I have been thinking about turbo's for a little bit,
and started to think of a few things,
but...
I don't know if my logic is correct, which it may be very wrong, but I would like to learn a little.
the way I think it is(yes, a little long and with really bad pictures),
is that the exhaust velocity is somewhat important, more so than just volume,
so, if you were to keep the volume the same but increase the velocity by making the exhaust manifold(at least the part to the turbo) narrower, you could increase the velocity and in theory have the turbo spool sooner than if the volume was the same but velocity was slower.
kinda like blowing through a thin straw(we will say .5 of an inch) at a pinwheel vs. a larger straw(one inch),
the smaller straw would make the pinwheel spin faster, right?
so, could this be applied to turbo's as well?
my idea,
would it make improvements to have a manifold that was split in 2 after the 4 runners(if that is what it is called) connect,
one with a valve on it that would be closed at lower rpm(or boost levels, whichever way would be most useful),this would force the exhaust through one side of the exhaust to increase exhaust velocity, in order to have the turbo see a faster Flow of exhaust gas and spool sooner than if the flow was slower through a larger pipe.
once the rpm's or boost was higher the valve could open and allow the exhaust to flow evenly(or close too), thought each pipe increasing the size of the manifold so that the gases could then move through the turbo without having too high of back pressure going into the turbo.
a very bad picture of what I mean, well kinda
the black arrows show exhaust flow at lower pressures/rpm/boost
the red shows higher pressure/rpm/boost
^^^^^^^^^ I really suck at using ms Paint
I think my whole idea is to decrease the boost lag(which I know can be very much reduced with a proper sized turbo and what not)
but would it even work?
does it make any sense at all, or do I have my turbo info all messed up
keep in mind it is late and I have never worked with turbo's before.
I do have the basic principals behind them, I just don't know specific things about turbo's
any thought would be great and I was just trying to see if this is a plausible idea, or if my theory is somewhat correct.
Cheers
Steve
seems like a decent idea, however there is so many problems to overcome in this situation... one would be room for such a manifold to be placed. second would be finding a valve that can operate under such high temperatures.... with inside manifold EGT's reaching over 1200 degrees it would difficult to find a valve that would handle such heat and not leak. Last, i feel a setup like this would cause a lot of turbulence inside the manifold, mostly under the low pressure situation where exhaust could have a chance to vortex back up into the high pressure side before its open and it seems it would add more volume to the manifold. It would probably need two valves one on each side of the high pressure side that would both open at the same time. This would a good idea to concept and test out.
is my thinking about exhaust velocity and volume somewhat correct?
and yes I do think that there would be some very big issues and kinks to consider, but I figured it could somehow work.
the other thing that I was thinking about is what would happen to boost levels when the second pipe was opened up, it would likely cause a drop in velocity and boost would drop, but it could be quick enough that it may not make a huge deal.
I am well aware that this is a very "what if" kind of idea, but it is fun to think about things like this.
I kinda got the idea from an rx7 with the secondaries that for reasons I am not thinking about right now, make the engine work better and have more power.
(I have the book somewhere, I just haven't looked at it in a while)
I'm sorry but just.. no.
if you want better spool, get a twin scroll manifold and a turbocharger equipped with a twin scroll exhaust housing, OR size your turbo properly.
It's a semi sound concept but chances are it would fail in execution, not t mention trying to cram all that behind the engine. My equal length manifold barely fits and it has no fancy valve thingy. The other thing you need to keep in mind is back pressure. The turbo and header is a big restriction, this causes back pressure. On one of the diesel trucks this pressure can actually get high enough to open the exhaust valve .... took guys a long time to figure out why they couldn't crack 750whp.
Honestly to eliminate lag there are easier ways.
1. Electronic boost controllers
2. Lighter turbine wheels
3. Better compressor housing
4. Antilag system
5. Ballbearing turbos
And so on.
these are things that I just didn't know and want to learn.
I have never worked with turbo's before so it is something new that I was thinking about.
I had never heard of a twin scroll manifold and turbo before, which I think is kinda what I was thinking about, just with a better result and design, didn't think about 2 separate scrolls on the turbine housing.
thanks for giving reasons on why it would not work well,
the way I see it,
every idea has a chance of being good, otherwise there would never be anything new in the world, right!
it's all a matter of finding new ways to do things to get better results, with some ideas just not working very well.
hell, think about the basic idea of a car engine right, and hybrid cars, they were all an idea at one time, with many failings along the way.
not that I am saying that my idea is good, just that it is an idea, that could be good.
cheers
steve
I'm all for innovation, but usually one learns about the subject at hand before trying to think of a way to improve on it.
turbochargers have been relatively unchanged since they were first invented and patented in the early 1900s
Steve, the honest science based answer is no. The turbo lag is not a function of velocity at all, only mass rate. You have to look at the exhaust turbine housing as a restriction to flow....a FIXED restrictor to flow at that. A turbo wont "spool" until the restriction condition is meet. Meaning until the "rate of mass" the engine is trying to push through the restriction is greater than what the restriction will allow without build-up of back pressure.
Velocity alone WILL NOT build back pressure, only a rate of mass will build back-pressure. What is a rate of mass?
Mass rate = Weight/Time or Mass/Time
So you see with the units of weight per second the "velocity" of the gases toward the turbo will make ZERO difference at all. Its all about MASS/TIME.
Example: A garden hose with a slightly smaller outlet on the end than the hose itself, turn the hose on just a little bit...the hose and hose end isn't even full of water but is flowing out freely...."rate of mass" condition isn't meet. Turn the hose on progressively higher , the hose end will eventually fill with the water column at the end(start to spool at the point of 100% water column at the end) and will start to generate back-pressure as the hose is further increased with flow.
The ONLY way to change a spool time of a turbo is to change the A/R of the housing. Which will do what? -change the restriction....which will do what? -change the amount of MASS required to start generating back-pressure on the restriction. ie: put a smaller end on the hose to achieve the 100% water column earlier or vise-versa.
Sorry to get all whopty whopty yada yada on it. But I hope that clears up a lot of misconceptions to how a turbo works. Its all about mass flow rate...thats it. Velocity doesn't make a $hit'n difference.
Edited 4 time(s). Last edited Wednesday, November 19, 2008 3:38 PM
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thanks Josh, that does clear it up alot, that is the kind of answers that I like, full of info that explain things.
I have to admit, it was late and it made sense at the time, but now that I think about it, with all the info you guys have given, I am maybe, kinda starting to think that I may have been not so right about it.
ok, so very wrong about it,
but I am learning,
I really need to do some more research on turbo's, not that I am going to turbo the car, I think I would like a supercharger for just a bit more power and still good reliability.
cheers
It helps alot to look at it different ways sometimes.
Another more technical way to look at it would be to look at the equation for mass rate:
Mass Rate = Mass/Time or Weight/Time or W/T
Mass Rate is calculated by the equation (Density)*(Area)*(Velocity):
If you let Ft = Length or L, Lbs = Weight or W, Seconds = Time or T
Density -> Lbs/Ft^3 or Weight/Volume or W/L*L*L
Area -> Ft^2 or L*L
Velocity -> Ft/Sec or L/T
If you put the equation together you get: Mass Rate = (W/L*L*L)*(L*L)*(L/T) <- this simplify's to W/T which follows what we already know so the equation works. Now lets look at the root equation of Mass Rate we got: Mass Rate = Density*Area*Velocity
Your thinking about modifying the AREA in order to increase velocity.....since both variables are to the same power when you decrease the area to increase the velocity you'll find the mass rate to stay the same. ie: Area = 3 and Velocity = 3 -> =9...now if you were to decrease the area to try and increase velocity you'll find Area = 2 and Velocity = 4.5 -> still equal to 9
Those are just BS numbers but you get my point. You can also see it another way if you were to multiply the raw dimensions of area and velocity together: (L*L)*(L/T) = L*L*L/T or L^3/T or Ft^3/Sec.
With the units of cubic feet per second you know that modifying the area of the pipe wont change the Ft^3/Sec (if you divide by 60 to get second into minutes, Ft^3/Min a.k.a. CFM ) since that is a measurement of the raw exhaust flow rate coming straight out of the motor.
Just another way to look at it.
Edited 1 time(s). Last edited Thursday, November 20, 2008 5:39 AM
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