Two flat plane, 4 crankpin crankshafts connected end to end with a 90 degree offset.Ģ. Apparently there were two possibilities.ġ. I'm still confused about which crankshaft configuration the different engines used. But I'm not at all certain about the initial versions of the P908 3.0 liter engine. I think the P804 1.5 liter F1 engine was too. I'm fairly certain the P910 2.2 liter and the final P908 3.0 liter engines were this way. Rory, I researched this a few years ago and came to the conclusion that the Porsche flat 8 engines were true boxers in that each piston had it's own crankpin. The offset between the neighboring connecting rods of the flat-8 with the plane four-throw crankshaft, causes an unbalanced inertia moment of 2nd order. zero kinetic energy eighty about ninety crankshaft degrees later the kinetic energy of the eight pistons maximizes. inertia moment about the crankshaft axis) when one piston is at the TDC, every piston has zero speed, i.e. The flat-8 with the plane four-throw crankshaft has perfect balance of the inertia forces, however it has a strong 2nd order inertia torque (i.e. The balance.exe program at the Teaching section of the web site helps. It needs balance webs on the crankshaft, it also needs an additional counter-rotating balancing shaft. Anyone know what was really going on there?Ī cross-plane crank like a regular V8 would need the extra balance weights that a V8 needs and would have a similar uneven firing order for each bank (compromising exhaust design).Ī flat-8 with cross-plane crankshaft needs more than the balance webs of the regular V-8. There are some references out there on the web to engine balance problems with the 908 sports car engine and that these were cured with a change of firing order. A cross-plane crank like a regular V8 would need the extra balance weights that a V8 needs and would have a similar uneven firing order for each bank (compromising exhaust design). Possibly quite acceptable for a 1.5 litre F1 engine. For instance, a flat plane four throw crankshaft as for an inline four would give perfect primary and secondary balance but cylinders would fire in pairs. The Boxer configuration, whilst obviously the best from the point of view of refinement, is not essential. My question is, what crankshaft configuration did these Porsche flat 8 racing engines use? However flat 12 engines are also referred to as “Boxer” engines and I have never read of one of those with such a (12 throw) crank. They are usually referred to as “boxer” engines, implying that the horizontally (almost) opposite cylinders each had it’s own crank throw and that these throws were 180˚ apart such that both pistons are at TDC / BDC simultaneously, "punching like a boxer" (?) There haven’t been many of these aero engines from Lycoming and Continental and from Porsche, the 1.5litre F1 and the later Sports Car racing engines of the 1960s.
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