We were able to get @jaytizzl
engine apart and take a look at what happened and have come up with a pretty good theory of the failure.
As has been reported earlier, we knew that there was a failure with the #1 cylinder from the hole in the block, but we wanted to come up with a theory of failure in this case to prevent it from happening again.
We removed the spark plugs to check for signs of damage and found that #1 and #3 spark plugs had damage -
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#3 Spark Plug
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The other spark plugs looked fine in cylinders #2 and #4. We removed the supercharger kit from the engine and proceeded to remove the valve cover, the header and intake manifold. Coolant was found in the in intake manifold and also in the header and exhaust. After removing the timing chain and tensioner, we removed the cylinder head and found the damage to the pistons and block below -
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Upon inspection of the block the piston in #1 cylinder was completely missing and had been destroyed. The piston in #3 cylinder was damaged and aluminum pieces of the pistons were found in cylinders #2 and #4 although the pistons in those cylinders did not show damage. Of note is that the rods in all cylinders, including #1 were intact, although #1 cylinder did have a bend and twist to the factory rod. The cylinder liners in cylinder #1 and cylinder #3 were broke and the cause of the coolant leakage into the intake manifold and exhaust. The bores in cylinder #2 and #4 appear to be clean with no scoring, breaks or marks on the walls.
Fortunately, we have been able to see first hand and in pictures a fair amount of failed engines now and the piston failure in #3 cylinder appears to be a different failure mechanism than #1. We have been able to note in other testing that the #2 and #3 cylinders will run slightly hotter than cylinder #1 and #4 under normal conditions due to the lack of coolant around the center of the bores where they meet the other cylinders. Cylinder #1 and #4 have coolant around a greater area and tend to run a little cooler. Many of the engine failures we have seen with other turbo kits has been due to excessive heat build in the engine, typically in cylinder #2 or #3. The piston in cylinder #3 appears to have had damage due to heat build first before complete failure. Looking at the top of piston #3 (3rd cylinder from the right) you will see that the center of the piston is still there, but it looks like pieces on the top edge of the piston started to pop up. We have seen pistons that look almost exactly like this in other engines that failed from heat build in the cylinders. The failure mechanism occurs by heat building in the cylinders from combustion, that heat can migrate down into the upper compression ring in the piston. As the compression ring gets hotter, it expands until it can not expand any further and eventually the ring gap in the compression ring is goes to zero. It is at that point as the compression ring tries to expand more and it is forced up and will put pressure on the upper ring land of the pistons. Once there is sufficient force from the ring, it will pop a piece off of the piston and then start to cause more damage.
The damage to cylinder #1 is more extensive and severe since the piston is completely missing from the bore and the bore is broke in several spots, once again of note is that the rods are still intact in all 4 cylinders.
We then removed the fuel injectors from @jaytizzl
engine and checked the fuel injectors in another Slingshot that has our supercharger installed. We started that Slingshot with our supercharger kit, MAP sensor and fuel injectors and noted the base MAP pressure and air/fuel ratio. Then we swapped in the injectors and MAP sensor from @jaytizzi Slingshot and readings were almost identical with no noted changed between the readings at idle. This leads us to rule out a failure of the injectors or MAP sensor as the most likely cause. We did not run the engine with our supercharger kit and the Alpha injectors and MAP sensor at full throttle, as typically if the injectors are not flowing correctly we typically have seen big differences at idle and we did not see that in this case.
After looking at the engine and the damage to #3 and #1 cylinders, and the report from @jaytizzl
that the MAP sensor was found out of the intake manifold we came up with a theory of failure that we believe is most probable. We suspect that the failure to the #3 cylinder took relatively more time to happen then that of the #1 cylinder. This lead us to believe that the MAP sensor started to be pushed out of the intake manifold, causing a small leak of pressure at the sensor first. This small leak would mean that the sensor would still see some boost, but the reading would be incorrect and not accurate to what was actually going into the engine. This condition would start to cause a lean situation in the engine and heat build in the cylinders, this is what we believe started to cause the damage in the #3 cylinder. We believe eventually the MAP sensor would have came out completely and at that point all boost reference to the ECM would have been cutoff and fueling would go very lean and a substantial amount pre-ignition or knock would have occured most likely breaking the piston in cylinder #1 and further damaging #3.
We wanted to test this theory to see if we could replicate the conditions that we believe happened to see if that scenario was possible. To do this, we used a stock intake manifold and made plates to block off the openings in the manifold and then hooked a cylinder leak down tester to the manifold. The cylinder leak down tester was choosen because it allowed us to adjust the pressure going into the intake manifold and see what pressure the manifold was holding at the same time.
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After setting up the intake manifold for testing, we pressurized the manifold to 11psi, which is the rated pressure of the Alpha supercharger kit. We did start to hear air escaping from the MAP sensor area before it reached 11psi. The pressure feeding into the intake manifold was maintained at 11 psi, however the pressure in the intake manifold was reading only around 5-6 psi at the MAP sensor. This lower pressure at the MAP sensor correlated with the findings of cylinder #3 that there was a lean condition for a period of time that caused the piston damage. With the pressure still being fed into the intake manifold, just tapping on the intake manifold to simulate engine vibration caused the MAP sensor to work itself out and eventually pop out while still at only 11psi. Although we were not there when the engine failed and it is very hard to know exactly what happened, based on the damage to the engine and the test with the MAP sensor on the intake manifold we are pretty confident that is what caused the engine failure.
As a side note, we did install one of our MAP clips onto the same MAP sensor that was on @jaytizzl
Slingshot and with the clip installed we were able to go over 30psi at the MAP sensor without the MAP sensor moving even a little bit and no leaks.
Since the MAP sensor becoming loose and eventually popping out seems to have caused the engine failure, we looked into the MAP sensor install more to figure out why there was an issue there. As noted earlier, the MAP sensor that was sent to @jaytizzl
for his install had the original orange ribbed seal that comes on the MAP sensor from GM and a black cut nipple to adapt the MAP sensor to the larger hole -
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When inserting the MAP sensor that was sent to @jaytizzl
in his kit into the intake manifold, we could press with a lot of force, but the MAP sensor would never seat all the way down to the bottom out. The reason we found in this case, was that the black rubber piece installed on this MAP sensor would balloon slightly when installed and prevent the MAP sensor from fully seating -
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We did contact Henry this morning to let him know what we found also.
Hope that helps, please let me know if you have any questions,