When it comes to BMW tuning the first thing you need to consider are the goals you have for your car. Is this is a daily driver, a weekend fun car, or a race track car that I am trying to extract maximum performance from? The answer to that question is crucial to figuring out the best tune for you.
BMW Tuning For A Daily Driver
If the car is to be driven every day, being slightly conservative on your tune is important. Also bearing in mind the torque limit of the engine and drivetrain components into your decisions. Here are the things that will limit your power gains from being safe:
- Strength of the engine.
- Fuel delivery of the fuel injection system.
- Ignition system capability to fire the increased pressure inside the combustion chamber.
- Strength of the drivetrain components.
- Octane of the fuel you are running.
- Turbo RPM Limit.
- Turbo or exhaust back pressure.
- Turbo compressor efficiency at the boost you are running.
- Heat exchanger’s ability to keep up with increase power and heat.
- Quality of the software.
- Traction (especially if the car is 2WD).
How Much Power Is Too Much Power?
Remember torque is what does the damage. Torque is the twisting action that is generated by the engine. This is like what you read on a torque wrench in lbs/feet or newton/meters. Most car companies build around a 50% safety margin into the engine and drivetrain components. This means that if the car comes with 500 lb/ft of torque, you can generally make 750 lb/ft safely before the drivetrain will start to break. This only refers to the engine and drivetrain strength. This does not mean that the rest of the engine management system (fuel delivery, ignition system, and heat exchangers) will handle this much power.
BMW Tuning Stage 1: Software
Stage 1 software tune is typically around 10-15% increase in power. This is very safe even for daily driving.
BMW Tuning Stage 2: Software, Intercooler/Heat Exchanger And Cold Air Intake
If you add a high flow intake system and larger heat exchanger or intercooler, you can achieve around 25-35% increase in power. This is very safe on stock engines using 93 octane pump gas. This car can still be driven daily and will typically last around 100k miles with normal maintenance.
BMW Tuning Stage 3: Software, Intercooler/Heat Exchanger, Cold Air Intake, And Larger Turbo(S)
If you add a high flow intake system, a larger heat exchanger or intercooler, and a larger turbo, you can achieve around 35-45% increase in power. This is very safe on stock engines using 93 octane pump gas. This car can still be driven daily and will typically last around 100k miles with normal maintenance. The larger turbo will have the negative side effect of increased turbo lag, so this vehicle will be less refined in traffic or stop/start scenarios where turbo response is nice to have.
BMW Tuning Stage 4: Software, Intercooler/Heat Exchanger, Cold Air Intake, Larger Turbo(S), And Methanol Injection
If you add a high flow intake system, a larger heat exchanger or intercooler, a larger turbo and a meth injection kit you can achieve around 45-55% increase in power. This is very safe on stock engines using 93 octane pump gas. This car can still be daily driven and will typically last around 100k miles with extra maintenance. The larger turbo will have the negative side effect of increased turbo lag, so this vehicle will be less refined in traffic or stop/start scenarios where turbo response is nice to have.
This is where it can get tricky. Methanol produces a lot of corrosion in the meth system. Therefore, failures with the components in the added Methanol injection system are common with age. This could be clogged nozzles, corroding lines, and premature pump/seal failures. If you run Methanol with software for pump gas (91-93 octane) and the Methanol fails, you just lose power in the moment.
If you tune the software of the engine specifically for the methanol to make more power and the meth fails, the engine will fail also. This is the most common failure in a turned car!
BMW Tuning Stage 5: Software, Stacked ECU (Piggy Back), Intercooler/Heat Exchanger, Cold Air Intake, Larger Turbo, Methanal Injection, Secondary Fuel Injection System, Removal Of The Exhaust Catalyst, And Reinforced Engine, Gearbox And Transfer Case Internals
At this level, you are exceeding the design limits of the car as well as the 50% safety margin. The engine and drivetrain must be strengthened to retain drivability. Even after you improve the engine and drivetrain internals, the next “weakest link” component will likely fail. Examples are; driveshafts, engine and transmission mounts, half shafts, transfer cases and differentials.
With this level of performance you can achieve around 80-120% of what the car was originally designed for. This car will require race gas (100 octane), diligence in Methanol operation and consistency, and the more frequent replacement cycle of wear items (clutches, differentials, axles, driveshafts, rubber mounts or U joints, hydraulic pumps, etc.) This is basically a racecar, which requires racecar levels of attention to detail and maintenance. This is no longer a daily driven vehicle.
The Problem With Some Aftermarket Tunes/Tuners
The OEM’s have placed layers of safety in the ECU software of your vehicle. This includes, but is not limited to; Exhaust Gas Temp Threshold, Engine Torque Limits, Drivetrain Torque Limits, Mass Air Flow Threshold, Fuel Flow Threshold, and Ignition Timing Limits just to name a few. These limits act as floors and ceilings, with a small margin for adjustment/correction built in to stay within the window of operation.
Good tuning companies will re-tune these limits, leaving the protections in place and resetting them to a higher limit based on the safety requirements determined by the new hardware on the vehicle. When this is done correctly, the tuning company will often provide a warranty with their aftermarket product because they are confident that your car and it’s powertrain will be safe. Many tuners do not really understand these limits, or do not want to spend the time and money to R&D and reset these limits, so they turn the Engine Safety measures off and will claim “they were in the way of more power!” This is a recipe for failure.
What We Are Trying To Achieve At Carbahn.
Improved Performance is generally faster acceleration or better handling, and in a perfect world, both. Once you exceed the limit of the tire, any additional power or additional handling hardware goes to waste, because the only thing contacting the road and allowing the force to be transferred into motion is overloaded. The TIRE. You see more torque does not always make a car faster. Once you exceed the traction capabilities of the tires, the torque goes up in (tire) smoke, and the car doesn’t go anywhere.
Let’s use drag racing cars as an example. Top level dragsters use slipper clutches, which reduces torque to the maximum amount the tire can handle at that time or speed. As the dragster goes faster (and downforce increases) the traction limit becomes smaller and the clutch reduces slip/adding power to the drive wheels. Done in a perfect world, and you have no traction loss during the whole run.
On a road-car, we have a transmission that increases torque at the rear wheels dramatically for acceleration from a stop. Lower gears have a greater torque multiplication than the higher gears. With modern high-performance turbo car’s, their powerband naturally has a surge of torque when the turbo becomes efficient, usually between 2500-5000 engine RPM. If that surge in torque causes the tires to break traction, that is an immediate loss of acceleration.
Most 2WD road cars with largest, sticky performance tires you can find can handle 500-550 lb/ft of torque before traction is an acceleration limitation. AWD cars can handle as much as 800 lb/ft without losing traction due to spreading the acceleration work load to the front 2 tires as well as the rears.If we make an exotic tune with 100% more HP we can gain a lot of durability by holding the torque to 50-60% over stock values. This torque limit can provide durability of the car’s drivetrain, as well less traction problems.
A great example would be the BMW M2, M3, or M4 with the S58 engine comes with 550hp and 500 ft.lb. of torque from the OEM. If we do a good job of tuning and spend money on proper hardware, we can make 1,100 hp and 750LB/ft torque with reasonable durability.