There was a lot of buzz around the Coates valvetrain circa 1995. (Animation is too good to miss)

Two decades later, I still don't see mass adoption of this "revolutionary" technology.

Coates Valvetrain

So what gives? Is there a technical reason to warrant the lack of adoption?

  • 1
    Cost of production and reliability (warranty issues), these are the main reasons new technology is slow to be adopted. – Moab Aug 26 '16 at 21:26
  • @Moab this has appeared since the 50's I think or at least early 70's several main auto manufacturers have used these in production cars over the years but it has not caught on. – Cc Dd Nov 17 '16 at 21:54

Volumetric Efficiency

The primary limitation would be the intake charge timing. The rotating chamber for the intake charge is limited to the volume of the chamber rather than the poppet valve style valve train that can be timed to allow for a longer period of intake as well as gaining the efficiency of an intake charge that is flowing into the combustion chamber without restriction.


  • Limitation of intake flow

  • Limitation of intake charge due to volume of the rotating chamber.

Although it appears the reliability gains of removing a poppet style valve from the system seem to be meaningful the performance restrictions of overall power potential for the engine seem to be quite restrictive.

  • really? I figured removing the valve would allow better flow? – Cc Dd Nov 17 '16 at 22:00
  • @CcDd It's because the chamber doesn't allow flow through so the charge is limited by the volume of the chamber. Maybe I should dig for a citation when I have some time rather than just stating it. – DucatiKiller Nov 17 '16 at 22:04
  • flow through as in valve overlap, or the little bit of extra pressure you get with suction, or something else? – Cc Dd Nov 18 '16 at 4:23

One thing I did read about this was that it worked best with fuels of natural gas and the like. Perhaps the lack of infrastructure for this fuel prevented any sort of penetration of the technology in modern designs.

It might also be too soon. If the technology needs to be proven, the design cycle for modern cars is about 5 years or so isn't it? If it took 4 or 5 years to prove out the technology, work on it's issues, like sealing, measure it's longevity, performance, fuel economy, emissions performance, etc, etc, it might not be ready for inclusion yet.

  • I believe GDI is a perfect example of this. I was reading about Honda experimenting with it in the late nineties, but it wasn't widely adopted for another 15+ years. – Lathejockey81 Aug 26 '16 at 21:14
  • Actually, the first GDI engines appeared at the turn of the last century before the start of WWI. The French Antoinette 8V engine (1902) used direct injection. Not that all innovations take that long to catch on… – dlu Aug 27 '16 at 0:13
  • I have heard rotary valve systems were used on several production cars. and started to appear in the 50's I think but not sure. – Cc Dd Nov 17 '16 at 22:05
  • @dlu blasphemy! you just gave the title of first big block to the French. But wow direct injection at the turn of the century. – Cc Dd Nov 18 '16 at 4:28

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