes, I was incorrectly assuming steady state flow.

From the analogy used, it looks like my camshaft greatly affects my exhaust sizing, right? I will start doing more research on a suitable camshaft. Does the following example demonstrate the correlation between the camshaft's exhaust duration (@ 0.050") and exhaust diameter:

225* (exhaust duration @ 0.050") x 4 cylinders = 900* ---> 900 (total exhaust flow duration per bank) divided by 720 (duration per cycle) = 900/720 = 1.25. Now, multiply my 1.75" primaries by the calculated 1.25 ---> 1.75 * 1.25 = 2.125" ----> ~2.25". The slightly larger size will help reduce frictional losses.

Warpspeed, is that the jist of how you came up with your #'s?



Dynoroom: I always enjoy this stuff! I may overcomplicate it, but that leads me to ask questions and find answers ---> better understanding! Even if it doesn't have a huge impact on my final results...it will help me understand the thought process and reasoning behind my decisions and allow me to prioritize different parts of my build .



ROGUE GTS: My goal is ~800 rwhp. I don't know how much boost will be required to achieve this (boost only shows the restriction through my motor ). The car is a 96 Mustang and will see 60% street duty along with the occasional Hot Rod Power Tour and, if my car is really fast, a Pump Gas Drags .

Have a good day!
Michael
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Warpspeed
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Posted: Sat Nov 10, 2007 12:41 am Post subject:

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Yes Michael, that is my general philosophy. It is not really that critical, and obviously it all has to work within standard available pipe sizes.

The important thing it to try to keep pipe velocities reasonably high, and keeping exhaust manifold volume as small as possible for best turbo response.
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INTMD8
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Posted: Sat Nov 10, 2007 6:50 pm Post subject:

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96Mustang460cid wrote:




ROGUE GTS: My goal is ~800 rwhp.


Well, fwiw, 1 5/8 primary ????? and 2.5in crossover pipes can easily support 1500hp in a single turbo application.

Personally, I would use the smallest primary tube possible while still being able to form it to the inside of your header flange (so you don't block off any of the exhaust port).

After that, 2.5 collectors/pipes merged into a T6 flange is more than adequate.
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exhausted
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Posted: Sat Nov 10, 2007 9:32 pm Post subject:

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Gentlemen,
I have built several serious street vipers dual turbos. 526ci, 263ci per bank.
1.75header, 2.5" into T-4 flange. 1500RWP+,30-33lbs, Hyd Cam,6500rpm and 8.95,184mph@ 3500lbs street car.
I would crossover to 3" but if that is too scary? 3.5", no bigger!
I agree with INTMD8, keep it small
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ROGUE GTS
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Posted: Tue Nov 13, 2007 12:33 am Post subject:

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8.95 @184?

ummmm....

Whos viper was that? I know damn near everyone with a fast viper and those numbers don't ring a bell.

You sure you don't mean 7.98 @ 183?

Oh and 1500rwhp @ 33psi isn't that special. 1585 @ 25 is. Backpressure is bad.

That being said if you're only going for 800hp from a 460bbf, it doesn't much matter what you do, you'll have no problem making the power. With such a low hp rating size it small and you'll be fine. The backpressure won't be crazy as you're not running 20+ psi.

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panic
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Posted: Tue Nov 13, 2007 6:16 pm Post subject:

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Of course, what was I thinking.

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blown265
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Posted: Tue Nov 13, 2007 8:31 pm Post subject:

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On turbo pipe sizing [and apologies 96Mustang460cid for jumping in on your thread but our question is similar] we are building a manifold for an I6, 265ci, with a T4 flange.
We're considering 1 5/8. primaries collected for cylinders 1,2,3 and 4,5,6 [firing order 1,5,3,6,2,4], merged into two 2 1/4, then into the T4- do these sizes seem appropriate?
Secondly, the housing is a twin scroll- should I keep the two 2 1/4 pipes separate into the turbine [rather than collecting them as they enter]?
The turbo will feed a positive displacement blower first, which will then feed the engine. The hp target, depending on block strength, thermal management, and tuning, is 2.2hp/ci.
Cheers
Paul
[edited for typo on firing order ]

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96Mustang460cid
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Posted: Wed Nov 14, 2007 11:19 am Post subject:

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blown265 wrote:
On turbo pipe sizing [and apologies 96Mustang460cid for jumping in on your thread but our question is similar] we are building a manifold for an I6, 265ci, with a T4 flange.
We're considering 1 5/8. primaries collected for cylinders 1,2,3 and 4,5,6 [firing order 1,5,2,3,6,4], merged into two 2 1/4, then into the T4- do these sizes seem appropriate?
Secondly, the housing is a twin scroll- should I keep the two 2 1/4 pipes separate into the turbine [rather than collecting them as they enter]?
The turbo will feed a positive displacement blower first, which will then feed the engine. The hp target, depending on block strength, thermal management, and tuning, is 2.2hp/ci.
Cheers
Paul


Panic,

Yes, I understand that each individual exhaust pulse is more like an oblonged sine wave. I also understand that each pulse will affect the pulses in front of and behind it and a huge chain reaction occurs until steady state conditions are reached (steady state never really happens though). Therefore, I'd think (not stating as fact) you could graph each wave take the sum of the pulses at time = xj and get a very rough shape.

Paul,

Ignoring the information provided by Panic ( no offense Panic) and going through the other examples provided in this thread, It looks like you're going larger than needed:

I'm assuming 225* exhaust duration @ 0.050".

(3 cylinders) * (225* duration) = 775*

(775) / (720*) = 1.076

(1.625" primaries) * (1.076) = 1.75" collectors

As Panic said, this is a very simplistic view and ignores a lot of the dynamics involved. It does make sense in my head though . Also, if your turbo has a divided housing, you'd benefit by evenly spacing the exhaust pulses into each half of the T4 flange. I've dealt with the 2.3 turbo'd engines quite a bit and know this makes a noticeable difference in spool time.

Guys, thanks for all your help and input!

Have a good day!
Michael
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blown265
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Posted: Thu Nov 15, 2007 2:29 am Post subject:

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Quote:
(3 cylinders) * (225* duration) = 775*

By the numbers I get 675 degrees [3 x 225], and applying that:
675 / 720 x 1.625 = 1.52 inch collectors per 'bank'. Seems way small to support 2+hp/ci? Your thoughts?
Cheers
Paul

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96Mustang460cid
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Posted: Thu Nov 15, 2007 8:40 am Post subject:

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blown265 wrote:
Quote:
(3 cylinders) * (225* duration) = 775*

By the numbers I get 675 degrees [3 x 225], and applying that:
675 / 720 x 1.625 = 1.52 inch collectors per 'bank'. Seems way small to support 2+hp/ci? Your thoughts?
Cheers
Paul


Oops, that's what I get when I don't use a calculator . Turbo's work much differently than N/A. Remember that a tuubo engine's exhaust is also pressurized (more than the intake). Therefore, it's much more dense.

Have a good day!
Michael
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blown265
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Posted: Thu Nov 15, 2007 7:46 pm Post subject:

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I agree that NA collectors will be larger than those feeding a turbine, but my current Pipemax spec collectors [fed by three cylinders and supporting 1.5hp/ci] are 2.5 inch each- an inch larger in diameter than what the above formula suggests, and I'm now chasing more hp.
I understand the need to keep velocities high and energy within the system, but maybe the formula used earlier is too simplistic. I certainly don't want more pressure in the exhaust than the inlet manifold, and am happy to sacrifice turbo response [via pipe size] for a clean cylinder blown down on overlap. The response on this turbo wont be early anyway as the rear a/r is 1.32.
The cam I'm using is the current blower spec item, 236/246 @ 50 on 113 lsa, so there is overlap with this stick, and I don't want the exhaust going the wrong way.
I feel [and I'm likely wrong] that such a small collector will be a restriction- in this case a pipe size smaller than my primaries/exhaust port. I'm biasing this turbo setup for a later boost threshold, so I guess I'm worried that too small a pipe size will compromise the rest of the setup.
Is my thinking flawed?
Cheers
Paul

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Old 12-28-08, 11:16PM   #3
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96Mustang460cid
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Posted: Thu Nov 15, 2007 9:36 pm Post subject:

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Post deleted due to misplaced logic.
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Dynoroom
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Posted: Thu Nov 15, 2007 11:48 pm Post subject:

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96Mustang460cid wrote:
blown265 wrote:
I certainly don't want more pressure in the exhaust than the inlet manifold, and am happy to sacrifice turbo response [via pipe size] for a clean cylinder blown down on overlap.


Paul,

You don't have a choice about this. That's how a turbo works -- i.e. a pressure ratio of 2.0 means your exhaust has twice as much pressure as your intake tract. By minimizing your cam's overlap, you can minimize any reversion/flowback into the cylinder.

Let us 'ass'ume we have a 2.0 pressure ratio and are running 14.7 psig (29.4 psia) boost. This means the exhaust system (up to the turbo) has 29.4 psig (44.1 psia) pressure.

Density = (absolute pressure) / (gas constant * absolute temperature)

Gas contant = constant
Temperature = constant (not exactly, but close enough)

Therefore, Density is directly proportional to pressure. If the exhaust pressure is three times that of atmospheric pressure (29.4 psig or 44.1 psia), the exhaust gases will also be three times more dense. With that being the case, your 1.52" exhaust is equivalent to 2.63"

3.14*.25*1.52^2 = 1.81 in^2

Above, I concluded that your exhaust is three times more dense ---->

1.81 *3 = 5.44 in^2

(5.44/(.25*3.14))^(0.5) = 2.63"

All of these calculations also assume the exhaust is an ideal gas (which it's not).

So, Paul, this is how it works in my head. That's why guys can make so much hp using such small exhaust systems. I'm not saying I'm right...(though I think I am)...I do invite people to dispute my reasoning .

Have a good day!
Michael

Edit: Paul, one more thing regarding cam overlap. Though people disagree, I am finding that many 'smart' people recommend less than 3* overlap @ 0.050". Some even have negative overlap -- i.e. -0.5*, ect.

Have a good day! #2
Michael


Hi Michael,
I'm not going to disagree with your ideas but I will add a different twist for others to think about.

1st I know what you mean when you talk about pressure ratio but you are using the term incorrectly. Not a slam just clarification. Pressure ratio in used with the turbocharger compressor map. The pressure ratio is the ratio of inlet pressure + boost pressure divided by inlet pressure. Example is 14.7 inlet + 18 lbs boost / 14.7 = 2.22 pressure ratio.

When back pressure goes past or higher than boost pressure we call it "crossover" less exhaust pressure than boost = positive crossover and goes to negative crossover when the backpressure goes higher than boost. This is the beginning of the end of the hp battle. As backpressure continues to climb hp output will start to level out generally speaking. I look at turbo systems in terms of output. If a guy wants 800 hp out of a 355" v-8 it's really no big deal what type of exhaust system you run as long as the turbo(s) (say T-04's) required to make the power are used. Now if you want to make 1400 + hp with the same engine you need different turbos (IMO) but the mass air flow increases so the exhaust system can now become a problem. The very high output turbo system in simple terms needs room in the exhaust system to allow the engine to move the air through it. Yes I use some formulas to design turbo exhaust systems but I'm not locked into "tuned" exhaust due to backpressure. I've made well over 1700 hp with "log type" systems.
As for pulse tuning, unless you have a flat crank v-8 or a inline 6 or 4 & run under 6000 rpm don't waste your time, JMHO.

As far as camshaft overlap goes it was a huge problem in the past when we ran constant flow fuel injection. Today with EFI I donít design my cams worrying about overlap. Cams are chosen with considerations to the type of use, hp wanted, etc. Turbo cams are like cylinder heads in that what works to make a normally aspirated engine run better will also help a boosted engine run better. Many of my cams have over 20 degrees of overlap @ .050.

Many of these ideas are in fact running in engines Iíve built and are racing & setting records. In this world people are always coming up with ways to build a better mouse trap, these examples above only show some of what I think Iíve learned in 25 years of building high output turbocharged engines. Your mileage my varyÖ.
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blown265
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Posted: Fri Nov 16, 2007 12:21 am Post subject:

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Quote:
a pressure ratio of 2.0 means your exhaust has twice as much pressure as your intake tract

I've usually used the term 'pressure ratio' in reference to boost in the intake, not as a relationship between intake and exhaust pressures. Most compressor maps use this definition as well. Working in absolute pressures, the pressure ratio of the inlet is:
boost + atmospheric / atmospheric,
so with, say, 20psi from the compressor, the pressure ratio of the inlet becomes
20 + 14.7 / 14.7 = 2.36.
This 2.36 figure is only a reference to conditions in the intake, not necessarily a measure of the backpressure pre-turbine. I dont believe there is a set relationship between the pressure in the inlet and that in the exhaust [ie 20psi of inlet boost will result in x pressure in the exhaust], but rather exhaust pressure is determined by the turbine/ exhaust pipe size/ cam /hp /etc.
Perhaps we're just using the term 'pressure ratio' to explain different things- my point/aim is to have as little pressure before the turbo as possible.
Regards
Paul

EDIT Mr LeFevers beat me to it and explained it much better as well. Thank you sir.

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blown265
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Posted: Fri Nov 16, 2007 12:47 am Post subject:

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Quote:
As for pulse tuning, unless you have a flat crank v-8 or a inline 6 or 4 & run under 6000 rpm don't waste your time, JMHO.

Mr LeFevers,
We have an inline six and a conservative redline. Could you expand on the pulse tuning mentioned [and how to achieve it]?
Cheers
Paul

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blown265
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Posted: Sun Nov 18, 2007 8:12 pm Post subject:

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The mention earlier of a tuned turbo system has me thinking further about our design.
It was advised in this thread to keep the tubing small and short, so a traditionally long primary tube and large collector [as per Pipemax NA specs] may not be ideal.
Pipemax does however, give a tuned 'shorty header' option, and for our combo it suggests a 15-18 inch primary [merged 3 into 1] and an 8 inch collector [x 2 into the turbine]. Diameters will be 1 5/8 and 2 1/4.
These lengths are workable for the engine bay we have, and while it may be a little more effort, is possible to build.
Any thoughts on whether this will be better/worse/ same for hp/ boost threshold/ etc ?
Thanks
Paul

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Warpspeed
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Posted: Sun Nov 18, 2007 8:48 pm Post subject:

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Just remember that conventional tuned headers/collectors are usually open to atmosphere at the far end, and it is the sudden large pressure drop at the open end that creates the negative return wave that is "tuned".

Turbo pipes operate into a turbo housing that is going to be relatively restrictive. Any return wave will therefore be positive, because what the primary pipes are feeding into looks more like a closed end than an open end at the turbo.

Forget conventional header tuning theory with a turbo. It does not work and is just not appropriate.

There is only one reason to run individual pipes right to a turbo, and that is to help prevent reversion where there are many cylinders with considerably overlapping exhaust pulses.

When an exhaust valve first opens, the flow is somewhat explosive in nature. If that port is closely coupled to another adjacent port, where the exhaust valve is at the very last stage of closing, you do not want to blast hot exhaust gas right into the second cylinder during valve overlap.

By running individual pipes right to the turbo, each pulse has to travel right to the turbo, then back along another runner to reach the vulnerable cylinder. By making the primary pipes long enough, interference can be reduced down to much lower Rpm. This can improve mid range torque and turbo response where long duration exhaust cams are used, and more than one exhaust valve is open simultaneously.

All this has nothing at all to do with conventional header tuning theory, where a negative reflected exhaust pulse is used to improve cylinder scavenging. It would be difficult to imagine a reflected pulse from a turbo header tube powerful enough to overcome say 30 psi of static turbine inlet pressure. But a couple of psi of exhaust depression during valve overlap on a normally aspirated engine can be well worth having.
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Dynoroom
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Posted: Sun Nov 18, 2007 9:32 pm Post subject:

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Mr LeFevers,
We have an inline six and a conservative redline. Could you expand on the pulse tuning mentioned [and how to achieve it]?
Cheers
Paul

Hi Paul,
My dad is Mr. LeFevers, I'm Mike.
What are you running for a red line?
What hp are you tring to make?
What do you want from your engine, what type of work/racing do you want it to do?
Pulse tunning requires a divided turbine housing, do you have one or is do they make one for your turbo?
Pulse tunning will not make more power, as a matter of fact it can hurt peak power sometimes but it CAN spool the turbine sooner in some applications. Lets find out what you really want to do.
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blow-thru
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Posted: Mon Nov 19, 2007 7:55 am Post subject:

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I've always had a problem with people who are not concerned with ecessively high exhaust back pressures on turbo engine for many many years.
This is not to single out anyone in particular as they have there own ideas and obviously work but I can not see the benefit of a higher pressure in the exhaust than in the inlet tract ....
I personally would try to reduce the backpressure to an absolute minimum...
Are turbo exhausts possibly one of those trade offs where which one is the lesser of two evils ???? or as was previously mentioned are satisfactury to a particular level say X hp then they become more scientific when you are pushing the limits of turbo sizing/engine limits etc ????
Dynoroom also reminded me of a little rule that I picked up and that is to build a turbo engine much like an N/A engine, as efficient as possible and then add the turbo ....
Cheers Carl...

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Posted: Mon Nov 19, 2007 7:34 pm Post subject:

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blow-thru wrote:
I've always had a problem with people who are not concerned with ecessively high exhaust back pressures on turbo engine for many many years.
Me too... The first thing to do with a new setup is to try to find the specs that you need to have the lowest backpressure possible...
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Posted: Mon Nov 19, 2007 7:45 pm Post subject:

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It fascinates me when you ask a hard core turbo freak how much boost his engine is running, he puffs out his chest and will tell you to within 1/10 of a psi. He may even have a very large boost gauge permanently installed right in front of his face, which he constantly watches while driving.

Ask the same guy what his total exhaust back pressure is, and he will probably go, "Huh??" and roll his eyes, What is that ???? I have never measured it. Hehehehehe..
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Unkl Ian
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Posted: Mon Nov 19, 2007 9:29 pm Post subject:

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And the same guy will tell you it takes "no power" to drive a turbo.

Some will even tell you that turbos don't create any back pressure.



But for some reason,the headers glow red.....




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Posted: Mon Nov 19, 2007 11:37 pm Post subject:

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One look at our data logger will explain the Red header Scared the crap out of me when we started to log EGT's years ago. I've used a guide of about 5psi backpressure over boost (30 to 40 in our case)as the point of diminishing returns (power) for our stuff, and it seems to work out. Look at the EGT's once you go over 5psid.
"All this has nothing at all to do with conventional header tuning theory, where a negative reflected exhaust pulse is used to improve cylinder scavenging. It would be difficult to imagine a reflected pulse from a turbo header tube powerful enough to overcome say 30 psi of static turbine inlet pressure. "
While I would think the gains of a true tuned header may be diminished at boost, I still think there should be some gains. The way I look at it, the reflective wave is not trying to overcome the 30psi, it is merely traveling with in it, or superimposed on top of it. Wouldn't traveling within an elevated pressure atmosphere would be more conducive to transmitting the sound and pressure pulses? Amplified if you will. I think that conventional header theory should be modified for turbo applications not disregarded. Yes they will run great without header tuning, but if there are possible gains to be had, and packaging doesn't require throwing theory out the window, why not try?
"But a couple of psi of exhaust depression during valve overlap on a normally aspirated engine can be well worth having"
Agreed, but in a turbo application, if the pressure at overlap can be depressed a couple of psi from whatever elevated pressure it's at, I could see potential gains. Could it also somewhat alter what the motor would like for lobe center on the cam / cams? Because of the greatly elevated EGT's and the increased backpressure, the speed of sound in that environment is increased, resulting in a different tuned length for the primary. I'm sure that's something that could be calculated by a brainiac like Mr Meaux. I'm not saying this is the way it is, just my opinion.

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Posted: Tue Nov 20, 2007 8:27 am Post subject:

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This is how I now design turbo manifolds now: two tuned lengths are used.
1. From valve to collector - tuned as normal.
2. from valve to a couple of inches into the turbine housing - tuned as a two-stroke engine exhaust.
Lengths are selected to have two pressure waves. One a negative, scavaging wave from 1 arriving at overlap. The other, a positive wave from 2 arriving just after EVC point.
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vincer77
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Posted: Tue Nov 20, 2007 1:26 pm Post subject: Crucified Cranks

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96Mustang460cid wrote:
Guys,

Does the following example demonstrate the correlation between the camshaft's exhaust duration (@ 0.050") and exhaust diameter:

225* (exhaust duration @ 0.050") x 4 cylinders = 900* ---> 900 (total exhaust flow duration per bank) divided by 720 (duration per cycle) = 900/720 = 1.25. Now, multiply my 1.75" primaries by the calculated 1.25 ---> 1.75 * 1.25 = 2.125" ----> ~2.25". The slightly larger size will help reduce frictional losses.




This is an interesting methodology. Setting aside for a moment the fact that this is a turbo (I for one do not want to discount Mike Lefevers experience) , there is one more thing to consider. Since this is a "crucified" crankshaft motor, the outlet size calculated is too small for NA motor in my experience, as two cylinders fire sequentially or 90 degrees apart and leads to a "crowded" condition in the collector. 90 degree V8s typically need larger collectors than flat crank V-8s or 4 cylinder engines. Also, you should be working with the areas of pipes, not the diameters.

So, following this logic, and to be on the safe side, assume that you will need the equivalent of two pipe areas to handle the 90 degree firing impulse. Therfore, D = sqrt(2 * (1.75^2)) = 2.47". This is closer to what we find works for an NA engine. The actual sizing will vary with other considerations such as cam timing valve sizing, lift etc...

Vince
Burns Stainless LLC

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96Mustang460cid
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Posted: Tue Nov 20, 2007 1:50 pm Post subject: Re: Crucified Cranks

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vincer77 wrote:
So, following this logic, and to be on the safe side, assume that you will need the equivalent of two pipe areas to handle the 90 degree firing impulse. Therfore, D = sqrt(2 * (1.75^2)) = 2.47". This is closer to what we find works for an NA engine. The actual sizing will vary with other considerations such as cam timing valve sizing, lift etc...

Vince
Burns Stainless LLC


Vince,

I'm not following your mathematics there. How do you come up with, "two pipe areas?"

D = sqrt(2 * (1.75^2)) = 2.47"

Does the (2) represent the doubled pipe size? Does the (1.75) represent the primary size?

Can you further explain it please.

Have a good day!
Michael
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Old 12-28-08, 11:17PM   #4
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Turbo exhaust sizing: primary vs collector vs merge vs turbo
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vincer77
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Posted: Tue Nov 20, 2007 2:17 pm Post subject: Re: Crucified Cranks

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96Mustang460cid wrote:
vincer77 wrote:
So, following this logic, and to be on the safe side, assume that you will need the equivalent of two pipe areas to handle the 90 degree firing impulse. Therfore, D = sqrt(2 * (1.75^2)) = 2.47". This is closer to what we find works for an NA engine. The actual sizing will vary with other considerations such as cam timing valve sizing, lift etc...

Vince
Burns Stainless LLC


Vince,

I'm not following your mathematics there. How do you come up with, "two pipe areas?"

D = sqrt(2 * (1.75^2)) = 2.47"

Does the (2) represent the doubled pipe size? Does the (1.75) represent the primary size?

Can you further explain it please.




Sorry for not being clearer - as my professors would sometimes say "obvious to the most casual observer....

I am saying that since the 90 degree crank motor has two cylinders firing 90 degrees apart, that a simple approximation is to assume that a pipe equivalent to two primary pipes is needed to adequately flow during this event. Actually it would be smaller, but as we are discussing a fairly simplistic model, it should suffice for now.

The area of the primary tube is given by Ap = 1/4*pi*dp^2. where dp is the diameter of the primary tube. The area of the collector tube is given by Ac = 1/4*pi*dc^2. Further,

Ac = 2 Ap , 0r,

2*1/4*pi*dp^2 = 1/4*pi*dc^2

solving for dc,

dc = sqrt(2*dp^2)

or,

dc = sqrt (2*1.75^2) = 2.47"

hope this helps.

Vince

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96Mustang460cid
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Posted: Tue Nov 20, 2007 2:41 pm Post subject: Re: Crucified Cranks

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vincer77 wrote:


Sorry for not being clearer - as my professors would sometimes say "obvious to the most casual observer....

I am saying that since the 90 degree crank motor has two cylinders firing 90 degrees apart, that a simple approximation is to assume that a pipe equivalent to two primary pipes is needed to adequately flow during this event. Actually it would be smaller, but as we are discussing a fairly simplistic model, it should suffice for now.


Vince,

Thanks for the clarification!

Firstly, I'd like to say that I'm simply discussing the matter and am not trying to start arguments . With that said...

In looking at the firing order of a 460 bbf, 1 5 4 2 6 3 7 8, the 90* firing occurs twice, one time on each bank of cylinders (4/2 & 7/. Even if we assume everything fires at 90*, it is certainly not steady state flow within this entire time frame.


1) Valve opens with high cylinder pressure
2) High pressure escapes due to pressure differential
3) At this same time, the piston accelerates upwards and mechanically forces exhaust gases out of the cylinder.
4) At 90* crank position (non-linear piston velocity vs. crank angle), the piston begins to slow down ---> less exhaust velocity out of head (excluding the valve area).


So, Vince (or others), with this being the case, can we safely assume the flow area needs to be doubled? Something else not accounted for at this point is the temperature/density gradient. The exhaust gases will be cooling off and become more dense (negating the need for more flow area).

As stated earlier, I'm not trying to argue...I'm just enjoying the discussion and trying to get a thorough understanding.

Have a good day!
Michael
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vincer77
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Posted: Tue Nov 20, 2007 7:00 pm Post subject: Re: Crucified Cranks

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[quote="96Mustang460cid"]vincer77 wrote:


Firstly, I'd like to say that I'm simply discussing the matter and am not trying to start arguments . With that said...

In looking at the firing order of a 460 bbf, 1 5 4 2 6 3 7 8, the 90* firing occurs twice, one time on each bank of cylinders (4/2 & 7/. Even if we assume everything fires at 90*, it is certainly not steady state flow within this entire time frame.

So, Vince (or others), with this being the case, can we safely assume the flow area needs to be doubled? Something else not accounted for at this point is the temperature/density gradient. The exhaust gases will be cooling off and become more dense (negating the need for more flow area).

As stated earlier, I'm not trying to argue...I'm just enjoying the discussion and trying to get a thorough understanding.

Have a good day!
Michael


In our experience, yes, and there is nothing steady state in an IC engine.

If you take a look at good 4 cylinder headers and at 90 degree V8 headers with merge collectors, you will note that 4cylinder collectors are usually smaller than V8 collectors. We have proven this to ourselves on the dyno as well. Flat crank motors, or 180 degree headers (think GT40) can also run smaller collectors.

We have hypothesized that the reason for this is the "crowded' condition in the collector, and though it does not seem obvious that you would need double the flow area, it seems to warrant it in practice. Yes, this only occurs for part of the cycle, but the collector needs to be capable of handling this event, even though it is too large for the balance of the cycle. You cannot use cycle averages here. When I looked at the model described by Warpspeed and you, and put my assumptions on, it came close to predicting the correct collector size for a racing V-8 running 1-3/4" primaries. So, at least for this excercise, the hypothesis fit the data.

As far as the temperature gradients, yes, the gases are cooling and are becoming denser, but that does not necessarily mean we need less flow area. Exhaust gas flow is compressible flow, not incompressible flow. It's behavior is not intuitive. In incompressible flow, such as water flow, it is possible to have a large pipe flowing into a small pipe. Assuming that the flowrate is the same, the velocity in the small pipe will be greater than in the large pipe, because the distance between molecules is the same, they have to move faster. So, other than a bit more pressure drop, the molecules are happy moving down the pipe.

In compressible flow, the distance between the molecules can change - it's compressible. A good example of this is a southern california freeway. If you try to merge 4 lanes into 3 lanes after Caltrans closes a lane what happens? the cars slow down, they get closer together and the flowrate usually decreases. Maybe we can call it a traffic shock wave.

Anyway, these are some concepts to think about.

Cheers,
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blown265
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Posted: Thu Nov 22, 2007 3:32 am Post subject:

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Quote:
But for some reason,the headers glow red.....

While we may have elevated pressure and heat levels [over NA] in the preturbine exhaust, I'd like to minimize the above effect [and its' side effects] by reducing these pressures as much as possible without compromising the turbos' function.
As mentioned earlier, if we're able to build two systems, one potentially better than the other, then the decision is made.
Quote:
What are you running for a red line?
What hp are you tring to make?
What do you want from your engine, what type of work/racing do you want it to do?
Pulse tunning requires a divided turbine housing, do you have one or is do they make one for your turbo?

G'Day Mike
The engine is a 60's designed 265ci I6 street/strip effort with a max redline of 6500 running on LPG [propane]. The engine is currently making 1.5hp/ci with a small roots blower- the new turbo aim is 2.2+hp/ci. We have a GT40 size 'hybrid' with a 1.32 a/r split rear housing. On the cold side, according to its' compressor map, I need run it at a PR of around 2.2 to realize the mass flow required for our hp/engine size/thermal efficeincy. I'd like to achieve this with as little inlet boost/ turbine pressure/ heat/ etc as possible, and I believe a 'good' turbo manifold will go a long way towards this. What constitutes 'good'? Pipe size? Rear a/r ? Your thoughts?
Thanks to all those who have shared their tuning methods in this thread, as this style of quality information is rarely available in turbo circles.
Cheers
Paul

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Posted: Thu Nov 22, 2007 4:17 am Post subject:

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My advice would be to leave the roots blower where it is, and just add the turbo to it as well. Let the turbo increase the airflow and boost pressure up to your new requirement, while the roots blowers contribution will ensure that boost pressure always exceeds turbine inlet pressure.

Twincharging is extremely effective in so many ways.
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blown265
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Posted: Thu Nov 22, 2007 4:48 pm Post subject:

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Quote:
My advice would be to leave the roots blower where it is, and just add the turbo to it as well.

G'Day Tony
That's what we are doing. In fact a discussion with yourself a while ago about the concept put the wheels in motion. Thanks!
Since that conversation, we've built a new car for the engine and have acquired the turbo and associated hardware. All we need now is to build the manifold.
I recall part of that thread dealt with the importance of keeping the turbine pressures as low as possible [hence the large rear a/r on our turbo], so you can see why I'm interested in a good design with respect to pipe size and potentially a tuned length as well.
Cheers
Paul

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Old 12-31-08, 06:41PM   #5
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Did anyone read this yet??
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Old 01-01-09, 01:59AM   #6
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I read it, its a very good thread! I never could understand how log manifolds could work as well as they do with a turbo. This thread provides some answers that I have been looking for. Exhaust can get very complicated when you try to compare n/a to boost requirements. I had many people tell me my stock manifolds wouldnt work well, they ended up working fine and I didnt have to change a single leaky header gasket all summer.

Mike.
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Old 01-01-09, 10:04AM   #7
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I found that looking for something else. It followed the same line of thinking of people here. There is the added element of guys who built more radical stuff in that thread and gives the readers here an idea of size/length and other variables to look at. Not to mention, where a "line" is drawn to where a more killer system is needed to HP levels that guys are shooting for.
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Old 01-01-09, 04:04PM   #8
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didnt read it yet been out plowing alot of snow lately Have read the replys though and cant wait to get caught up on some reading and researching.
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Old 01-08-09, 02:10AM   #9
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Here is a good exhaust thread going at ttf.......

http://www.theturboforums.com/smf/in...topic=121489.0
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