The Design and Balance of V8 Engines: A Comparative Analysis

In the world of internal combustion engines, V8 designs are particularly popular due to their power output and efficiency. However, the design of a V8 engine is not just about raw power; it also requires careful consideration of balance and vibration control. In this article, we will explore two types of V8 designs: cross-plane and flat-plane engines, and discuss their advantages and disadvantages.

Cross-Plane V8 Engines

A cross-plane V8 engine is characterized by the fact that its cylinders are arranged in a way that creates a flat plane of movement for the pistons. In this design, cylinders one and two are connected at the top, while cylinders seven and eight are connected at the bottom. This configuration results in a unique balance of primary forces, with each cylinder's up-and-down motion being balanced by an equal force on the opposite side.

The cross-plane V8 engine also has a secondary balance, which is achieved through the use of counterweights. These counterweights help to balance out the moment created by the uneven firing order of the cylinders, ensuring that the engine remains smooth and vibration-free. The primary forces in this design create a moment on the crankshaft, which must be countered by the heavy counterweight system.

The cross-plane V8 engine has several advantages. One of the most significant benefits is its secondary balance, which results in a smoother engine operation with less vibration. This makes it well-suited for applications where smoothness and quiet operation are essential, such as in luxury cars or high-performance vehicles.

On the other hand, the cross-plane V8 engine has some disadvantages. The heavy counterweight system required to achieve this balance adds rotational inertia to the crankshaft, which can make the engine feel less responsive. Additionally, the large size of the crankshaft and counterweights can increase the weight and size of the engine, making it more difficult to handle and maneuver.

Flat-Plane V8 Engines

A flat-plane V8 engine is a design that combines elements of both inline-four engines and traditional V8 engines. In this configuration, cylinders are arranged in two banks, with each bank firing in unison. The first and fourth pistons fire together, while the second and third pistons fire together.

The flat-plane V8 engine has a unique characteristic: it lacks secondary balance. Unlike the cross-plane V8, which achieves its balance through counterweights, the flat-plane V8 relies on the inherent balance of the inline-four design to smooth out the firing order. However, this lack of secondary balance results in vibration and imbalance, particularly noticeable during exhaust scavenging.

The advantages of a flat-plane V8 engine are largely related to its performance capabilities. With fewer counterweights and less rotational inertia, the engine can rev more quickly and produce more power. Additionally, the flat-plane design allows for lighter weight materials and shorter strokes, which reduces the effect of secondary imbalance.

However, the flat-plane V8 engine also has significant disadvantages. The lack of secondary balance makes it prone to vibration, particularly during exhaust scavenging. This can be detrimental to the overall smoothness and quiet operation of the engine. Furthermore, the high-performance nature of this design means that it is often used in racing applications, where durability and reliability may take a backseat to raw power.

Conclusion

In conclusion, both cross-plane and flat-plane V8 engines have their advantages and disadvantages. While the cross-plane V8 offers smooth operation and vibration-free performance, its heavy counterweight system can make it feel less responsive and more difficult to handle. The flat-plane V8, on the other hand, excels in terms of power output and responsiveness but requires careful design and engineering to mitigate its lack of secondary balance.

Ultimately, the choice between a cross-plane and flat-plane V8 engine depends on the specific application and requirements. For high-performance racing or luxury vehicles where smoothness and quiet operation are paramount, the cross-plane V8 may be the better choice. However, for high-output applications where power and responsiveness take precedence over refinement and vibration control, the flat-plane V8 design is worth considering.

"WEBVTTKind: captionsLanguage: enhello everyone and welcome in this video i'm going to be explaining cross plane versus flat plane v8 engines now if you haven't already watched my video on v8 engines you may want to check that out prior to watching this so the way they get their name flat plane versus cross plane basically just has to do with the crankshaft and what it looks like so with a cross plane crankshaft um you can see the crankshaft that goes up here out to the right back over to the left and then down and so if you're looking at it uh from towards this crankshaft if you're looking into it you're going to have cylinders one and two are going to be connected up at the top cylinders seven and eight connected down to the bottom uh five and six on the left three and four on the right just like we've drawn here now the flat plane v8 everything's going to be in a flat plane hence the name so we've got one and two seven and eight which are going to be up high and then three and four five and six which are going to be down low and then this will simply rotate and those will change so that's what it'll look like looking on to the crankshaft so let's kind of analyze the forces that are going on with each of these and that'll help us determine why both of these exist so looking at a cross plane what we're going to have here is the cylinder in the front is going to be up near top dead center this one at the rear down at bottom dead center and then these two are going to be offset 90 degrees and they're going to be a flat so that's how this system is going to be set up so these will be rotating and basically what we've got going on here is you've got your primary forces being balanced out here except they're offset so they're going to kind of uh it's going to create a moment on this crankshaft so we're going to have to do is add counterweight and so counterweights are going to be what's balancing out these primary forces and balancing out this moment that's going to want to kind of torque this engine now the great thing about cross-plane v8 engines and why they are used is look at the secondary forces so we've got two forces going down two little forces going up these are going to balance each other out hence it's going to have a secondary balance so now that's the great thing that's why this engine is used but let's look at a flat plane engine so basically a flat plane engine is the equivalent of two inline four cylinders so this flat plane v8 is basically two inline fours where you've got the first and fourth piston are going to be in unison going up and down and then the second and third will be together going up and down now if you've watched my video on four cylinders you know that the primary forces are going to balance out but the secondary forces aren't so an engine a flat plane v8 is going to have a secondary engine imbalance and so there's going to be vibration because of that and that's why this is sometimes preferred over it so let's talk about advantages and disadvantages of each type so cross plane v8 as we said secondary engine balance so it's got a smooth engine little vibration so that's why it is used the disadvantage well because of this engine moment here that's created you're going to have to have a heavy crankshaft to balance out that piston movement and so that heavy crankshaft means additional rotational inertia a less responsive engine also by having a larger crankshaft or by adding these counterweights on you're going to have a larger crankshaft and that can in turn mean a larger crankcase and so by increasing the size of the crankcase you may have to raise the engine up a bit and then you're going to have a higher center of gravity versus a flat plane uh v8 engine also one thing uh is the uneven firing order for scavenging the exhaust scavenging so i'm going to explain this more detail in a future video but basically uh the pulses of the exhaust aren't exactly uh even whereas they are on the flat plane they alter between each cylinder bank so advantages of a flat plane v8 well it's not going to have as much counterweight on the crank so that means less rotational inertia it's going to have a more responsive um crankshaft so your engine is going to rev up a little easier and you're going to have less power going into rotating that crank more going to the wheels also the exhaust scavenging because the exhaust pulses are going to alter from bank to bank um disadvantages as we've mentioned the secondary imbalance so the reason flat planes aren't as common is because of this secondary imbalance and so the reason they are use those for racing because in racing applications you're not necessarily as concerned about the secondary engine balance you just want a fast revving engine that doesn't drain any power out of it um it's not going to last forever but it's a racing application so it doesn't need to and so this is typically used in higher end cars and also in higher end cars you're going to have lighter weight materials on shorter strokes and in doing this you're really reducing the effect of the secondary imbalance so you can have a fairly vibration free flat plane v8 uh depending on how much money you throw into it so thank you for watching if you have any questions or comments feel free to leave them belowhello everyone and welcome in this video i'm going to be explaining cross plane versus flat plane v8 engines now if you haven't already watched my video on v8 engines you may want to check that out prior to watching this so the way they get their name flat plane versus cross plane basically just has to do with the crankshaft and what it looks like so with a cross plane crankshaft um you can see the crankshaft that goes up here out to the right back over to the left and then down and so if you're looking at it uh from towards this crankshaft if you're looking into it you're going to have cylinders one and two are going to be connected up at the top cylinders seven and eight connected down to the bottom uh five and six on the left three and four on the right just like we've drawn here now the flat plane v8 everything's going to be in a flat plane hence the name so we've got one and two seven and eight which are going to be up high and then three and four five and six which are going to be down low and then this will simply rotate and those will change so that's what it'll look like looking on to the crankshaft so let's kind of analyze the forces that are going on with each of these and that'll help us determine why both of these exist so looking at a cross plane what we're going to have here is the cylinder in the front is going to be up near top dead center this one at the rear down at bottom dead center and then these two are going to be offset 90 degrees and they're going to be a flat so that's how this system is going to be set up so these will be rotating and basically what we've got going on here is you've got your primary forces being balanced out here except they're offset so they're going to kind of uh it's going to create a moment on this crankshaft so we're going to have to do is add counterweight and so counterweights are going to be what's balancing out these primary forces and balancing out this moment that's going to want to kind of torque this engine now the great thing about cross-plane v8 engines and why they are used is look at the secondary forces so we've got two forces going down two little forces going up these are going to balance each other out hence it's going to have a secondary balance so now that's the great thing that's why this engine is used but let's look at a flat plane engine so basically a flat plane engine is the equivalent of two inline four cylinders so this flat plane v8 is basically two inline fours where you've got the first and fourth piston are going to be in unison going up and down and then the second and third will be together going up and down now if you've watched my video on four cylinders you know that the primary forces are going to balance out but the secondary forces aren't so an engine a flat plane v8 is going to have a secondary engine imbalance and so there's going to be vibration because of that and that's why this is sometimes preferred over it so let's talk about advantages and disadvantages of each type so cross plane v8 as we said secondary engine balance so it's got a smooth engine little vibration so that's why it is used the disadvantage well because of this engine moment here that's created you're going to have to have a heavy crankshaft to balance out that piston movement and so that heavy crankshaft means additional rotational inertia a less responsive engine also by having a larger crankshaft or by adding these counterweights on you're going to have a larger crankshaft and that can in turn mean a larger crankcase and so by increasing the size of the crankcase you may have to raise the engine up a bit and then you're going to have a higher center of gravity versus a flat plane uh v8 engine also one thing uh is the uneven firing order for scavenging the exhaust scavenging so i'm going to explain this more detail in a future video but basically uh the pulses of the exhaust aren't exactly uh even whereas they are on the flat plane they alter between each cylinder bank so advantages of a flat plane v8 well it's not going to have as much counterweight on the crank so that means less rotational inertia it's going to have a more responsive um crankshaft so your engine is going to rev up a little easier and you're going to have less power going into rotating that crank more going to the wheels also the exhaust scavenging because the exhaust pulses are going to alter from bank to bank um disadvantages as we've mentioned the secondary imbalance so the reason flat planes aren't as common is because of this secondary imbalance and so the reason they are use those for racing because in racing applications you're not necessarily as concerned about the secondary engine balance you just want a fast revving engine that doesn't drain any power out of it um it's not going to last forever but it's a racing application so it doesn't need to and so this is typically used in higher end cars and also in higher end cars you're going to have lighter weight materials on shorter strokes and in doing this you're really reducing the effect of the secondary imbalance so you can have a fairly vibration free flat plane v8 uh depending on how much money you throw into it so thank you for watching if you have any questions or comments feel free to leave them below\n"