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Some forged pistons have forge suitable alloy which have greater rates of expansion than cast types. And that can cause a problem with some turbocharged applications. I suggest finding some good advice and reading of the book 'Maximum Boost'.
Peak pressures and stresses can be higher in non turbocharged engines where the timing is agressive and the load imposed by high RPM's is very high. A turbo charged engine has retarded ignition at boost and is used at lower RPM's. At WOT and high RPM's the pistons are seeing 15 psi or higher at TDC on the intake stroke and probably twice those pressures at the exhaust stroke. This lessens the tensile loads that would want to tear the piston and connecting rod apart, compared to the NA engine.
Forged pistons for NA engines have the objective to be strong and light at the same time. A good piston for a turbo charged engine needs enough bulk metal in the piston crown to transfer the heat away. The piston land just above the top compression ring is subject to overheating. It is the practive of modern engine design to move the top ring closer to the piston top. This has made the thermal situation much more critical and it is been found that the engine oil increasingly wants to coke in the top rings. This has been a driving force in the development of new engine oil standards. Another reason to run synthetic.
So you want a piston with the appropriate expantion coefficient that has more metal placed for heat transfer rather than been optimised for lightness and strength for high RPM's. That been said, there may be some forged pistons that will work very well, but some are not a good choice just becuase they are forged.
So those are some things to consider. It is possible to spend more money on a forged piston that will NOT be a better solution than pressure cast piston.
posted by 208.24.17...
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