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Can someone do some maths for me? Piston speed calculation

Bimmubishi

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Joined
Jul 15, 2003
Messages
5,702
Location
Boston, Massachusetts
I did a little boo boo this weekend at Duryea hillclimb and over spun my motor. I knew it was high but I didn't know how high. Anyway the engine still runs but the oil squirter got taken out and bent the piston skirt a little which left an aluminum skid mark on the cylinder wall. Not sure if anyone has spun a 2 liter this high but here it is.


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belize1334

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Joined
Nov 18, 2003
Messages
3,316
Location
Bozeman, MT
You want piston speed? The equation for piston displacement is h = (s/2) (cos(th) + sqrt(4 r^2-sin(th)^2) where h is the height, s is the stroke and r is the rod/stroke ratio. To get the speed you let th = w t and then differentiate. The expression is long. Then to get the max value you differentiate AGAIN and set the result equal to zero which tells you the time and you plug it in.

OR

You use the interwebs to find this.

Using stroke = 88mm = 3.46456" and rod = 150mm = 5.9055" I get vmax = 12876 feet/minute which works out to about 65 meters per second. But keep in mind that it's piston acceleration that really kills parts. Read the "strokeornot" white paper to see how piston acceleration rises with rpms. You can find it with a quick google search. I suspect that you'll decide you were well into the crazy nasty high rpm range.
 
Last edited:

Diego

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Dec 9, 2007
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2,132
Location
In a van down by the river, Iowa
That's some force.... /ubbthreads/images/graemlins/shocked.gif
 

Barnes

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Feb 9, 2003
Messages
6,249
Location
Richland, WA
Dude, your pistons just went to plaid.
 

Rausch

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Dec 21, 2004
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Cleveland, OH
^ /ubbthreads/images/graemlins/rofl.gif
 

curtis

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May 4, 2003
Messages
11,892
Location
Clarksville TN
^ Oh my God Barnes thats the funniest thing you've ever posted. Now I have to have corrective surgery because I just ruptured my liver laughing so hard. /ubbthreads/images/graemlins/rofl.gif /ubbthreads/images/graemlins/rofl.gif /ubbthreads/images/graemlins/rofl.gif


As for you F1 engine builder post picture of said pistons and then have them shadow boxed and hung up in the shop. /ubbthreads/images/graemlins/worthy.gif No scratch that, take them in for an MRI or something, I'd love to see the fissures inside that bad boy. Its absolutely amazing some lived our junk isn't designed for this like big boy racing.

here enjoy the last paragraph
 
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