Piston speed – Mr. Gasket 8703 Hot Rod Calculator User Manual
Page 55
U
ser
'
s
G
Uide
— 53
PIston sPeed
Piston Speed is an important factor when building an engine, es-
pecially if that engine is being built to run short distances at wide
open throttle, such as drag racing. Piston Speed is the speed,
typically in feet per minute, at which the piston moves up and
down within a cylinder.
As your engine’s crankshaft rotates once, your cylinder’s piston
travels two strokes (up one and down one). The piston’s speed is
not constant throughout its travel. It may go from 0 to 100 miles
per hour and back to 0 during a single stroke. However, if the
Piston Speed is too fast, the result can be disastrous for your
engine.
With advanced math, you could calculate the exact Piston Speed
at any particular point in the crankshaft rotation. Fortunately,
knowing the average Piston Speed is all you need to calculate
when you are building your engine. Modern metal materials
enable higher Piston Speeds today, upwards of 3,500 feet per
minute.
Piston speed — Based on RPM and Stroke
For this example, your Stroke is 3.48 inches, and you want to
calculate the Piston Speed at 4,000 RPM.
KeysTroKe
disPlay
0.
1. Enter your Stroke and the RPM for which you want to deter-
mine Piston Speed:
sTroK 3.48
in
rPM 4000.
2. Calculate the Piston Speed at 4,000 RPM:
fPM 2320.
*
M/Min 707.136
(cont'd)
UG8703E-B-inside.indd 53
3/3/2010 3:04:00 PM