The differences between flat plane and cross plane crankshaft

Intro

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.

Flat plane crankshafts

Crankshaft used in the Shelby GT350 and GT350R

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)

Cross plane crankshafts

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)

Summary

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!

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Comments (8)
  • I never noticed this before but a cross plane crank does a paradiddle. Maybe that’s why we tend to think of muscle car V8s as sounding more musical?

    1 year ago
    2 Bumps
    • Possibly, but the way the exhaust is setup can play a major role in the sound of it. For instance, the Voodoo has unequal length headers which is why it sounds different from say a...

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      1 year ago
      2 Bumps
    • Well a paradiddle has to do with rhythm. The exhaust setup will certainly effect the timbre of the engine sound but I’m suggesting that the burble you get from these types of V8s has a...

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      1 year ago
  • If we take McLaren for example, their flat-plane crank engines are not short of torque. two clever turbos will sort the torque out and clever valve lift. Cross plane to me sounds a bit prehistoric

    1 year ago
    1 Bump

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