If the weight of a F1 Crankshaft is about 20 lbs , then how light is the Crankshaft in a Champ car or Winston Cup car ? On a another Thread someone said a NASCAR Cranshaft is about 28 lbs, but that sounds very light to me. I would think that Rotating mass in a F1 Engine would be alot lighter but I could be wrong.
Crankshaft Question
Started by
slipstream
, Aug 10 2001 06:16
10 replies to this topic
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#2
AdamLarnachJr
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Posted 10 August 2001 - 07:11
I think F1 is about 25lbs... and a winston cup crank.. the lightest crower makes "stock" is 32lbs.
#3
Engineguy
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Posted 10 August 2001 - 08:21
25 lbs is the lowest I've seen for an F1 crank, but there may be some lower... very short stroke allows small bearing journals and small couterweights. Use of titanium rods also reduces counterweight size.
My understanding is that NASCAR cranks that weigh in the mid to low thirties are used only for qualifying where duration is short and restrictor plate races where power is way down.
My understanding is that NASCAR cranks that weigh in the mid to low thirties are used only for qualifying where duration is short and restrictor plate races where power is way down.
#4
slipstream
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Posted 15 August 2001 - 00:17
Thanks for the info guys. Now I have another basic Engine tech Question. What is the best way to determine the@Weight of the Rotating mass of a Engine ? Would you look@at the max RPM, Stroke, Engine Weight, or all of the above ? The reason I am asking is because a Friend says that the 2.65 L V-8 Engines used in CART have less Rotating Mass than F-1 Engines and have quicker Engine Acceleration. I am sure he is wrong but I need some facts to prove it.
#5
AdamLarnachJr
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Posted 15 August 2001 - 03:21
Here is my uneducated take on that;)
First off, the crankshaft is shorter in a Champ car V8, the throws should be lighter since their is less displacement, and the overall assembly should be much lighter because there are less cylinders, and therefore less rotating members.
You might argue however that there are more more cylinders in a F1 V10, therefore crankshaft stroke and bore would be smaller, and the Champ car V8 engine would need to have a bigger bore and larger stroke. The V8 engine has 31.25cc's more displacement in each cylinder, but it also has 2 less connecting rods, pistons, valve assemblies, and camshaft tappets, as well as the two rod journals on the crankshaft.
Another factor in engine revolution speed is the amount of power is being produced... or is this just bs? I noticed that the more power produced, the faster the engine revs up... like in a TF engine... big rotating assembly, yet it can rev from idle to 10,000rpm faster than the speed of light:) And that is an 8000cc plus engine.
First off, the crankshaft is shorter in a Champ car V8, the throws should be lighter since their is less displacement, and the overall assembly should be much lighter because there are less cylinders, and therefore less rotating members.
You might argue however that there are more more cylinders in a F1 V10, therefore crankshaft stroke and bore would be smaller, and the Champ car V8 engine would need to have a bigger bore and larger stroke. The V8 engine has 31.25cc's more displacement in each cylinder, but it also has 2 less connecting rods, pistons, valve assemblies, and camshaft tappets, as well as the two rod journals on the crankshaft.
Another factor in engine revolution speed is the amount of power is being produced... or is this just bs? I noticed that the more power produced, the faster the engine revs up... like in a TF engine... big rotating assembly, yet it can rev from idle to 10,000rpm faster than the speed of light:) And that is an 8000cc plus engine.
#6
jdowns
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Posted 15 August 2001 - 12:51
Here is my educated, but often completely wrong take on that ;)
If, by rotational mass, they mean angular moment of inertia (physics term), then it's normally related to radius squared. Ie. if you have to simple disks, each of 10 kg's, but one is 10cm across, and the other 20, then the wider one will have exactly four times the inertia of the narrower one. So, two similar engines (by weight) can have very different inertias (based on throw and fly wheels, etc.). Another issue is the effect of the reciprocating mass(es). That article desmo posted about the W12/V12 comparison used 1/3rd of the conn rod weight in it's calculation of rotational mass.
I'd guess that the CART engine would spin up faster. Being simplistic, a slightly smaller engine made of the same materials (they're both just steel cranks) will have similar, or probably smaller inertia, plus 50-100 extra horsepower (depending on who you listen too), plus (possibly most importantly), it only needs to spin up to 15,000rpm = 1/6th less than F1.
Many questions there, but the biggest one is the lag in the turbo?!?
Adam, angular acceleration (rate of spin up) is simply torque / inertia. In metric terms, a 10kg disk of 10cm radius will have a moment of inertia of 1/2 * m * r^2 = .05 kg.m^2. A torque of 100 Nm will give it 100/.05 = 2000 rads/s/s = 19,000 rpm per second. Double the torque, double the rpm per second (linearly). It's not related to power. I'm not putting those figures forward as indicative of F1, or anything, they're just nice round figures ;)
If, by rotational mass, they mean angular moment of inertia (physics term), then it's normally related to radius squared. Ie. if you have to simple disks, each of 10 kg's, but one is 10cm across, and the other 20, then the wider one will have exactly four times the inertia of the narrower one. So, two similar engines (by weight) can have very different inertias (based on throw and fly wheels, etc.). Another issue is the effect of the reciprocating mass(es). That article desmo posted about the W12/V12 comparison used 1/3rd of the conn rod weight in it's calculation of rotational mass.
I'd guess that the CART engine would spin up faster. Being simplistic, a slightly smaller engine made of the same materials (they're both just steel cranks) will have similar, or probably smaller inertia, plus 50-100 extra horsepower (depending on who you listen too), plus (possibly most importantly), it only needs to spin up to 15,000rpm = 1/6th less than F1.
Many questions there, but the biggest one is the lag in the turbo?!?
Adam, angular acceleration (rate of spin up) is simply torque / inertia. In metric terms, a 10kg disk of 10cm radius will have a moment of inertia of 1/2 * m * r^2 = .05 kg.m^2. A torque of 100 Nm will give it 100/.05 = 2000 rads/s/s = 19,000 rpm per second. Double the torque, double the rpm per second (linearly). It's not related to power. I'm not putting those figures forward as indicative of F1, or anything, they're just nice round figures ;)
#7
AdamLarnachJr
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Posted 15 August 2001 - 15:43
When *I* say power, I usually mean engine torque:) I know thats confusing as hell, but I dont subscribe to the horsepower tells all theory... guess I should say torque from now on:)
So for a Top Fuel engine.... 4000ft. lbs... and a rotating mass of 75lbs... = ?
So for a Top Fuel engine.... 4000ft. lbs... and a rotating mass of 75lbs... = ?
#8
jdowns
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Posted 15 August 2001 - 23:04
Depends on the radius of the mass. For a cylinder, inertia is .5*m*r^2, for a cylinder offset from the axis of spin, but parrallel to it it's .5*m*r^2 + m*h (h is offset from axis, or the stroke here), a thin rod rotating about one end is 1/3*m*r^2, a thick rod is a complex formula...
This is why I'm not sure if I'm talking about the right thing. I know what angular inertia is from physics, and it's definately the thing you use to calculate rotational acceleration, and it's definately related to radius squared (that's why fly wheels have a large radius, if you increase the radius by 10, you get 100x the inertia for the same weight), but I'm not sure if that's rotating mass....
From my last example, take that 10kg mass that has the 100Nm of torque applied to it, but increase the radius to 20cm. Acceleration is now only 4,800 rpm/s, down by 2/3 for the same weight, just by changing the radius.
You can't calculate rotational acceleration from just the weight of the rotating bits, without taking the distribution of weight into account.
Power-vs-torque
I still like power, but it doesn't apply in this case. It is an abstract idea, it's not what gives you the kick in the back, but if you want to compare the possible performance of two engines, use hp. Two engines of similar torque can give completely different performance. Just look at the torque of an F1 engine, less than my 4.1l 6 in my Ford, but put them on a track and hp's comes in to play...;)
Sorry if any of that's a little dry, just woke up :yawn:
This is why I'm not sure if I'm talking about the right thing. I know what angular inertia is from physics, and it's definately the thing you use to calculate rotational acceleration, and it's definately related to radius squared (that's why fly wheels have a large radius, if you increase the radius by 10, you get 100x the inertia for the same weight), but I'm not sure if that's rotating mass....
From my last example, take that 10kg mass that has the 100Nm of torque applied to it, but increase the radius to 20cm. Acceleration is now only 4,800 rpm/s, down by 2/3 for the same weight, just by changing the radius.
You can't calculate rotational acceleration from just the weight of the rotating bits, without taking the distribution of weight into account.
Power-vs-torque
I still like power, but it doesn't apply in this case. It is an abstract idea, it's not what gives you the kick in the back, but if you want to compare the possible performance of two engines, use hp. Two engines of similar torque can give completely different performance. Just look at the torque of an F1 engine, less than my 4.1l 6 in my Ford, but put them on a track and hp's comes in to play...;)Sorry if any of that's a little dry, just woke up :yawn:
#9
AdamLarnachJr
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Posted 16 August 2001 - 00:20
You mean gears and rpm comes into play:) j/k
#10
slipstream
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Posted 16 August 2001 - 00:25
Once again thanks for the info about my question on rotating mass, this is a great forum:) I do not know about the Crankshaft weights but I do know that F1 Engines have lighter Clutches and no Flywheel which would help the Engine to spin up faster. And how important is the Rotating mass to Acceleration ? Last year I read that the Ilmor-Mercedes had very quick Acceleration through the Gears because of its quick Engine Acceleration and Gearbox.
#11
jdowns
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Posted 16 August 2001 - 09:21
OK, here's my 2c worth:
The V12-W12 comparison document lists the V12 crank (6 throws) as 13.4kg, and the W12 (4 throws) at 11.3. Averaging the two to 5 throws (V10) gives about 12.4kg (27 lb). The radius of the crank was 25mm. The radius of the offset part (crank pin?) was 18mm. The offset of the crank pin from the axis of rotation is 1/2 the stroke = 22mm (44mm stroke for a V10). I'm allocating 1/2 the mass to the straight part of the crank (the part through the bearings), and the rest to the crank pin + the counterweight (don't ask me why, I simply don't know any better ;) ). I'm going to give the counterweight the same moment of inertia as the crank pin (probaly not correct, but I have not better figures with which to calculate it). I = moment of inertia.
I of straight part of crank = .5*m*r^2 = 0.0015 kg.m^2
I of crank pin = .5*m*r^2+m*offset^2 = 0.002 kg.m^2
I of counterweight = 0.002 kg.m^2 (arbritrarilly the same as the pin)
-----------------------
I total = 0.0055 kg.m^2
Power = change in Kinetic Energy per second (alternate physics definition, there are several). Kinetic energy =.5*I*omega^2 (omega = rads/second, 1 rad/s = 9.5 rpm). So, if we calculate the kinetic energy (KE) @ one rpm, and again at another, then the change in KE divided by the time taken to rise in rpm will be the hp required to do it.
KE (15,000rpm) = 6,800 Joules
KE (17,000rpm) = 8,700 Joules
If it takes 0.7s (I started up my F1 sim game and looked at the telemetry after the start for 2nd gear, 15K-17K ) then you have 1,900/.7 = 2.75Kw = 3.7hp. This would be greater in 1st gear, and lower for higher gears.
But, this doesn't include the gearbox, clutch, conn rods, timing gears, cams, etc., etc.,... Even if you double it to 7hp, I don't think it would make a huge difference (especially since each team/code couldn't vary much +/- from any other).
Caveat: Although I'm quite sure of the physics and maths, the figures and guestimates are quite likely way out, so please don't go designing an F1 engine on the above ;). I also haven't double checked anything, as I have a physics assignment due tomorrow, and need to get on to it (I wonder if I can submit this for extra points?!?).
The V12-W12 comparison document lists the V12 crank (6 throws) as 13.4kg, and the W12 (4 throws) at 11.3. Averaging the two to 5 throws (V10) gives about 12.4kg (27 lb). The radius of the crank was 25mm. The radius of the offset part (crank pin?) was 18mm. The offset of the crank pin from the axis of rotation is 1/2 the stroke = 22mm (44mm stroke for a V10). I'm allocating 1/2 the mass to the straight part of the crank (the part through the bearings), and the rest to the crank pin + the counterweight (don't ask me why, I simply don't know any better ;) ). I'm going to give the counterweight the same moment of inertia as the crank pin (probaly not correct, but I have not better figures with which to calculate it). I = moment of inertia.
I of straight part of crank = .5*m*r^2 = 0.0015 kg.m^2
I of crank pin = .5*m*r^2+m*offset^2 = 0.002 kg.m^2
I of counterweight = 0.002 kg.m^2 (arbritrarilly the same as the pin)
-----------------------
I total = 0.0055 kg.m^2
Power = change in Kinetic Energy per second (alternate physics definition, there are several). Kinetic energy =.5*I*omega^2 (omega = rads/second, 1 rad/s = 9.5 rpm). So, if we calculate the kinetic energy (KE) @ one rpm, and again at another, then the change in KE divided by the time taken to rise in rpm will be the hp required to do it.
KE (15,000rpm) = 6,800 Joules
KE (17,000rpm) = 8,700 Joules
If it takes 0.7s (I started up my F1 sim game and looked at the telemetry after the start for 2nd gear, 15K-17K
) then you have 1,900/.7 = 2.75Kw = 3.7hp. This would be greater in 1st gear, and lower for higher gears.But, this doesn't include the gearbox, clutch, conn rods, timing gears, cams, etc., etc.,... Even if you double it to 7hp, I don't think it would make a huge difference (especially since each team/code couldn't vary much +/- from any other).
Caveat: Although I'm quite sure of the physics and maths, the figures and guestimates are quite likely way out, so please don't go designing an F1 engine on the above ;). I also haven't double checked anything, as I have a physics assignment due tomorrow, and need to get on to it (I wonder if I can submit this for extra points?!?).
