I wonder if anyone has experimented with reed valves in addition to the ordinary intake valves? To those not familiar with a reed valve, it is mostly used in the intake on two-stroke engines, and it is basically just a flap-door that allows air (or fluid) to flow in one direction only, see here. There have been made engines with reed valves only, that use the pumping effect in the crankcase caused by the piston movement to force-feed a cylinder, look here. (btw, there's some other really hairy stuff at that site, spend some time browsing!) I have been toying for years with the idea to use a custom intake with a reed valve in each runner, placed close to the cylinder head, but I've never had the time or money to make it a reality. The reed valve opens only when there is movement in the intake runner, so it will allow the use of a camshaft with a very long intake duration, and automatically close when the piston is on the upstroke and the rush of intake mixture comes to a halt, but before the ordinary valves close. With such a cam you would normally have a lot of blowback into the intake manifold, and a nervous engine that hardly idles at all and with low torque at low revs, but will run great at high revs. With reed valves in each intake runner, you will have an engine with an ordinary idle and smooth running at low revs when the reed valve takes over the function of the ordinary valve, and high power at high revs when the effect of the reed valve is negligent and the long duration allows a better cylinder fill. It gives some of the same effect as variable-length intake runners combined with a variable lobe camshaft! The reed valve can be used with both carburetted and injected engines, and will typically be very effective together with a long runner type intake with Dellorto side-draft carbs or similar setup, where blow-back is a great problem. It will also be useful in some blower and turbo applications, but I guess some very careful calculations of the dynamic compression is needed.

Another use that relates to threads about oil control, are large reed valves working together with vindage trays and crankscrapers in the oil sump to control the movement of oil.

Comments anyone?
Olaf

_________________
Aspenized

That's an interesting idea. Those pyramid valves in the link look like the have a fine mesh that could cause the fuel to drop out of the mixture, but the concept is sound.

If you could figure out a way to vary spring pressure with engine load and RPM could you get the same results by just removing the entire intake valvetrain except for the valve and the magic spring? The low pressure in the cylinder would pull open the intake as much as it was needed so you'd have variable lift and duration with the added benefit of losing a ton of weight in the valve train.

Hi fzmax. The valves pictured are actually not the common configuration as they have opening flaps on four sides, a two-flap 'roof' design is more common. The mesh you see is probably the threads in the semi-transparent composite material in the flaps. These sprung flaps are sealing tight like valves - and keeps it tight - on a 10-12000 rpm two-stroke race engine! People have tested the idea to use only these reed valves in an ordinary four-stroke engine, but because of the temperatures involved, there are problems in the application. Because the reed valve will be set quite deep in the head/intake, the volume around it gives a low compression, and is not very practical for other reasons than to play with technology!
Using the reed valves as I described in addition to ordinary valves, will not alter the engine in any other way, and may be a real power booster with the right camshaft, in addition to making such an engine usable on the street.
Olaf

_________________
Aspenized

How much restriction to flow would the reed-valves add?

_________________
Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

This is an intriguing idea. The first thing I'd do is get a modern 4 stroke OHV single cylinder engine and try it there. It's possible the big carmakers tried this and decided variable valve timing/lift and variable intake runner would be more dependable or flexible??

Cool.

Lou

_________________
Home of Slant6-powered fun machines since 1988

As far as I know, Honda has a model called xr500 (atv or bike?), that is a four-stroke with a reed valve to control blow-back and give smooth operation on low revs in the terrain. Some digging in the first link I gave, and googling some names and references may give some interesting answers, I cannot remember them all. Olaf

_________________
Aspenized

Hi emsvitil. I don't know. The valves open very easy, but I am certain both size and angle of attachment and opening will have great influence on the flow figures, increasing with larger flow. There is some very complex maths involved to calculate that, so I guess that an old fashioned flow bench and a good selection of valves and fixtures, followed by dyno runs, may give the best answer to that question, as usual...
Olaf

_________________
Aspenized

would this type of reed valve system only work on a single cylinder engine? It seems that if you had two cylinders one going up and one going down then the crank case volume would not change much? Just a thought could be wrong.


Joe

_________________
1964 barracuda 198 slant

Reed valves are used in multi-cylinder two cycle engines where there are seals in between crank throws.

I didn't know that the XR used them. I would hazard that such an arrangement might be beneficial on singles that use a progressive two carburetor setup, for the secondary carburetor.

MC Trivia:
The only place where a two cycle had a common crank area for more than one cylinder was with the Split-single two cycle racing engines of the early 1900's, AFAIK. Puch and DKW used this arrangement. A slave cylinder was used to "Supercharge" a single cylinder engine. The slave cylinder didn't have an ignition, and was vented to the exhaust system. Two pistons moving in and out at the same time increased the volume of A/F brought into the crank area, and transfer ports sent the charge to only the cylinder that had the ignition. These machines had some interesting issues.

Back to reed valves:
Reed valves have reliability issues and also would make a large restriction in the intake. They would create a delay. Tuning of the runner would be impacted. Engineering would need to be done to make such an arrangement work. Power will be reduced using this arrangement where the runner isn't designed to work with it. The delay would effect much of the scavenging effect that overlap events are meant to create.

A single backfire would likely destroy the reed valve. They can be pretty delicate.

CJ

_________________
Part of Tyrde-Browne Racing

It does seem obvious you would have to design an intake manifold/carb/EFI system to use reeds properly.

Lou

_________________
Home of Slant6-powered fun machines since 1988

The XL/XR 500 single cylinder Honda motorcycles (1979-83-ish) had reed valves on them that were supposed to make better low end power. AFIK, they didnt use this setup on the street only 500 ascot.
When they replaced it with a 600cc "radial four valve" motor, they went with staged twin carbs instead of the reeds.


AS far as reliability, reeds have been used on outboard motors for decades.

You know ceej, my first bike was an old and very run down 125cc DKW, 1954 model. At a mc meet, I ran into a DKW with the extra 'compressor' cylinders, a 350cc if I remember right, and I actually got to test drive it! Sounded strange, and didn't impress me at the time; I had just done a wheelie on a Kawa 500!

To all:
The function of the reed valve is easier to understand if you draw a parallel to a 4 barrel carburetor with vacum operated secondaries, or the 'air-door' of a Carter AVS or a TermoQuad; nothing happens without moving air through the bores. The reed valves can be used of any engine configuration, be it a single, 4, 6 or 8 cyl. It works just like an extra valve in the intake. It stays open when there is suction, and closes the second the flow stops. That gives the camshaft some extra time to start and finish the valve lifting, while there still is pressure enough in the cylinder to keep the reed valve shut. You can start opening the intake valve earlier while the exhaust still flows out. The reed valve opens by itself only when needed. That means that you can have the ordinary valves stay open for a longer time (long duration on the intake), so that when the engine starts to suck in the mixture from the intake and the reed valve opens, the ordinary valves are already open and can give a larger flow. When the intake cycle stop, some 10-30 degrees after BDC, the reed valve closes immediatly when the intake flow stop moving. The ordinary valves are still full open, giving max flow to the last moment of the moving intake mixture, before they start closing. And that closing happens without having to think about the normal valve timing because there is no blowback to the intake because of the reed valve. The valve timing is set up from how the intake and exhaust normally works, a reed valve allows you to 'cheat' on the normal timing. That is why the engine can have a normal idle and low revs function, and still utilize the normal valves' long duration at high revs. That also brings me back to emsvitil's question about the restriction of the flow; it may be that the added advantage of an earlier opening intake valve may outweigh any flow restriction, it just gotta be tested. As of making a practical solution, I envision a plate placed between the normal slant manifolds and the cylinder head, with reed valves for each intake bore sticking into the cylinder head intake runners as far as possible without restricting the movement of the flaps. A test run with any kind of race camshaft should give an indication of the potential advantage right away. I shall take a look at the costs involved and see if I can come up with a test of some kind, I have an extra slant coming in after 5 feet of snow have melted away!

And to correct myself according to the laws of physics - I know some of you are a bit fuzzy about that - the intake mixture is not 'sucked' in, it is pushed in by the surrounding air pressure because of the lowered pressure in the cylinder as the piston moves down and creates a void. Basta!
Olaf

_________________
Aspenized

My old Yamaha RZ 350 had a reed valve intake, also had an adjustable exhaust outlet (YPVS). The reason the the reed valves work well is because of the high rpms a 2-cycle engine sees. The powerband would start at around 7500 rpms- controlling blowback is more important than restrictive flow when the engine is spinning that fast.
Theres a lot of different reeds material too- metal, fiberglass, carbon fiber...also varied thicknesses.

Point being that I see no real benefits at lower RPMs (0-6000ish).
My experience with reed valves is limited to blueprinting the engine on said motorcycle.

Just my opinion

_________________
<img src="http://farm4.static.flickr.com/3173/2992308402_5481afb26e_t.jpg">

A reed valve has an entirely different function in a two-stroke engine, where you suck the intake mix into the crankcase, and the down-moving piston then pushes the mix into the combustion chamber. Using a reed valve in a two-stroke allows you to place the ports in the cylinder wall in a better position to increase scavenging. It is acting different in a four-stroke engine. The fact that you have the original set of valves present in a four-stroke engine, will make the reed valve alter the practical valve timing at lower revs when using a hotter cam.
Olaf

_________________
Aspenized

I see your point. But the main function of a reed valve (at least in my experience with them) is to prevent blow back of air/fuel mix back through the carburetor on the compression/exhaust stroke and not for better port position, transfer ports along the cylinder wall usually accomplish better scavenging- the reed valves basically seal off any escape route for the mixture.
My point in my previous post was that the reed valves are effective on the intake side because of the high rpms, also the intake event is 2 times that of a fourstroke per revolution - in effect more pressure or mass velocity, to open/force the reed valves open.
Leading me to believe that this would be a hard task to accomplish on a slant intake.

Again just my opinion...if you were to ask me if I had some data to back this up, I would say no.

_________________
<img src="http://farm4.static.flickr.com/3173/2992308402_5481afb26e_t.jpg">