Function

Here V8 engines are described whose cylinder benches form an angle of 90°. Having a steady ignition interval crankshafts with two connecting rods on one journal are possible. The crankshaft above does not have all its headers arranged in a level. Two of the four headers were twisted when warm and received thereby the stability gained by forging.

How it works

There are basically two kinds of V8 engines (90 °). They differ in the firing order which is primarily determined by the crankshaft. For example, in the racing sport a crankshaft with 180° from header to header (flat-plane) is often used. If there would be instead of two only one connecting rod per header, it would be a crankshaft for the four cylinder in-line engine. This shows also in the firing order: 1-8-2-7-4-5-3-6. If you take the numbers 1-2-4-3, you receive the firing order of a left rotary four cylinder engine. The remaining 8-7-5-6 resemble the same for the second cylinder bank, left rotary in direction of the traffic, if you would number them vice versa.

The forged and surface-hardened Mercedes crankshaft consisting of chrome molybdenum steel of 2006 is shown on top. You can recognise that it concerns a V8 engine by the wide bearings for the connecting rods and particularly the two oil bores. Indeed, the headers are assigned in an angle of 90° to one other (cross-plans). To the right the double row roller chain is engaged going to the camshaft drive, thus marking the front of the engine. Completely to the right there is the chain drive presumably to the oil pump. Take a look at the corresponding cylinder block in picture 2. This displays that all left connecting rods are assigned to the rear cylinder bank with the numbers 8-7-6-5 (from the left to the right) and all right connecting rods belong to the front cylinder bank with 4-3-2-1. crankshaft Together with the first piston of the front cylinder bank the piston of cylinder 6 of the rear cylinder bank is at TDC. Therefore, the following basis arises for the firing order: 1-_-_-_-6-_-_-_. Up to this point there is no alternative firing order for this engine. Only after a rotation of the crankshaft of 90°, the cylinders 3 and 5 would be possible. 5 was selected to have a change in cylinder bank. Now the firing order becomes already a little more complete: 1-5-_-_-6-3-_-_. Another 90° further, cylinders 4 and 7 are possible. Again, going for the change, 4 is selected: 1-5-4-_-6-3-7-_. Now only 2 and 8 are left.

Unfortunately, the continual change of the cylinder banks cannot continue. Either the next ignition or the next after next ignition occurs on the same side. Thus there are two solutions of equal importance: 1-5-4-8-6-3- 7-2 or 1-5-4-2-6-3-7-8. The Mercedes engine shown on top has the second option.

If the cylinder numbering does not deviate from the standard, you can recognise from the firing order according to which principle the crankshaft is stepped. Thus the crankshaft with the firing order 1-8-4-3-6-5-7-2 (series-V8) must have 90 °-heading, because with the numerical order 1-4-6-7 (every second number) no four cylinder firing order is recognizable.The V8 is hot at the moment (2007) also as a racing engine. The engine of the touring car does not deviate much from the standard engine. It is with a third less cubic capacity clearly shorter and its nominal speed is increased by about 1500 rpm. It produces about 100 kW more. The formula 1 is much more vehement, of course. They manage with half the cubic capacity and triple the nominal speed double performance. Additionally, there is also half the weight of the engine and a fourfold mileage. If once again a manufacturer states, that they inserted a Formula-one engine into a street car, do not believe them. No manufacturer can afford to pay so many warranty cases because of engine troubles after approx. 2000 km. 06/07

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