Comment by OptionOfT
14 hours ago
What I am surprised by is that cams are still used to operate the valves.
Given to how precise these need to be these days, I would've guessed they would've switched to electronically actuated valves.
14 hours ago
What I am surprised by is that cams are still used to operate the valves.
Given to how precise these need to be these days, I would've guessed they would've switched to electronically actuated valves.
It’s because of the good enough precision at low cost that we use cams, it’s extremely difficult to get precise movement and the forces and speeds required when an engine is operating at >5000 rpm. It’s not impossible but the trade offs are rarely worth.
The exact valve timing isn’t really a big factor in emissions as much as temperature control and exact AFR control. I mean valves need precise timing to avoid coming into contact with pistons but if you’re already at that level of precision then you gaining more precision won’t really reduce your emissions.
Of course being able to change the timing of your valves helps with both efficiency and emissions, but VVT does that pretty well.
Fiat (and other's I'm sure) have the [MultiAir system](https://www.caranddriver.com/features/a16580674/fiats-multia...) which doesn't use cams to actuate valves
And here's an example of someone that retrofitted a Miata to use a similar [air-actuated valve system](https://youtu.be/E9KJ_f7REGw)
The very first image at the very top of the MultiAir article shows, prominently, a camshaft and the cams used to actuate the valves.
I was going to point to Koenigsegg’s Freevalve system and, in the process of looking for a link, learned that it was cancelled.
> What I am surprised by is that cams are still used to operate the valves.
Kinda, it's all continuous variable valve lift now:
https://en.wikipedia.org/wiki/Variable_valve_lift
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