GMDAT ignition system

[Genie47]

GMDAT cars use wasted spark ignition system. If I'm not wrong, the Opels use the same thing but not the newer ones. So how is it different from the normal distributor system from the cars in the 80s and early 90s and how it affects our spark plug choices.

 

OK with the wasted spark ignition system, there is no distributor. It uses a crank sensor indicator to know where the "top dead centre" (TDC) is, then uses the signals from the sensor and the map information to determine when to fire the spark (twice per revolution).

 

The EMS is aware of the TDC position from the crank sensor and by counting teeth can tell exactly where the engine position is at any time. It uses this information together with the information from the throttle position sensor/MAP sensor to look up the appropriate ignition timing settings from the ignition map. It is then able to determine exactly when to fire the coils. Each coil is fired once per engine revolution at exactly opposite positions in the engine's rotation, because when cylinder 1 & 4 are at TDC, cylinders 2 & 3 are at BDC and vice versa. The spark travels to both of the paired cylinders.

 

Taken from: http://www.vandiemenracing.co.za/basics.htm

 

Now knowing all this how does this affect your choice of spark plugs?

 

Obviously the spark plugs are firing when producing power and when they are not producing power. You get twice the wear for the same amount of revolutions! So you need a spark plug that can withstand this stress.

 

Using the normal copper/iron/nickel ones will have them worn by 10k. At most can be used up to 15k. You will need to change plugs every oil change to keep the engine running in tip top condition.

 

Since they are firing twice and also in the reverse direction as well, you need a hard wearing tip and hard wearing ground. The choice is obvious. You need double platinum plugs. There are also iridium/platinum plugs as well. With such plugs. 100k km interval can be achieved.

wasted.bmp

Edited May 27, 2005 by Genie47

[Topgun7557]

Now I understand better. But does a Platinum tip plugs can last up to 100km?

[Genie47]

Double platinum plugs not just platinum tipped. This kind of wasted spark system is hard on the spark plug.