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Brucelee · 12-22-2007, 06:32 AM

Piston Speed

Vehicle speed and engine speed are both obvious quantifications we consider every time we turn the ignition over and step on the gas. But piston speed is something just as important, and is more often than not forgotten about.

It's usually measured in feet per minute and is the rate at which the piston travels up and down the bore. But the rate changes, as you might expect, alongside rpm changes.

At high rpm, the piston can reach speeds over 100 mph as it nears the center of the cylinder and then slow down to a near stop at the top or bottom of its stroke. It's not hard to see the abuse both the rods and pistons undergo from this extreme acceleration/deceleration process.

The strains imposed by these excessive speeds can snap connecting rods and crack piston skirts. Another not so serious side effect is that power can be lost due to the piston outrunning the flame front. Piston speed is related to crankshaft stroke, so being able to calculate it can potentially help you steer clear of a dangerous situation before swapping in that stroker crank on your next buildup. (fig. 4

12-22-2007, 06:32 AM	#8
Brucelee Registered User Join Date: Jun 2004 Location: Des Moines, IA Posts: 8,083	From an engine builder Piston Speed Vehicle speed and engine speed are both obvious quantifications we consider every time we turn the ignition over and step on the gas. But piston speed is something just as important, and is more often than not forgotten about. It's usually measured in feet per minute and is the rate at which the piston travels up and down the bore. But the rate changes, as you might expect, alongside rpm changes. At high rpm, the piston can reach speeds over 100 mph as it nears the center of the cylinder and then slow down to a near stop at the top or bottom of its stroke. It's not hard to see the abuse both the rods and pistons undergo from this extreme acceleration/deceleration process. The strains imposed by these excessive speeds can snap connecting rods and crack piston skirts. Another not so serious side effect is that power can be lost due to the piston outrunning the flame front. Piston speed is related to crankshaft stroke, so being able to calculate it can potentially help you steer clear of a dangerous situation before swapping in that stroker crank on your next buildup. (fig. 4 __________________ Rich Belloff