[Z06] What is it with the #7 cylinder?
07-15-2010, 01:40 PM
#41
Drifting
It sure looks a lot like a detonation issue, piston cracked and broke away from the upper ring land groove.
Other issues could cause this too, such as localized coolant jacket overheating (hot spots). (Those that remember the early 03 Cobra rear cylinder cooling issues can relate) That also makes sence since #7 is the farthest from the water pump. The excessive heat could cause undue localized expansion in the cylinder area. The reduced cylinder wall to piston clearance could litteraly "grab" a compression ring and pop off the top of a comparatively "brittle" hypereutectic piston pretty easy. A lean tune could aggravate the poor design, coupled with an extended period of WOT ... resulting in, KABOOM. Not saying so... just a thought.
Other issues could cause this too, such as localized coolant jacket overheating (hot spots). (Those that remember the early 03 Cobra rear cylinder cooling issues can relate) That also makes sence since #7 is the farthest from the water pump. The excessive heat could cause undue localized expansion in the cylinder area. The reduced cylinder wall to piston clearance could litteraly "grab" a compression ring and pop off the top of a comparatively "brittle" hypereutectic piston pretty easy. A lean tune could aggravate the poor design, coupled with an extended period of WOT ... resulting in, KABOOM. Not saying so... just a thought.
and was waiting for someone to point this out. This issue goes back to (at least) the 60's performance engines. Our family business was an independent auto repair shop from the late 50's-early 90's, and we constantly saw evidence of the #7 and #8 cylinders' exposure to greater heat due to its lack of proximity to the water pump. In an engine with thinner cylinder walls to duct heat away, I'd think the effect of an increase in surrounding coolant temperature is going to be even more significant. Detonation and over-expansion are natural results of piston temperatures too high for their application. A eutectic piston is going to be less susceptible to thermal expansion than a forged Al piston, but more susceptible to failure from detonation. The failure, whether by detonation or expansion, or both, occurred right where one would expect it--at the weakest point--the ring land.
07-15-2010, 04:19 PM
#42
So basically, make sure your tune is solid, that you're getting proper fuel, that your cooling system is working well, and try not to wring it out while it's heat soaked and that should help keep the back cylinders from giving up the ghost?
