I was curious just how much stress i put on my 549 spinning it 8,000 rpm and came up with this. At 4.315 stroke, at max piston speed, that piston goes up to 102 mph at roughly mid stroke, then back to zero at tdc and bdc. Piston speed calcs say 5800 . I am happy to report no pistons left thier assigned positions!!

My Sonny Leonard 762 Hemi had a 5.375" stroke and made max power at 7,300 rpms. I think Sonny wanted me to shift it higher than that. I would hate to calculate the piston speed. And of course the pistons and pins weren't light. That sounds stressed to me.

Rick, i come up with a piston speed on your motor of 7166 at 8,000 . That means those pistons hit roughly 122 mph and back to zero twice per revolution. Unreal! If my math is right, that would mean they go zero to to 122 mph 267 times a second! Looking at these numbers, i am happy at the fact that the only good wrist puns i could find two+ years ago were .210 wall dlc coated!

Have a nice day

Any idea what the G force would be ?

But average piston speed is not the issue here.
Its also the max speed at mid stroke coming to a complete stop in half the stroke measurement.

edit;Now that I have had a chance to reflect on this topic, should RMS enter this conversation?

'"These calculators are for entertainment value only."


Ok.

My calc of 122 mph was Max piston speed at mid stroke on the Sonny Leonard motor. So zero to 122 mph in one quarter revolution, at 8,000 rpm, in a distance of 2.65 inch.

Using the Wallace calculator for my new 572 C.I. motor (4.5 x 4.5) says it will have a "mean piston speed" of 5700 FPM with a max piston speed of 8953.53 F.P.M..
I'll test the shift RPM to see what the combination wants to go as fast as possible
I'm wondering if "mean" means "average"

I would say yes.

The formula posted is distance traveled in feet per minute, not maximum spoed. Max piston velocity would be stroke x 3.1416 ( distance of crankpin travel in one revolution), or 5.3 x 3.1416 = 16.65,,/12=1.3875 feet x 8000=126 mph? I may have a digit or so off as i came up with 122 mph or 126 mph for the 5.3 stroke SonnyLeonard motor. About 185 to 190 Gs of acceleration using an online calculater. So a piston and pin weighing 898 grams would feel like about 380 lbs? That seems low on g force,,,,,, did i miss something?

Thank you, but more vividly, the piston goes from a dead stop to the calculated max speed in the half the distance of the stroke, seeing 190? g's and then on the other half of the stroke the assembly sees a negative 190'?g's as it reaches dead center and stops once again. Totally ignoring all combustion pressure spikes/heat. Absolutely brutal IMO.

My math is incorrect . I googled g force on pistons and saw numbers like 8,000 Gs? I will go back and see if i can find the correct formula

The danger point is maximum piston acceleration, the highest tensile load, which is what breaks things.

Where:
Z = acceleration in f/s/s
N = RPM
S = stroke in inches
n = rod ratio (rod length / stroke)

Z = N^2*S*(1+(1/2n))÷2189

Metals are mostly Isotropic, so I am not seeing tension alone being the weak link here, as shape plays a part with compressive loads, or why con rods are not solid round rods. but your added point of highest acceleration is the real concern, no matter which direction, IMO.

Mountain Motor Pro Stock turn to 8500 or slightly more, the piston speed on one of those would scare most people.

Polyspheric, thanks for posting the formula. Can you help me out a bit,,, i don't know what the little a between N and 2 stands for, or the* . The rest i get. Then i would like to calc G forces, to see how my deal compares to others that run different strokes and rpms.

"^" means exponent, in this case squared (power of 2)