Turbo header design

[Greg Hermann]

>WOW!  Thank you Greg!
>  Now, how do you accomplish the task of giving the exhaust gasses
>somewhere to go freely during the "blowdown" part of the exhaust stroke?

Well, err, the long enough tubes which are small enough in diameter, and
have ienough internal volume are what seem to do that. As long as the
pressure in the cylinder is about 1.8 (or more times) the pressure in the
port when the exhaust valve opens, the gas flow into the port will be at
Mach 1. There are plenty of folks who would argue with me, but I believe
that the reason that you need shorter, larger diameter tubes for higher rpm
ranges is cuz the speed of sound in the exhaust gas is still about the
same--same temp, remember--and you still need the same volume of tube to
exhaust into in less time.

What is the best header design to accomplish this for turbo charged
engines?  For NA engines?

I (again folks will argue) think that the tri-wye type design is best for
fours and eights, either turbo or NA. Three into one for sixes. Same type
of design for all. The difference is after the throat in the collector.

 Is there one technique that seems to be more effective than other
techniques?  Is it pipe width, or length or both?

I believe in matching the tube VOLUME to the cylinder displacement, as I
described. shorter fatter tubes for higher engine speeds cuz the gas does
not move down the tube any faster, even though the engine is turning
faster.

>  Also, what is "sonic energy"?  I know it refers to sound but I have
>never thought of sound as being part of exhaust energy.  How does sonic
>energy create a scavenging pulse?  Is it something you have to design into
>the header?  If so, what is the criteria for the design?  I guess what I
>am trying to ask, is, how do you look for this in a specific header
>design?  What tells you that the header design uses sonic energy
>effectively?  How does the tri-wyes header relate to the above?

All I really meant to try to get across was that if you get a higher
proportion of the exhaust gas moving inside the header tubes at Mach 1, you
will have more momentum energy to make productive use of . Four into one,
tri-wye and individual stacks all have their own proponents for different
applications. Most folks will say that individual stacks are plenty good
enough when an engine only is asked to work hard AT OR ABOVE its torque
peak rpm.  Witness dragsters. I think most folks would agree that tri-wyes
have the widest torque band. Some would claim that four into ones will make
better top end power than a tri-wye. My preference is for tri-wyes, with
360 degree separation between pulses into the primary pairs of tubes.

I probably developed my (admitted) prejudice cuz for several years I had an
Alfa which used the tri-wye header design, It was a daily driver which made
about 170 HP out of only 100 cubic inches . It made a mockery out of claims
that tri-wyes do not make any top end power, and although its cams were
such that there was not a lot of torque below about 4600 rpm,, it would
pull smoothly from about 1200 rpm if you floored it in fifth gear and asked
it to! This despite very large venturis in its Webers and 11.5:1
compression ratio.
>
Answering all of your questions in detail would likely take at least a
decade of thorough study, and a couple of books!!

You might try reading "Scientific Design of Exhaust & Intake Systems" by
Phillip H. Smith, ISBN # 0-8376-0309-9. Amazon.com has it. It presents a
good start on the subject.

But remember--although headers do offer many improvements to an engine's
performance, it is pretty costly to build them in a manner that will be
reliable for a long time. This is why most manufacturers do not use them,
and why really good headers cost mebbe ten (or more) times as much as speed
shop #@$% !!

If you ever get a chance to stop in Harlingen, Texas, take a close look of
some of the exhaust plumbing on the old war-birds in the Confederate Air
Force. They (most) all had recip engines which were carefully engineered,
by some damn good, talented engineers, to get every last ounce of power,
and as much fuel economy (for longer range and/or lighter tanks) reliably,
from as little weight as possible, with money no serious object. There are
some fascinating  lessons in exhaust plumbing techniques to be learned
there!!
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>>Regards, Greg
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