Atlblkz06
02-17-2009, 02:53 AM
So the Ferrari F430 uses a 4.3L V8. The V8 block configuration is the same as any Ford or GM V8 - 90* V8.
So why does the engine sound so incredibly different?
It seems that the answer is in the crankshaft:
Regular V8s use a cross-plane crankshaft (X) but the more exotic cars use a Flat-plane crankshaft (-)
CROSS PLANE CRANK:
Notice that the nodes are setup in an "X" or "+" configuration. The crank pins are 90* apart.
http://www.icbm.org/erkson/personal/V8Cross.jpg
Considering the illustration.
http://www.autozine.org/technical_school/engine/smooth_counterweight1.jpg
Assume the counter weight in vertical position is heavy enough to balance the crank throw, con-rod and pistons. When the crankshaft rotate 90°, the counter weight is repositioned to the right, but the piston doesn’t go to the left, and the con-rod just partially moves to the left. Only the crank pin moves completely to the left. Now you can see the system is not balanced. The counter weight will generate a net force towards the right.However, for 90° V8, when such a heavy counter weight moves to the right, the piston from another bank will cancel it completely, because their movement are exactly opposed at this moment. (see illustrations below) The same result can be found for the counter weight moving to the left. Therefore 90° cross-plane V8 employs full-weight counter weights can achieve near perfect smoothness.
DISADVANTAGES: The disadvantage of cross-plane V8s is also about the counter weights - not only increase the weight of engine, they also contribute to rotational inertia, thus making the engine less responsive and less revvy, dropping upper rev limit and top-end power. Moreover, the larger counter weights usually requires a larger crankcase to house them, thus raising the height (and more important, center of gravity) of the enigne
FLAT PLANE CRANK:
PC: Notice that the nodes are setup in an "-" or "|" configuration.
The crank pins are 180* apart.
http://www.icbm.org/erkson/personal/V8Flat.jpg
Flat-plane V8 is named according to the shape of the crankshaft, which is in a flat plane. It is very much like two inline-4 engines mated together. In particular, it achieves end-to-end balance because the first piston and last piston of a bank is exactly in the same position, so are the center two pistons. This is just the same as straight-four engines, therefore the sound of flat-plane V8 is usually somewhat like a pair of four-pot engines screaming simultaneously, unlike the rumble-bumble of cross-plane V8s. As both banks run like an inline-4 engine, there is second-order vibration. For a 90° flat-plane V8, the sum of second-order force generated in the 2 banks is - by simple vector analysis - 1.41 times (root-2) of the force generated by each of the inline-4 it consists of. And the direction of vibration is left-right instead of top-down. In other words, while displacement increases 100% compare with the inline-4, the second-order vibration increases just 41%. That makes the flat-plane V8 more refined than an inline-4 although it is not as smooth and quiet as cross-plane V8.
To exotic sports cars, less refinement is not a big problem. Especially they usually employ short stroke and light weight pistons / con-rods, the second-order vibration is greatly reduced.
BORE X STROKE:
To reduce the second order vibrations and to give the engines a high degree of it's rev-happy tendency, the engines are usually over-square. The bore is much greater than the stroke.
An F430 engine has a 3.62" Bore but only a 3.19" stroke. Compare this to a 4.125" bore and an almost equal 4" stroke in the GM LS7.
Awesome video explaining the two:
VIDEO (http://www.youtube.com/watch?v=RpWC0PDhdFo)
Keep in mind that this video is actually an infomercial and is very biased and pro-crossplane since thats what they're trying to sell.
I hope this info helps :cheers:
SOURCE:
http://www.autozine.org/technical_school/engine/smooth4.htm
So why does the engine sound so incredibly different?
It seems that the answer is in the crankshaft:
Regular V8s use a cross-plane crankshaft (X) but the more exotic cars use a Flat-plane crankshaft (-)
CROSS PLANE CRANK:
Notice that the nodes are setup in an "X" or "+" configuration. The crank pins are 90* apart.
http://www.icbm.org/erkson/personal/V8Cross.jpg
Considering the illustration.
http://www.autozine.org/technical_school/engine/smooth_counterweight1.jpg
Assume the counter weight in vertical position is heavy enough to balance the crank throw, con-rod and pistons. When the crankshaft rotate 90°, the counter weight is repositioned to the right, but the piston doesn’t go to the left, and the con-rod just partially moves to the left. Only the crank pin moves completely to the left. Now you can see the system is not balanced. The counter weight will generate a net force towards the right.However, for 90° V8, when such a heavy counter weight moves to the right, the piston from another bank will cancel it completely, because their movement are exactly opposed at this moment. (see illustrations below) The same result can be found for the counter weight moving to the left. Therefore 90° cross-plane V8 employs full-weight counter weights can achieve near perfect smoothness.
DISADVANTAGES: The disadvantage of cross-plane V8s is also about the counter weights - not only increase the weight of engine, they also contribute to rotational inertia, thus making the engine less responsive and less revvy, dropping upper rev limit and top-end power. Moreover, the larger counter weights usually requires a larger crankcase to house them, thus raising the height (and more important, center of gravity) of the enigne
FLAT PLANE CRANK:
PC: Notice that the nodes are setup in an "-" or "|" configuration.
The crank pins are 180* apart.
http://www.icbm.org/erkson/personal/V8Flat.jpg
Flat-plane V8 is named according to the shape of the crankshaft, which is in a flat plane. It is very much like two inline-4 engines mated together. In particular, it achieves end-to-end balance because the first piston and last piston of a bank is exactly in the same position, so are the center two pistons. This is just the same as straight-four engines, therefore the sound of flat-plane V8 is usually somewhat like a pair of four-pot engines screaming simultaneously, unlike the rumble-bumble of cross-plane V8s. As both banks run like an inline-4 engine, there is second-order vibration. For a 90° flat-plane V8, the sum of second-order force generated in the 2 banks is - by simple vector analysis - 1.41 times (root-2) of the force generated by each of the inline-4 it consists of. And the direction of vibration is left-right instead of top-down. In other words, while displacement increases 100% compare with the inline-4, the second-order vibration increases just 41%. That makes the flat-plane V8 more refined than an inline-4 although it is not as smooth and quiet as cross-plane V8.
To exotic sports cars, less refinement is not a big problem. Especially they usually employ short stroke and light weight pistons / con-rods, the second-order vibration is greatly reduced.
BORE X STROKE:
To reduce the second order vibrations and to give the engines a high degree of it's rev-happy tendency, the engines are usually over-square. The bore is much greater than the stroke.
An F430 engine has a 3.62" Bore but only a 3.19" stroke. Compare this to a 4.125" bore and an almost equal 4" stroke in the GM LS7.
Awesome video explaining the two:
VIDEO (http://www.youtube.com/watch?v=RpWC0PDhdFo)
Keep in mind that this video is actually an infomercial and is very biased and pro-crossplane since thats what they're trying to sell.
I hope this info helps :cheers:
SOURCE:
http://www.autozine.org/technical_school/engine/smooth4.htm