From: Miki <
awdturbodude@yahoo.com>
To: <
BC-BFLegacyWorks@egroups.com>
Sent: Thursday, January 11, 2001 8:14 PM
Subject: [BC-BFLegacyWorks] Once more about boost control
> Hi everybody!
>
> I'm sorry for once again bothering you with boost control, but I just
> don't get it...
No worries, and good to hear from you!... and it sound's like you are pretty
much on to it as far as your boost control. Depending on how far you want to
with raisng the engine performance, you are reaching a point where you may
want to take alternative paths.
> OK, I have the problem with too much boost on my car (occasionly even
> 20-21psi, as you probably have read), and I'm now considering
> installing a manual boost controller (e.g. the HBC) to prevent my
> engine from exploding.
Yes, I knew you would have problems, and it sounds like you had some boost
creep. I think driving in your colder climate would have prevented your
engine not exploding earlier!
A boost controller can come in many forms, both pneumatic and electronic
controlled, and this function can also be included in the ECU.
> Now, the question is, can the HBC be of any help in this?
> Can the boost be set to a max figure with the HBC?
> If I get it installed and set correctly, is the boost then always
> kept below a certain max figure?
I don't know the HBC... yet
> How the heck do these gadgets work???
Working back from the turbo wastegate... we need to open this to either not
overspeed the turbo or control the intake pressure. The wastegate actuator
is controlled by an electronically controlled vacuum switching solenoid...
the factory setup is for the ECU to "pulse" the solenoid with a pulse width
modulated (PWM) signal providing proportional control of the wastegate
actuator. The control progam employs feedback from the MAP sensor and
others. The proportional conrol and range parameters are set within the
firmware of the ECU according to the factory.
The disadvantage of PWM control, is that the wastegate is opened earlier but
only slightly so the waste flow is narrow, and as revs increase the
wastegate opens more often and wider. Although wastegates all tend to leak
slightly anyway, this setup uses a control / feedback loop that can have a
fluttering and creep effect on the engine / turbo dynamics.
The alternatives are to control the wastegate differently, which can be
achieved by...
1 - pneumatic bleed / restrictor / accumator valves
2 - piggy back sensor conditioners (engine cut/fuel defend from
overboost/overspeed/over-rev etc).and replacement ROMs / piggy-back ECU
(boost controllers)
3 - complete replacement ECU
Boost controllers design varies and can incorporate various elements of the
control actuators and feedback loop sensor conditioning, but they usually
maintain closure of the wastegate at an earlier or controllable point of the
engine rev range, and open quickly at the preset boost pressure.
The objective with this setup is to build maximum boost as early as possible
in the rev range, however the engine dynamics become more "snappy".
The disadvantage with this approach, whether it be 1 or 2 above, is that
they are a piggy-back approach to "altering" the ECU firmware or factory
progam. In the quest for more power, this system of piggy-back workarounds
can become a bit of nightmare... unless you have a clear idea of your engine
performance goals.
As performance goals increase, you will need control of engine cut / fuel
defend, a modified engine map, etc... and a replacement ECU may end being
the better path.
> I have a "bleed valve" thing on my map sensor (you know this), would
> that still be necessary with the HBC?
Hmmm... normally the bleed valve (a piggy-back!) is in the vacuum solenoid
to waste gate actuator, and not the MAP sensor.
The objective of this setup is to delay the action of wastegate opening, and
it is usually one of the earlier modifications performed... after say,
exhaust and intake.
Whilst a simple bleed valve works, there are arguably better combinations of
valves or accumulators
The MAP sensor "sees" boost and vaccum and the usual workaround for a MAP
sensor is to add an electronic piggy-back signal conditining device to
change the sensor's analog output span.
The objective is to modify the output curve effect of the ECU map.
The disadvantage is at some point with high boost gains the MAP sensor
"flat-lines" it output as it is actually at full pressure (internal
mechanical span as it is only a silicon strain bridge mounted on a
diaphragm), and the piggy-back has provided semi-controlled modification of
the factory progam pertaining to control of wastegate actuation, but the
consequent impact to the ECU map / engine cut is haphazard.
A bleed valve on the MAP sensor will achieve the same sort of result but
more crudely.
Very high boost setups would probably use a replacement ECU with a
replacement MAP sensor of the appropriate pressure rating.
So Miki... that was an introduction to control / feedback loops, and an idea
of the issues in maintaining balance and control in the quest for more
power. Don't get me wrong, any of the above approaches is perfectly valid,
depending on your end goal.
In my experience with other people's EJ20 high performance modifications,
the factory ECU gets ditched fairly early, otherwise all the piggy-backs
become a pain to manage... but it all depends on how much power and
reliability you want. ... In your case, with your EJ20... I think that you
may be heading into 250-300hp territory where a replacement ECU is arguably
the better path... at some point you need to take control of the ECU map, as
fuel control and lean-out becomes an issue. Whilst the EJ20 doesn't seem to
be sensitive with the ignition timing running a bit too far retarded, a
lean-out condition at high boost / revs is very, very damaging.
My 2 cents...
John Gillon
www.clubsub.org.nz
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