# Custom ECU functions

> Custom ECU functions: Pop&Bang, Hardcut, Launch Control, torque delivery, throttle pedal, FLAP OFF and VMAX OFF. What each one does and its legality.

- URL: https://www.reprogramacionesmbv.com/en/ecu-remapping/custom-functions/
- Index for AI (llms.txt): https://www.reprogramacionesmbv.com/en/llms.txt
- Versión en español: https://www.reprogramacionesmbv.com/reprogramacion/funciones-a-medida/
- Reviewed: 2026-10-15

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Some people don't want more power, they want the car to do something specific: pull away better from a standstill, have a less snappy pedal or sound different when they lift off. Here each function is explained separately, with the wear it causes and what the rules say.

**In short:** Custom functions are specific changes to the ECU (engine control unit) software that aren't necessarily about more power: Pop&Bang (crackles when you lift off the throttle), Hardcut Limiter (a sharp cut at the rev limiter), Launch Control (pulling away from a standstill at a fixed rpm), torque delivery adjusted per gear, throttle pedal sensitivity, exhaust valve control (FLAP) and the speed limiter (VMAX). They can be ordered on their own or together with a Stage remap. Some increase wear or noise and others have clear legal limits: the limiter on lorries and buses is never touched. Price on request depending on the function and vehicle, in the Community of Madrid (the Madrid region).

We carry out all of these functions both for private customers and for track cars, Pop&Bang, FLAP OFF and VMAX OFF included. What changes is how you use them: for each one we tell you what the rules say if the car is driven on public roads.

## Pop&Bang

**What it is.** The crackling you hear from the exhaust when you lift off the throttle, typical of competition cars.

**How it works.** On the overrun, the stock ECU cuts injection. With Pop&Bang a small amount of fuel is still injected and the ignition is retarded, so part of the mixture burns in the manifold and the exhaust rather than in the cylinder. It's a petrol engine function; on diesels, what gets programmed under a similar name is something else (see Hardcut).

**What it wears.** That combustion outside the cylinder raises exhaust temperature considerably. It punishes the **catalytic converter**, the **turbo** and, over time, gaskets and silencers. A damaged catalytic converter ends up turning on the engine warning light and failing the ITV.

**Legality.** This is where the main problem lies: noise. The Reglamento General de Circulación (Spain's General Traffic Regulations, art. 7) prohibits driving while exceeding the established noise limits.

**Pop&Bang on road cars**

Crackles on the overrun increase the vehicle's noise and punish the catalytic converter. On a car driven on public roads it can mean exceeding the noise limits (art. 7 of the General Traffic Regulations) and, if it damages the catalytic converter, a defect at the ITV. We recommend it for track use only and, if you ask for it, we programme it at a moderate intensity and in a way that can be removed.

## Hardcut Limiter

**What it is.** A sharp cut when the engine reaches maximum rpm, instead of the stock soft cut. On diesels it's often called "popcorn", after the stuttering sound it makes.

**How it works.** As standard, as the engine approaches the rev limit, the ECU gradually trims torque. With Hardcut the engine revs freely up to the limit and then cuts injection abruptly, again and again for as long as you hold the pedal down.

**What it wears.** Repeated shocks through the transmission and engine mounts if it's overused. On diesels, each cut produces a spike in temperature and smoke.

**Legality.** It doesn't change the power stated in the documentation, but it does change the vehicle's noise at the limiter. Reasonable use, and the track if you want to push it.

## Launch Control

**What it is.** An aid for pulling away from a standstill with maximum traction: the engine is held at a fixed rpm while you wait and, when you let go, the launch is repeatable.

**How it works.** On manual cars, the ECU detects the clutch pedal pressed and the car stationary, and limits revs to a chosen value; when you release the clutch it lifts the limit. Many sporty automatics already have it from the factory, and it's adjusted in their transmission control unit.

**What it wears.** It's the function that's hardest on the drivetrain: **clutch**, dual-mass flywheel, driveshafts and differential. Every launch is a load a stock car isn't expecting to take often.

**Where it makes sense.** Track starts, drag racing or hill climbs. On the road, launching like that serves no purpose.

## Torque delivery

**What it is.** Changing how torque arrives in each gear, not how much total torque the engine has.

**What it's for.**

- **Softening first and second** on cars that spin their wheels when pulling away or on wet roads.
- **Protecting the transmission** by limiting torque in the lower gears, where loads are highest.
- **Making the curve more linear** if the car delivers everything at once and is hard to modulate.

It's one of the most useful and least known functions. It's often ordered together with a [Stage 1](https://www.reprogramacionesmbv.com/en/ecu-remapping/stage-1/) so that the extra torque doesn't just turn into wheelspin.

## Throttle pedal

**What it is.** The accelerator on a modern car doesn't pull any cable: it's a sensor that tells the ECU what percentage of pedal you're pressing, and the ECU decides how much torque to request for that percentage.

**What gets adjusted.** That relationship between pedal and torque. It can be made more direct (more response in the first part of the travel) or more progressive (easier to modulate). **It doesn't add power**: the engine delivers the same at full throttle, only how you get there changes. For economical driving, the approach is the one in [Eco remapping](https://www.reprogramacionesmbv.com/en/ecu-remapping/eco/).

## FLAP OFF (exhaust valve)

**What it is.** Many sports cars have a valve in the exhaust that the ECU opens or closes depending on rpm, load or driving mode. With it closed the car is quieter; open, louder.

**What gets adjusted.** Having the valve always open, always closed or opening under different conditions. It's also used to clear the fault warning when the valve has failed and been removed.

**Legality.** The vehicle was type-approved with a specific way of managing that valve. Leaving it open all the time increases noise and, as with Pop&Bang, the limit is in art. 7 of the General Traffic Regulations. If what you have is a faulty valve, the sensible thing is to repair it after [diagnostics](https://www.reprogramacionesmbv.com/en/vehicle-diagnostics/).

## VMAX OFF (speed limiter)

**What it is.** Many cars have a top speed limited electronically by the manufacturer, for commercial reasons or because of the tyres fitted as standard. VMAX OFF removes or raises that limit.

**Speed limiter: two very different cases**

**Lorries, buses and other vehicles required to have a speed limiter**: we never touch it. Taking part or helping in fitting or activating anything that alters how the speed limiter or tachograph works is a **very serious offence** (art. 77.m of RDL 6/2015, Spain's Road Traffic Act).

**Cars with a manufacturer's limiter**: no rule requires them to have one, but the general maximum speed in Spain is still the one in the General Traffic Regulations (art. 48), well below those limits. Removing it only makes sense on a track, and requires the **tyres and brakes** to be up to that speed: the tyre's speed rating marks the maximum it can take.

## Which functions can be combined

| Function | With a Stage remap | On its own on stock | Recommended use | Main wear or risk |
|---|---|---|---|---|
| Pop&Bang | Yes | Yes | Track | Catalytic converter, turbo, noise |
| Hardcut Limiter | Yes | Yes | Moderate use | Transmission and mounts |
| Launch Control | Better with a Stage | Depends on the car | Track | Clutch and driveshafts |
| Torque delivery | Yes | Yes | Road and track | None: it protects the transmission |
| Throttle pedal | Yes | Yes | Road | None |
| FLAP OFF | Yes | Yes | Depends on noise | Noise |
| VMAX OFF (cars) | Yes | Yes | Track | Tyres and brakes |

If a function changes data shown on the ITV card or what was type-approved, it may be a modification: it's explained on [legality, ITV and insurance](https://www.reprogramacionesmbv.com/en/legality-itv-insurance/). On motorbikes, similar functions are requested with their own particularities: see [motorbikes](https://www.reprogramacionesmbv.com/en/motorcycles/). And if you're a garage, you can order any of them through our [file service](https://www.reprogramacionesmbv.com/en/trade/file-service/).

## Price

Each function is **price on request**, because it depends on the ECU and on whether it's programmed on its own or alongside a remap. Ordered with a Stage remap, it's quoted as part of the same job; our remaps start from from €200 + VAT (€242 including VAT).

Tell us which function you want and what for (road or track). We'll confirm whether your ECU accepts it, what it involves and the price.

## Frequently asked questions

### Can I have a function without a Stage remap?

Yes. Functions such as pedal or torque delivery adjustment can be programmed on the stock software without touching anything else. Others, such as Launch Control, make more sense if the engine has already been remapped.

### Can they be switched off later?

Yes. The software can be rewritten without that particular function, or the car can go fully back to stock. We explain it on [back to stock software](https://www.reprogramacionesmbv.com/en/back-to-stock-software/).

### Will my car accept these functions?

It depends on the ECU and on how that model manages the throttle, exhaust or clutch. Some functions need signals that not every car has (for example, the clutch pedal switch for Launch Control on manuals). With the make, model, engine and year we'll confirm it.

### Can you remove the limiter on my large van or lorry?

No. On vehicles that are required to have a speed limiter, tampering with it is a very serious offence for whoever does it and whoever helps. We explain it on [commercial vehicles](https://www.reprogramacionesmbv.com/en/commercial-and-agricultural-vehicles/).

### Will the ITV pick up Pop&Bang?

At the ITV (Spain's compulsory periodic vehicle inspection, similar to the UK MOT) the exhaust system is checked and noise and emissions can be measured, and a catalytic converter damaged by the crackles usually ends up showing. Beyond the ITV, the problem is on the road: driving while making noise above the limits is prohibited and the police can fine you for it. That's why we recommend it for track use.

## Sources

- [Royal Decree 1428/2003, General Traffic Regulations, arts. 7 and 48 (BOE, Spain's official gazette)](https://www.boe.es/buscar/act.php?id=BOE-A-2003-23514)
- [Royal Legislative Decree 6/2015, Spanish Road Traffic and Road Safety Act, art. 77.m) (BOE, Spain's official gazette)](https://www.boe.es/buscar/act.php?id=BOE-A-2015-11722)
- [Royal Decree 866/2010 on the processing of vehicle modifications (BOE, Spain's official gazette)](https://www.boe.es/buscar/act.php?id=BOE-A-2010-11154)