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If you are working on a classic tuner car like an R32 GTR, an Evo 1-9, or an early Honda, you’ve likely encountered the "resistor box." These cars were built using Low Impedance injectors. However, if you look at any modern high-performance injector, including the entire Excess Injectors range, they are almost exclusively High Impedance.
Why did the industry move away from Low Impedance technology, and what does it mean for your build? Here is the breakdown of the electrical "tug-of-war" inside your fuel system.
The Electrical Difference
"Impedance" is a measure of electrical resistance, measured in Ohms.
- Low Impedance (Peak and Hold): These injectors have low resistance, typically between 2.0 and 4.0 Ohms. They require a high initial burst of current to "snap" the injector open, followed by a lower current to hold it there.
- High Impedance (Saturated): These have higher resistance, typically 11.0 to 16.0 Ohms. They use a much lower, constant amount of current to keep the injector open.
Why Low Impedance Used to Be King
In the 1980s and 90s, if you wanted a "big" injector (anything over 500cc), it had to be Low Impedance.
Because the internal coils and magnets were heavy, you needed a massive "jolt" of electricity to move the heavy internal pintle quickly. High Impedance injectors back then were too slow to handle high flow rates. This is why older ECUs were designed with complex "Peak and Hold" drivers, or why manufacturers used "Resistor Packs" to prevent the ECU from burning out.
Why High Impedance is Better
As technology advanced, manufacturers learned how to make the internal components of an injector much lighter and the magnetic coils much more efficient. This led to the rise of the High-Flow, High-Impedance injector.
Here is why modern ECUs (like Haltech, Link, and Motec) and tuners prefer them:
Less Heat, More Reliability
Because High Impedance injectors use less current, they generate significantly less heat. Heat is the enemy of electronics; it causes resistance to change and can lead to injector "drift" or total failure during a long race or a hot summer day.
Simplified Wiring
With High Impedance injectors, you don’t need a resistor box or a specialized "Peak and Hold" driver. You simply wire them directly to the ECU. This means a cleaner engine bay, fewer points of failure, and a much easier installation process.
Superior Precision (The "Short Pulse" Game)
Modern High Impedance injectors, like the ones used in Excess Injectors kits, are incredibly fast. They can open and close with microscopic precision. This allows a massive 1500cc injector to deliver the tiny, precise amount of fuel needed for a smooth 800 RPM idle, something that was impossible with older Low Impedance technology.
Can You Swap Between Them?
- Upgrading to High Impedance: If your car originally came with Low Impedance, you must delete the resistor pack when upgrading to Excess Injectors. If you don't, the signal will be too weak to open the new injectors.
- The Risk: Never plug a Low Impedance injector into a modern ECU designed only for High Impedance. The low resistance will draw too much current and can literally melt the injector drivers inside your expensive ECU.
The days of choosing between "fast" Low Impedance and "reliable" High Impedance are over. Modern engineering has given us the best of both worlds.
By using High Impedance injectors, you get a simpler fuel system, a cooler-running engine, and the ability to run massive flow rates without sacrificing driveability. It’s why every set of Excess Injectors is built on high-impedance cores, engineered for the precision demands of modern tuning.