Inhibitor turret damage

The tooltip (at the start of the game) for an inhibitor turret says it deals 170 damage with 4 attack speed, ignoring 75% armor. That would mean 680 damage per second. If you have 46 armor (so 11.5 effectively), it would be 680*89.7% = 610 dps. And obviously that grows as the game progresses. I tested it on Hecarim with said 46 armor and 822 health. He should die to an inhibitor turret in 1.34s. Instead, it takes more than twice as much - around 3.5s. Which means the actual dps is only 822/3.5s = 234, or 261 without armor. So, with 4 attacks per second, it only deals 65 damage (or its attack speed is actually about 1.5, not 4), as opposed to 170 mentioned in its stats.