XLR8 Automotive

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Published: May 11, 2012

An engine uses the 3 sides of the fire triangle (Fuel-Heat-Oxygen) to create power.


The fuel (petrol-diesel etc) comes from the fuel tank via a fuel pump, injectors & carried into the engine by the airflow.
The Air is brought in by displacement, when the piston goes down this creates volume & this volume is filled by the inducted air.
The Heat comes from a ‘spark plug’. This is a device that gives the current generated in the coils a route to earth across the gap between the electrodes of the spark plug.
The spark plug is a simple device & does its job well providing it is the correct grade for the application.
Spark plugs do not give more power etc & it does not matter how many earth electrodes they have(multi electrodes only extend the life of the plug) ,the engine will not get more power from a spark plug, but it can lose power from using the wrong one and also may destroy you engine!
These engine damagers are typically heard & named as per the noise they create:

  • Pinking, this is a light metallic noise which is created typically (but not always) when the spark arrives too soon , the pressure raises to quickly & the piston ‘rattles’ over Top-Dead-Centre (TDC), this is not really a engine damager and is usually cured by ‘retarding’ the spark timing.

  • Knock, When the spark ignites the mixture this creates a flame from which spreads from the spark plug end, to the end of the cylinder until all the mixture is burning: Sometimes though something within the cylinder (foreign body, hot spot etc) can cause a second flame front to start, this now travels towards the first flame front & collides with it creating a ‘knocking noise’
  • Bang! Detonation/Pre ignition:
    This is where the compression of the engine causes the charge to heat up too much, this excessive heat generated heat must be removed or it will cause the mixture to ignite before the spark arrives. Instead of having a controlled ‘burn’ from the spark plug, it is now an ‘explosion’- This places huge strains on the engine components & creates excessive amounts of heat. It can melt pistons & destroy other parts. The main cause of this problem is almost always an incorrect spark plug (running too hot) and you must use a cooler grade (the ability of the spark plug to ‘cool down’).

Plug grades:
As explained, the spark plug plays a huge part in the running of the engine, Fitting a grade which is too cool will cause the plug to dispel all of the heat generated too quickly & the carbon deposits will stick to the electrode & reduce the conductivity .
If you fit a plug with a grade too hot, then the electrodes will burn away the carbon deposits but unless the heat is removed it could ignite the mixture before the spark arrives!

When the spark arrives at TDC it takes only 50ms for the whole mixture to be fully burning & thus creating the most force. At low RPM this is fine, At high RPM’s though when time the spark arrives at TDC the piston may already be half way down the bore by the time the mixture is fully burning, this will lose power. So to cure this problem we must send the spark before the piston has reached the top of the bore, this way by the time the piston arrives at TDC the mixture is fully alight & all of the expanding force can be used to push the piston down the bore (this is known as ‘spark advance’- the opposite of 'retard').

This Article is written completely by XLR8. It is our property & is protected by copyright 2005. Any unauthorized copying is strictly prohibited.