I've heard multiple mechanics discussing that an atmospheric 4 cylinder engine that has 8 valves, is more efficient power-wise and has better fuel consumption below the 3000rpm mark.
While a 16 valve engine would be more efficient power-wise and also have better fuel consumption, ONLY above that same 3000rpm mark.
Therefore, that's why 16 valve engines were more sought after for performance/tuning, since they also allowed a higher RPM max band-margin.
What do you guys think? Is this correct?
One of the biggest differences - other than high-rev capability - with 4 valve vs 2 valve engines is that 4 valve engines can give a "flatter" torque curve. Here's some content from one of my favorite sources on engine design, Kevin Cameron over at Cycle World
"The advantage of four-valve designs over two-valve systems has to do with the greater total valve perimeter of two intake valves compared to the perimeter of a single intake. This allows a four-valve design to create valve-flow area more rapidly as the intakes lift, and that allows the paired intakes to equal a single intake’s airflow delivery with much less valve duration. Since shorter valve-open time gives an engine a wider torque range, this is a desirable change."
https://www.cycleworld.com/story/blogs/ask-kevin/motorcycle-valve-curtain-area-explained/
I would like an example of the "2-valve engine that has greater efficiency power-wise and better fuel consumption" - It sure looks to me like all the major manufactures have retired their 2-valve engines and replaced them with 4 valve engines. All - from Aston Martin to Volkswagen.
Thank you for the detailed answer @Glen_stet
- The point that was discussed, was only regarding that a car with a 4 cylinder engine with 8 valves, would be optimal when driven under 3000rpm for fuel consumption-wise and performance-wise, thus being a much more "calm" and lighter engine (which as an extra, also reduces tear and wear, overall).
- In contrast, in the case of an engine also with 4 cylinders, but with 16 valves, reaches its full potential only when driver after the 3000rpm mark (thus as an extra, are more desirable for youngsters on a budget who wish to do tuning to further increase performance, despite the extra wear and tear, overall).
Do you agree?
All I know is it sounds more expensive. How much is the purported gain in performance?
