[Diy_efi] RE: Throttling intake air -- references

[Mike]

Yeah I agree, though when cruising or even up an incline
its very unlikely your wastegate would be 'modulating',
mine is a simple diaphragm to a lever to open a flap,
which only moves about 0.25inch... and doesnt open at
all until I get to 10.5psi. ie. Its slammed shut, there
is absolutely no modulation at all - nothing to drive it
open except manifold pressure via a diaphragm.

The fact I can gently reduce throttle and control boost
with my foot from any pressure to any other pressure up
to 10.5psi (provided I dont run out of road) suggests
some elctronics can do the same thing.

Besides the messy flow at the turbine outlet it occured
to me that since we throttle the engine power and boost
anyway by using the foot pedal, why not extend this when
we have flybywire by having the ecu do effectively the same
thing then we can dispense with the wastegate - provided there
is an appropriate PID type control - then it should result
im more efficient operation with less fuel consumed comparatively
due to improved exhaust flow and no venting via a wastegate if
the ECU/TB is doing the right thing...

The aero issue, Brian brought up, and yes its apples vs oranges,
in completely different control environment due to large
inlet pressure changes. I get the impression some participants
on this list think I meant flapping the throttle the same way
some controllers flap the wastegate (which I didnt) and I also
get the impression there is a certain dogma in needing to
think wastegate bypass is the only way of doing it, it certainly
has some momentum but it doesnt mean its best overall in terms
of fuel consumption since it also isnt best control systems
theory.

Heck you could also help control boost by cylinder skipping
fuel if at the extreme end of bosot - but thats another story ;)

rgds

mike


At 07:47 AM 16/1/2003 -0800, you wrote:
>All this discussion has been interesting - for what I
>don't know.
>When I drive a car, I get in it and count on a)My ECU
>controls the right AFR, b)My wastegate opens when my
>turbo exceeds the boost level I desire for my engine
>so that even though I continue to accelerate I don't
>blow the head right off (hopefully I have properly
>matched my AR to the engine to reduce surge and
>overspooling) c)My BOV works so that when I see the
>friendly local Johnny Law and snap off the throttle -
>it dumps my escess boost.
>
>Now when I drive on the highway with my cruise on, I
>surmise that my EGT's are much lower, my turbo is
>spooling slower, wastegate is barely modulating unless
>I go up a hill and come under load conditions.
>
>What I've been reading is comparing an aero
>application which is continually under load vs
>automotive applications where load fluctuates
>constantly - Apples vs Oranges IMO.
>
>=====
>Jerrit Ekama
>
>OHB Tuning
>Custom fabrication of performance parts for your Mercedes, VW, BMW, Audi.
>U.S. domestic and foreign vehicle repair and maintenance.
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>IM: OHBenz
>
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