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Discussion Starter #1
Can anyone explain the color difference on this??? 300 miles on a built 2.3L motor... 93 octane 20 psi. Piston broke from a faulty timing map.

 

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Discussion Starter #3
wiseco 8.8:1 stroker pistons (.040 over) mated to Eagle H beams. HG was blown on 3 cylinders... they all look the same.
 

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I've seen this type of burn pattern before on a 420A with a big turbo kit. Melted the pistons on the dyno. EGTs < 1400F, AFR ~12:1, boost=16psi. The problem was really crappy valve timing due to crappy cams that could NOT be degreed correctly to eliminate the overlap.

No guarantee that this is what caused your problems, but it looks familiar although not as severe. Do you have an idea of how the cams were installed? What cams?
 

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Discussion Starter #6
They are webcams 546/547. But A/F were not high, less than 12.0:1 and boost was not excessive... like i said 20 psi.
 

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just some help....your not that far from chicago. If you want give Mitch from engine techs a call. He works at a machine shop located in chicago and this guy knows his shit....i would not trust anyone else with building anything but him. he would probably help answer most of your questions..here is the shop number 1773-338-8400
 

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Man i had the same problem with a motor that i used to have. I built up pretty much the same stroker with 8.8-1 compression pistons, ran it for about 1,000 miles with a 14b set at 12psi, and when i ended up pulling the head. The same exact bullshit. I pulled it apart and sent one back to weisco and they told me that it was due to excessive heat, said i was running way too much boost. I asked them, since when is 12psi from a 14b over excessive. They laughed at me and said that there is no way that was the case. Fuckers. They wouldn't give me a new set. I think they made a bad batch or something.
 

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The heat is not due to boost, timing, or lean AFR. It's due to reversion when the intake and exhaust cams overlap too much and/or too soon. Essentially the exhaust in the port reverses direction when the intake cam opens. The exhaust blows down onto the piston first, and then backwards through the intake port.

That's what happened to the 420A I described in my previous post. That's what your piston looks like.
 

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Discussion Starter #10
The cams are obviously off... i'm retarded and took of the sprockets that were somehow degreed (non-adjustable ones that have been.... "adjusted") from the cams when i installed them. I am sure that what you say has contributed to the damage... in addition to the timing problems i have.
 

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Looks like piston erosion from severe detonation to me. The blown head gasket confirms detonation also. The pistons have a beadblasted or pitted appearance in the clean area don't they? Every 4g that I have seen torn apart with detonation damage has been on the intake side, just like your example. Some of the more excessive cases even smear aluminum onto the cylinder wall.

I doubt cam overlap had anything to do with this. More than likely if the intake cam was moved, your base timing was also moved, that along with "miffed" timing maps caused your damage.

Probably the same case with the 420a spoken of earlier. Move the intake cam, change the base timing. NA ECU's run a lot of timing, thats why your EGT stayed cool, combustion completeing inside the engine, not in the exhaust manifold like when a 4g ecu starts pulling timing and sending EGT through the roof. There is some great reading on EGT and how useless it can really be around somewhere.

JRM
 

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In my experience detonation caused by spark advance timing has made EGTs skyrocket. Up to the point of detonation EGTs decreased with each degree of timing added. When the SA was advanced to the point of moderate/severe detonation EGTs shot up very high very quickly. That did not result in melted pistons though. I've never popped a 4G motor with detonation, so I can't agree or disagree with your observations of detonation location. It sounds reasonable though. You make a good point about the cam sensor on the intake cam and what happens when you adjust the cam phase. That could have played a factor here. If so, it should have resulted in very high EGTs accompanying the detonation.
 

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Lets take a closer look into the engine...

How hot is a combustion event? 3k-4k degs F. maybe more.

What is the melting point of aluminum? 1480 degs F.
We'll use aluminum because it holds the lowest melting point of the components in our engines' combustion chamber.

So what is detonation anyway? The uncontrolled combustion that occurs AFTER the sparkplug has already ignited the mixture.

Now, I'll ask what keeps our engine components that have direct contact with the combustion event from melting. Easy you might think, but there is more than meets the eye. Almost all will first mention the cooling system, better called the temperature management system but we'll save that for another time. Not many think of the small thermal boundary layer that exists in the thickness of a few molecules or so along all edges in the combustion chamber. This area does not support combustion and is a great insulator to our pistons, cyl walls, and valves. This layer has a huge role in keeping our parts from melting.

We all know that poor intercooling will lead to high intake temperatures, and in turn can lead to the onset of detonation. We also know that high pressure in the combustion chamber can lead to detonation. Now, hold your hand near a flame, feel the heat?

During the combustion event, we have pressure building because the fuel is burning and expanding. Also we have a tremendous amount of infared heat moving about. The heat moves at the speed of light, the flame front might move at about 30-150 feet a second, more or less, depending on things like chamber design, turbulence, swirl and AFR.

If you think about it, the slower the engine speed, the longer the unburnt mixture is subjected to pressure and heat. Keeping all parameters the same and increasing engine speed can ward off detonation.

Back to our combustion event.
Here near the edge of the chamber, on the intake valve side we have a pocket of rich unburnt mixture heating up and being pressureized. BLAMO, it becomes unstable and combusts before the already burning flame front reaches it. This cause a huge pressure spike in the cylinder, that of a jackhammer sized blow out in all directions. This chaos also goes as far as to destroy the thermal boundary layer, letting our parts absorb a lot more of the heat of combustion, our frail piston can't take the most severe of these conditions for more than a few seconds before overheating, scuffing, melting and/or mechanically eroding. Headgaskets are usually compromised as well.

I use pistons, and they're usually the first part damaged because they have the longest and worst suited path for heat to take to escape them. Now lets talk about what happened with our EGT's.

Another fact...

A set amount of fuel can only make so much energy, period. Given imperfect conditions it can create less energy, but never more then its max yield.

So lets think about this in a scientific mindset. Our engine is running, and starts detonating. The amount of fuel we are using has not increased. Our fragile internal engine parts aren't insulated anymore, they're absorbing more energy from combustion. What will our EGT do? If you said decrease, you're right. A detonation condition does not creat any more energy, the same amount of energy, or less, is being produced, but now more of it is absorbed by the combustion chamber and passed on to the cooling system than before, less energy is going out the exhaust. Severe detonation may be noticed by higher coolant temperatures also.

But when I see knock in my datalogs, my EGTs are increasing, will be your arguement. Yes, they will increase, read on.

Why does your EGT rise with detonation? in the example of most modern vehicles with knock control, the ECU pulls timing, and sometimes adds fuel in an attempt to stop the detonation. This causes the mixture to ignite later in the cycle, and still be burning as it passes though the exhaust port and past your EGT probe. This is why your EGTs rise during detonation. This is how I feel people melt down engines and say "EGT read fine." This is why I think EGT is inferior to a wideband O2 and proper software to monitor a knock sensor.

Another thing to consider with increaseing SA and suddenly having a EGT increase is Preignition. Preignition is more devistating than detonation. It can be brought on by mild detonation superheating an area, and will cause EGTs to skyrocket.

This is not a cut and paste from somewhere on the interweb, this was written by me after years of research trying to understand how these damn things work. I hope this helps anyone who reads it.

Jesse
 

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I hope it helps someone too. Nice post.

I still see nothing that explains how/why cam timing could not cause the problem. I too have a lot of experience with tuning. That doesn't make me an expert though. I agree with most of what you've posted, but it is only an introduction with many loopholes for contradiction of the implied theory. That's the nature of the beast though. Hence there is still no perfect model for engine combustion.

Back on topic.

Poor tune = burnt up engine. Tuning is tricky, but it isn't voodoo. It seems that way though because the consequences for screwing up can be very expensive unfortunately. If you'd like some pointers for tuning, let me know. I don't know how far you want to get off topic. :)
 

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Discussion Starter #17
lambertvr4 said:
Back on topic.

Poor tune = burnt up engine. Tuning is tricky, but it isn't voodoo. It seems that way though because the consequences for screwing up can be very expensive unfortunately. If you'd like some pointers for tuning, let me know. I don't know how far you want to get off topic. :)
Basically that's it, I think a lot of things DID contribute to this, mainly the extreme (for my setup) timing advance. However, the cam issue probably played an additional role and either way it is a problem that is getting fixed, and hopefully shows a better burn next time the head comes off.

4 degrees of additional timing =
Blown Metal HG ($90)
Pistons (x2) ($240)
Cam Gears ($160)
Head work ($50)
Grand total this time $540 (not bad)
 

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Discussion Starter #19
I wouldn't even want to think the cost of my buildup/setup in "labor" dollars... I've put a lot of time in this damn thing over the past 6 months (and more to come).


I couldn't afford this car if i didn't work on it.
 
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