Hondata Reflash - RSX Type S 2005-2006 K20Z1

  • Sale
  • Regular price $499.99
Shipping calculated at checkout.

Reflash your 2005-2005 RSX Type S engine computer.

  • VTEC window from 4900 to 5800 rpm
  • 8600 rpm Rev limit, increased from 8300 rpm
  • Maximum torque gain 12 ft/lbs torque at 6000 rpm
  • Maximum power gain 20 hp at 8000 rpm
  • Peak torque increases by 6 ft-lbs
  • Peak power increases by 8 hp
  • Very wide flat smooth torque curve. 90% of peak torque available from 2200-8000 rpm.
  • Fully dealer compatible - works with all Honda scan tools and equipment

This is for an ECU reflash - the ECU is not included.  Hondata does not sell direct - the reflash must be purchased from a Hondata dealer. The ECU reflash form must be sent with your ECU.

We do not recommend the use of nitrous or forced induction for this reflash. For these applications use the K-Pro.

What if you have modifications?

What will work well:

What is not recommended:

Check your catback exhaust carefully. The internal diameter of the rear muffler is often smaller than stock. If this is the case you will probably make less power than stock with more noise. It will work OK with a stock airbox but you will not see these advertised power gains, and you may feel a dip after VTEC.

If you have a race header you will run lean. This is not a result of the Hondata reflash. Even the stock ECU will run lean with a race header. If you intend to run race headers you have two choices:

  1. 05-06 RSX Race header reflash
  2. Hondata K-Pro for the 05 RSX.


Within USA this product is legal only for racing vehicles which may never be used upon a highway.

Sales Region US Only
EPA/CARB status (USA) Competition vehicles only
Model RSX
Year 2005-2006
Market US
Trim Type S
Engine K20Z1
Transmission MT
Part Number 37820-PRB-A13

Dyno notes: This dyno reads about 8-10% higher than a typical dynojet, but is directly comparable with any other dyno plot on this site.

Tuning notes

Power was made by advancing the ignition, lowering the VTEC point, advancing the camshaft angle and leaning out the top end (from 7500rpm up).

A VTEC "Window" was programmed in. This means the VTEC point is no longer fixed but varies according to manifold pressure (very closely related to throttle position) At sea level the VTEC point is 4900 rpm. At part throttle the VTEC switches at 5800 rpm. This allows you to cruise at 5300 rpm ( for example) on the lowcam and switch to the highcam just by giving more throttle. Also, as you rise in altitude, the VTEC point rises to 5800 rpm to reduce power loss after VTEC switchover.

You may feel a small dip at VTEC. Rest assured that even with this small dip you will have more power than before. You may also find the VTEC switch is smoother and quieter than before. Do not worry. VTEC is not missing; it is still operating.

This engine is sensitive to fuel quality and knock. With a higher octane fuel the ECU may advance the ignition slightly and make a little more power.

Overall the driving improvements to the 05/06 RSX mirror the 02-04 RSX reflash.

Will Hondata be doing any other 05/06 RSX reflashes?

Hondata has a reflash for an 05-06 RSX-S with race header and intake for those who do not intend to modify their car any further. There are far too many combinations of cams, intakes, headers, pistons, turbocharging and supercharging to develop with a reflash for every combination. We cannot make a reflash for all these combinations. A programmable system such as the K-Pro will allow your car to be tuned precisely for your modifications.

Can I upgrade to the K-Pro later?

Hondata will be offering no upgrades from the 05/06 reflash to the K-Pro. The K-Pro is based off an 04 RSX ECU. The 05/06 ECU is completely different and cannot be upgraded to a programmable system like the K-Pro. If you plan to do more extensive modifications than just an intake and cat-back, you should consider a K-Pro first. Should you get the reflash and later decide to purchase a K-Pro, you could sell your reflashed 05 ECU.


The K series ECU, in order to be re-programmed must have a functioning immobilizer system. Three items must be sent to Hondata: the ECU, the ignition key and the immobilizer. The immobilizer works as normal after the ECU has been re-flashed.

Tools needed:

  • Philips screwdriver
  • 10 mm socket and drive
  • Time needed : 10-15 minutes

Removing the immobilizer (Civic Si, RSX / Integra)

Under the steering column remove the three philips screw holding on the bottom plastic cover.

Depress the bottom cover along its top edge where it meets the top cover to separate the plastic clips. Rotating the steering wheel 45 degrees can help.

Lower the steering column and remove the bottom plastic cover from over the height adjustment lever.

Unclip the green connector immobilizer connector and unscrew the securing two philips screws.

RSX ECU removal

The ECU is located in the passenger's footwell. The kick panel is removed after depressing the centers of three small plastic buttons around the front covering panel.

Unplug the three wiring connectors and remove the two front most 10mm locating bolts, plus the rear bolt. The ECU will slide out easily - if it does not, then check that the rear bolt has been loosened or removed.

K20A3 Civic Si ECU removal

The Civic Si's ECU is located in the passenger's footwell behind the glove compartment.

Unclip the lower plastic panel:

Unplug the three ECU connectors.

Remove the lower two 10 mm bolts.

Open the glove compartment and push out from behind the two bump stops. The glove compartment will drop after this is done.

Undo the last 10 mm bolt and slide the ECU down.