Re: 2.5 AFM & DTM & F1 intake

["dion fields" <noid@domain.elided>]

>>> The restrictor used by the DTM is a mere 28mm (1.1"),
>>> and these normally aspirated V8s make around 450bhp.

>> that's a restrictor plate, though. a 1.1" hole in a plate is less
>> restrictive than a length of 1.1" diameter tubing. 

a simple plate with a hole stuck in the middle, in an intake
system, would destroy the flow properties.  the engine 
builders taper the tubing to and from the restrictor.  physics
dictates the taper angles to keep the flow as laminar as 
possible.  but yes, that restriction is at only one point, not
the entire system.  kind of like the AFM being smaller than
the rest of the intake.   smaller internal diameter of the AFM
will give stronger and more accurate readings for the computer.
that is why BIG carburetors work poorly at low RPM - the
flow needs to be sufficient for accurate fuel metering.

>> in an F1 engine, the plenum is at atmospheric pressure, 
>> and flow rate to the valves is controlled by varying the length 
>> of the runners from the plenum to the valve.

the variable length intake runners used on F1 engines, and
the variable plenum designs on many production engines
are not designed to vary the flow rate.  the diameter of the
runners remains constant.  changing the length changes
to tuning of the pressure waves created from the opening
and closing of the valves.  a certain length runner times
the strong pressure wave at a certain RPM to create a
kind of supercharging effect.  this helps fill the combustion
chamber.  longer runners work best at low RPM, and shorter
runners at high RPM.  intake plenums can be designed
for variable volume for differerent RPMs, like honda and
others have done. on the toyota FX-16 and MR2 4 valve 1.6L,
there was one runner per intake valve.  one of these runners
had a electronically controlled butterfly valve that was closed
at low RPM and open in the mid range.  this WAS a variable
flow design in an effort to increase flow velocity at low RPM
by only using one valve.  Yamaha tried something kinda
similar on the legendary V-Max motorcycle ( of course, they
design many of toyota's motors ).

i heard cosworth currently designs its motors with a maximum
intake velocity of 450 ft / min ( or is it ft / sec? ).   many
production engines have big enough intakes to only allow
up to 350 or so.  some engine builders actually add epoxy 
to the intake ports to smooth the flow before the valve and 
increase the velocity !  

someone could do the math and see where the stock 2.5 v6 
AFM is at, velocity wise. some sources say you want the
velocity to be no higher than .6 mach, then the flow becomes
too strangled for optimal performance.   every engine builder 
has different opinions, expecially the classic thought, where
"bigger is always better."     just like SUVs.


of course these are just my observations, and i could be
all wrong about this universe and the cars that race in it.
maybe Eric Storhok could chime in and offer his insight.

-dion fields
-73 GTV
-los angeles


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