A standard Porsche 944 has a single coil which is timed by the DME to give the correct dwell and ignition advance for the engine conditions. The spark is distributed to the correct cylinder by the use of a distributor driven from the camshaft.
There are two main drawbacks with this system. Firstly the length of the lead from the coil to the spark plug is long and the spark must bridge a gap in the distributor housing. This reduces the spark strength at the plug, meaning that the spark is less effective at igniting the fuel and giving a clean burn.
The second issue is that of dwell time. Dwell is the time that it takes to charge up the coil ready to deliver a spark. The purpose is to ensure that the current flowing through the coil is at its peak when it is discharged generating the maximum spark voltage. The standard 944 coil needs a minimum of about 4.5ms to generate peak current at 14.5V.
So what’s the problem here then. This bit of math helps to understand the problem, if we need4.5ms to charge the coil and we need ~1ms to discharge it properly this gives us a required time of about 5.5ms to generate and discharge a top quality spark. The DME needs to generate a spark every half rotation of the engine. So if we use the time of 5.5 ms for half a rotation and double that to give 11ms per revolution this gives us a figure of ~5500rpm. This figure is important as above this engine speed the 944’s coil is not fully charged and is not delivering the full spark strength! Although on a standard engine this gives good spark performance up to the peak torque for the standard camshaft above 5500 rpm the spark strength will tail off reducing torque and power. When you improve the engines ability to breathe above 5500rpm you will be further let down by your spark strength.
So what’s the solution to these problems?
Lets take a look at wasted spark and find out. A wasted spark system has two or four coils and no distributor. So it has shorter leads and no gaps for the spark to bridge before the plug. It works by firing the plugs in banks. Two spark plugs, in cylinders 1 & 4, about TDC (Top Dead Centre) and the other two, in cylinders 2 & 3, about BDC (Bottom Dead Centre) meaning that each cylinder receives a spark in its compression stroke and during its exhaust stroke (wasted hence the name).
The next major benefit of having two or four coils is that you can charge the two banks at the same time meaning that you have an entire rotation of the engine to charge the coil to generate a spark with a wasted spark system. This results in a top quality spark all the way to 7000 RPM and beyond, more torque and more power. A four coil solution is best as the coil is only driving a single plug, but modern coils still produce a great spark when driving two plugs.
Our AugTronic system gives the 944 DME the ability to drive wasted spark systems of either two or four coils and is the only cost effective 944 native solution for doing so! It’s also a piece of cake to install! We can provide two or four coil solutions. Contact us for further info.