Everything you ever wanted to know about performance upgrades (but were afraid to ask).

BMW M2 with AC Schnitzer performance upgrade and engine optic.

AC Schnitzer have been tuning BMWs and MINIs for over 30 years. Early efforts included big-bore engines with wild cams and even superchargers bolted on. Things have moved on, but the subject of performance upgrades is still one that takes up more of our time when talking with customers than any other. The bewildering range of terms used (remaps, chips, flashes, tuning boxes…), the technical differences between them and the pros and cons of each tuning method is enough to make your head spin. Then there are the warranty implications to consider. Oh dear!

Thankfully, AC Schnitzer offer a clear upgrade path that won’t cause you any sleepless nights. It’s not for everyone, as we’ll see in a moment, but for many BMW and MINI owners there is no better choice than AC Schnitzer.

“I’ve seen AC Schnitzer upgrades advertised – they are expensive!”

It’s fair to say that we hear this comment often, and we’re aware of course that there are many less expensive alternatives out there. But there are sound reasons behind this. Let’s take a look at them.

Worldwide, many AC Schnitzer dealers are also BMW dealers. AC Schnitzer is owned by the Kohl BMW Group. So AC Schnitzer aim their product range at new and nearly new cars (under 3 years old). All AC Schnitzer upgrades must meet the following requirements:

  • The upgrade must not alter the vehicle software
  • The performance increase must be safe and legal, for you and for the car
  • The power delivery characteristic must be like standard
  • There must be no change to servicing and diagnosis procedures
  • The car must still meet all emissions requirements
  • The engine components and drivetrain must still be covered by warranty.

“Can’t I just get a re-map?”

Leaving aside the highly variable quality of software tuning (re-maps) on the market, AC Schnitzer upgrades are always made with hardware. This means an extra engine control unit (ECU) mounted in the engine bay to take care of the tuning duties. AC Schnitzer don’t offer tuning via software because this can affect the car’s warranty, and also means that if BMW needed to apply a service update that software could be overwritten. BMW check your car every time it visits the dealer to see if the software has been altered from standard. Inconvenient, at best. At worst, a major warranty claim could be denied.

AC Schnitzer engine control unit and loom. The red/blue twisted pair is the CANBUS connection.

“So it’s an expensive tuning box then.”

In a way, yes, but a sophisticated one. Unlike some tuning boxes which simply manipulate boost sensor or fuel pressure information to increase power without any safety checks, or allow the owner to flip dip-switches without knowing what they are getting into, the AC Schnitzer control unit is developed to be safe for anyone to use. On a brand new car, from day one. To prove it, AC Schnitzer warrant the engine and drivetrain for 3 years – the same as the BMW warranty.

To enable this the control unit (in most cases) connects to the CANBUS system on the car which carries all the sensor information. It constantly monitors channels like boost pressure, exhaust gas temperature (EGT), injector duration and many other inputs, to make sure that the performance increase is being delivered in a safe way. The full power increase is only available when the engine is fully warmed up, and running on the recommended fuel (98 octane on petrol engines). We can only give an engine warranty by tuning the car in this way.

“Tell me more about this warranty.”

All AC Schnitzer performance upgrades include a warranty that runs alongside the BMW factory warranty from the date of first registration. In the UK, this is for the first 3 years of the car’s life. The warranty stays with the car, not the owner.

There are conditions. Read more about them here. But in essence this warranty is the best available in the tuning world. It’s designed to cover any faults arising from the tuning that BMW won’t cover. In most cases an engine fault will be unrelated to the tuning and will still be rectified under your BMW warranty, but should you need it we can step in. AC Schnitzer in Germany will help diagnose and rectify the problem and our network of friendly BMW and independent dealers will help too.

“My car is 5 years old, what now?”.

We may still be able to offer tuning, but we can’t warrant the engines on older cars, sorry. Please contact us for advice.

“I want to buy/move/sell a used AC Schnitzer upgrade – what happens with the engine warranty?”

Contact us with details – we may be able to help with warranty in these cases.


AC Schnitzer performance upgrades are the best option for new and nearly new cars. They cost more than other tuning products because they are the best developed, from the best BMW tuner, with the best warranty.

  • Safe and reliable power increase
  • Driveability just like standard
  • 3 year engine/drivetrain/OPF warranty included
  • No need to remove upgrade for servicing
  • BMW service updates can be applied as usual
  • Can’t be accidentally overwritten
  • Can be ordered at selected BMW dealers

6 thoughts on “Everything you ever wanted to know about performance upgrades (but were afraid to ask).

    • Hi Kenny, AC Schnitzer don’t use software to tune cars for the reasons described in the article. We also don’t tune Audis, so sorry I can’t comment on the effectiveness of a software tune on an Audi. The RS4 is a great car though!


  1. I bought used car which is equiped with ac schnitzer power kit, but I dont know if its still working. Is there any way of checking it?

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