Detonation Damage???

Change Pistons or not?

  • Change pistons?

    Votes: 1 50.0%
  • Don't change piston?

    Votes: 0 0.0%
  • Change just most damaged piston?

    Votes: 1 50.0%

  • Total voters
  • Poll closed .


Active Member
Not sure whats causing this. No debris in the chamber. We suspect it could be detonation damage. All the marks in the picture look almost the same up close. Possibly timing issues. This is happening in the 7 the heaviest(7 shown in picture), then in the 6 not as badly, then in the 4 and even less damage. Any ideas or suggestions??

Should we change piston?


  • P2210010.JPG
    138.1 KB · Views: 532
  • P2210009.JPG
    131.7 KB · Views: 532
Id suggest changing the piston but that looks more like damage from a foreign object,like a bit of valve spring or keeper or a small screw, bits of porcelain, etc. notice how the lowest edge (6-o,clock appears to be damaged where and trapped debris would settle until it exited the exhaust port, between,bouncing around in the engine, that can easily travel up and out of one intake and into another during the overlap period ,that was being compressed between the quench are and the piston
detonation damage tends to be concentrated more on the piston edge, valve notches or other places that are not as easily cooled as the flat surface of the piston, and usually looks like the aluminum's been partly melted or frosted ... Page_3.php ... index.html ... piston.pdf
We thought that also might be the case. Possibly part of a spark plug. The marks are all pretty much uniform so that makes more sense. But we have yet to find the debris. Thanks.
it could easily have been flush out the exhaust at some point

if the edges of the piston lands look rounded off slightly and FROSTED that's the results of detonation, the rough stuff it micro sized bits of molten piston aluminum , that got transferred to the combustion chamber and exhaust port surfaces

btw heres typical detonation damage, and in this case, resulting from a bit of nitrous, that boosted the pressure, but the results would be similar on a high compression engine subjected to crappy fuel and high loads at high rpms without nitrous, notice the sugary/frosted appearance and rounded edges of the melted areas



damage to the ring lands can be caused by detonation or just the ring gaps set to tightly


detonation from crappy octane fuel or the wrong ignition advance curve way out of adjustment can beat pistons to death




why cast cranks and high stress and rpm are a bad idea




Detonation - Causes and Effects

This article was taken from a series of postings on the Supra Club of New Zealand mailing list. The contributors were Stuart Woolford and Tony Bryant. The article was edited together by Cully Paterson.

Knock, detonation, pinging, pre-ignition, etc are basically two things:

1 - Compression ignition, usually from over-advance of ignition and/or excessive compression (e.g. having added a turbo to an NA engine without lowering the compression) - this only happens after ignition, and is where the last of the combustible mix ignites from over-pressure during the last of the burn, giving a sudden detonation. A little is OK, and keeps the cylinder clean ;) but causes larger stresses in an engine, this is what knock sensors monitor, as the detonation produces quite specific, and audible, noises.

2 - Pre-ignition/thermal ignition, this is often caused by too 'hot' spark plugs or hot-spots in the carbon crud that builds up in cylinders. It causes the combustible mix to start burning from a point/cause other than the spark plug ignition spark. This can be VERY bad if it happens very early in the compression stroke, where it can destroy an engine in one cycle! This is, fortunately, less common, however it can be caused by runaway compression ignition. This causes additional heat to build up and the can cause pre-ignition to start, and to then happen progressively earlier in the cycle (until BOOM!).

The causes of knock can be:

* Excessive compression - increases pressure / temperature

* Not enough octane rating - fuel more likely to explode

* Wrong mixture - excessive heating / lowering effective octane

* Ignition timing - too much advance increases peak cylinder pressures a LOT

* Poor cooling - leading to high cylinder temps and pre-ignition

* Dirty cylinders - more candidate points for pre-ignition

* ECU/sensor fault - lots of options

and no doubt more.

The most 'efficient' place for an engine to run if often just on the edge of knock (from compression ignition) - so many modern ECUs use a knock sensor to hold the engine just on the edge of knock, but preventing damage due to excessive knock.

'Lean knock' is sometimes not actually a lean mixture (in fact, very lean mixtures will misfire, not knock), but rather an insufficiently rich mixture, as rich mixtures will delay the burn and burn cooler, thus reducing the chances of knock. This is very typical of the behaviour of turbo engines under boost, where they are deliberately run very rich to prevent the onset of knock. This explains why turbo engines in perfect condition can often be seen producing black smoke under power. On the other hand, get the mixture too rich, and the temperatures start coming back up rapidly...

  • Is knocking the same as pinging and detonation?
Yes, It all refers to the same phenomenon, which is the simultaneous burning of all/most of the fuel/air mix, due to the auto-ignition temperature of the unburnt mixture being exceeded.

We have a few possible heat sources.

1) Normal ignition. The normally controlled burning process obviously adds heat to the whole mixture.

2) The compression itself. In the same way a turbo heats its compressed air, the piston will heat the mixture at it compresses it.

3) Pre-ignition. Where a hot spot initiates ignition in addition to the spark plug, thus burning the mixture faster than usual.

When knock happens, its usually a combination of factors e.g. over-advanced timing combines the heating effects of 1 & 2, thus hitting the auto-ignition temperature, and wammo! the whole mixture goes up simultaneously, resulting in a "step" pressure rise, and general destruction eventually ensues.

  • So are the ECUs quick enough to regulate the air/fuel ratio and keep knock under control? Surely at high RPM the rate of change is going to become fairly critical?
The effect at a higher rpm, is less noticeable because of 2 reasons:

1) The difference in injector duration between boot planted and not at all is less at higher RPMs. e.g. from my own map:

1.0 atm, 5000 RPM ~ 7.0 ms

1.0 atm, 1000 RPM ~ 7.0 ms

0.3 atm, 5000 RPM ~ 2.1 ms

0.3 atm, 1000 RPM ~ 1.2 ms

I.e. if you boot it at 1000 RPM you are momentarily providing 17% of the required fuel, vs. 30% at 5000 RPM. 17% is a lot more likely to ‘lean misfire’ than 30% is. Also higher turbulence at higher RPM will allow a leaner mixture to fire.

However it's not quite that bad, because the MAP (which is what controls %VE and hence injector duration) doesn't change THAT fast - the plenum takes some time (independent of RPM) to fill when you snap open the throttle. So you never end up with figures as bad as that just described, you just run a touch lean for a few cycles.

A software throttle pump is often touted as a way around that, but once again, the ECU has to react fast enough, so you're back to square one. The ECU must react at at least the same speed as the minimum plenum fill time. That’s why huge throttle plate(s) tend to exaggerate this effect.

As for the effect on the engine: pretty negligible. Lean engine damage is caused largely by heating effects (e.g. melting a piston), which is obviously a longish term effect, i.e. in the order of 10s of seconds. Lean induced knock however is a cycle by cycle effect, BUT I don't think its a concern because

a) The mixture is likely to be lean enough to be below peak temperatures.

b) You're off boost, and hence also will be well below peak temperatures.

An aside on knock:

Note that knock is a combustion temperature related phenomenon. Richening the mixture cools the combustion down via evaporation of the excess fuel. Leaning the mixture to well lean of 14.7:1 (= the perfect mixture) cools it down via the excess air having thermal inertia. Ignition of course effects the peak pressure, and hence temperature rise via compression. Knock is most likely to happen around the area of 14.7:1 where neither the fuel or air cooling effects occurs.

I believe you've got more fuel hanging around in suspension in the plenum and runners, due to the average amount of fuel being consumed (==duty cycle). This provides a certain amount of "reserve" fuel.

Conclusion, I think you're safe from bad transients.
Last edited by a moderator:
I agree with Grumpy on the possible spource of the damage. The thing that would concern me is the damage right at the 6 o'clock position on the piston. Looks like it may be into the edge- if that's the case, make sure there aren't any sharp edges- good place for a crack to start.

Welcome to the forum!!

Hope you will check in often now that you have are just like one of the family now!!! :p

OK what caused this

"OK Grumpy ,what caused this"

you might want to pull a spark plug and use a flex micro cam to inspect inside the cylinder

this is also a good inspection tool ... pv618.aspx

GOOGLE PV-618 and PV-636

High resolution lens provides a clear image of objects as close as 3/4 inch and over one foot away while providing a wide 40 degree field of view.
Powerful lamp illuminates dark crevices on-demand with the push of a button conveniently located on the handle.
Ergonomically designed handle is comfortable to hold and allows one-handed focusing and light activation.
Rugged and water resistant, ProVision is made of high impact ABS and flexible cable sheathing. (Note: Shaft is water resistant, not the handle.)
PV-618 and PV-636 models have .23” diameter, flexible, non-obedient cable. Durable carrying case included.
Accessories available to optimize ProVision for specialized applications.
Made in the USA

Cable Length: 18" (457.2mm)
Cable Diameter: .23"
Handle Length: 6" (152.4mm)
Handle Width: 1.43" (36.2mm)Overall Length: 24" (609.6mm)
Weight of Scope w/ Carrying Case: 1 lb. 5.7 oz (615 g)
Field of View: 40°
Optimal Viewing Distance: Min. .8" (20mm); Max. is dependent upon ambient lighting conditions.
Lamp Volts: 2.7 volts (Halogen)
Power Source: 2 AA batteries (not included)
Pressure Necessary to Operate Lamp: 2.9 avg. p/psi; 3.2 max. p/psi

heres a cheaper version that works with a lap top computer


GCA 5.5mm Diameter USB Waterproof 6 Led Endoscope Borescope Inspection Wire Camera (5m)
Price: $18.50 & FREE Shipping on orders over $49. Details

    • Waterproof wire endoscope
    • Diameter:5.5mm head, 5 meters long flexible tube
    • High resolution 1.3MP with 1/12" VGA CMO
    • 6 LED lighting adjustable, can be inspected the hard-to-see areas.
    • Waterproof : IP67, 60°Viewable Angle. Can take photo & video and save in your computer

Its very difficult to come up with a 100% sure diagnosis without on site detailed examination of all the parts, obviously it helps to measure and know the circumstances that were involved,I wish I could examine all the components like heads, head gasket, and the block, bearings etc.
but just looking at the pictures, it might be detonation related but looking carefully , Id say the ring gap was minimal or there was a good deal of crud behind the rings and that might have restricted movement and cooling, a leaking head gasket letting coolant into the combustion chamber and the in ability to compress liquids being at least a factor, it looks like the ring ends touched locking the piston in the bore for an instant resulting in a busted ring land in the piston, OR you got into a hydraulic lock, condition as coolant got in past the head gasket , heat or detonation damaged.







Last edited by a moderator:
Re: OK what caused this

detonation in an engine is only occasionally audible , to the cars operator, many people wrongly assume if they can,t hear a ping or knock theres no detonation occurring.
yet detonation will still raise temperature in the combustion chamber ,to the point that it starts a cascade effect,and can still significantly raise the combustion temperatures and weaken the rigidity of the aluminum alloy used in a piston. as little a a few seconds running time under high loads and high rpms can result in detonation damage to a piston and rings.
Detonation is the unwanted burning of fuel in the combustion chamber during firing. The fuel is ignited by something other than the spark plug. This is very bad for an engine. It will usually damage the head gasket and blow it out. However it does put more stress on the cylinder head also.
Causes of detonation:
1. Low Octane Gas.
2. Timing incorrect.
3. Too much boost.
4. High engine temperature.
5. Oil entering the intake tract or cylinders.
6. Spark plugs too hot or gapped too wide.
7. Weak ignition system.
8. Carbon buildup in the combustion chamber.
9. Air charge is too hot.
there are chances of pre-ignition and knocking, if temperature of the inlet air is higher than normal. As the temperature of the air will be higher, the temperature of air-fuel charge will also be higher (petrol engine) which means there are chances of ignition of air-fuel mixture even before the piston reaches its precise point during normal combustion.

The above picture gives a general idea about how knocking occurs.






related info and links

detonation related




Last edited by a moderator: