Water Injection Thread

[Greg Hermann]

>>
>> Header tuning is done to help scavenge the cylinder and ensure a clean fresh
>> charge.  Turbo charging does the same thing by increasing the pressure at
>> the intake side.  The turbine on the exhaust side represents a restriction.
>> If it didn't the turbine wouldn't turn!  As such, no tuning of the exhaust
>> is going to help move the gases through the pipes any faster or better.  You
>> could make the turbine less restrictive but this is tuning the turbo to
>> higher rpms with more lag time on the bottom end.
>
>totally wrong
>because turbo exhausts are operating under higher pressures
>they are even more responsive to exhaust tuning than NA cars
>properly designed headers befroe a turbo cna make massive power gains
>
>Clive

OK--time for my $.02!!

Clive is absolutely right. I am becoming convinced as time goes by that
tube volume is the essential factor in the design of ANY header--it appears
to me that it wants to be about 125--140% of individual cylinder
displacement. Larger diameter, and shorter for higher rev ranges, smaller
diameter and longer for lower rev ranges, but always in the stated volume
range. MAYBE slightly larger diameter for headers on a turbo, cuz the gas
in them is denser, and therefore suffers more friction loss in flowing
through a given tube size. Sound velocity in a gas (of a given molecular
weight) varies ONLY with temperature, so tubes for a turbo motor may also
want to be a bit LONGER, cuz they are HOTTER.

The tricky part with turbo headers is that any turbine, at a given mass
flow rate, will make the same power at a lower pressure ratio if the inlet
temp to it is HIGHER. And, since the outlet pressure of the turbine is
predetermined by the atmosphere and the exhaust system, lower inlet temps
to the turbo mean more back-pressure on the engine, and therefore less net
output at the same boost level. Therefore, to make turbo headers work
properly, and to really see HOW MUCH GOOD they REALLY do for an engine's
performance, you DAMN WELL HAVE TO insulate them--(we all know how much
heat tube headers throw off!!) And , if you are going to insulate the
exhaust on a turbo motor, it had damn well better either be cast out of
duriron (very high nickel cast iron) or fabricated properly (spelled TIG
welding done with a full internal argon purge) out of 321 and/or 347
stainless steel. (If you want it to last for any length of time.)

I do not think that any of us think that Hooker fabricates their headers at
this level of technology. (And I kinda doubt that they have anybody who
would have a clue where to start!) The fact that headers made the right way
out of 321 SS work, and with extremely high reliability, has been well
proven on huge radials by people like Curtiss-Wright and Pratt & Whitney.
If you do not have the resources to do it yourself, Burns Stainless, for
one, can do whatever you might want, the right way, in 321 SS, or is quite
happy to sell you the bits and pieces with which to do it yourself. BUT, it
AIN"T cheap, even just to purchase the materials!!!

Now for the more sophisticated stuff. First of all, any turbine runs more
efficiently with a STEADY inlet pressure. Any engine runs more efficiently
with tube headers--turboed or not. How to reconcile these two things?? It
is known as a pressure recovery accumulator. If you have room, (a mighty
big if) run the header tubes into a typical, properly sized
convergent-divergent collector, and THEN  run the megaphone from the
collector into an accumulator chamber which feeds the gas to the turbine,
at a fairly steady pressure. This pressure will also be distinctly higher
than the pressure which the engine "sees" at the throuat of the collector
(you are now converting the velocity energy in the exhaust gasses back into
static pressure with a reasonable degree of efficiency!)

The next place where there is a LOT of unexplored potential (and less need
for room to explore it) is at the outlet of the turbine. The gas comes out
of the turbine in a tight spiral at a velocity of about Mach .75 in most
cases. Most downpipe designs just dump it into a way bigger pipe, creating
a jump to lower velocity, turbulent flow, an extremely inefficient process.
There is a lot of room for creative thinking in fabricating a downpipe
transition piece which would convert some of this (very significant amount
of) velocity  energy in the gasses back into static pressure as the gas
enters the downpipe! Why would this help?? cuz the turbine would now "see"
a static pressure at its outlet which might even be below the atmospheric
pressure at the end  of the tailpipe!! And because , at given temperature
and mass flow conditions, turbines make power depending on the absolute
pressure ratio across them, you would get the same turbine power output
with less backpressure on the engine, and, therefore, more power for free.
YES, you would need a bigger turbine wheel and housing, cuz the DENSITY of
the gas flowing through the turbine would be lower at the now lower
pressures even though the mass flow would be the same.

Regards, Greg