Technical Information Boost Tuning on the R18 Engine


This article details forced induction tuning for the 2006-2011 R18 Civic.

Map sensors

The stock map sensor is good for 10 pounds of boost. We have not seen any built R18 motors, but if you install an Acura RDX MAP sensor (plug and play) you can boost up to 26 pounds. The Hondata 4 bar map sensor will not physically fit the intake manifold and cannot be used.

Injector requirements

Injector Size (cc) Supported HP (% over stock)


185 160 (10%)
RSX-S  / 06+ Civic Si 310 230 (65%)
Acura RDX 410 300 (115%)
Modified Honda Civic (K20 or R18) 520 380 (170%)

Our pick is the Acura RDX injector. It has a great spray pattern, fits the fuel rail perfectly, starts and idles well and supports over double the stock HP. RDX injectors require new wiring leads.

The 06 Civic Si / RSX-S 310 injector is a straight bolt in and supports low boost with the stock air flow meter housing.

Modified Honda injectors need to be measured for flow after alteration. The spray pattern and atomization is not as good as stock. Starting may take 1-2 seconds longer.

See injector calibration with an Air Flow Meter.

Air Flow Meter requirements

The stock Air Flow Meter (AFM) is about 2.4" in diameter and limits the Civic to about 210 HP or about 50% over stock. For higher HP, you will need a larger intake pipe with a recalibrated AFM.

A 3" diameter pipe for the AFM housing is suitable for 350-400 HP.

Fuel system Guidelines

Firstly high octane. 91-93 octane.

The fuel pump for the R18 Civic has the same part number as the Civic Si, so we know it will support 300 HP. We haven't yet measured fuel line diameter and pressure drop at high HP levels.

The Honda ECU is not designed to deal with an injector that flows less as manifold pressure increases. The ideal way to set up a boosted engine is with a return line fuel system.

Here is the reason why. As the boost increases, the injector flows less. As an example, consider an injector with 40 psi of fuel pressure and 40 psi of boost in the intake. When you open the injector,no fuel will flow. With a return line system the fuel pressure increases with boost keeping the pressure across the injector constant.

There will also be a pressure drop in the fuel lines as the fuel flow increases, but we suspect it will not be excessive for power levels in the 250HP range based on our testing with boosted Civic Si engines.

However, our testing so far indicates boosted R18 engines in the mid 200s for power levels can be tuned with a returnless system.

By way of example, lets take a Civic at about 8 pounds of boost making about 240HP. At peak boost, the fuel pressure across the injector will be reduced by 8 psi from about 61 to 53 psi. This reduces the flow of the injector by 7%. This can easily be compensated for by:

  •  -  Increasing the fueling in the boosted portion of the WOT compensation maps by a similar amount.
  •  - Altering the AFM calibration to add more fuel at the levels of airflow where the car is known to be in boost.
  •  - Or a combination of both

At this point the strength of the R18 engine is not known for high power levels in excess of twice the stock output, but we would guess that as you approach HP levels close to 300 HP you will need to build a stronger engine and install a return line system.


These dyno charts show our R18 Civic fitted with the HBAR Motorsports Turbo Kit. The exhaust used was a stock cat-back which is too small for these power levels and was likely limiting power.

  • Stock  - green line
  • 4 psi boost - red dashed line
  • 7 psi boost - red solid line - a gain of 78 ft-lbs torque and 92 HP.