How to Dyno Tune your VTEC Honda

This post was originally written by John at StockSpyder.com.

Many people ask me questions about dyno tuning their Hondas, both in N/A and boosted applications. With the advent of affordable engine management in this day and age, it makes sense to see many people taking the power of their PCM into their own hands.

As with any dyno session, your car should be in perfect running condition and with all fluids, wires and hoses checked. A dyno should be NO LESS dangerous than if you were to go WOT down the street yourself, always remember that.

Here are my step by step processes to dialing in your VTEC Honda.

A. Dial in your VTEC crossover point.

If you have a Hondata or VTEC Controller, now would be a good time to set your VTEC switchover point to redline, or close enough to it.

Make one dyno pull in third gear, and determine the highest rpm in which the hp tails off without the engine entering VTEC. Set your VTEC crossover point to 300 rpm before this point for your optimal VTEC engagement point.

We take a look at our Project Fit’s dyno plot for a close look at what we are talking about.

Using this example, we set our VTEC engagement point to 300 rpm just before the hp begins to fall off. Some use torque as a better starting point, the preference is up to you of course.

B. Move on to Low throttle settings or STFT

You can opt to do one of 2 things here, either do the mathematical equation for injector sizing and dial down the fuel  map accordingly, or do it on the fly.

I prefer to set a baseline using the injector sizing equation, and then dialing it in on the fly from there. With a stoichmetric mixture as a target ratio, 14.7:1 is what we are aiming for, most importantly at highway speeds.

i.e. when your stock injectors are 440cc and you upgrade to 750cc injectors, your base low throttle setting should be -40% of the base tune in question.

Now with your baseline dialed in, you can move forward to tuning your Wide Open Throttle ( WOT ).

If you are not familiar with what size injectors you run, or are confused by my usage of #lb injectors or XXXcc injectors, use this conversion chart below.

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

Remember to maintain or bring your STFT as close to zero as humanly possible to prevent your PCM into tripping a rich condition or limp mode. For more information on STFT, try looking at myHow to Tune Your Super AFC writeup.

C. Dialing in your Wide Open Throttle.

You can now initiate a baseline pull in 3rd gear ( or 4th for you boosted cheaters ) and identify where the torque curve begins to fall in contrast to your rpm. This will be the target rpm for your fuel controller to modify to extract the maximum power from your vehicle safely.

Now using a wideband sniffer ( preferably ) lay the A/F curve vs the rpm/torque plot to see where you need to enrichen or lean out the fuel mixture. Be aware of what target A/F or Lambda reading you are aiming for, this will depend on what kind of power adders you have on the car and what you are aiming to do with the tune.

Now comes the balancing act of IPW ( Injector Pulse Width ) and injector duty vs how much fuel is available to you at what time. Your main goal is to create a broad torque powerband without heavily taxing your IPW or duty cycles.

Remember that 80% duty cycle is a industry standard, anything about that mark and I start getting worried. Call me paranoid.

For most all motor setups, our ideal air/fuel mixture is 13.5:1 to create a safety window in which the vehicle can perform without worry. For turbo or boosted applications, anywhere from 11.5:1 to 11:1 will be your target depending on how much load you are putting on the motor and how high your duty cycles currently are.

Next up : How to dial in your vehicle’s overlap and ignition timing.

Happy Tuning!

Posted by Hans Desjarlais

After accidentally locking himself in a scrapped '85 Renault for several hours at the age of 5 years old, Hans developed a love/hate relationship with cars which eventually became an obsession. Right out of high school Hans started his first business importing and selling Japanese engines. After selling the business in 2008, he launched Import Insider to obsessively cover the auto industry and offer advice and tips to import car enthusiasts.

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