When running one of our supercharger kits you will need to consider how to control your ignition timing. The method used will largely be driven by the performance level that you are targeting. Higher boost levels require better and more accurate ignition control.
A basic lesson in ignition timing
The reason for needing variable ignition timing is that when ignited, the air-fuel mixture burn always takes the same amount of time to generate peak-cylinder-pressure. i.e. from the time that the spark ignites the mixture it will always take the same amount of time for the explosion to fully form.
To make use of this power, we need to make sure that the peak-cylinder-pressure (PCP) occurs when the piston is travelling downwards and the con-rod angle is at its optimum. This ensures that we have maximum power transfer, and we make the most from our air-fuel explosion
So, as it always takes the same amount of time for PCP to form, when the engine is running faster, we need to trigger the ignition event earlier in the crank rotation to ensure that the PCP events occurs at the optimum rod angle. This is why we need variable ignition timing. In its simplest form, it uses the manifold vacuum or engine speed via centrifugal force to advance the ignition as engine speed increases
But what about boost?
Well, here's the thing. The time between the ignition event and peak-cylinder-pressure is not actually fixed. Other environmental factors also influence how long the burn takes. One such factor is pressure. The higher the pressure, the more dense the mixtur, the quicker the burn happens and the sooner the PCP event occurs. So now, not only do we need to deal with variation in engine speed, but we also need to consider boost.
If we do not manage ignition timing relative to boost, what can happen is that the PCP event will happen too soon and the crank position and rod angle will not be at its optimum. This means that the PCP event actually places force on the piston, rod and crank too early in its rotation, at a sub-optimal location, which can lead to mechanical damage. The most common being piston damage such as broken ring lands. This is very similar to pre-ignition or detonation which also causes the PCP event to happen too soon.
In its simplest form, a modified distributor, that is limited to a 'safe' overall advance will function adequately. The modification limits the overall advance to a safe amount, so the ignition event and subsequent PCP event is restricted from occurring too early in the crank rotation.
Ignition control strategies
A basic modified distributor is absolutely fine for low boost applications and works well with our budget kits or applications that target approx 6psi of boost. It is however a compromise when compared to a proper boost referenced set up as it essentially ignores the actual amount of boost, which does impact drivability at partial throttle. Fortunately the supercharger provides additional power at partial throttle, and so this compromise is largely unnoticed.
A proper boost referenced setup properly controls both RPM based ignition requirements and boost related ignition requirements, and to do this it needs to monitor manifold boost and vacuum as well as engine speed. The benefit with this type of ignition control is that ignition control is optimised at partial throttle and power delivery is not only better but smoother. There are a few different strategies available...
CB Black Box ignition control
CB Performance's 'Black Box' ignition controller will provide full boost referenced ignition control. This unit connects in series wth the coil wire between the coil and distributor and also connects to the manifold to measure boost / vac. The distributor itself is then locked so that the black box controls ignition advance. This is a great solution for our vintage kit which uses a short style distributor. The CB black box controller can easily be mounted behind the fan shroud to retain a period looking engine bay.
We can provide ignition maps for the CB Black box
The main limitations with this style of system is that they are still reliant on a distributor. This has a much lower spark voltage than a solid state distributor-less system , such as our own crank-fired distributor-less ignition system, (5-10kv compared to 50kv). The small diameter low resolution trigger setup also does not provide really accurate ignition control. It is also susceptible to variations as a result of distributor drive play
123 Tune+
A per the CB Black Box, We can provide ignition maps for the 123 units. However, the 123 Tune+ distributors offer no actual benefit over running a stock distributor and CB Black box unit, which is about a third of the price .
If you are keen to spend money. Our recommendation is the black box for a budget or low boost build, or our own in house manufactured crank-fired distributor-less system for performance and higher boost applications. (our complete set up actually costs less than the 123 unit)
Just as with the Black Box unit, the main limitations with this style of system is that they are still reliant on a distributor. This has a much lower spark voltage than a solid state distributor-less system, such as our own crank-fired distributor-less ignition system, (5-10kv compared to 50kv). The small diameter low resolution trigger setup also does not provide super accurate ignition control. It is also susceptible to variations as a result of distributor drive play
We actually do not recommend the 123 units for any of our applications, as it offers no benefit over running a stock distributor and CB Black box unit, which is about a third of the price. It is also more expensive than our own crank based ignition controller, which is infinitely better.
Crank-fired distributor-less ignition system
For higher boost performance applications we recommend moving to a crank based ignition controller such as our own unit. This style of setup offers the ultimate in ignition control and is what the pro's use. Whilst many consider such set ups to be complex and difficult to program. Our units come pre-programmed. Just hook them up, the set initial timing and away you go. There's absolutely no need to program any maps, or ignition curves etc. It is designed specifically to work with Aircooled VWs and the provided MAP works out of the box for ALL boosted and N/A aircooled VW setups.
Our distributor-less unit uses a modern coil pack and delivers approximately 50kv at the plug, which is absolutely where you should be on a high boost setup. The more boost you have, the higher the spark voltage is needed to initiate the plasma arc. This is because the higher density of the air-fuel charge has a much higher resistance, requiring a stronger potential difference (voltage) to initiate the plasma arc (spark).
Our crank fired setup uses a traditional 36-1 trigger wheel set up, which is much more accurate than the tiny trigger disc used inside the 123 unit, or the points used in the black box solution, so there's minimal risk of ignition creep, which can be a major contributor to detonation. As it is crank triggered it also does not suffer from distributor drive play, which can be an issue with distributor based set ups.
Our system also comes as standard with boost, temperature and inlet air temp sensors for full ignition control. It will manage boost control and water methanol injection and also supports running a digital dash. No comparison really. As soon as you move into adding boost, or running a performance setup, you need much more accurate control of your ignition timing, which is exactly the reason we designed our unit.
Of course the above doesn't really even start to touch on the capabilities of our ignition system, which is the same software used in our EFI systems. For a more detailed breakdown visit the product page in the store.
Summary
Our recommendation is to use a modified limited distributor for low boost budget applications (approx 6psi).
If you can stretch to the cost, adding the CB Black Box controller works really well and will provide better drivability than running a modded distributor alone and provides better control for slightly higher boost applications
If you are targeting higher boost or building a performance system. We recommend our own in house manufactured crank-fired distributor-less system. This is capable of supporting up to 3 bar of boost. It is a professional grade system that is designed for all applications, not just the AMR500. It will control everything from turbo's to top-fuelers.