Today we’re delving into the subject of Launch Control. What it is, how it works and how it can help you win races!
But before we get into the specifics of things, we need to understand the problem that we’re trying to solve.
In order for a car to launch consistently we need the engine RPM, throttle position and manifold pressure to be in a state that makes exactly the right amount of power in order for the car to take off as quickly as possible every time.
We also need to be able to alter this launch power depending on the racing surface and the track conditions.
In order to achieve these right launch conditions we employ a function universally known as Launch Control.
This fairly ambiguous term describes a whole range of different engine management functions.
Is the car automatic or manual? Is it turbocharged or supercharged? Does it make the required launch power under its own steam or does it need a little help to get there? Let’s go through a few common scenarios and explain what’s actually happening in order to get the car to take off.
Aux RPM Limiter
The most basic form of launch control is the Auxiliary Rev Limiter. When the clutch or brake pedal is depressed or the trans brake is active a secondary engine rev limiter is activated preventing the engine from revving past this value.
Let’s use 5000RPM as an example. The engine will react exactly the same as it normally would (same fuelling, same ignition timing), except the rev limiter that’s normally at 9000RPM is now at 5000RPM.
We have the option of cutting fuel, ignition or both in order to achieve a consistent launch RPM, as well as the option of a hard cut, soft cut or cut-off rev limiter. All these allow us to change the sound and speed of the rev limit noise from smooth and relatively quiet to aggressive and wild!
This limit allows the driver to hold the throttle flat and the engine to bounce off the lower rev limit in order to launch consistently.
Building on this strategy, we can now look at the Launch Control function, which is similar to the Aux RPM Limiter but with a little more functionality.
This feature controls the launch rev limit but allows us to map the limit vs. a 3D table. We can look at throttle position and boost pressure for example but you can choose any tables.
This allows the driver to have a higher launch RPM at 50% throttle and low boost, thus inducing more exhaust flow, resulting in more boost pressure, resulting in more power.
When the desired boost pressure has been achieved the driver can go to full throttle which will drop the engine RPM to the mapped launch RPM and you’re ready to go!
The same method of mapping the launch RPM vs. throttle position can also help tame big, powerful, fire breathing drag cars when trying to bring them into the staging beams, reduce engine wear as much as possible and even confuse your competitor when the RPM limit keeps changing depending on the racers right foot.
The launch control function also allows us to make fueling and ignition changes while the function is active. Typically a little more fuel would be added in order to assist with in-cylinder temperatures, but the ignition timing is a little more tricky.
If the engine’s turbocharged and equipped with a Clutch then you’d want to massively retard the ignition timing so the spark event occurs after top dead centre – sometimes up to -20 degrees or even more.
Firing the ignition event this late means the exhaust valve will be open or just about to open and all that energy goes straight into the turbochargers exhaust housing and spools the turbocharger up. Once the engine’s making boost pressure (loaded against the retarded ignition timing) it is then making power.
With this power it can make more power and finally get to the desired launch RPM and boost pressure but without loading the engine against the retarded ignition timing it wouldn’t ever get there.
This methods is sometimes referred to as Launch Anti-Lag, however with this method there’s no exhaust manifold air injection like you have with Rally Anti-lag.
Using the Torque Converter
If the engine’s bolted to a torque converter then we need to tackle this a little bit differently. The engine already has something to load against so retarding the ignition timing will only hurt the engine power and even stop the engine from coming on boost.
The best method in this setup is to apply the trans or foot brake then apply full throttle. If the engine reaches the desired launch RPM and manifold pressure then things are good, if it doesn’t – we might want to add ignition timing to try and increase engine power in this area.
Keep in mind however the ignition map should already be tuned in this area to make the most engine power possible.
If you still have no luck, you might want to increase the engine’s down low power using Nitrous and the Elite’s advanced nitrous control strategy. We could add a dry Nitrous fogger which would be activated only when the trans brake input is active and when the engine is below the launch RPM.
All the same safety features are used, like the engine needs to be over a pre-programed coolant temperature, between chosen manifold pressures and over a certain throttle position. The ECU then triggers the Nitrous solenoid and applies the desired ignition retard depending on how much Nitrous is being used.
If it still doesn’t come up you could either add more Nitrous or change to a more slippery torque converter – but that’s going to be a lot of work!
You could tie any of the Launch RPM methods together to create a kind of “3 Step” style strategy where the first step is a Burnout Limit, the second is the Launch Limit, and then finally the third “step” is the engines main RPM limiter.
As you can see, there are many options available and it’s not really just three “steps”. Each limit has its own flexibility resulting in different limits for different situations which results in different outcomes. And each can be programmed to get the perfect launch from your car every time.