Re: Ram air?

[QSHIPQ@aol.com]

In a message dated 97-06-17 15:19:02 EDT, you write:

<< On Tue, 17 Jun 1997, DeWitt Harrison wrote:
 
 > absolute temperature are omitted. They do succeed in making a good
 > point, though. It is noted that any benefit from "ram air" intake
 > ducting comes from bringing cool air into the engine, not from
 > increased inlet pressure. They cite standard aftermarket air filters for
 THEN Graydon Writes:
>> The temperature thing is certainly important, but feeding the engine air 
 >>at 1psig is definitely better than at 0psig unless there are other 
>> mitigating factors.   That would mean for example that my turbo only has 
>> to pump the air 13psi delta instead of 14psi delta.   That menas the 
 >>turbo will spool up faster.  I think that might mean too, that the turbo 
 >>couild run at 15 psig, adn be at the smae efficiency as it was before at 
 >>14psi. >>
Ram air into a non turbo EFI engine may be good.  No proof really on Ram air
into a turbo motor (WITH EFI - WITHOUT, Forget it - see archives), you would
have seen it by now.  The argument is the same as Blow off Valve feedback
graydon.  You are creating turbulence and changing Po to Ps, that the
computer and turbo and WG has to constantly compensate for.  Po (atmosphere)
at the inlet of the turbo is assumed too.  Ps (speed) isn't the same as say a
two step (Lancia's S4 prorally car comes to mind) turbo or supercharger
system, becuz they assume Po at the first inlet of the primary turbocharger.
 And remember, the S4 uses the supercharger at low speeds, then it is
completely bypassed at high speeds favoring the turbo.  A twin turbo
(progressive/sequential) assumes Po in the first turbo, and Pa (first turbos
absolute peak - at least close to anyhow) into the second turbos intake
blades, a different blade design on the second turbo.  

Spinning the 'fan' with Ps or Pbov (blow off valve dump pressure) is really
not helping either, the turbine is freewheeling off boost, and at a very high
rate of speed, so adding Ps and/or Pbov isn't doing as much to keep spinning
the turbo as the freewheel concept is.  Prolly doesn't hurt, but any gains
prolly offset by turbulence in the pipe.   AND you still have exhaust gas
velocity that will exceed Px forces that you apply to the cold side.  Putting
a cumbustion material and a spark plug into the EM, that will do the trick,
and has been done on the audi PR cars.  The best turbine speed is achieved on
the hot side of the turbo, not the cold.

15 PSI will be an absolute number, again, controlled at the IM.  Few will
take the jump that Ps into the turbo cold side will give you Pa  (absolute) -
Ps.  Not without a redesign of the cold side blades.  The cold side of audi
turbos assume Po in the design, most turbos do.  You would need to modify the
blades to accept pressure into the equation.  Not impossible, but not
practical.  The aerodynamics of turbo blades are an exact science, changing a
constant to a variable will have an effect, prolly not the desired nor
intended however.  I like the thinking tho.

For all practical purposes, forget Ram Air into CIS.  Forget Ram Air into EFI
turbo systems.  Getting cold air TO the inlet is all you have to do for
'gains'.  Po, is best left as a constant, not a variable.  Protecting the Po
and Pb (boost) air from ALL heat to the valve will give you much higher
gains. Especially in an MC motor.

Scott
'87 5ktq/w
'84 Urq