Youre kidding right?
Pre-ignition can cause detonation, and vice versa, but they are not one in the same. Detonation is when instead of there being a burn of the mixture, there is an instantaneous detonation of the mixture.

http://www.not2fast.com/NACA/naca-tn-93.pdf
http://www.not2fast.com/NACA/naca-report-493.pdf
http://www.not2fast.com/NACA/naca-report-855.pdf
http://www.not2fast.com/NACA/naca-tm-899.pdf

Im not saying it wasnt foreign material, but my money is on detonation.
Those uncanny, round, pits are a fairly common sign of detonation. Either that or people have been accidentally ingesting BBs for years.

Your cited papers date back as far as 1922. For much of this the 20th century, there were two competing theories regarding engine knock, the autoignition theory, and detonation theory. For decades now, the scientific and engineering community as practically unanimously accepted the autoignition theory as standard. This was what is taught at a university if you take, for example, a masters level course on combustion.

Unfortunately, it seems the 'aftermarket' hasn't figured this out yet.

STFU. Nobody cares about semantics. You're just wasting bandwidth, trying to convince everyone how great your education/knowledge/whatever is.


Nobody fucking cares. :jerkit:






OP: The head can obviously be fixed, unless higher resolution shows more severe damage. If you don't mind opening the motor up again, sure, re-use the piston. Be sure to sand down and lips or sharp edges.


For my time and money, I'd replace it. It just doesn't makes sense, to me, to re-use it. However, if you can't find a replacement, you're obviously mechanically inclined to the point which you could "easily" replace it, if need be.

Interesting. So other than semantics what is the practical difference?
If it's not detonation of the mixture outside of the flame front is it something fundamentally different or is it a similar condition given a scientifically accurate name?

Tom,
It's not just semantics, the two words actually describe very different phenomenon. What you're describing is correct, and is the cause of knock, but it is known as autoignition. A portion of air/fuel mixture that is outside of the advancing flame front (commonly called 'end gas') autoignites due to the temperature and pressure history which it's been exposed to. This end gas burns very rapidly, and is responsible for the rapid pressure rise and waves within the cylinder. Autoignition is also the principal by which diesel engines operate. The detonation theory differed in that it hypothesized that the flame front speed accelerates to sonic velocity, rapidly consuming the remaining air/fuel mixture (detonation), resulting in the pressure rise. Optical/video studies of actual combustion have shown the autoignition theory to be the correct one, by observing combustion of the end gas prior to the flame front reaching it.

Scott,
Ignorance is bliss. Go ahead and crawl back to your hole.

It is non-standard, uncontrolled, fuel/air charge ignition. It has a half-dozen names, which don't really matter.


What does matter, is it can send rods through the side of the block, and we know how to detect and mitigate this danger.

Detonation, knock, ingested ball bearings, doesnt really matter. Sand the piston and put it back in. Figuring what did this might be a good idea before you start it back up though.

I have some minor pitting like this on one of the pistons in my engine right now.
I have no idea what caused it - the only thing disintegrated in my engine was the turbo and that was on the exhaust side.

https://www.miataturbo.net/attachmen...ine=1393494748

http://imgur.com/iuIIFGT

https://www.miataturbo.net/attachmen...ine=1393494748

http://imgur.com/oLMsnju

On my way to a professional shop. Lets get another opinion :idea:

Will keep you posted!

This is foreign object damage. The material in piston & head is displaced locally at each site, not eroded as it would be with det.

Those are obviously meteor impacts

https://www.miataturbo.net/attachmen...ine=1393533226

Please, continue. I haven't had the pleasure of watching anyone argue with JKav recently. :rofl:

Im not even arguing. With the higher res it does look more like it ingested something that made some big pits before getting ground down and made some smaller pits.

Unless maybe he wants to argue that it does not look like the moon. In which case Im down for whatever.

Cool.

Good thing the rest of us plebs know exactly what 99.99% of the world is referring to when they say "detonation."

Please make a new thread in which you educate the ignorant masses.

Something mashed into the head and pushed metal away from the center. I have seen lots of detonation and also some pretty amazing FOD and that isn't even close to a detonation pattern or style. It is most definitely FOD.

EDIT: FOD=foreign object damage

To me it looks like you swallowed a rock that then shattered on the first cycle and smashed again.. big/small pits. Either that or your turbo is spitting ballbearings.

So, I talked to a professional shop. These guys are doing nearly all engines of all brands in our area. They say it was a foreign object and its not a problem at all to use the piston again. Just sand down the edges and its good to go.

And I cannot get a replacement, pistons are different meanwhile...

We will put it together in the next 2 weeks and see what happens.