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Originally posted by billege
Poppet valves, if not activated with hydraulic systems, must have clearance readjusted periodically.
ahem, bullshit.
That's why we invented hydraulic lash adjusters. Oh, they said, "if not activated with hydraulic systems." This statement is just meant to imply an adjustment problem with regular valves.
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Well, I would call that a hydraulically activated system, essentially. I've owned a number of pure pushrod engines, and they were a stone cold bitch to maintain at peak tune. The bike engine I'm working now is a pushrod engine and it's pretty much standard practice to have spare tappet covers in your tool box as they have to come off so often that you will lose/break them. Valve adjustement IS a problem with poppet valve engines, it is just less of a problem with hydraulic ones (this is not to say that Coates valve would not take some sort of adjustment, but it seems like that is done by the designers and stays as is, a possible weakness of the system, really)
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Lessse, a 5.0L (assume ford? stock? that's what they seem to be implying) revving at 15k is impossible for reasons other than the normal valvetrain. The piston velocities at such an insane speed would: (and take your pick, any is just as likely as the next...)
Send the piston flying off the connecting rod.
Snap the rod like a cheap stick.
Melt the main bearings.
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Quoted from the article "A five-litre poppet vavle engine tested on a dynomometer under the same loads and conditions at 5500 produced 480 BHP and 454 foot pounds of torque." I really cannot recall a stock Ford, or any other, 5.0 litre engine producing 480bhp. So, not a stock engine, I would assume. I would, however, agree with the surmise that the engine grenaded at 14k rpms. It just seems unlikely, then again, they could have used F1 quality components and design that could take such extreme rpm.
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"The air traveling in through the inlet venturi of a combustion engine inlet travels at a speed of up to 450ft a second. In normally aspirated engines this works fine, but in poppet valve engines, the BHP and torque decreased as the air traveling in does not increase in speed unless a turbo or supercharger is incorporated."
This statement is essentially meaningless. Really, what the hell are they even saying? What works fine in a naturally aspirated engine? The speed of the intake air?
I've never worried about air inlet speed when building an engine. I don't know who has.
Air speed is a non-issue, air flow is. The size and shape of ANY inlet and outlet must be carefully designed to make air flow smoothly, I have no idea how air speed is a factor here.
While we're at it, forced induction systems to not increase the speed of intake air. They increase the volume of air inducted. That's why turbo/super chargers are both just AIR COMPRESSORS. That's why they have COMPRESSORS, to force more Cubic Feet/Minute of air into the intake.
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While air-flow is important, speed is also important as it becomes a major factor in turbulence. Too much speed is due to overly opened ports/runners, and accompanied by too little turbulence causing poorer quality mix. Going back to the bike engine I referred to earlier, in the CB750, one of the classic head tuning tricks was to open the intake ports as wide as possible. I've seen rock-solid data that show this to be a bad idea as it allows too much speed and kills mix. It is better to D-shape the port and make a flat-spot, slowing down the mix and increasing turbulence (while keeping similar cfm numbers if done right).
Moving back to the article though, speed can denote many things. To an untrained person reading a basic article in a non-automotive publication, speed can easily be a (poor) substitute for cfm (speed being distance travelled in a given unit of time, but can also refer to simply how fast a given action is performed, in this case movement of air per unit of time). This is a basic article intended to give an overview of the Coates system to someone that is likely not terribly familiar with autmotive engineering and design. It is not an article written by a car guy for car people.
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"At higher RPMs the poppet valve tends to float or bounce and is unable to service the cylinder and chamber to capacity with air and fuel mixture."
That's why engines HAVE redlines. Beyond a certain RPM valves do float, this is bad. This is also a valve SPRING problem, not a valve type problem. If you want a high RPM ceiling, you build an expensive, lightweight, strong valvetrain. Then you can rev higher without float.
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Um, valve float IS a problem endemic to poppet valve engines. It is a big problem. There is no real way around it either. This is what the Coates system is designed to prevent. I have my problems with the article as well, but the theory is sound. If you research the idea a bit more, you'll likely find that this article is simply poorly written due to its' intended audience.