This really confuses me. On the late steam engines, you let in as much steam as possible to start the engine, and "notch up" as you pick up speed so you waste less fuel. Some stationary engines even had rotary valves.

I understand VTEC, but if you could buy stick-shifts surely you could time the valves manually and on-the-fly.

  • 3
    $\begingroup$ You can buy stick-shifts... But will giving drivers control of valve timing mean a benefit? They can't use indicators properly, or brakes... $\endgroup$
    – Solar Mike
    Apr 1, 2023 at 18:48
  • 1
    $\begingroup$ Trains not only have multiple, trained operators but also do not need to worry about steering at the same time. $\endgroup$
    – DKNguyen
    Apr 1, 2023 at 19:18
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    $\begingroup$ @SolarMike Turn signals. Say it right ;) $\endgroup$ Apr 1, 2023 at 22:06
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    $\begingroup$ @EthanMiller I did say it right, it's your lack of vocabulary: bonnet or hood? tire or tyre? $\endgroup$
    – Solar Mike
    Apr 2, 2023 at 8:21
  • $\begingroup$ Older engines had fixed valve timing because the mechanical complexity just wasn't worth it. As mentioned in the answers, newer engines have solved this with electromechanical control -- but things still happen too fast for a person to keep up with. $\endgroup$
    – TimWescott
    Apr 4, 2023 at 1:47

2 Answers 2


The ECU already incorporates variable valve timing - cars do have buttons to change the ECU tune such as "eco" or "sport" mode - this may adjust the valve timing/lift.

The answer is that consumer cars are meant to be simple to operate, and that most variable valve timing features are done automatically via the ECU - with the valve timing/lift change kicking in at a point where engineers have determined to be optimal. Too many controls would be considered overwhelming for the average consumer. Enthusiasts adjust their valve timing via custom ECU tunes, and other similar features such as manual boost controllers. Adjustments may be made between races, etc. but are not usually done while driving (though this is technically possible)

  • $\begingroup$ I'll be that there's combinations of settings (including the valve timing) that would destroy the engine in short order, too. Or if not in a few seconds, then well within any reasonable warranty period. Were I Ford or GM, I would not want to bring out a valve timing control for people to destroy their engines with. $\endgroup$
    – TimWescott
    Apr 4, 2023 at 1:46
  • $\begingroup$ You could arguably allow only a range of valve timing settings that are within a safe range and allow the operator to select them before going for a drive- but again this would not be of use to most customers - in effect what the OP is asking for is accomplished with "eco" or "sport" mode. The engineers already tuned the ECU to have the best valve timing for either performance or fuel economy $\endgroup$ Apr 4, 2023 at 1:52

Let's view your question from an inventive perspective, i.e. how do inventions evolve (over systems, not necessarily over time)? It may not directly answer your question, but puts it into a broader context.

There are a few well proven generic pattern which allow identification and "sorting" inventioens, i.e. inventive concepts. This is one so called line of evolution:

  • go from ... to ...
  • solid (mechanical solution)
  • liquid or gaseous (thermal solution)
  • electric (all solutions from electrostatic)
  • magnetic (all solutions from magnetostatic)
  • electromagnetic (all solutions Maxwell allows)
  • fields / information (non-physical realisations)

What they have in common is an ever increasing trend in so called Ideality, when moving from top to bottom. Which implies e.g. an ever inceasing degree of integration:

$Ideality := \frac{({all.useful.actions} + {some.more.good})}{({all.harmful.actions} + {cost})}$

Let's illustrate it.

Mechanical solutions are typically amongst the first inventions. We all know mechanics, we can easily develop ideas around it and make a prototype in our hobby rooms: mechanical valve timing.

Keen inventors may have noticed, that mechanical operations do create or do need heat to function. They may come up with ideas using this harm (temperature) for good (e.g. via expansion of liquids or gases): thermal valve timing.

Keen inventors may have noticed mechanical movement and remember electrostatic effects, like we know from Van der Graaf's generator, noticeable in escalators. When movement can create a proportional amount of electrostatic charge, it might be used for ... electrostatic valve timing.

Out-of-the box thinkers may feel better from using (small) magnets to replace, augment or simplify mechanical interactions. After all magnets can attract or distract permanently, allowing for better gears, bearings, levers etc: magnetic valve timing.

Inventors with a background in electronics may want to replace larger parts of mechanics with limited reliability by electronics with a much higher un-reliability limit: electromagnetic/electronic valve timing.

Finally, why using clumsy PCB-electronics at all? Let's replace their function and action ("field") by information, i.e. a handful of nano-sensors feeding some computer (of a few square-milimeters) : field or information valve timing.

As you can see, it's a process of continuously identifying new available resources and replacing previously necessary ones. In tendency, this leads to ever increasing Ideailty:

$Ideality \longrightarrow \frac{good \uparrow}{bad \downarrow} \longrightarrow \infty$

Now, Ideality is an idealized term in this context. Understand it more as a trigger for motivation. Real systems can only approximate Ideality, but it's not less breathtaking. Just try to envision:

  • the bulky mechanical valve timing control and its final almost absent digital implementation
  • or look at your parents or grandparents bulky tube receiver, which evolved over transistor radios to a fraction of a square milimeter on-chip today in full HiFi stereo inside your mobile phone ...

So the ideal system will almost be absent, BUT all its useful functions are still there plus a few more goodies, AND most of its harm is gone, costing next to nothing any more.

Applying this mental concept to engineering gives breathtaking results, almost on-the-fly.

As I said in the beginning, it's a scheme to order inventive concepts. Often the appearance in time is similar, but usually kind of jumps. You probably need some effort to dig out electrostatic valve timing control, though it may already exist. If not: invent it, next improve it to beat todays performance champ.

Coming back to your question why ... not ...? the answer in a nutshell is: we probably found solutions with higher Ideality, meanwhile.

  • $\begingroup$ Pretty irrelevant answer , seems a bit like an AI bot. $\endgroup$ Apr 4, 2023 at 1:49
  • $\begingroup$ Relevance is a matter of perspective. // I think you overestimate what AI can do (Artificial Incompetence) … $\endgroup$
    – MS-SPO
    Apr 4, 2023 at 2:53

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