Missed this thread. Ha Ha.
First off: The compression difference between the 2 motors in question are due to piston dish volume AND combustion chamber volume. The C14 has more piston volume AND more combustion chamber CC. The 2 motors share the same crank, rods, wristpins, headgasket, valves, and springs. The head itself and the block (cases) are different. I'm 99% certain that the piston-to-deck clearance is also the same. Compression height of the C14 and ZX14 pistons are also the same (compression height is the distance from the centerline of the wristpin to the highest edge of the piston).
Second: Those articles are fairly informative, but they miss a bit too. Modern CNC, stress modeling, and forging has come a loooong way in the last few years. A finished forged/CNC'ed piston is pretty light; they can get rid of a lot material that doesn't need to be there. Another big thing they miss is grain structure and metal alloy. Without going off the deep end in manufacturing lingo, forging makes for a stronger & less brittle piece of metal than casting, and you can forge superior alloyed metals that you would not be able to cast without great difficulty/flaws.
I agree. Very informative.
And from that information, I would speculate that piston failure in a turbo C14 has little to do with whether the piston is forged or cast, and everything to do with just the design of the piston.
Yes and no. The design of the piston plays into the weakness of a cast piston over a forged item. If you look at a Zx14/C14 piston, they have to cut the relief for the intake valves -real- close to the top ring land... the portion there gets just a few mm thick at the edge of the piston. Under really high cylinder pressures (boost/nitrous/sustained high compression) that really thin piece will get hot... hot enough to potentially start altering the mechanical properties of the metal (which are determined by the alloy and process of which it is made ie: forged or cast). In the case of the cast metal, the constant heating and cooling at or near that point will cause it to get really brittle and start to crack. The rapid acceleration forces of the piston will eventually work these cracks into failures (read: energetic dis-assembly). You could speculate that if our C14 cast pistons were completely uniform in the dish and of sufficient thickness (ie no valve reliefs or irregularities) that they would be more suitable for boost/nitrous/high compression. I would agree that they would last a lot longer under such abuse, but you would eventually see a similar failure around the edge of the piston somewhere. Forging is just a necessity when you are talking about 200+ horsepower per liter of displacement. The shear mechanical strength advantage of a forged piston would argue that, let alone the metallurgy.
Does that clear it up a bit? Or did I make it worse?
