dave williams
rec.autos.tech  05-15-93
- -> ago (I'll have to dig it up, it was GOOD). I was, that this rotating
  -> valve is fundamentally a better way to go than current technology,
  -> but by the time someone came up with it the current setup had
  -> been engineered for so long (very mature technology) that starting up
  -> with rotating valve wasn't worth it (or something like that).
- The *real* problem is, rotary valves don't breathe well.  The valve
  forms part of the port, which changes in size as the valve opens and
  closes.  This does horrible things to airflow.  The valve also opens and
  closes at a leisurely rate compared to modern high-acceleration cam
  profiles.  You could add an eccentric mechanism or elliptical sprockets
  to drive the rotary valve, but you still have the airflow problem.  The
  rotary also severely limits possible combustion chamber shapes, and most
  of the possible shapes aren't particularly attractive from either
  maximum power or minimum emissions standpoints.
- The conventional poppet valve WORKS.  The auto industry would ditch it
  in a heartbeat if it would get them another point on the CAFE or make it
  easier to smog a car.  If the Formula racers could get even a little
  more BMEP out of some weirdo arrangement, they'd do it.  Back in the
  early days practically every possible scheme of controlling inlet and
  exhaust gasses was tried; poppets are neither the simplest nor the
  cheapest, but they meet the requirements for airflow and durability.
- -> Although the problem with rotating valves is, how do you lubricate
  -> them without lubricant findind it's way into the hole (cumbustion
  -> chamber)? Some weirdly shaped rings around each end of the hole?
- It's actually an excellent application for ceramic materials, which can
  take the heat, aren't mechanically loaded, are dimensionally stable, and
  don't require lubrication as long as appropriate materials are selected.
  Unfortunately, as I mentioned above, they are a solution to a problem
  that doesn't really exist.

[email protected] (Dave Williams)
fordnatics  11 Dec 1999
- -> I only see two roadblocks to the Coates rotary valves and that is
  -> sealing the combustion chamber, and materials/metalurgy.
- The problems are more like distortion under thermal load and very poor 
  airflow characteristics.  The rotary valve doesn't snap open 
  instantaneously; for most of its cycle it flows significantly *less* than a 
  poppet valve.  The rotary valves also severely limit practical combustion 
  chamber shapes. 
- -> As far as RPM is concerned, you should indeed be able to rev a motor
  -> to a higher RPM than with a cam operated valvetrain.
- Assuming, of course, that the poppet valves are the limiting factor. Coates 
  claims you can bolt their heads on a stock 5.0 short block and spin it to 
  10,000 RPM.  It *might* be possible, if you rate the lifespan in 
  milliseconds. 
- -> It's plain fact that cams held F1 engines back. They now use
  -> pneumatic valves that virtually eliminate the parsasitic losses of a
  -> camshaft. I say virtually, since there still needs to be some sort of
  -> engine powered compressor to pressurize the actuators. Pneumatic
  -> valves offer a world of tunabiltiy above and beyond a cam actuated
  -> system, even those with variable
- F1 cars use pneumatic *springs*; O-ringed cups under a conventional 
  camshaft, just like a Model T had.  There are no engines with pneumatically 
  actuated valves.  There are a very few Diesel engines with hydraulically 
  actuated valves; the hydraulics limit their response time to *seconds*, but 
  that's okay for multi-ton engines that turn 500 RPM. 
- -> The rotary valve concept is far from a dead concept. I think it is
  -> far from a perfect science but if people spent half the time working
  -> on solving its deficincies, instead of working on poppet valves, we
  -> would not be using cams and poppets anymore. Mainly cams.
- Quite a few very sharp engineers and more than one company have spent 
  decades working with rotary valves.  The problems are complex and not easily 
  solved, even when cost is no object. 
- Poppets have many advantages compared to the alternatives.  Herren Otto und 
  Diesel were no fools. 
- -> especially the ones in F1 use. Now, the teams can infinitely vary the
  -> valve timing across a wider rev range, and generate lift scenarios
  -> that were not mechanically possible in cam driven designs.
- They might, if such things existed.  They don't.
- -> A 302 could stay together at 10000 rpm, but not with a pushrod, cam
  -> actuated valvetrain. Too much mass to accelerate and decelerate. But,
  -> the bottom end, if assembled to the precision of some of the bike
  -> motors, using the proper material,  could stay together. However,
  -> keep in mind its design was never
- You mean, if it wasn't a Ford 302, but a blueprinted aftermarket duplicate?  
  How about we shorten the stroke, go to titanium rods and carbon-carbon 
  pistons while we're at it?  It's still a Ford 302, right? Mike Wesley would 
  say it was still stock. 
- -> What if there was an engine designed specifically for Coates rotary
  -> valves?
- And... what?
- -> Oh yeah, what about a Wankel engine. It's far from dead, but it is a
  -> great example of great ideas that don't make the cut.....
- The Wankel is an interesting example of the fact that almost any engine will 
  run, given intake, compression, combustion, and exhaust cycles. The 
  combustion chamber shape is very poor if you're concerned with efficient 
  combustion, even with multiple plugs per rotor.  Keinichi Yamamoto and his 
  crew finally solved the seal problem, but the chamber shape issue is 
  inherent to the design. 
- -> What about gas turbines?
- Gas turbines are excellent, as long as you don't have any worries about 
  tremendous volumes of very hot, loud exhaust, jet airplane scream from the 
  intake side, and the fact that they are only efficient at full power.  Fiat 
  and GM built some gas turbine trucks once, but the engines were a poor fit 
  even in that application.  They're the cat's ass for trains and aircraft, 
  though.