with all the sweet new one off manifolds being made i figured id get a thread going so we'all can discuss things.

now i know each person has there own design, space requirements, and end goals. so no fighting about how "mines bigger then yours foo!", please remember that each member wants somthing different for their car. :P

now im lookign for most anything pertaining to theory, fabrication issues, tricks and designs.

so i guess ill start off with some questions to the pros out there and get this started off:

Materials
now if i have this right, one of the best materials to use would be Inconel because of its high-heat properties and low expansion. down side is cost and hard time to machine it as the heat from machining hardens it further. so towards that goal we could go with Titanium, but again that takes some know how to weld and is price prohibitive.
now we look at steel mixes. i know that SS looks pretty and all and can be made to look one of the best when polished, but it somewhat tricky to TiG as the back purging needed for it. and then there is mild steel which welds fairly easily but dosent look the greatest but is cheapest.

but how do the different materials compare to the "Inconel Grail"? for a light competition motor do i really need the expense adn trickyness of the exotics or even SS? can a nice manifold be done with just mild steel?

Design
i know exhaust pulse theory has a lot to do with how well a manifold delivers power and the efficency with which it does this.
but how much do we really loose in a street car by not having a true "equal length" set up? anybody have any possible number to throw out? granted trying to reproduce large test groups on a 2G budget is not likley but even some theory on this might help in the future designs that people may come up with.


i just threw some stuff to get started so feel free to discuss stuff on your own now :P and hopefully this sparks some nice discussion

I hope some others chime in... I've been waiting for this day, although I'm not quite ready for it yet I'll throw in what I have found so far. I've started a few threads in the past on the subject and have spent hours flooding my brain on the subject-about every spare moment I can find for the past couple of years- We refere to it as "the sickness" at my shop.


My thoughts


Material:

Keep in mind that this is mostly a matter of opinion, everybody has they're own.

It all depends on what you are trying to build, a low budget street car, or the ultimate race car. I feel that every material has its place. If your low on cash, use mild steel. It is easy to obtain, easy to work with, cheap to machine, and easy to weld. You can creat any shape your imagination desires if you take your time and use some creativity. If you want it to look nice and last a little longer you can always have it ceramic coated-wich will also hold heat and help the turbo. Stainless, although there are many grades, some better than others, is actually very similiar to mild steel. It of course just resists corosion a little better depending on the grade. Now if you are building that ultimate race car, money is not an option, and weight is a huge factor, then start looking to the exotics and the alloys. They have great characteristics, but come with a heafty price. Most street cars and average racers are usually content with stainless steel.







Ahh... Theory.... Thats exactly what it is, but there are a few things that remain constant. Thermal dynamics, laws of inertia, sound and its components, just to name a few. Intake and exhaust theory is deffinatly something I cannot ignore, no matter how hard I try. I do my own testing, under strictly controlled conditions, and literaly have piles of data laying every where I can leave it lay. The hardest part of it all? I chose to turn the boost down and use my eclipse as my Daily for the summer, so its often hard to steal the MS out of it to do the actual testing.



Here's what I have found so far:


Turbo manifolds, no matter how crazy they look, are still just what they are called. Some are more efficient than others -I.E. log to full length tubular- but serve the same purpose. What I have found, and have repeatable rusults to indicate, is that equal length is deffinatly better than a log. There are sound waves in action, along with individual columns of hot gas, that are very powerful but very fragile, and must be allowed to co-exhist but opperate independantly. If your lengths vary, you interupt the smooth natural flow of things, and they start to cancel eachother out. Most log manifolds work simply because there is volume of gas and velocity present, not the most efficient, but it works. Equal length gives seperation up until the last possible moment, and if the correct cylinders are joined; 1-4, 2-3 and then those two are joined after that, there is almost complete seperation. Allowing for the most efficient and powerful use of the actual sound pulses and their parts. Each part is generally known as: initial pulse, reflection, and rarfraction. Each is obviously how the heated air column is being affected by the changes in its vibration and pressure. These are all things that many have studied for many years, but taking this information from the N/A world into the F/I world is still a somewhat new thing. Take Garret turbos for example, the GT line have specially designed turbine's that are meant to harness this power. "Pulse tuned" is the big phrase everybody uses, But they are simply using N/A mathemaics with a turbo driven motor and seeing some results, but not always the most efficient. I have been working with alot of different mathematic formulas, and have narrowed down to a few. But they still are yet to be refined. Because naturally something that was mathematically correct for a super heated mass of air comming from a N/A engine, is not going to be correct for a PRESSURIZED mass of superheated air coming from a turbo driven engine. It's close, but not quite. And there are so many variable's to consider. Your actual maximum CFM, the shape of the port affects velocity, the cross sectional area of the port and the runner tubes, the length of the tubes of course, the angle of convergance, and these are only a few. They can be accuratly calculated, but then the choice of turbo and its characteristics will sway the actual results one way or the other. With out going into the actual functions of the particular above mentioned theory I'll simply leave some basics I have found to be "true" for now and give some others a chance to add to this.


If the individual sound pulse is properly aligned (by primary lenght) with the exhaust cam timing (opening and closing events), the primary tubes are properly sized for the actual flow rate of exhaust, and the collector used does not interfere with this process, then the amount of curves and the degree of measure will have little or no effect on the actual flow rate.


The amount of heat retained within the manifold directly and proportionatly effects the boost threashold and efficiency of a turbocharger.

The amount of backpressure within the manifold is usually between 2 and 3 times the amount of boost the turbocharger is producing-there are exceptions!

With my Morrison tester, I have recorded negative pressures at the exhaust port on a properly tuned manifold. Wich by most logic is impossible because the turbo is mostly a "cork" in the exhaust. But it is proof that the sound pulse has enough energy to still create a vaccum at the valve when it has opened for the exhaust event, and thus creates a scavenging effect identical to a N/A cam/header combo wich increases VE and in the end the power output of the engine.


With proper design, a manifold can cause a turbo to cross the boost threashold mmuch sooner than any log or basic equal length manifold ever will. If the pulses are utilised in such a way that they force the turbo to spool at a much lower RPM than otherwise possible, the Boost situation initiates the chain of events that uncontrolled will cause the motor to increase boost and eventually destroy itself. Basically, the small amount of poaitive pressure seen by the motor creates more power, wich creates more active exhaust, wich spools the turbo, wich makes more pressure, wich creates more power.... get My point.




I know some of this may be basic knowledge to a few of you, but unfortunatly its still an untapped resource in the world of F/I. And unfortunatly there's not enough people out there interested enough in this sort of thing to realy drive the subject. Especially with our platform.

good lord, i dont have time to read/think about this or respond right now. good info here tho. my gay ass thoughts to follow soon :) lol

I can't really tell you the right or wrong way to design a manifold, but I can tell you how I did it. I wanted to build a manifold that offered good low RPM power off boost, made efficient use of exhaust energy to spool the turbo quickly and linearly, and looked as cool as possible. This is for a daily driver, so proper cooling, power steering, and air conditioning had to be retained. I scoured the web and my old engineering textbooks for theory, practical design tips, and "formulas". I found plenty of the first two and not so much of the last one. I could not afford any flow simulation software that I was at all confident in. Any formulas that I found had a disturbing number of assumptions in them. It seemed impossible for an individual to design a manifold that would do exactly what they wanted. Eventually, I decided to take a little theory, a lot of practical design tips, a couple formuals, and some instict and see what I could make. I accepted that my manifold would likely not function exactly as designed, but would get close enough.

I decided to make a 4-2 long tube manifold feeding a twin-entry turbine housing. My first step was to design a head flange (in SolidWorks). I made the openings in the flange match the exhaust ports on my head. The inner surface of the port has a circumference of about 5.284 inches. That is essentially identical to the circumference of the inner surface of 1.5" nominal schedule 10 pipe. The ID of that pipe is 1.682 inches. A matching inner circumference lets me transition from the flattened oval port to the round runner as seamlessly as possible. Sharp steps or fast expansions cause my flow to lose energy. Yay! That determines my primary runner size. Now I can mis-use a formula that is marginally meaningful for normally aspirated headers and even less meaningful for turbo manifolds. Here we go.

Not yet.

Warning!

I am pulling these formulas from 2 year old notes, taken from sources I can't recall, and written over a series of months on scrap paper that seems to have been wetted repeatedly, crumpled, and is stained with what I hope is rust.

Optimum RPM = (A1 X 88200) / V

_A1 = flow area of primary runner
_A1 = (Pi X D1^2) / 4

__Pi = 3.1416...
__D1 = inner diameter of primary runner
__D1 = 1.682 in.

_A1 = (3.1416 X 1.682^2) / 4
_A1 = 2.222 sq. in.

_V = volume of one cylinder
_V = engine displacement divided by number of cylinders
_V = (121.8 cu. in.) / 4
_V = 30.45 cu. in.

Optimum RPM = (2.222 X 88200) / 30.45
Optimum RPM = ~6436

You may have noticed that the units don't make sense. 88200 comes from simplifying several formulas and will cancel out "inch" units used for the area and volume. Anyway, 6436 RPM seems reasonable as that is about where the stock engine hits peak horsepower. Now that we have chosen a primary runner diameter that is optimized for a reasonable RPM, we can determine the total length of one runner.

P = <((2.1 / D1)^2) X 19.97> - 3
P = total length of one runner

_D1 1.682 in.

P = <((2.1 / 1.682)^2) X 19.97> - 3
P = 28.1 in.

OK, I don't remember what the 2.1 number is. The 19.97 was the result of simplifying a couple other formulas and probably cancels out units. I think the 3 had something to do with flow length from the valve to the outlet of the exhaust port on the head (I probably winged that one). I end up with 28.1 inches of runner. A little long, but seems feasible. I believed that merging runners 1 to 4 and 2 to 3 would broaden the range of optimum efficiency, so I need to come up with a secondary runner diameter.

D2 = ((2 X D1^2)^0.5) X 0.93
D2 = inner diameter of secondary runner
D2 = ((2 X 1.682^2)^0.5) X 0.93
D2 = 2.21 in.

That formula essentially maintains flow area when merging two equal diameter pipes into one pipe and then multiplies it by the mysterious 0.93 scaler. I have already chosen to use common schedule 10 pipe, so I am limited in size choice. 2" nominal pipe has an inner diameter of 2.157 inches. Since I am expecting significant error with these formulas anyways, I use the 2" schedule 10 pipe.

Actual D2 = 2.157 in.

Now, where do I merge my primaries? A rule of thumb gave me a range and I chose 15 inches.

P1 = length of primary runner
P1 = 15 inches

How long are my secondaries?

P2 = length of secondary runner
P2 = P - P1
P2 = 13.1 inches

In summary, I decided to use 1.682 inch inner diameter primaries with length of 15 inches and 2.157 inch inner diameter secondaries with length of 13.1 inches.

Earlier, I chose to use common schedule 10 pipe. In the sizes I will use, it has a reasonably thick wall at 0.109 inches. That makes it fairly easy to weld and strong enough to stand up to high temperature abuse. I chose 304L stainless steel for its moderate corrosion resistance, reasonable price, and weldability. Elbows in standard and tight radii are readily available to give me some design flexibility.

All that is left is to design a manifold having the calculated dimensions that will fit in your engine bay. I reproduced common pipe components in SolidWorks. I included straights, standard radius elbows (22.5, 45, and 90 degree), tight radius elbows (22.5, 45, and 90 degree), and transitions in 1.5" and 2" schedule 10 pipe. Based on a rule of thumb, I chose all transitions to expand/reduce at a maximum angle of 10 degrees on each opposing side (assuming concentric expansion/reduction). The exhaust port to primary runner transition had a 10 degree angle on both sides. The eccentric transition from the secondary runner to turbine housing port had a 0 degree angle on one side and a 20 degree angle on the other side. I figure that is almost as good as 10 degrees on both sides. With a little trigonometry, you can calculate the length of each transition. The merge collector was designed with a similar rule of thumb. With all of the parts designed, I calculated the "flow length" of each. The flow length would be the distance a particle would travel from the inlet to the outlet the component, maintaining itself in the center of the flow area at all times. For flanges, pipes and transitions, the particle travels a linear path, so it is just the physical length of the component. For elbows, you take the bend radius (measured at centerline) and calculate the circumference of a circle having that radius. Then take the angle of the elbow (22.5, 45, 90 degrees) to define a sector of that circumference (360 degrees). Once you have all of the flow lengths, you can start to put the pieces together. The goal was to have all four primaries the exact same length and both secondaries the exact same length respectively. Suddenly, the engine bay is very small. I had to really snake some of those pipes around to get them to fit. Another rule of thumb is to avoid any elbows in your primaries until you have acheived 4 inches of flow length from the exhaust port. Finally, you would want the last few inches before the turbine inlet port to be as straight as possible, unless you knew which side to bias flow towards to acheive the most torque on the turbine shaft. Pictures of my intermediate results are here: http://forums.2gnt.com/dcboard.php?az=show_topic&forum=8&topic_id=101224&mesg_id=101224&listing_type=search

I say intermediate results because I have spent a year afterwards making coolant pipes, fitting various fans, fitting various A/C condensers, making a full diameter downpipe, adding V-band joints, revising turbo supports, and making heat sheilds. When I am "done", I'll make a follow-up post.

Corbin

'95 ESI-T
Now with more power and fewer leaks



Gimme fuel...Gimme fire...Gimme that which I desire

Corbin, are those formulas based on the 2nd wave? The primary length and distance before the merge seam shorter than usual, but I try to calculate for the third wave because my findings have shown that there is still positive pressure at the exhaust port any sooner than that. And also, where there any calculations involved for compensating for the difference in air density due to the increased temperatures? I only ask because like you say, there is no real "concrete" methods to this, and simply want to compare to my calculations and findings.

Mark,

My texts were pretty light in this area, so I followed a manifold designing guide pulled from an online magazine and compared it to some info from other forums (I can't find them for the life of me). That is why I used the disclamer:

"Now I can mis-use a formula that is marginally meaningful for normally aspirated headers and even less meaningful for turbo manifolds. Here we go.

Not yet.

Warning!

I am pulling these formulas from 2 year old notes, taken from sources I can't recall, and written over a series of months on scrap paper that seems to have been wetted repeatedly, crumpled, and is stained with what I hope is rust."

I would have loved to have seen the meat of the formulas where you can account for different assumptions and input your chosen data. I like to research and calculate (I often keep a couple text books/calculator/notes on the night-stand), so I was irritated that I could not do that. If you can recommend some texts, I would like to hear it. What I do know is that I am happy with the manifold. It provides enough off-boost power that I can accelerate with traffic in town and cruise through the mountains on the interstate without breaking 5 in. H20. When you apply more throttle, the boost comes up smoothly and linearly.

Corbin

'95 ESI-T
Now with more power and fewer leaks



Gimme fuel...Gimme fire...Gimme that which I desire

very enjoyable thread to read. u guyz r too smart 4 me