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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.
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