S300 Boost Control
The S300 can control boost by using a duty cycle controlled output on OBD1 ECU
pin A11 with a
boost control solenoid to regulate air to the wastegate.
Boost may be fixed, or varied by gear, with two settings which allow for
wet/dry, pump/race gas or street tire/slicks settings to be selected with an
- All US ECUs have the circuitry, but not components, for the PWM (pulse
width modulated) output. JDM ECUs do not have
the circuitry and cannot be used.
- Components must be added to the ECU for the PWM output to work.
- The cost is $50 to have Hondata add
the necessary components to the ecu, which is the recommended method to
avoid damaging the ECU. This does not include the cost of the
- Dealers can purchase the necessary components to enable Boost Control.
Dealers should contact Hondata to order these components.
How does boost control work?
The ECU produces a square wave at a fixed frequency and variable duty cycle.
Applied to a solenoid, the impedance of the solenoid results in a linear motion
of the solenoid valve orifice.
The wastegate is normally connected so that manifold pressure acts on a
diaphragm, so opening an exhaust bleed valve (the wastegate) at a certain
manifold pressure. With a boost controller, additional air pressure is used on
the other side ('the top') of the diaphragm, so that more manifold pressure is
needed to open the wastegate - so the engine makes more boost. By varying the
amount of air pressure on the 'top' side of the diaphragm with the solenoid, the
ECU can control boost.
Because the solenoid can only add air pressure to hold the wastegate shut,
the minimum boost is determined by the wastegate spring pressure. Therefore you
need to run a spring which gives the minimum boost you want. The maximum boost
is determined by many factors, but generally will be 2-4 times that of the
- Most important: first set a boost limiter which is the maximum you wish
to run, making sure you do not set a limit that exceeds the limits of your
- Record the boost without the boost control solenoid in place. If you
ever want to run less boost than the recorded value, replace the spring and
- Connect the boost control solenoid, enable the ECU output and set the
duty cycle to 1%. Record the boost level. Typically there should not be more
than a 1 lb increase from the baseline. You should not use values of
0% or 100% as it will not work.
- Add 5% to the duty cycle and record the boost over the rev range. At
around 20% duty cycle the boost level should start to increase with each
run. Record the duty cycle and corresponding boost level. If the boost
spikes or falls off, check the solenoid plumbing.
- Keep increasing the duty cycle until you have reached the maximum boost
level you/your engine/your turbo/your injectors/the dyno can handle.
- Enter the duty cycle and boost values into the parameters 'Pressure vs
Duty Cycle' table. This tells the ECU what duty cycle it needs to obtain a
certain manifold pressure.
- In the 'Boost by Gear' table enter your target boost for each gear. If
you want high/low boost settings, enter your alternate boost values in the
second 'Boost by Gear' table and set up an external switch under 'Low/High
- Check your gear ratios are correct.
Test by datalogging. The duty cycle is recorded and can be compared to
the target tables. Any problems usually arise from the way the solenoid and
wastegate are connected - check these first.
For more information see the SManager help file.
Do I need my existing manual or electronic boost controller?
No, the s300 boost control output replaces both types of boost controller.
All you need is the ECU modified and a boost control solenoid.
How do I add the components to the ECU?
Either Hondata or your dealer can add the components to the ECU.
See the OBD1 ECU
Socketing form. The ECU components can be installed by the dealers.
Is this different from a quad stage boost controller?
Yes, a quad stage boost controller is actually four manual boost
controllers. The duty cycle controlled output is superior because it offers more
settings (two sets of five boost settings) and is compensated for air
temperature to give a more consistent boost level. Not to mention it is simpler,
smaller, lighter and cheaper.
Why set boost by gear, not speed?
Assuming your aim is to maximize acceleration, then you need to utilize as much
of the tractive capacity of the front tires as possible. The tractive capacity
of the front tires is almost constant - it actually decreases a little with
speed as the tire footprint shrinks and with front end aerodynamic lift. In
order to provide a constant torque at the wheels to keep the tire at the peak
tractive effort, two things are obvious: 1. The engine should have as flat a
torque curve as possible (in the rev range) and 2. The engine should make more
torque in each gear to offset the change in torque multiplication from the
engine to the tires when you shift gears. You cannot do this by speed or rpm
since this makes the torque output dependent on your shift point. By setting the
boost level in each gear you are in effect altering the engine torque level to
obtain the same wheel torque level, adjusted for inertial effects. If this all
makes no sense to you then drive a high powered vehicle with boost by gear and
you will understand.
solenoid do I use?
The solenoid and wiring connector are the commonly available GM part numbers
#1997152 and #12102747. You can also purchase the solenoid and wiring through
your dealer for $50.
Can I use other solenoids?
Possibly. We have only tested the GM and MoTeC solenoids, and only offer support
for these solenoids.
How do I wire up the solenoid?
See the help topic in the SManager help file, or reference the diagram
How do I connect the solenoid to the wastegate?
See the help topic in the SManager help file, or reference the diagram above.
How much boost can I make on a given spring?
It depends on exhaust back pressure, but generally 2-4 times the spring value is
The boost drops off at high rpm.
Check where you have connected the pressure line for the wastegate. It is best
to use the manifold.
The boost spikes.
Your wastegate position may be off-center or undersized.