Common Engine Knock Causes

Common Engine Knock Causes


Engine knock or detonation is the leading cause of engine damage for most performance vehicles. It’s an inconsistent and improper ignition of the mixture in the combustion chamber that can result in damage. Although most performance vehicles endure some knock or detonation, it’s not a desirable condition. Most of these engine knock causes can be easily avoided if owners just took the time to properly maintain their vehicles.

However that doesn’t stop engine knock from killing engines. Some of the leading engine knock causes can come from the smallest detail, which is why high-performance engines need constant maintenance. If you happen to be modifying your car or vehicle, and want to avoid engine knock, here’s just a few of the biggest causes to engine knock below.

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Engine Knock Causes to Avoid

Lugging your engine – This is a condition that can cause more than just detonation, it can destroy your engines. This is when your engine load is too high for the engine speed your are operating at. Not sure what this means?

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For example, if you are going up a grade or hill and shift into far too high of a gear.

This results in a low engine speed, and when you press the accelerator all the way down, this creates a high amount of load.

The problem is your engine computer is injecting less fuel than what is needed, and the lack of engine RPM means that oil pressure isn’t enough to handle this load. Otherwise known as lugging the motor, it’s a common mistake for first time turbo kit newbies. Most people associate low RPM with low load and for most cases this is true.

However low RPM also gives your engine longer periods of time to detonate and knock. As your engine speed or RPM increases the faster you are away from the moment your engine compresses the mixture. This is a big reason why true engine dyno tuners add ignition timing slowly as RPM begins to increase.

Improper Tune – It’s not just an improper dyno tune or wrong fuel map in your piggy back computer. This can also mean the wrong parts, or the wrong combination of parts on your car. Whenever you add more performance bits to your vehicle, you are changing the state of tune.

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Less than ideal gas mileage is one of the minor drawbacks. Engine failure or damage is one of the major ones. Make sure to do the right amount of homework to ensure that you don’t damage your engine. When installing new performance parts, make sure that they don’t need a tune to operate safely and function as they should.

High engine temperatures – If you haven’t already upgraded your radiator, it’s a good idea to do so now. Keeping things cool and your engine filled with coolant is an excellent way to maintain your engine.

When you are racing however or putting the vehicle through extended periods of stress, coolant can begin to boil. This evaporation of coolant can lead to extreme heat conditions in your engine, which could warp your head or cause a loss of compression.

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What’s more high engine temperatures is one of the leading engine knock causes because the higher heat can cause heatspots in your engine.

Detonation can arise when the hot spot in your combustion chamber gets hot enough. Broken engine is what usually comes after when you don’t handle engine heat properly.

Valvetrain Advance – One of the lesser known engine knock causes, adjusting your valvetrain is one of the oldest tricks in the book. By installing aftermarket cam gears, you can adjust or dial in the engine overlap to increase performance. Here’s a quick look at how improper valvetrain adjustment can cause engine knock.

  • Improper intake cam retard – When the intake valve closes later, it moves the overlap to later in the RPM range. This can cause a problem with a lack of ignition timing, especially because you are effectively lowering compression ratio.
  • Too much Intake cam advance – This does the exact opposite of retarding the intake cam gear. You are raising the dynamic compression ratio and without the right tuning or fuel adjustments you are ruining your engine.

One of the biggest things to remember is that pressure and temperature rise as your dynamic compression ratio increases. That’s why valvetrain advance is one of the more common engine knock causes for performance vehicles.

Fuel Quality ( or lack thereof ) – One of the biggest questions we get here is which fuel do we prefer or which one is the best gas? Although fuel quality is a smaller factor, it’s definitely one to consider as causing engine knock or detonation. It’s more than just crappy fuel however, unless you are planning on converting to E85 permanently, the brand of fuel also plays a role.


For instance 93 octane from Chevron will have a vastly different detonation threshold over the same octane from another vendor.

There can also be differences between formulations of fuel as well. Many fuel manufacturers produce a winter formulation as well as a summer version. These formulations have different mixtures of additives that can change your experience.

This has to do with fuel reactivity, which plays a role in how well the fuel can resist auto-ignition. In the simplest terms this means that higher octane fuel will of course be better than low octane fuel, but only if your vehicle calls for it. We went over fuel economy and some of the biggest myths behind it, and one of the leading myths is putting in higher octane fuel even though your car doesn’t call for it.

Improper spark plugs – One of the biggest engine knock causes in performance vehicles, you want to make sure that you run the right plugs in your engine.

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Colder Heat Range plugs have more insulation and shed more heat into the combustion chamber roof. They will always reduce detonation, but too cold of a plug can cause other issues like misfiring, lower performance, and fouling.

Hotter Heat Range plugs have less insulation and shed less heat into the combustion chamber roof. They will increase the chance of detonation but a sufficiently hot plug is needed to maintain a healthy combustion cycle. All spark plugs have ratings on them that let you know how hot or how cold of a plug you are looking at.

Colder spark plugs feature more insulation, which sheds and disperses more heat. These kinds of plugs will reduce detonation so it’s often recommended that you run a colder range of spark plug. Don’t overdo it however, because too cold and you can run into a completely different range of problems. Issues like fouled spark plugs or engine misfire can replace your engine knock causes.