When we think about performance tuning, we tend to think of certain vehicles. Usually, it’s some classic American muscle, or a JDM hero car, or increasingly these days, some kind of big ol’ truck. Hybrids are the last thing that comes to mind. Meanwhile, it turns out the original Honda Insight is actually pretty easy to tune with some incredibly low-buck mods.
Tuning an engine for more power can be easy or difficult depending on what you’re working with. If you’ve got an old emissions-choked Malaise era donk, you might just pull off some emissions equipment or fit a new carb. If you’re working with something fuel injected, you can swap out a few components or bolt on a turbo, and then retune or replace the ECU. For a hybrid, though, it can be more complicated. It’s difficult to tune either the electric motor or the engine without fully replacing the factory management systems. And that’s no easy task—there aren’t a whole lot of aftermarket engine computers out there for the job.
And yet, there are people out there tuning the Honda Insight quite easily, using what is called a “current hack.” It doesn’t require the wholesale replacement of Honda’s engine management system, nor does it require the replacement of expensive electronic or mechanical components. It’s all achieved by tricking the controller for the Insight’s hybrid motor, making it think the motor is drawing less current than it actually is.
Performing the hack involves modifying the Insight’s Motor Control Module (MCM) and Battery Control Module (BCM). The MCM is equipped to sense the current flowing through the motor, and the BCM is equipped to sense the current flowing through the battery. To enable the Insight to send more current to the motor to make more power, it’s necessary to modify both.
Sensing current is performed with a current shunt. A current shunt is essentially a resistor of known value. If you then measure the voltage drop across that resistor, you can calculate the current flowing through it using Ohm’s law, where the current, I, is equal to the voltage divided by the resistance.
Here’s the trick: the Insight’s control hardware is calibrated to a known resistance for the current shunt. If you change that resistance, you can trick the controllers into thinking less current is actually flowing than it is. For example, if you halve the resistance of a current shunt without recalibrating, the controller will allow twice as much current to flow.
In the case of the Insight, the so-called “40% hack” is the most popular. It’s so termed for the amount of extra power it enables the car to run. Where the Insight’s Integrated Motor Assist delivers 13.4 hp stock (10kW), with the 40% hack, it delivers 18.8 hp. The hack involves adding resistors to the MCM and BCM so they only read 70% of the actual current value.
But wait, how does that add up to 40%? Well, let’s imagine the modules are set to a current limit of 100 amps. Then, the current shunt’s actual resistance is dropped by 30%, so that the controllers only see 70 amps when 100 amps is flowing. In that case, if the controller is seeing 100 amps, it’s actually outputting 142 amps – 42% higher. It’s referred to as the “40% hack” for ease. It’s also possible to use different value resistors to run a “20% hack” or a “60% hack” if you want to change the current limit of the motor by a lesser or greater degree. In the latter case, the higher current flow tends to throw codes as the transistors that control the motor can’t keep up. The 40% hack is considered a “safe” boost for stock cars without major modifications.
Modifying the BCM in this way is fairly easy. The stock current shunt consists of two large resistors that are readily visible on the board. Soldering in another resistor in parallel helps reduce the total resistance of the shunt by the appropriate amount. It’s a little counterintuitive, but yes, adding another resistor in parallel actually cuts the total resistance. Why? Think of an electric wire like a pipe. A bigger pipe can flow more water. Adding on an extra pipe to the two already there allows more water to flow—i.e. there is reduced resistance!
The MCM is harder to modify—mostly because it senses the current flowing to the motor in eight wires. Each has its own current shunt which requires modification. However, to get around this, a forum user called Bull Dog (no relation to Bob “Bulldog” Briscoe) along with another named retepsnikrep whipped up an easy solution. It’s a PCB that’s already preloaded with resistors for each shunt. It’s designed to drop onto the MCM’s existing board with solder points in all the right places to hook the resistors into the right points of the circuit. It’s not a beginner job, by any means, but it’s about as easy as installing a modchip in a console. The latest versions even feature tiny DIP switches to select 20%, 40%, or 60% current boosts.
There’s just one thing left to do to enable the power boost. There’s a fuse that serves as a further limit on the output from the Insight’s battery. This has to be swapped out to allow higher current flow. A 150 amp fuse is recommended for using the 40% hack. It’s difficult to change out, requiring the removal of the hybrid battery to gain access. Plastic tabs also have to be removed to make room for the larger 150 amp fuse, compared to the 100 amp stock part. However, this swap is necessary to avoid blowing the stock fuse with excess current draw from the motor.
Based on forum posts, the cost of the hack is usually well under $100. The 5.3 hp boost might not sound like much, but it’s a bargain at that price. Compare it to people buying cold air intakes for $1,000 which maybe add 5 to 10 horsepower, if you’re lucky. By comparison, this is allegedly a sure thing as long as your Insight doesn’t have a completely worn-out and tired battery that can’t deliver the extra current.
It bears noting that this “current hack” technique isn’t just limited to Honda hybrids. I know this, because I’ve actually done it myself! It’s a popular way to get more power out of a cheap electric scooter. I used this trick to boost the power of my Razor E300, albeit with often smoky or fiery results.
In the case of the Insight, there are plenty of users reporting success with the 40% boost. On YouTube, Insight owner gray25xt posted a video showing the acceleration of their 2003 Insight with a 40% current hack installed along with an aftermarket lithium battery pack. It’s similar to the third-party lithium-ion packs developed for the Toyota Prius. However, in this case, the 40% current hack allows them to make the most of the extra current capability of the lithium-ion batteries. They report slashing their 0-60 mph time down to 9.0 seconds, down from 10.5 seconds when the car was stock and factory-fresh. That’s a big drop to claim for just 5.3 additional horsepower from the hybrid system, and it’s worth noting that it’s not a scientific comparison with multiple runs averaged out.
There is still plenty of praise to be found out there for the hack. YouTuber 100PercentJake noted the hack was transformative in the way the Insight drives. “It’s like a real car now!” he exclaims as he does a pull in second gear. The original Insight was infamous for its slow acceleration. In a car like that, it’s clear that it doesn’t take much additional power to make a noticeable improvement. He finds little numerical difference in acceleration tests, which he puts down to his weak battery, but says the car has more “pep” when driving around town. In a later video, he fits a lithium replacement pack which he credits with drastically improving the car in concert with the 40% hack.
Should you expect great things from the 40% hack? Well, it really depends on the state of your first-gen Insight. The newest examples are pushing 20 years old, with hybrid batteries that aren’t necessarily at their best anymore. On a car like that, you can always throw $100 at doing the hack to see if it works for you. It’s cheap enough that if it doesn’t make much difference, you’re only out a few cases of beer. If you’re doing a lithium battery swap, though, the upgrade seems like a much stronger proposition, given the fresh batteries are more capable of delivering the greater current flow enabled by the hack.
Ultimately, the current hack will only net around 5 horsepower at most, but it’s probably the cheapest 5 horsepower you’ll ever get. If you’re confident working on electronics and know how to work with a hybrid battery safely, you might find this is a great mod for your first-gen Insight. If not, best leave it to the pros. With or without the hack, your Insight isn’t beating anyone at the stoplight drags anyway.
Image credits: L. Day, Peter Perkins, 100percentJake via YouTube screenshot