Introduction

This page is designed to provide basic technical information for people looking to upgrade to boost. It describes the operation of the stock computer and the changes Hondata has made to accommodate boost functionality.

The short version

From the Parameter window select Protection

• Set your cold boost cut to 5 psi;
• Set your hot boost cut to 10 psi;
• Set your overheating temperature to 220
  
  

Upload the program to the ECU. Total time taken should be less than 2 minutes.

All the tunes listed above were created through dyno testing to be used as a good starting point for tuning a vehicle with a similar setup. In our testing the tunes have given more power than any piggyback system it replaced. It is our opinion that the tunes listed are also safer and more reliable than any piggyback we have tested. Hondata recommends that everyone running a boosted engine have it fine tuned on a dyno.

Technical information - How it works stock

This graph is representative of a stock RSX-S ignition timing table for the high cam at 30 degrees. The index on the left hand side is RPM and the index running left to right labeled mBar is for the vacuum level in the intake manifold. The air pressure is read directly from the MAP sensor.

Columns 9 and 10 are the columns the ECU runs in at open throttle on a naturally aspirated car at sea level.. As you climb in altitude the air pressure drops, so in Colorado the car would only get to columns 7 and 8. As you can see the ignition advances as the air pressure drops and retards as the air pressure increases.

Technical information - How it works - Piggybacks and the map sensor.

A piggyback system is one that cuts and intercepts wires between the ECU and engine sensors. A piggyback usually fools the ECU by manipulating sensor inputs.

A common technique for piggyback systems to control fuel is to manipulate the MAP sensor signal.

For example lets say you installed 440 injectors. 440 injectors spray about 40% more fuel than 310 injectors. The map sensor line is cut and diverted to the piggyback, where the voltage is reduced by the appropriate amount before it is fed the the ECU. At 6000 rpm, column 10 the fuel value is 2311. The piggyback alters the map sensor voltage so that the stock ECU sees fuel from column 6 - in this case the value 1361 which is 40% less fuel than the value 2311.

Unfortunately, this also has the effect of advancing the ignition - which is the opposite of what you need a boosted vehicle. So what was 22 degrees in the example below will now be 35 degrees of timing. The good piggyback systems allow you to correct for this by retarding the ignition timing.

When the cylinders are filled with more air as in a boosted engine the air-fuel mixture burns faster. If you do not change (retard) the timing the flame front will reach the top of the piston while the piston is still coming up the bore. This will put tremendous pressure on the engine. The possible results are blown head gasket, damaged bearings, bent rods and collapsed ring lands. So, as boost pressure increases, you need to retard the ignition timing for both reliability and power.

Technical information - How it works - Hondata modification

This is how Hondata (and any good engine management system) handles boost. Hondata has added boost columns 11 through 16. The units in boost are measured in pounds for this graph.

The ECU uses interpolation to derive fuel and ignition values for boost levels that are not directly on a column. For example if your boost level is 6 pounds at 6500 rpm the ignition value will be halfway between 15 and 12 degrees - which will be 13.5 degrees. Note that the values for ignition under boost are significantly less than that for the naturally aspirated columns. The numbers here are taken from a turbo tuned to 10 pounds of boost. Quite a difference compared to the values of 22-35 degrees above and far far safer.

The stock map sensor can read up about 11 pounds of boost. For levels above that you will need to upgrade your map sensor

Behind the scenes changes

Internal PA sensor.

At wide open throttle the stock ECU switches from reading the map sensor mounted on the throttle body to read the internal map sensor - the PA sensor. This is fine for a naturally aspirated car, but for a boosted car running at altitude with a piggyback it has the effect of advancing the ignition by reducing columns from which ignition (and fuel) is read. In the example above of boosting in Colorado, the stock ECU would advance the ignition about 6 degrees.

Extra useful stuff

Bigger injectors typically have a spray pattern which can cause a lumpy idle. So we recommend increasing the idle speed.

Closed loop operation.

With the introduction of a wideband oxygen sensor for the K series the stock ECU can and does run closed loop at full throttle. While 14.7:1 is ok for a naturally aspirated vehicle it is far too lean for a boosted vehicle and will cause hesitation. Typically this hesitation occurs while rolling onto the throttle from a cruise and for several seconds after a gear change. Hondata eliminates this by switching to open loop based on manifold pressure.

If you have removed your catalytic converter, you will get a secondary oxygen sensor code. Switching off OBD II will disable this error code.