Valves suck

[2strokebloke]

I hate poppet valves, for nearly it's entire existence, it has been these stupid valves that have been the 4-stroke engines weak point.
Burnt valves, pitted valves, sticking valves, noisy valves, valve jobs (ewww!)

Until somebody comes out with a workable rotary valves I'm going to continue viewing the 4-stroke-cycle as far from perfect.
My two favorite types of engine, 2-stroke, and wankel, do not have need for poppet valves, nor should any engine!
But I look back and revere those designs that sought to eliminate these horrible things, inventions like the sleeve valve engine, and the rotary valve.
Inventors have been working on rotary valves, and yet the rotary valve is not in any car being produced today. My question is why? It's been decades in development, and can potentially solve most problems we associate with poppet valves.
Has anybody heard of any recent developments in engines with unconventional valves?

[FYRHWK1]

you have 3 choices, a 4 stroke with poppet valves, a 2 stroke without them or a rotary. The first makes less power then the 2 stroke but a 2 stroke is about as dirty as an engine gets, there's also the problem with no change in "valve" timing because the ports dont move, then theres the rotary, a torqueless wonder with little reliability. It's up to you but poppet valves seem to be the best choice around, rotary valves have unacceptable sealing, I believe ducati had a valve that rocked back & forth but that had reliability problems too, rotaries have their ports without any variable timing so they're stuck too, the only advancement is using poppet valves and solenoid control. Maybe one day rotary valves will work, but they havent yet.

[ivymike1031]

hey, you left out the two-strokes with poppet valves.

[911GT2]

Turbo rotaries have low reliabilities.

The new ones (RX-8) should have excellent reliabilities with 12A durability and 13B turbo power. Only time will tell though.

[2strokebloke]

Actually, the Aspen rotary valve seemed very promising, but I've haven't heard anything about it in the past decade! And it looked to be very neat design.
2-stoke engines, can have variable exhaust timing, controlled by a butterfly type valve in the exhaust port which increase or decreases exhaust backpressure depending on engine speed. However, in a 4-stroke there really isn't any change in valve timing.
Rotary engines aren't very unreliable, that's just the reputation they got from the Ro-80, which was one of the earliest rotary engined cars, and therefore can't really be jugded (as in, you can't say a piston engine is unreliable just because a 1899 Panhard was!)

[ivymike1031]

Originally posted by 2strokebloke
2-stoke engines, can have variable exhaust timing, controlled by a butterfly type valve in the exhaust port which increase or decreases exhaust backpressure depending on engine speed. However, in a 4-stroke there really isn't any change in valve timing.

You might want to look around online a bit for info about variable valve timing. I assure you that such a thing exists, and is becoming increasingly popular (for four-stroke engines).

The butterfly valve you're referring to doesn't change the "valve timing" of the two-stroke engine any more than a variable geometry helmholtz resonator changes the valve timing of a four stroke engine. Both devices influence scavenging, not valve timing.

Using the "butterfly valve" reasoning introduced above, everybody who ever put a header on his car influenced "valve timing" in the process. Sounds a bit silly to me.

[Neutrino]

you guys might wanna read this:
http://www.automotiveforums.com/vbulletin/t94233.html

[2strokebloke]

Actually Ivy, I could argue that because a 2-stroke engine does not have a dedicated exhaust stroke, the the backpressure in the exhaust system not only controls how the exhaust gasses can leave, but also when they can leave.
The effects of putting a different exhaust on a 4-stroke are different than the effects of putting different exhausts on a 2-stroke (a 2-stroke relies on the exhaust system to make power, put on a muffler made for a 4-stroker and you'll barely have enough power to move along a level surface)

And about variable valve timing, none of my 4-stroke cars have it, so I don't really see valveless engines at a disadvantage there. In fact, valved engines have many disadvantages! (most of them caused by the valves themselves)

[ivymike1031]

Actually Ivy, I could argue that because a 2-stroke engine does not have a dedicated exhaust stroke, the the backpressure in the exhaust system not only controls how the exhaust gasses can leave, but also when they can leave

You could, but you'd sound pretty silly. Exhaust and intake tuning work in pretty much the same way in both cases; the two stroke is just more sensitive to them. Valve timing on a four stroke is similar to port position on a two stroke. You wouldn't say that your butterfly valve can do exactly the same things that moving the port can do, would you?

And about variable valve timing, none of my 4-stroke cars have it, so I don't really see valveless engines at a disadvantage there.

Talk about the silly things one could say... Here, let me match you one-for-one on that. "About valveless engines, none of my cars are like that, so as far as I'm concerned they don't exist."

[ivymike1031]

Originally posted by 2strokebloke
In fact, valved engines have many disadvantages! (most of them caused by the valves themselves)

Luckily for the four-stroke poppet-valve fans out there, the advantages of this configuration at this point in time far outweigh the disadvantages, making it the most popular configuration currently in use. Better driveability, less harmful emissions, lower noise levels, and better fuel economy, to name a few advantages...

[2strokebloke]

"Better driveability, less harmful emissions, lower noise levels, and better fuel economy, to name a few advantages..."

The only reason we still have poppet valves is because for most engineers they they were simply "good enough" not because they were the best.
With rotary vavles, better volumetric efficiency can be gained, valve noise can practically be eliminated becacause the valve rotates instead of clapping open and shut, and no matter how fast the engine revs, valve float would be totally impossible.

As to 2-stroke exhaust, no the port itself will not move, therefore port timing itself is not actually changed, but the backpressure causes a huge change in performance, I guess I worded it badly, I did not mean to write that 2-strokes have variable port timing, but that essentially the same effects of such can be had with this valve.

Let's just say this, my 2-stroke car's engine has five moving parts, produces 1.19hp per cubic inch @ 5500rpm (better than most muscle cars, and better than a Viper) is ultra reliable, I've never had to deal with valves, because it doesn't have any. This means, I've never had to change a timing belt (or gears, or chain) never had to set valve clearance, never had the engine eat a valve, or burn a valve either, never had a sticking valve etc. etc. And I certainly can not write all of that about that about my 4-strokers.

Also, if you're literate, you'll never see that I debated the existence variable valve timing, I just stated that it wasn't on any of my 4-strokers and it wasn't on my 2-stroke either.

The poppet valve is old and outdated (and has been for more than half a century now) is it not time we look to a better alternative?

[ivymike1031]

However, in a 4-stroke there really isn't any change in valve timing

And about variable valve timing, none of my 4-stroke cars have it, so I don't really see valveless engines at a disadvantage there.

Also, if you're literate, you'll never see that I debated the existence variable valve timing, I just stated that it wasn't on any of my 4-strokers and it wasn't on my 2-stroke either

yawn... You'll never see that I debated the existence proper grammar. Also, if you're literate, you'll never see that I didn't say you did.

Perhaps you should re-read the thread. All I said was that the logic you used in the second statement listed above was very similar to "if I don't have it, it doesn't exist." To be more precise, perhaps I should have said "if I don't have it, I don't see it as an advantage." Oh well. Your literacy is helpful lesson me.

my 2-stroke car's engine has five moving parts

can you name them?

[2strokebloke]

"You'll never see that I debated the existence proper grammar. "

Five moving parts: Two pistons, two con rods, and one crankshaft.
2+2+1=5

[FYRHWK1]

Originally posted by ivymike1031
hey, you left out the two-strokes with poppet valves.

didn't even know they had those :o but yeah i suppose you could have them, and the valve timing could be changed, unless they just stuck a valve in a port to allow them to retard the "timing"

Turbo rotaries may be less reliable then the NA counterparts, but i've seen more then 1 NA blow it's front seal because of a hot summer day and semi low oil level (meaning he didn't add a quart every half hour) the oil temp shot through the roof and pop, 1 blown rotary. Now i'm a fan of being in touch with my car, but anything that regularly eats oil and has to be watched or else it'll blow is too much for me. I can set my valve lash every week or 2 in a short amount of time, and maybe the new one will be more reliable, but i suppose i'm just going to stick with my personal preference.

As to rotary valves. . .
911GT2 put it perfectly, to create a perfect seal you would have to have alot of contact, you have 150-200+ psi in the chamber, sealing a circular ball valve without actually covering the edge leading to the intake/exhaust ports requires an extreme amount of pressure, ESPECIALLY since the pressure will be forced away from the ball valve and directly to that hairline seal around the valve. Because of the amount of forc e needed to keep the valve sealed you'd have alot of wear and alot of friction, which requires oil, oil that would be burnt up on the seal and cause carbon deposits to build up.

They would score the seal and eventually create a leak, meaning the valve and seal would be under constant watch of wear & tear. The oil would also create terrible emissions, something that will never be allowed again by the damn tree huggers, even for very small production run cars. Sounds alot like another motors big problem doesnt it? these are the reasons rotaries go as well, and i dont think adding the rotaries biggest weakness to a piston engine would help many people.

Now what i want to know is this, since theres no forces testing it's tensile strength (that i can imagine anyway) would Si be possible? it would require no lubrication and doesn't absorb heat like a metal rotary valve and seal would. I'd definitly be all over a system like that, I believe Si can hold quite a bit of compression force (my professor has compared it to concrete, extremely strong in certain areas, but just the inverse in others) so the pressure need to keep a seal would be doable, but i haven't done a ton of research in the area either.

[ivymike1031]

re two-stroke w/ poppet - one example that I'm 100% sure of is the 710 engine from GM/EMD: http://www.gmemd.com/en/locomotive/i...ine/710engine/

I believe the configuration is also found on some tractor engines, and some ship engines. Dunno about smaller vehicles.


Five moving parts: Two pistons, two con rods, and one crankshaft

So I suppose it has journal bearings, not roller bearings, and you're counting the piston pins as parts of the conrods, and the piston rings as parts of the piston. No oil pump, fuel pump is not counted, TV damper is not counted (or not present), and the engine is air cooled (or water pump is not counted)?