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billege · 02-06-2004, 03:20 AM

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.

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.

While we're at it, let's dig some more BS out of this article.

Gas, auto engines in the 70s, lead or no, NEVER made anywhere near 55% thermal efficiancy. The BEST desiels today come close to that level of efficiancy. Gas today gets you 20-odd %, that's the best ones.

Lead was used to raise the octane level, which allowed for higher compression ratios. This had NOTHING to do with the valves.
The valves, specifically the seats, were designed to take advantage of the lead in the gas for use as lubrication. Not the main source of lube, mind you, just take advantage.
Remove the lead, remove the advantage, thus some redesigning was in order.
This was in no way a "failure" in the poppet valve concept, as the article implied.
If everyone was putting a magically cheap 120 octane gas in the tank, compression ratios could easily jump up to 15:1, with poppet valves working just fine.
In fact, vehicles adapted to burn natrual gas do take advantage of it's higher octane, and DO run 14:1 and the like ratios.

"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.

"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.

I'm not going to deconstruct the rest of the article, but it's full of shit, and that make me seriously doubt anything they may be on to here.

02-06-2004, 03:20 AM	#7 (permalink)
billege Watcher Location: Ohio	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. 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. While we're at it, let's dig some more BS out of this article. Gas, auto engines in the 70s, lead or no, NEVER made anywhere near 55% thermal efficiancy. The BEST desiels today come close to that level of efficiancy. Gas today gets you 20-odd %, that's the best ones. Lead was used to raise the octane level, which allowed for higher compression ratios. This had NOTHING to do with the valves. The valves, specifically the seats, were designed to take advantage of the lead in the gas for use as lubrication. Not the main source of lube, mind you, just take advantage. Remove the lead, remove the advantage, thus some redesigning was in order. This was in no way a "failure" in the poppet valve concept, as the article implied. If everyone was putting a magically cheap 120 octane gas in the tank, compression ratios could easily jump up to 15:1, with poppet valves working just fine. In fact, vehicles adapted to burn natrual gas do take advantage of it's higher octane, and DO run 14:1 and the like ratios. "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. "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. I'm not going to deconstruct the rest of the article, but it's full of shit, and that make me seriously doubt anything they may be on to here. __________________ I can sum up the clash of religion in one sentence: "My Invisible Friend is better than your Invisible Friend."