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Savage Beast Performance Parts
Posts: 10667
Oklahoma
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Everything affects everything else. When you change one aspect it dictates changes elsewhere, whether crank throw or rod length. I don't remember what the maximum piston speed that is traditionally acceptable, my mind has lost it. But there is a limit, and everything has to be constructed around that. The newer materials may have extended it slightly, but if so I doubt it would be by much.
I just found this; hope it is helpful. According to this guy the material science is critical in keeping a piston together as the forces increase. There are some interesting numbers here. *************
2RobHughes (Automotive)23 Mar 04 22:17 I work for a company that races and sells high performance motorcycle engine parts...here's a post I put up on one of the enthusiast boards when people started talking about wanting to raise the redline of their bikes from 5K to 6K or more. FYI the bike is Yamaha's Warrior an air cooled V-twin that displaces 102ci stock and the connecting rods are scary long and skinny...lol
From the postings:
At 5000 rpm your piston goes from a complete stop to 66mph in 2 1/4 inches in just .003 seconds.
Interesting Warrior Engine facts/figures:
Engine RPM/ Piston Velocity mph/ G's exerted on rotating mass. 1000 / 13.25 / 40.49 2000 / 26.50 / 161.98 3000 / 39.76 / 364.47 4000 / 53.01 / 647.95 5000 / 66.26 / 1012.43 6000 / 79.52 / 1457.90 7000 / 92.77 / 1984.36
For Comparison at "redline":
Chevy 350 Engine RPM/ Piston Velocity mph / G's exerted on rotating mass. 6000/ 62.20/ 1140.15
Formula 1 engine Engine RPM/ Piston Velocity mph/ G's exerted on rotating mass. 17,000/ 83.56/ 361.27
2004 R1 Engine Engine RPM/ Piston Velocity mph/ G's exerted on rotating mass. 12,500/ 78.58/ 250.12
2004 R6 Engine RPM/ Piston Velocity mph/ G's exerted on rotating mass. 15,500/ 79.98/ 315.69
2004 V-Rod Engine RPM/ Piston Velocity mph/ G's exerted on rotating mass. 9000/ 76.14/ 174.50
OK guys for those who are not bored by this...here's the math.
I did my math in feet, just to keep from having to change the numbers up at the end, but trust me it's the same.
Warrior Stroke=113mm or .370735 feet. Distance traveled by crank per revolution 1.16632 feet (remember that the circumfrence is "pie"* diameter) Revolutions per minute=5000. Distance crank travels per minute=5831.608202 feet Distance crank travels per hour=349896.4921 feet or 66.2682 miles per hour.
So if the crank shaft is traveling at this rate the pistons reach this max velocity twice per revolution at 9 o'clock and 3 o'clock since they are traveling at the exact speed that the crankshaft is, remember at 12 and 6 o'clock the pistons are "stopped".
To calculate the G-Force you have to take your revolutions per second (rps) which is 83.3333 (at 5K)and figure how long it takes for one revolution or .0120 seconds (1/83.3333). The piston goes from a dead stop at 12 o'clock to full speed (or 97.1934 ft/second) in 1/4 a revolution or in .0030 seconds. So the average acceleration in a second needs to be calculated or how many times per second does this event occur 1/.0030 = 333.333 times per second, now multiply this by the speed at full acceleration (97.1934*333.333) gives the figure of 32397.82 ft/second/second as the average acceleration. G-Force is 32ft/second/second. Divide 32397.82 by 32 to get the average G's exerted on the parts...or 1012.432 G's. Whew....if you hung with my math you deserve a gold star...lol
A piston weighs in at around 400grams, so at full G's right when it is stopping it "weighs" an astonishing 892.79 lbs!!!
The g's are exponentially related to the RPM and crankshaft length relationship. The Warrior crankshaft goes from 33mph at 2500rpms with 253G's to 66mph at 5000rpms and 1012G's. At 10,000 it would be 132mph with 4050G's.
The F1 crankshafts are, I forget exactly, but like 1.65 inches. Do the math Gotta, no scare tactics here, pure physics. I was just joking about the connecting rods, but it is something to think about when you start wanting to get a few more revs out of your bike.
This calculation has nothing to do with bore or weights in the calculations demonstrated.
Rob Hughes Orient Express Powersports
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