Summary

Next question comes from Kyle who's asked, how is the piston to cylinder clearance decided? OK so this is going to be driven primarily by the material that the piston is made out of. So for a factory piston, it's likely to be cast, the alloy that is used for the casting doesn't tend to grow very much with heat.

00:00 - Next question comes from Kyle who's asked, how is the piston to cylinder clearance decided? OK so this is going to be driven primarily by the material that the piston is made out of.
00:11 So for a factory piston, it's likely to be cast, the alloy that is used for the casting doesn't tend to grow very much with heat.
00:22 In the aftermarket world, we're almost going to always be using a forged piston.
00:26 And there's two material options when it comes to the alloy for forgings.
00:31 There's 4032 and 2618, both have pros and cons.
00:35 The more common 2618 forging which is what I've got here, that's the highest strength forging.
00:42 But the difference, or one of the main differences between the materials is the silicon content in that alloy.
00:49 And with the 2618, the silicon content means that the piston is going to expand more as it heats up.
00:57 So what this means is that a forged piston with a 2618 alloy will require more piston to cylinder wall clearance than a 4032 casting, our 4032 forging I should say, which in turn will require slightly more clearance than a factory cast piston.
01:14 So that's our first driver.
01:16 The second though is the application.
01:18 Understandably, just like our piston rings, the more heat that we're producing in the combustion chamber, the more heat's going to end up making its way into the crown of the piston, the more the piston will expand so the piston to cylinder wall clearance for a low power naturally aspirated engine, will be less than for the same engine specification that's turbocharged running high boost.
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