The differences between a flat plane and cross plane crankshaft
If you’ve clicked on this article, I assume you want to know about the two main different types of crankshafts (if not then, oh well). The two that I will be covering will be the cross plane and flat plane crankshafts. Even though they are used throughout the motoring world in a variety of applications, the one I will be focusing on is in V8 form. So let’s get into it and not waste anymore time.
With each crankpin journal (the bits the connecting rods attach to) at 180 degree intervals, the flat plane crank tends to be higher revving than it’s cross plane counter part. That’s because the pistons are firing evenly between their banks (L,R,L,R,L,R,L,R, etc.) while a cross plane fires unevenly (L,L,R,L,R,R,L,R,L,L,R,). Because of this, flat plane cranks tend to be less balanced than their cross plane counterparts, but being more responsive because less weight is needed to carry counterweights to balance out vibrations from the engine.
Advantages: Lighter, tends to be more rev happy, easier packaging
Disadvantages: Not as torquey, less smooth than a cross plane setup
Verdict: If you prefer revs over power Honda fanboys intensify, this is the way to go. Hardly any cross plane setup can compete as far as revs go. However if you want to make more power and a smoother powertrain, the cross plane is for you.
Applications: Porsche 918, any McLaren model, Ford GT350/R
P.S., the typical firing order for a flat plane crank is 1-5-3-7-4-8-2-6 (for Ferrari V8s anyways)
In just about every other application, V8s use a cross plane setup. Instead of the crankpins being at 180 degree intervals, the cross plane has them at 90 degree intervals. This allows for a distinctive burble not found in flat plane V8s. Another thing not found in flat plane V8s? The firing order. The firing order for a Voodoo V8 is 1-5-4-8-3-7-2-6. The firing order for Coyote V8 is 1-5-4-8-6-3-7-2. Even though cross planes won’t rev as high compared to flat planes, they make up for it in the power department. Cross planes normally tend to have more torque than a flat plane. Not only that, but cross planes are smoother because they have balancing shafts to smoothen out any vibrations.
Advantages: Smoother than a flat plane, can make more torque
Disadvantages: Bigger than a flat plane, can’t rev as high
Verdict: The classic is sometimes the better than the modern (even though the flat plane is older if I remember correctly)
Applications: Most american muscle cars (LS, Coyote, Hemi)
To sum up, for an endurance car, a flat plane would probably be better seeing as you can rev more which could give you the upper hand over someone else. A cross plane crank would be better for drag racing because you get that low end torque which can get you off the line quicker. In the end, I prefer revs over power, so I would take the flat plane crank, but let me know what you guys would rather have (Vote here.) If you have any suggestions or ideas, shoot ‘em at me in the comments, who knows, I might just pick it and write about it. But until next time, I will see you later. Goodbye!