Suck Squish Bang Blow part 5: Avoidance of Detonation
By Mike Kojima
Detonation is perhaps the deadliest sin you can inflict upon your motor. It is usually caused by gluttony, another bad sin, gluttony for more power. Detonation is the result of going too far in the quest for power. Pushing things to the limit when eking the last bit out, too far for your fuel's octane, too far for your fuel system's flow capacity, too much heat for your cooling system to dissipate, the list goes on and on. All of these can lead to a quick end to your motor. Really bad detonation can destroy any engine very quickly, about the only way quicker would be to dump out your oil while it's running full tilt. A built engine with tough forged pistons, coatings, racing rods and fortified crank and bearings will still succumb to detonation, it just takes a little longer.
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| Wow! We have actually seen worse though. This was a turbo 1.8 Audi 5 valve motor. These engines have really small turbos with owners that like to turn the boost up to the moon via “chipping”. Small turbo, lots of boost means a lot of backpressure and a lot of hot exhaust gasses retained in the cylinder. Not good. |
We had better try to define the phenomenon. Detonation usualy happens as the result of improper modification and tuning. Detonation simply put is the uncontrolled burning of the air fuel mixture in the engine's cylinders. Detonation generally happens when the fuel air mixture auto ignites by being compressed too much, kind of like hitting a non-safety match head or toy cap with a hammer. Compressing the fuel air mixture makes it hot by the ideal gas law (pv=nrt for those of you that care). Simply put, the molecules of fuel and air when squeezed together closely bump and rub together causing the temperature to rise until the mixture explodes out of control sometimes without the help of the sparkplugs. Fuel quality and things that affect cylinder pressure influence this.
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| Engine main bearings hammered by detonation. We have seen worse, we have seen broken main caps and distorted main bores caused by detonation. |
The other main causes are something getting too hot in the cylinder acting like a glow plug in a diesel, making the mixture auto ignite and firing the sparkplug too soon. Detonation puts a tremendous strain on all the internal engine parts and is the leading cause of death for built, high performance motors. Detonation blows head gaskets, burns pistons and valves, cracks ring lands, bends rods and pounds bearings.
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| Usually the sparkplugs are the first engine component to be damaged by detonation. A melted ground electrode is common. If you are lucky that's the only thing damaged. When the center electrode is damaged or melted, the cylinder is usually toast. |
