Difference between cross-plane and flat-plane crankshafts!

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Cross-Plane vs. Flat-Plane Crankshafts: The Difference! In the world of V8 engines there is an exciting debate between proponents of Cross plane and Flat-plane crankshafts. Both designs have advantages and disadvantages that are fascinating to fans and engineers alike. While the Cross-plane crankshaft is primarily installed in American V8 engines and provides the characteristic sound of muscle cars Flat plane crankshaft common in European high performance vehicles and racing cars.

What is a flat-plane crankshaft?

The Flat plane crankshaft, an older design that was used in the Ford Model A, for example, is characterized by cranks that are all in one plane. This results in a firing sequence that alternates from one cylinder bank to the other, allowing for optimal exhaust gas flow. The design does not require large counterweights, resulting in faster speeds. However, the flat-plane crankshaft suffers from secondary vibrations.

What is a Cross-Plane Crankshaft?

In contrast, there is Cross-plane crankshaft consists of four offsets that are arranged in two levels, each offset by 90 degrees. The design ensures the typical “burble” of a V8 engine as two successive exhaust blasts are directed into the same exhaust side. The cross-plane crankshaft requires larger counterweights for good engine balance, which results in less secondary vibration but also lower rpm and top speed.

Advantages of the flat-plane crankshaft

The flat-plane crankshaft is characterized by a lower mass and therefore less inertia, which leads to faster accelerations. The alternating firing order between the cylinder banks achieves a more even exhaust gas pulse distribution, which enables optimized performance. Examples of vehicles with flat-plane crankshafts include the Ferrari F430 and the Ford GT350 Mustang.

Balance problems with flat-plane crankshafts

Although flat-plane crankshafts have lower primary vibration, they are more difficult to handle in terms of secondary balance than cross-plane crankshafts. The secondary vibrations caused by an imbalance of forces at 270 and 90 degrees can be problematic with larger displacements.

Summary

In summary, both cross-plane and flat-plane crankshafts have their specific advantages and disadvantages. While the flat-plane crankshaft is known for its fast acceleration and efficient exhaust routing, the cross-plane crankshaft offers better balance and the characteristic sound that many associate with American V8 engines. The choice between these two ultimately depends on the specific requirements of the vehicle and the driver's preferences.

Cross-plane vs. flat-plane crankshafts

1. General definitions:
   • Flat plane crankshaft: Offsets in one plane, angle of 180°.
   • Cross-plane crankshaft: Two levels, offset angle of 90°.
2. Comparison of the designs:
   • Both types for V8 engines with 90° bank angle.
   • Flat plane preferred in racing vehicles (e.g. Ferrari).
3. Storage:
   • V8 crankshafts stored five times.
4. Ignition sequences:
   • Flat plane: 1-8-2-7-4-5-3-6.
   • Cross plane: 1-8-4-3-6-5-7-2.
   • Different firing sequences affect performance and sound.
5. Technical Differences:
   • Flat tarpaulin with less counterweights, faster revving.
   • Cross plane required larger counterweights for balance.
6. Applications:
   • Flat plane often in European sports cars and racing cars.
   • Cross plane often in American V8 engines.
7. Ford Mustang GT350:
   • Flat plane with unusual structure: up-down-up-down.
   • Larger counterweights for balance.
8. Balance problems:
   • Flat plane tends to secondary vibrations.
   • Cross-plane balanced by counterweights, however sluggish when revving.
9. Flat-plane crankshaft properties:
   • Low primary vibrations.
   • Lower weight, less inertia.
   • Faster and higher turning compared to cross plane.
   • Better exhaust flow.
   • Loss of the typical “muscle car” sound.
   • Higher secondary vibrations.
10. Cross-plane crankshaft properties:
    • Easier to balance, especially with secondary balance.
    • Larger counterweights necessary.
    • Typical sound of American V8 engines.
    • Not as fast and high revving as flat plane.

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