Technical Information S300 boost control

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 external switch.


  • 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 solenoid.
  • 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 minimum pressure.


  1. 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 map sensor.
  2. 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 repeat.
  3. 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.
  4. 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.
  5. Keep increasing the duty cycle until you have reached the maximum boost level you/your engine/your turbo/your injectors/the dyno can handle.
  6. 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.
  7. 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 Boost Control'.
  8. 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.

What 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 below.

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 possible.

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.