Intake air speed vs Mass flow. Good question

[mark kibort <mkibort@xxxxxxxxxxxxxx>]

Message text written by INTERNET:kennedy@domain.elided
>ne point, however; for my E36 M3, only tests on that would be relevant. =

The engine
is limited by the size of the inlet valves; it is unclear that any minor
pressure
change outside will actually speed air flow through the valve.  Few other=

cars are
bottlenecked at the same place.
<
Brian,
Your wrong hear, the  engine only takes a fixed (fixed by your
displacement)  if you are a 3 liter , you take air at about 300cfm at 600=
0
rpm .   Speed is determined by the ports and valves, but   minor pressure=

changes will effect your air density by definition, and will help .    do=
es
your car loose power at altitude?    (Remember, your speed air going into=

the chamber can vary, but the mass air flow in CFM does not change.  this=

is a key point )
You bet it does. for example.   We took a 3300 lb car up to tahoe, ran th=
e
60 to 100 tests and got 12.6 seconds.  at sea leve and at the same temp i=
t
was 7.9seconds.  that equates to about  a 70 hp loss for a 290 hp  V8.   =

(very close to a New M3 weight and performance)     That 70 hp was lost
only for a 3 psi difference in air density.    Its not a linear scale but=

close as you may expect 30 hp for 1.5 psi and 10hp for about .5 psi.   Th=
is
what we saw with the ERAM.   Just as 7 psi with an intercooler can produc=
e
close to a 100 hp.   (just look at the 993 turbo vs the N/a version  as
stock is 282 and turbo is 425 for .8 bar or about 11 psi, thats 135 hp)

I dont want to argue the wellknown benefits of Turbo/Supercharging.  thin=
k
of the  ERAM is a electrically powered supercharger that only gives .5 ps=
i
boost.    I like to think of it as a electric ram air system as that real=
ly
is what it is designed to do.

mark

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