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Mr. Grinch
11-27-2000, 09:06 PM
<i><br>this is an impressive calculation... but what does piston speed really mean? shouldnt the higher the piston speed mean more losses to friction? does that affect significantly? <p>might it possibly be a factor in determining engine wear and reliability? it doesnt make much sense to me at the moment<p>joe<p></i><br>

Mr. Grinch
11-27-2000, 09:23 PM
- Does it mean more losses to friction? <br>Not necessarily. Design, weight, materials, are all factors here as we are comparing different engines. More cylinders could add frictional losses too. But you're also getting more losses from reciprocating mass, probably much more significant. I'm just guessing though.<p>- Does it affect engine wear and reliability?<br>Certainly does, but only in comparison to the same engine run at different average piston speeds. You can't directly correlate piston speeds between different engines any more than you could compare clock speeds on different families of processors. <p>At best, I think high piston speeds among different engines would infer<br>- special materials usage. Stronger metals. Forging vs cast construction.<br>- closer tolerance machining methods<br>- more critical break-in methods<br>- attention to mass / momentum reduction in moving parts.<p>It's just another value to compare. Fun to calculate but doesn't mean much in itself, like 0 to 60 times for example. <p>But look at the stroke on the M3, it's the longest. This plus the high redline is what puts the average piston speed so high. A "typical" Formula 1 engine will have several thousand more RPM, but a much shorter stroke. So while BMW likes to point out the similarity in piston speeds to F1, the similarity ends there. The stroke design is basically the exact opposite. Just like NSX and M5 have the same average piston speeds at redline, but if you look at the piston / stroke design, the honda V6 is extremely short-stroked in comparison to the BMW V8.<br>

Mr. Grinch
11-27-2000, 11:34 PM
Calculations for Average Piston Speeds. Excuse the mistakes. Happy to add more if you want. <p>It would be nice to know instantaneous piston speeds as well instead of just average, but harder to calculate since acceleration is not constant, and change in acceleration over time is not constant either. Although maybe you could use a polar equation to represent acceleration since it's governed by a circular motion. I don't want to remember Calculus, hurts the head too much.<p>1 revolution = 2 strokes in a 4 stroke engine. <br>Distance piston traveled in 1 revolution = 2 x stroke<p><br>E46M3 BxS = 87x91 from bmw web page<br>S2000 BxS = 87x84 from www.supercars.net<br>NSX-T BxS = 93x78 from www.supercars.net<br>E39M5 BxS = 94x89 from www.supercars.net<br>McLaren F1 BMW V12 BxS= 86x87 from www.supercars.net<br>Ferrari 360 BxS = 85x79 from www.supercars.net<p>AVERAGE PISTON SPEED AT REDLINE:<br>Obviously the speed changes through the stroke but I only know how to calculate the average, not the max.<p>BMW E46 M3 M3:<br>8000 rev/60sec * 2strokes/rev * 91mm/stroke<br>= 24.3 meters per sec <br>BMW quotes "close to 25 meters a second" so I'm not very far off!<p>HONDA S2000:<br>9000 rev/60sec * 2strokes/rev * 84mm/stroke<br>= 25.2 meters per sec<p>ACURA NSX:<br>8000 rev/60sec * 2strokes/rev * 78mm/stroke<br>= 20.8 meters per sec<p>BMW M5:<br>7000 rev/60sec * 2strokes/rev * 89mm/stroke<br>= 20.767 meters per sec<p>McLaren F1 BMW V12:<br>7500 rev/60sec * 2strokes/rev * 87mm/stroke<br>= 21.75 meters per sec<p>Ferrari 360<br>8500 rev/60sec * 2strokes/rev * 79mm/stroke<br>= 22.38 meters per sec<p><br>It's safe to say the S2000 has the higher average piston velocity at redline. I'd go one step further and say it's got the higher average piston velocity over a road course, because running 1000 rpm (or more) higher than the M3 engine in most driving wouldn't be unusual at all.<p>NSX and M5 don't come close. One is your classic short-stroke honda, the other your classic stroked V8.<p><p>

5er
11-27-2000, 11:59 PM
<i><br>Calculations for Average Piston Speeds. Excuse the mistakes. Happy to add more if you want. <p>It would be nice to know instantaneous piston speeds as well instead of just average, but harder to calculate since acceleration is not constant, and change in acceleration over time is not constant either. Although maybe you could use a polar equation to represent acceleration since it's governed by a circular motion. I don't want to remember Calculus, hurts the head too much.<p>1 revolution = 2 strokes in a 4 stroke engine. <br>Distance piston traveled in 1 revolution = 2 x stroke<p><br>E46M3 BxS = 87x91 from bmw web page<br>S2000 BxS = 87x84 from www.supercars.net<br>NSX-T BxS = 93x78 from www.supercars.net<br>E39M5 BxS = 94x89 from www.supercars.net<br>McLaren F1 BMW V12 BxS= 86x87 from www.supercars.net<br>Ferrari 360 BxS = 85x79 from www.supercars.net<p>AVERAGE PISTON SPEED AT REDLINE:<br>Obviously the speed changes through the stroke but I only know how to calculate the average, not the max.<p>BMW E46 M3 M3:<br>8000 rev/60sec * 2strokes/rev * 91mm/stroke<br>= 24.3 meters per sec <br>BMW quotes "close to 25 meters a second" so I'm not very far off!<p>HONDA S2000:<br>9000 rev/60sec * 2strokes/rev * 84mm/stroke<br>= 25.2 meters per sec<p>ACURA NSX:<br>8000 rev/60sec * 2strokes/rev * 78mm/stroke<br>= 20.8 meters per sec<p>BMW M5:<br>7000 rev/60sec * 2strokes/rev * 89mm/stroke<br>= 20.767 meters per sec<p>McLaren F1 BMW V12:<br>7500 rev/60sec * 2strokes/rev * 87mm/stroke<br>= 21.75 meters per sec<p>Ferrari 360<br>8500 rev/60sec * 2strokes/rev * 79mm/stroke<br>= 22.38 meters per sec<p><br>It's safe to say the S2000 has the higher average piston velocity at redline. I'd go one step further and say it's got the higher average piston velocity over a road course, because running 1000 rpm (or more) higher than the M3 engine in most driving wouldn't be unusual at all.<p>NSX and M5 don't come close. One is your classic short-stroke honda, the other your classic stroked V8.<p></i><br>

courtney
11-28-2000, 12:13 AM
BMW claims the mclarin has 84ft per second and the E46 has 81ft per second piston speeds...Somehow your calculations showed the mclarin alot slower then that...if you want ill find the numbers on the mclarin...your other calculations seem right...<p><p><i><br>Calculations for Average Piston Speeds. Excuse the mistakes. Happy to add more if you want. <p>It would be nice to know instantaneous piston speeds as well instead of just average, but harder to calculate since acceleration is not constant, and change in acceleration over time is not constant either. Although maybe you could use a polar equation to represent acceleration since it's governed by a circular motion. I don't want to remember Calculus, hurts the head too much.<p>1 revolution = 2 strokes in a 4 stroke engine. <br>Distance piston traveled in 1 revolution = 2 x stroke<p><br>E46M3 BxS = 87x91 from bmw web page<br>S2000 BxS = 87x84 from www.supercars.net<br>NSX-T BxS = 93x78 from www.supercars.net<br>E39M5 BxS = 94x89 from www.supercars.net<br>McLaren F1 BMW V12 BxS= 86x87 from www.supercars.net<br>Ferrari 360 BxS = 85x79 from www.supercars.net<p>AVERAGE PISTON SPEED AT REDLINE:<br>Obviously the speed changes through the stroke but I only know how to calculate the average, not the max.<p>BMW E46 M3 M3:<br>8000 rev/60sec * 2strokes/rev * 91mm/stroke<br>= 24.3 meters per sec <br>BMW quotes "close to 25 meters a second" so I'm not very far off!<p>HONDA S2000:<br>9000 rev/60sec * 2strokes/rev * 84mm/stroke<br>= 25.2 meters per sec<p>ACURA NSX:<br>8000 rev/60sec * 2strokes/rev * 78mm/stroke<br>= 20.8 meters per sec<p>BMW M5:<br>7000 rev/60sec * 2strokes/rev * 89mm/stroke<br>= 20.767 meters per sec<p>McLaren F1 BMW V12:<br>7500 rev/60sec * 2strokes/rev * 87mm/stroke<br>= 21.75 meters per sec<p>Ferrari 360<br>8500 rev/60sec * 2strokes/rev * 79mm/stroke<br>= 22.38 meters per sec<p><br>It's safe to say the S2000 has the higher average piston velocity at redline. I'd go one step further and say it's got the higher average piston velocity over a road course, because running 1000 rpm (or more) higher than the M3 engine in most driving wouldn't be unusual at all.<p>NSX and M5 don't come close. One is your classic short-stroke honda, the other your classic stroked V8.<p></i><br>

Mr. Grinch
11-28-2000, 12:23 AM
The calculations are right. If anything is wrong, it's the numbers. It's obvious to see, with a shorter stroke and a lower redline, the V12 is going to have a lower average piston speed.<p>Please note there is more than one McLaren F1 engine. There are likely differences between years, not to mention the Lemans / GT race ready version, no doubt might be stroked and have 8000 RPM on tap. <p>If you can get more info, please post! Thanks!<p>Obviously though, the power and torque speaks for itself... the only way to go is V12 :-)<br>

joe
11-28-2000, 09:00 AM
this is an impressive calculation... but what does piston speed really mean? shouldnt the higher the piston speed mean more losses to friction? does that affect significantly? <p>might it possibly be a factor in determining engine wear and reliability? it doesnt make much sense to me at the moment<p>joe

Chuck
11-28-2000, 09:51 AM
Very nice calculations.. If you want to determine the instantaneous velocity at a particular point in time V(t) you would need to generate a function that would represent the acceleration with respect to time A(t), I would assume that it would be something like A(t)=K*sin(Wt)+C since it would be a cyclic. Once you have that equation you can take the derivative of d[A(t)]/d(t) and that would give you V(t). Once you have V(t) you can plug any number of the variable time (t) and that will give you the instantaneous velocity at a particular point in time. This is what I remember from Calc-101 about 8 years ago..

marc b
11-28-2000, 10:46 AM
The peak instantaneous piston speed is equal to the rotational velocity in radians/sec times the crank radius (1/2 stroke)...so in other words, take piston stroke*rpm/60*pi...or roughly 38m/s for the M3....125ft/s! (damn thats moving for a metal on metal contact....<br>now think about it this way, if you assume that you average 3000rpm over the life of the engine (ok, so some of us cruise at 85/90 on the highway, sue me), that means that (assuming 50mph average lifetime speed) in 50,000 miles the pistons have slid over 32000km! (20,000miles!) not bad for a high temperature scraping ring metal on metal contact....its amazing what they can do with cylinder liners these days<br>-m<br><i><br>Calculations for Average Piston Speeds. Excuse the mistakes. Happy to add more if you want. <p>It would be nice to know instantaneous piston speeds as well instead of just average, but harder to calculate since acceleration is not constant, and change in acceleration over time is not constant either. Although maybe you could use a polar equation to represent acceleration since it's governed by a circular motion. I don't want to remember Calculus, hurts the head too much.<p>1 revolution = 2 strokes in a 4 stroke engine. <br>Distance piston traveled in 1 revolution = 2 x stroke<p><br>E46M3 BxS = 87x91 from bmw web page<br>S2000 BxS = 87x84 from www.supercars.net<br>NSX-T BxS = 93x78 from www.supercars.net<br>E39M5 BxS = 94x89 from www.supercars.net<br>McLaren F1 BMW V12 BxS= 86x87 from www.supercars.net<br>Ferrari 360 BxS = 85x79 from www.supercars.net<p>AVERAGE PISTON SPEED AT REDLINE:<br>Obviously the speed changes through the stroke but I only know how to calculate the average, not the max.<p>BMW E46 M3 M3:<br>8000 rev/60sec * 2strokes/rev * 91mm/stroke<br>= 24.3 meters per sec <br>BMW quotes "close to 25 meters a second" so I'm not very far off!<p>HONDA S2000:<br>9000 rev/60sec * 2strokes/rev * 84mm/stroke<br>= 25.2 meters per sec<p>ACURA NSX:<br>8000 rev/60sec * 2strokes/rev * 78mm/stroke<br>= 20.8 meters per sec<p>BMW M5:<br>7000 rev/60sec * 2strokes/rev * 89mm/stroke<br>= 20.767 meters per sec<p>McLaren F1 BMW V12:<br>7500 rev/60sec * 2strokes/rev * 87mm/stroke<br>= 21.75 meters per sec<p>Ferrari 360<br>8500 rev/60sec * 2strokes/rev * 79mm/stroke<br>= 22.38 meters per sec<p><br>It's safe to say the S2000 has the higher average piston velocity at redline. I'd go one step further and say it's got the higher average piston velocity over a road course, because running 1000 rpm (or more) higher than the M3 engine in most driving wouldn't be unusual at all.<p>NSX and M5 don't come close. One is your classic short-stroke honda, the other your classic stroked V8.<p></i><br>

Hagen
11-28-2000, 11:32 AM
Nice calcs. No need for calculus really. Since the piston is connected by a straight rod to the crankshaft, all you need to know is the radius of the crank and the length of the piston arm. The fastest piston speed will be when the crabk is 90 degrees to the direction of piston travel.<p>Anyway, now that I've added that, I'll just bow out because my head hurts and I don't wanna do the calcs.<br>

Mr. Grinch
11-28-2000, 03:22 PM
Definately looks like a test for the oil used.<br>

M3 1/2
11-28-2000, 05:27 PM
Maximum piston speed is about Pi/2 (1.6 times) greater than the average speed. <p><i><br>BMW E46 M3 M3: 24.3 meters per sec <p>HONDA S2000: 25.2 meters per sec<p>ACURA NSX: 20.8 meters per sec<p>BMW M5: 20.767 meters per sec<p>McLaren F1 BMW V12: 21.75 meters per sec<p>Ferrari 360: 22.38 meters per sec<br></i><br>


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