Remap vs Tuning Box: What's the Difference?

A remap changes the software inside your car’s engine control unit (ECU), so the settings the ECU controls can be recalibrated for your engine. A tuning box is a separate module fitted between the engine’s sensors and the ECU. It adjusts the signals the ECU receives and leaves the ECU’s own software as the factory wrote it.

In short

A remap rewrites the ECU’s own calibration. A tuning box works from outside the ECU and leaves its software untouched.
A remap can change the parameters the ECU controls, such as turbo boost, fuel injection, ignition timing and throttle response. A tuning box can only change the signals it is connected to.
On most modern cars a remap is done through the OBD diagnostic port, with the ECU left in the car.
Every BHP UK remap is written in-house from the file read from your own car’s ECU.

How each one works

The ECU is the engine’s computer. On a modern car it controls how much boost the turbo makes, when and how much fuel is injected, when the spark plugs fire, the fuel rail pressure, variable valve timing, throttle opening and how quickly the throttle responds.

Manufacturers have to set all of this for every market a car might be sold in, for owners who skip maintenance and for poor-quality fuel. They also down-tune some cars to fit market categories: a lower model is often the same engine, mapped at the factory to make less power. Our FAQ gives the BMW Mini One and Mini Cooper as an example. Our guide to ECU remapping explains this in more detail.

A remap works on that factory calibration directly. The software is read from the ECU, the calibration is changed, and the new file is written back. At BHP UK we always remap the file we read from your vehicle’s ECU, so the remap is bespoke to your car. We never reuse a remap and never use generic “off the shelf” files. Because our map writers work in-house, we can set a remap up for what you want from the car: economy, all-out power or towing.

A tuning box, also sold as a tuning module or “piggyback ECU”, is an extra unit fitted between the engine’s sensors and the ECU. It changes what the ECU is told, and the ECU then runs its unchanged factory software on that adjusted information.

Side by side

	ECU remap	Tuning box
How it works	The ECU’s own software is read, changed and written back	A separate module between the sensors and the ECU adjusts the signals the ECU receives
What it changes	The calibration for parameters the ECU controls, such as boost, fuel injection, ignition timing, fuel rail pressure, throttle opening and throttle response	Only the signals the module is connected to. The ECU’s own maps and limits stay as the factory set them
Fitting	Through the OBD diagnostic port on most modern cars. Some ECUs are read and written on the bench or in boot mode	Installed as an extra unit between the sensors and the ECU
Removal	Standard software is written back to the ECU	The module is taken out. The ECU’s software was never changed
Typical drawbacks	The result depends entirely on the map, so it has to be developed and tested for your engine.	It works around the factory software rather than changing it, so anything the ECU decides internally stays the same.

What a remap can change that a tuning box can’t

A tuning box can only change the signals it is connected to. Everything the ECU decides internally, including its own maps and the limits it sets, stays as the factory wrote it. A remap edits that calibration directly, so it can change how the ECU behaves, not just what it is told:

The ECU’s own maps, such as fuel rail pressure, ignition timing and variable valve timing, rather than the readings they are based on.
The limits the ECU sets, which a tuning box leaves in place.
Throttle opening and how quickly the throttle responds, which the ECU controls itself.

Our remaps are developed for linear power delivery, more low-down torque, better throttle response and improved drivability on the road.

How each one is fitted

Normally, on most modern cars, we can reprogram the ECU through the car’s OBD port. On vans, we connect a laptop and tuning equipment to the OBD diagnostic port, so the ECU does not have to come out of the vehicle. Some ECUs can’t be reached that way and are read and written with the unit removed (bench) or opened (boot mode). Our guide to OBD, bench and boot-mode remapping explains the difference.

A tuning box is fitted as a separate unit between the sensors and the ECU, and the ECU itself is not reprogrammed.

Taking it off again

A tuning box comes off by removing the module. A remap is reversed by writing standard software back to the ECU. Our FAQ is clear on this: “We can always return your car to standard should you ever need it to.” Read more in Can a remap be reversed?

How we develop a remap

Before we remap a customer’s car, we have already developed the remap for that make and model. We test the standard car on the road and on our Dynojet 424 XLC² rolling road, logging air-fuel ratio, intake air temperature, coolant temperature, exhaust gas temperature, spark advance, turbo boost pressure, power and torque. We then write test maps step by step, test them on the dyno and finish on the road to make sure they work in real driving. Read more about our dyno development.

Talk to us

Look up your car in our remap finder to see the figures for your engine. Call 01282 779 000 for a free consultation, contact our Burnley workshop or find a local BHP UK dealer.

Frequently asked questions

Is a tuning box the same as a remap?

No. A remap changes the software inside the engine control unit (ECU). A tuning box is a separate module fitted between the engine's sensors and the ECU, and the ECU's own software is left as the factory wrote it.

Can a tuning box be removed?

Yes. Because a tuning box does not rewrite the ECU, taking the module out leaves the ECU running the software it always had.

Can a remap be undone?

A remap is a change to the ECU's software, so the ECU can be given its standard software again. As our FAQ says: "We can always return your car to standard should you ever need it to."