# Need help S14



## nssn240 (Aug 12, 2007)

If I am gonna make my car turbo, what pistons do I need to use? The low compression pistons forged or low compression pistons regular?


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## rogoman (Dec 16, 2004)

Forged pistons. However consider the following info:

Standard forged pistons as a rule require more piston skirt to cylinder wall clearance. That's because they expand so much more after the engine reaches normal operating temperature. Piston-to-wall clearance is generally around 0.004" to 0.007" depending on manufacturer. OEM pistons, which are cast, use clearances of 0.0008" to 0.002". Because there is more rocking of the forged pistons in the cylinder due to more clearance, the rings wear more rapidly plus you get that cold startup piston slap. 

With the turbo you need to run forged pistons: however look into using the new silicon hypereutectic pistons which are around 30% stronger then standard cast. They are a T6 heat treated aluminum piston which allow you to run a small piston-to-wall clearance. TRW also has a special aluminum alloy forged piston that requires less piston-to-wall clearance.


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