Time and time again the question “Which V8 sounds better?” has rolled of the tongues of most car enthusiasts. European V8s have a high revving loud note while American V8s have low raw rumble.
Great examples are the C8 Corvette and the Ferrari 458 Italia. So why the sound difference? Exhaust systems definitely have an impact that even within the European cars you can distinguish a McLaren from a Ferrari.
Linked at the end of article are two videos of the C8 Corvette and Ferrari 458 Spider
The difference lies in the type of crankshaft used, either flat-plane crank or cross-plane crank. Traditionally, flat-plane cranks have been used in four cylinder engines but European V8s use it while American V8s use the cross-plane crank.
The crankshaft is what is connected to the pistons via a connecting rod and the point of connection is called the crank journal. The positioning of the crank journals are what dictates the firing order of the engine and the type of crankshaft.
For a cross-plane crank, the crank journals are on two planes with a 90° angle between them thus from a frontal view the planes form a cross. In a flat-plane crank, as the name suggests the journals are flat on one plane separated by a 180° angle.
So in a cross-plane crank, for every 90° rotation a cylinder fires and for a flat-plane crank, a cylinder fires after every 180° rotation.
Picture a V8 with its two banks and cylinders numbered from 1 to 8, take one bank to have the even numbers and the other have the odd numbers. With that in mind, the firing order of the C8 Corvette is 1-8-7-2-6-5-4-3 and as you can see there are two even numbers (2-6) following each other meaning at some point two cylinders in one bank of the engine fire consecutively thus the firing order is uneven. This means the exhaust gases leaving the engine are also uneven resulting in a pulse that produces the rumble we know.
In flat-plane crank V8s, the firing order alternates between the two banks thus the exhaust gases are even which is effective in terms of the scavenging effect (explanation for another day). Due to the less resistance as an effect of even exhaust gases, the engine with flat-plane crank can rev to higher RPMs.
As we wrap it up, this is not to say that some American V8s don’t have flat-plane cranks or vice versa. It’s just that traditionally cross-plane crank is more common in American V8s whereas flat-plane is used predominantly and almost exclusively by European manufacturers.
The Ford Mustang Shelby GT350 uses a flat-plane crank and it can rev to 8200 RPM compared to 7000 RPM of the standard Mustang GT. Mercedes-AMG M156 6.2-liter V8 from the legendary SLS AMG uses a cross-plane crank.
Each type of crank has their benefits and drawbacks but when it comes to engines its a matter of showing your engineering muscles and reducing the drawbacks.
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