Quote:
Originally Posted by Irace86.2.0
Incorrect. The specs: The FA20 is 86x86 which is a shorter bore and stroke than the Yaris motor. The FA24 has the same 86mm stroke as the FA20, so the stroke is shorter than the Yaris, but it does have a larger bore of 94mm. The point is the Yaris has an extra 4mm of stroke, which means piston speeds are higher for any given RPM. The bore is larger on the FA24, but the Yaris could have heavier pistons considering the specific output of the Yaris engine is higher than the FA24, and each cylinder has to manage much more . Think about it.
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Damn, I was wrong, sorry. I always thought it was the stroke they increased on fa24 compared to fa20. Now I see.
Quote:
Originally Posted by Irace86.2.0
The Yaris is making more hp with less cylinders, so each rod and piston is working harder. If they bother were tuned for 400hp, the Yaris would be dealing with 133hp per cylinder, but the FA24 would be dealing with 100hp per cylinder—about 30% less. At 400hp, the Yaris would be putting out 250hp per liter. The FA24 would be putting out 167hp per liter—about 33% less stress per liter. If the FA24 put out 250hp per liter it would be making 600hp.
Three cylinder engines also have a power stroke every 120 degrees vs 90 degrees of crankshaft rotation, and they are less balanced, so they require more balancing shafts.
Considering the strength needed in the powertrain, the extra stroke and the engine imbalance, the rpms are lower. Because there is less cylinders, each cylinder sees higher pressures per hp. Because there is less displacement, the engine has to work harder to attain the same output like a short man having to lift the same weight as a big man. For all these reasons, I would rather have the FA24.
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I think all this bore and stroke thing doesn't really matter in this case since the engine's redline is on 7000 and you don't have to spin it all that much to get the torque.
And if it's properly balanced with the shafts I don't care about it's natural imbalance - I've driven 3 cylinder mini cooper and it felt perfectly smooth, not much difference with the 4 cylinder cooper s engine (which is b48 and btw powers junior Supra).
And if we go on with bmw engines - this yaris 3 cylinder is actually very similar to bmw s55 engine (though split in half), which powers m3 and m4 - both have the same stroke (89.7 - yaris, 89.6 - s55) and same power per liter ratio (261/1.6=163 hp; 493/3=164 hp). And s55 is highly tunable.
But anyway I share your excitement on fa24 (though skeptical of it's being enough).
