advantages of the flat motor
Discussion
Primary imbalance is due to the reciprocating components, that is the piston & rod travelling up and down the cylinder, or more specifically side to side in the case of the flat 6 911 engine. This primary force is counteracted by a balance weight built into the design of the crankshaft.
Secondary imbalance is due to the said crank balance weights acting at 90 degrees to the cylinder axis where they are opposing just the big end weight of the rod, obviously this secondary force is up/down in the case of the 911 engine. The beauty of the 911 is that the opposing pistons "box" each other 1/4, 2/5, 3/6, so the balance weights are on adjacent crank webs which are set at 180 degrees to each other on the crank, thereby cancelling each others' vertical forces (more or less).
The more or less is because the weights are not exactly in line front-to-rear, so there are still some front/rear imbalance forces acting on the parts, but this is taken care of by using a stiff crank/main bearing/crankcase assembly (unless it is a 996 of course!
).
Secondary imbalance is due to the said crank balance weights acting at 90 degrees to the cylinder axis where they are opposing just the big end weight of the rod, obviously this secondary force is up/down in the case of the 911 engine. The beauty of the 911 is that the opposing pistons "box" each other 1/4, 2/5, 3/6, so the balance weights are on adjacent crank webs which are set at 180 degrees to each other on the crank, thereby cancelling each others' vertical forces (more or less).
The more or less is because the weights are not exactly in line front-to-rear, so there are still some front/rear imbalance forces acting on the parts, but this is taken care of by using a stiff crank/main bearing/crankcase assembly (unless it is a 996 of course!
).I'm not sure about all this balancing stuff.
I think that a Flat engine that is designed the way that Porsche did is easy to manufacture on small machine tools. In some ways this is better, because a machine tool that is smaller is cheaper for a given level of precision.
Because the crank case is naturally split in the centre, I'd have thought that the whole casting process is much more straightforward.
If the engine hangs from the car, rather than being suported by it, it makes an engine out easier, with less equipment. The hanging engine suits a flat design.
It probably doesn't matter so much with a rubber belt, but if you are using a timing chain, you really need to have two with a flat engine, whereas, you might get away with one in the vee configuration.
The oil distribution around the engine is more difficult in a flat engine.
I think that a Flat engine that is designed the way that Porsche did is easy to manufacture on small machine tools. In some ways this is better, because a machine tool that is smaller is cheaper for a given level of precision.
Because the crank case is naturally split in the centre, I'd have thought that the whole casting process is much more straightforward.
If the engine hangs from the car, rather than being suported by it, it makes an engine out easier, with less equipment. The hanging engine suits a flat design.
It probably doesn't matter so much with a rubber belt, but if you are using a timing chain, you really need to have two with a flat engine, whereas, you might get away with one in the vee configuration.
The oil distribution around the engine is more difficult in a flat engine.
jolley said:
Flat six is one of only three engine configurations that has no primary or secondary imbalances. (The others are straight-six and V12.)
My little brain cannot understand how the straight 6 and V12 cannot have imbalances.
Also, would the Subaru Flat 4 not also be balanced?
Straight or flat 6s are naturally balanced because you always have 2 pistons at top dead centre, 2 pistons at bottom dead centre, and 2 pistons right in the very middle of the stoke, as they are all moving up and down, so they in effect cancel each others vibrations out.
V-12s and flat 12s work the same way, except it's 4 TDC, 4 BDC and 4 in the middle of the stoke.
Flat engines are nicknamed Boxers because the pistons move laterally like a boxers arms as they throw a punch and because the pistons are moving side to side instead of up and down like in an in-line engine less vibration will occur but a flat 6 or 12 will be smoother than a flat 4.
Yep, Porsche made a 1.5litre flat eight for Grand Prix racing in the early sixties - I think it won one GP in the hands of Dan Gurney. They popped it in the odd sportsracer as well and it sounds absolutely gorgeous! Also, wasn`t the 908 a flat eight?
As mentioned above, the 917 in all its derivatives had a lovely , big flat 12 as did various Ferrari`s.
As mentioned above, the 917 in all its derivatives had a lovely , big flat 12 as did various Ferrari`s.
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