The oaf-ish-ul "why ecoboost goes boom" thread
Posted by fiasco
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Finally uploaded some pictures.
Here's the pistons from motor #1 (low miles, overheated a bunch of times, made it an entire season and then some). They all basically look like this. 
The head for engine #1 has ZERO signs of detonation. Engine #2 (30k mile junkyard motor, made it through Idaho, DooWops, and recce of Rocky) 
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Mark Hille Mega Moderator Location: The hills of CT Join Date: 10/04/2011 Age: Midlife Crisis Posts: 135 Rally Car: I have two crap boxes |
I don't think detonation is sustainable no matter how much money you spend on pistons. Better pistons will be more forgiving and give you a little more buffer but it doesn't sound like that is the solution to the problem. Those marks on the piston/head.....there are some pistons with marks (dings not detonation) that look like they weren't self induced. Like there aren't any bits big enough broken off to cause the damage. Were piston bits from the one cylinder traveling to the other cylinders or was there foreign contamination? How is your turbo looking? I would check to see what octane fuel the desert trucks/buggies are running. I would be very, very, very surprised if adding fuel and not taking some timing out (or lowering boost) was the end all be all solution to your problems. I don't think your current tune (or your current octane, whichever way you want to look at it) is close enough for just that. 
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The marks, we'll call them dents, definitely look like foreign matter. The heads and pistons with the dents came from the high mileage junkyard motor. So the dents are found on the quench pads of every combustion chamber, even the ones with pistons with just a little bit of detonation erosion. The turbo looks fine, and there was no foreign material in the intake manifold or any of the plumbing. Maybe they were already there when we picked up the motor...?!
I need to talk with the guy at Ford about the differences in the tunes and what fuel the trucks are running. I fully agree that pulling timing is going to be much better at keeping the motors happy. |
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I'm bored so here goes....
It is possible that the only reason engine damage occurred was because the intercooler setup was inadequate and this caused unsustainably high intake air temperatures. The ECU tried to prevent engine damage by going into limp mode (lower boost, pulled timing, and possibly more fuel, maybe even less spark events) but was then shut off causing it to reset in which case it returned to normal operation and continued to damage the engine by causing detonation. This is possible....but it seems a little unlikely. Why wouldn't it go into limp mode again immediately? There are 2 types of air sensors for the lima. A metal one and a plastic one. I have used both and have used them in both aluminum pipe and silicone pipe both pre and post intercooler. There was no difference in performance that I could tell and I was logging the temps to see. The sensors only got heat soaked when the car was off. When the motor was started there was only a couple of seconds that it read hot and then everything went to normal.....unless the position is total crap or the sensor is not working I don't think this is the only cause of the problem. It is only my personal opinion but I would be willing to bet that if you had been running 110 octane race fuel both motors would still be running. The tune isn't crap. The tune was developed by Ford who has a shit ton of resources. The Motorsports tune is probably partially based off of the production tune and both probably had hours and hours and $$$$$ and $$$$$ to develop them. But, like Pete said, you get more power by sacrificing the safety buffer inching closer and closer to detonation and engine failure. All of that testing is based specifically off fuel octane. If the tune is developed for a certain octane, and you run a lower octane, you are going to detonate the motor and it is going to blow up. PERIOD. A safe AFR for a turbo car is around 11:1 to 12.5:1? It isn't so hard to get in that range. Yes you can make more power with a little more or a little less depending on your setup but if you lean it out and it starts to detonate you aren't making shit for power. I personally would never run a turbo car without a wide band. I like to know things are where they are supposed to be and if I have a problem I like to be able to look over and see that AFR isn't the cause. I'm sure there are others like me who are running the Ford motorsports ECU and if it was super lean they would know about it and be shouting it from the hills...maybe not. I would bet more on low fuel pressure from a mechanical problem than on ford being too lean. Easy and fairly cheap way to find out. There is only so much power available in the AFR. Way more power exists in the boost and in the timing. I doubt Ford is trying to make it up in the AFR. The only real variables are the engine temp and the intake air temp. If they go too high the ECU would need to compensate by adding fuel and pulling timing. This is going off of memory but the rate timing gets pulled is only like 1 degree for every 50 degrees F above 200 or something like that. I don't think we are talking about pulling 10 degrees of timing when the intake air is too hot but maybe I'm wrong. The problem with a hot motor and hot intake air is PREIGNITION. The fuel starts to burn before the spark and basically leads to the same demise. Pre-ignition can be caused by a hot piston...a piston that has sharp edges on it that has formed a hot spot...a piston with dings in it like the ones pictured above. It is possible those sharp edges were causing pre-ignition but if they came after the piston broke and not before it broke it isn't the cause of the main problem, detonation is. What is the easiest way to prevent detonation (or pre-ignition) on an engine that is running proper timing? More octane. You might not make more power but your safety buffer just got a whole lot bigger. 
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