Why various V8s sound different
04-25-2008, 09:32 PM
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Why various V8s sound different
This came from a discussion of why Ferraris sound different from many other V8s, but I thought it might interest some of you as well. It not only covers the difference of flat plane cranks vs conventional, but also firing order and how induction/exhaust pulses can influence things
"The classic Ferrari 'sound' comes from a number of interacting elements that line up n a synchronized chorous.
First comes the flat plane crankshaft. This gives each cylinder bank an even firing order LRLRLRLR whereas the typical american V8 has an off kilter firing order LRLLRLRR. The even firing order means that the intake and exhaust pulses are also synchronized and evenly spaced.
Next comes the headers. These headers are tuned for the power band of the engine, not too big, not too small, not too long not too short. The headers cause much of the low frequency rumble from these engines by setting up a standing wave pattern of pressure pulses.
Next come the intake system. Here the air path is essentialy straight (e.g. no turns) that enables the air to flow into the cylinders with minimal resistance. The straignt air flow and low resistance enables the velocity stacks to be tuned with the header to broaden the power band.
As the intake valve opens (with the still open exhaust valve) air begine to travel into the cylinder even before the piston starts dwonward from the negative pressure wave from the header. As the intake valve closes, there is considerable momentum in the air flow. When this reaches the closed intake valve, pressure builds until a positive pressure pulse runs up the intake and velocity stack finds air at atmosphereic pressure and sends a negative pressure wave back down. This negative pressure wave runs into the intake valve and sends a negative pressure wave back up the intake and VS, causing a subsequent positive pressure wave. much of the high frequency music of these engines comes directly from this process.
Just under the resonance point of the header there are an even number of intake cycles so that when the intake valve opens there is already positive pressure and momentum to take the fresh charge into the cylinder (also) even before the piston starts downward. Just above the resonance point of the header there is another even cycle count in the intake puls train. There are generally 8 or 10 cycles on the low intake resonance and 8 or 6 on the high RPM intake resonance. These broaden the powerband of the motor.
Finally, the throttle plates are positioined at the center of the intake path and at anything less than WOT damp out even order harmonics in the intake resonance so one hears the primary, 3rd order, 5th order,... of the air movements turned into that sonorous chorous. Even order harmonics end up sounding like an amplifier with cross over distortion, while odd order harmonics sound like an amplifier cliping the peak. Any music buff will tell you that odd is much better than even in sound quality.
The modern V8 engines also employ a 2 stage set of resonators. The air box covering the intake tracks is tuned such that at header resonance a positive pressure wave is above each intake velocity stack just before the intake valve opens. The great rush of air into the cyclinder reinforces this 'standing' wave resonance. These are known as helmholtz resonators.
At the end of this resonator is a smallish tube leading to the largish air filter box. The size and length of this tube damp out the resonator standing wave such that the mass air flow sensor gets a nice smooth flow of air and can thereby be used to give precise control to the FI system.
The difference betewwen Ferrari systems and other manufactures, is that Ferrari works to get the sizes, volumes, and resonance points to actually line up and sing. Whereas others just get them close enough to deliver the power."<ul><li><a href="http://www.ferrarichat.com/forum/showthread.php?t=195067">the whole thread</a></li></ul>
"The classic Ferrari 'sound' comes from a number of interacting elements that line up n a synchronized chorous.
First comes the flat plane crankshaft. This gives each cylinder bank an even firing order LRLRLRLR whereas the typical american V8 has an off kilter firing order LRLLRLRR. The even firing order means that the intake and exhaust pulses are also synchronized and evenly spaced.
Next comes the headers. These headers are tuned for the power band of the engine, not too big, not too small, not too long not too short. The headers cause much of the low frequency rumble from these engines by setting up a standing wave pattern of pressure pulses.
Next come the intake system. Here the air path is essentialy straight (e.g. no turns) that enables the air to flow into the cylinders with minimal resistance. The straignt air flow and low resistance enables the velocity stacks to be tuned with the header to broaden the power band.
As the intake valve opens (with the still open exhaust valve) air begine to travel into the cylinder even before the piston starts dwonward from the negative pressure wave from the header. As the intake valve closes, there is considerable momentum in the air flow. When this reaches the closed intake valve, pressure builds until a positive pressure pulse runs up the intake and velocity stack finds air at atmosphereic pressure and sends a negative pressure wave back down. This negative pressure wave runs into the intake valve and sends a negative pressure wave back up the intake and VS, causing a subsequent positive pressure wave. much of the high frequency music of these engines comes directly from this process.
Just under the resonance point of the header there are an even number of intake cycles so that when the intake valve opens there is already positive pressure and momentum to take the fresh charge into the cylinder (also) even before the piston starts downward. Just above the resonance point of the header there is another even cycle count in the intake puls train. There are generally 8 or 10 cycles on the low intake resonance and 8 or 6 on the high RPM intake resonance. These broaden the powerband of the motor.
Finally, the throttle plates are positioined at the center of the intake path and at anything less than WOT damp out even order harmonics in the intake resonance so one hears the primary, 3rd order, 5th order,... of the air movements turned into that sonorous chorous. Even order harmonics end up sounding like an amplifier with cross over distortion, while odd order harmonics sound like an amplifier cliping the peak. Any music buff will tell you that odd is much better than even in sound quality.
The modern V8 engines also employ a 2 stage set of resonators. The air box covering the intake tracks is tuned such that at header resonance a positive pressure wave is above each intake velocity stack just before the intake valve opens. The great rush of air into the cyclinder reinforces this 'standing' wave resonance. These are known as helmholtz resonators.
At the end of this resonator is a smallish tube leading to the largish air filter box. The size and length of this tube damp out the resonator standing wave such that the mass air flow sensor gets a nice smooth flow of air and can thereby be used to give precise control to the FI system.
The difference betewwen Ferrari systems and other manufactures, is that Ferrari works to get the sizes, volumes, and resonance points to actually line up and sing. Whereas others just get them close enough to deliver the power."<ul><li><a href="http://www.ferrarichat.com/forum/showthread.php?t=195067">the whole thread</a></li></ul>
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