How To Dyno Tune Your VTEC Honda

November 15, 2013

Dyno Tuning your VTEC Honda can often be a worrisome ordeal especially if you are relatively new to the scene of tuning and modifying your car’s fuel and ignition maps. Whatever flavor chassis dyno you prefer, it’s important to remember that it’s not always about the horsepower number but rather the efficiency and longevity of the vehicle you are building.

Today we’ll be showing you How To Dyno Tune Your VTEC Honda, and walking you through each step.

Things to do before dyno tuning :

Service your car – For so many reasons you want your vehicle to be it’s absolute mechanical condition when you are dyno tuning. Meaning all fluids, wires and hoses checked and double checked to prevent any accidents or problems while on the dyno.

Most dyno disclaimers include a cleaning fee that can be significant, especially if you are talking about an in ground dyno.Tip : Tuning and making a pull on a chassis dyno should be LESS DANGEROUS for your vehicle than going down the street WOT.

UEGO / Sniffer – Make sure the dyno facility offers wideband services or at the very least has an exhaust sniffer if you do not have a wideband or similar air/fuel reading device equipped on your performance car.

Check your Long Term Fuel Values – Using a datalogger or similar device check on your long term fuel values to see exactly what the value is. What is Long Term Fuel Trim? the long term fuel trim is a value or rather average of the short term fuel value, which is a value that the ECU determines based on your 02 readings.

Your narrowband 02 sensor is a very important sensor that tells the ECU how much oxygen is in your exhaust stream, which is turn is how lean or rich your engine is running. The ECU will enrichen or lean out the injector pulsewidth in order to lean out or enrich the fuel mixture based on the value of both fuel trims.

This is called “closed loop” and it’s important to have this value as close to 0 as possible, by way of tuning your part throttle conditions as close to stoichiometric as possible if you are retaining a catalytic converter. This will prevent the long term fuel value from changing the mixture at the points in the fuel table when the ECU is not in “closed loop”

For more information on how to tune closed loop operation, check out our How To Tune Closed Loop Operation here.

jdmafcdatascreen1 — How To Tune Closed Loop Operation

Tune your low throttle settings

This can be achieved quickly if you are willing to do some math in regards to the injector sizing in your vehicle. If you are using the stock injectors and fuel setup of course the part throttle settings will not be too far out of whack. ( we hope )You will want to aim for as close to stoichiometric values as possible during part throttle operation to bring your short term fuel and long term fuel values as close to what the ecu wants as possible.

If you are using upgraded injectors you can elect to either tune the vehicle on the fly which can be expensive if you are renting the dyno by the hour, or calculate your base fuel settings on what size injectors you are using. As stoichmetric mixture is our target ratio and 14.7:1 is what we are aiming for, take your stock injector size and calculate it against the new injector size to determine the baseline of your part throttle tune.

For example: if your your stock injectors were 440cc and you upgrade to 750cc injectors, your base low throttle setting should be -40% of the base tune in question.

Need a conversion table?

Conversion Formulas

To convert cc / min to lbs. / hr. – Divide by 10.5
To convert lbs. / hr to gal. / hr. – Divide by 6
To convert cc / min to gal. / hr. – Multiply by .015873

Doing this will allow you to get a quick baseline and slowly adjust from there, making your job much more manageable and easier to complete.

After you are done with your part throttle settings you can move onto Wide Open Throttle tuning ( WOT )

Know what A/F to aim for – As stated earlier make sure to tune your vehicle to stoichiometric in part throttle and low loads if you are using a catalytic converter and driving frequently in “closed loop” operation.

For most naturally aspirated applications the “target air fuel ratio” is commonly in the 12.5:1 – 13:1 range depending on varying modifications and conditions. For turbocharged or supercharged applications common targets are 11.6:1 – 11.2:1 depending on what modifications and what level of fuel and intercooling involved.

Dial in your VTEC crossover point – Using your VAFC or Buddy Club VTEC controller you want to dial in your VTEC engagement point to redline or as close as you would comfortably like it to redline.

Make one dyno pull in third gear and then find the highest point in engine revolutions (rpm) where your horsepower falls off without the engine engaging VTEC. Set your VTEC crossover point using your controller of choice to 500 rpm before this horsepower falloff point.

We take a look at a 2008 Honda Fit dyno plot for a close look at what we are talking about.

You’ll see here that we’ve set the VTEC crossover point to 500 rpm before the horsepower tails off on this stock Honda Fit. You can elect to use torque as a similar or improved starting point for the crossover but we prefer to reference horsepower.

Wide Open Throttle – Once you have determined your baseline settings go ahead and take a baseline pull in 3rd gear and identify where the torque curve begins to fall off in relation to your Engine RPM. Using the wideband reading we discussed earlier compare the torque curve falloff against the air/fuel overlay and find out where the ‘holes’ in your fuel map exist.

These ‘holes’ are preventing you from achieving maximum efficiency and power in your VTEC Honda, enrichen or lean out the fuel mixture according and be aware of what air/fuel mixture you are aiming for. If your tuning device has the capability, disable closed loop operation to prevent your target air/fuel mixture from moving around.

IPW vs Injector Duty – Now comes the very delicate act of balance between how much fuel is available to you at what time vs your injector duty and Injector Pulse Width (IPW).

Anything near or approaching the industry standard of 80% duty cycle means you really should be increasing the amount of fuel available to you, either by way of increasing fuel flow or pressure at the rail.

By modifying the high throttle fuel maps you are increasing both power and reliability by trying to reach your target air/fuel ratio. Make sure your conditions are repeatable and that you are always aware of what air/fuel ratio your vehicle is running at.

Don’t rush it – Make sure to take time between pulls to allow your car and all the various parts of your engine to cool off, including but not limited to your intake manifold, exhaust headers, intake pipe, intercooler, turbocharger and much more.

Hope you enjoyed part 1 of How To Dyno Tune Your VTEC Honda, stay tuned for part 2.

Good Luck on Tuning your VTEC Honda!