"Thump-8" 4 stroke 1/8th scale engine
08-23-2009 | 08:13 AM
#31
Tech Initiate
Joined: Jul 2009
Posts: 31
Those are all valid points. However, one can't compare F1 technology to a hobby glow engine. I've yet to see a roller follower in a model engine. Few valve trains for model engines have been optimized as they currently exist. There has been no demand for high RPM four stroke engines for cars. All of the engines which exist are based on the needs of model airplanes, power at low RPM <12kRPM. The OS S-C use only stronger springs and a new cam. The 40 additionally has slightly oversize valves. I don't think it's practical to grind a model sized cam with the kind of tolerances required for the aggressive opening lift curves being thrown around here. Pneumatic valve springs in models? The best we can hope for is forced induction like the patented YS engine.
The only way to improve the opening speed of the rotary valve is to increase it's diameter or axial length, which brings to light other concerns. Disc valves leave few options due to size constraints.
Two stroke model engines are virtually the same for cars and airplanes at the top end of the power/displacement heap.
The only way to improve the opening speed of the rotary valve is to increase it's diameter or axial length, which brings to light other concerns. Disc valves leave few options due to size constraints.
Two stroke model engines are virtually the same for cars and airplanes at the top end of the power/displacement heap.
08-23-2009 | 04:07 PM
#32
maximo, I really dont know like you said, I dont have THAT system in front of me, but really, how is it possible that the rotary valve in this design opens completely or enogh for any substantial flow with 2 deg of crank rotaion? look at the picture! just rotate it in your mind with out david blaine in the room and you will see, who cares what they say, its simple mechanics that can be seen from the picture, its almost exactly like opening our 2stroke crankshafts(?), but worst, divided by 2, how can 1 degree of camshaft rotation open up a rotary valve that is about 90 degrees of its circumference? I dont see it man. It will probably take about 90 deg of rotation to open the valve to full flow,then the valve will be there for an instant (ok, unless the valve is expossed completely in the chamber like it is in the upper section of the picture for, I dont know, about 90 deg? - but then compression goes to the trash and piston weight tothe roof trying to get the compression back) and then it will be the other 90 deg closing it.
Only with that disadvantage the system probably can be easely bettered by a good poppet cam, a good roller cam can open a valve at least ~90% of full flow in ~10 -15 deg not 34 like an engine designed for swirl and low end torque. One of us really does not understand something here because to me this is more than simple when applyed, dont get me wrong, it can be me
its just that I gave a lot of thought to that type of design years ago with big-name people that really know their stuff and at the end of the day there where two things that the system did not do with any effyciency - opening/closing the valves (extremely slow and again linear and cooling /lubricating the exhaust valve, look at the struggles that the wankle engine has had through its life span to keep its act clean and fuel efficient.
In our earlyer designs our rotary valves even had that same exact round shape in the opening and closing faces and then we noticed that the port opens "quicker" only because it robs it from the area under the curve, the thing that gives you all the power.
Im telling you Ive been there.
Im telling you, if it where good the big dogs would be using it, a lot of people do a lot of mind burnouts over that design and end up with the classic power maker. I'm a proud one
, dont worry, theres space for you 
And just for the record, that head probably requires a different ehaust manifold/header, and different intake manifold, and it obviouslly has a diferent cam, if you put a good head/cam/intake/hearder combination to a 5L ford you can obtain 500 to 550hp, and thats done every day just take alook at any mustang mag. if you do the really trick stuff you can get 750 from 302 cubic inches, again, its been done every day, no turbos or alcohol or nitro, just high octain gasoline, compression and flow.
X
Only with that disadvantage the system probably can be easely bettered by a good poppet cam, a good roller cam can open a valve at least ~90% of full flow in ~10 -15 deg not 34 like an engine designed for swirl and low end torque. One of us really does not understand something here because to me this is more than simple when applyed, dont get me wrong, it can be me
its just that I gave a lot of thought to that type of design years ago with big-name people that really know their stuff and at the end of the day there where two things that the system did not do with any effyciency - opening/closing the valves (extremely slow and again linear and cooling /lubricating the exhaust valve, look at the struggles that the wankle engine has had through its life span to keep its act clean and fuel efficient.In our earlyer designs our rotary valves even had that same exact round shape in the opening and closing faces and then we noticed that the port opens "quicker" only because it robs it from the area under the curve, the thing that gives you all the power.
Im telling you Ive been there. Im telling you, if it where good the big dogs would be using it, a lot of people do a lot of mind burnouts over that design and end up with the classic power maker. I'm a proud one
, dont worry, theres space for you And just for the record, that head probably requires a different ehaust manifold/header, and different intake manifold, and it obviouslly has a diferent cam, if you put a good head/cam/intake/hearder combination to a 5L ford you can obtain 500 to 550hp, and thats done every day just take alook at any mustang mag. if you do the really trick stuff you can get 750 from 302 cubic inches, again, its been done every day, no turbos or alcohol or nitro, just high octain gasoline, compression and flow.
X
08-23-2009 | 06:04 PM
#33
By their own website, it is a spherical rotary valve driven by chain, belt, or gears off of the crankshaft. Such a design, regardless of the details will have certain advantages and certain disadvantages to a conventional valve system. This is engineering FACT, not speculation. Now whether or not they have managed to get the advantages to outweigh the disadvantages and result in a truly superior system is unknown. My guess is that they have not but I would be very happy to be wrong.
I am not skeptical because I fear new technology, I love new stuff. But you have to understand that people have been trying to come up with better valve systems for 4 stroke motors for over a hundred years (including similar rotary systems) and ALL have failed to replace poppets in high end performance. This system may very well wind up being great for street cars or sport racing but that doesn't mean it will win at the highest levels. Everyone thought AAC was the next big thing but good old ABC just won the worlds.
Personally, if I was an engineer working on all out high tech race motor design, I think I would be working on some sort of slide valve with electro-mechanical actuation. I certainly wouldn't be wasting my time on any form of crank driven rotary valves. Even if someone gets them to work, mine has more potential on a strictly theoretical standpoint.
I am not skeptical because I fear new technology, I love new stuff. But you have to understand that people have been trying to come up with better valve systems for 4 stroke motors for over a hundred years (including similar rotary systems) and ALL have failed to replace poppets in high end performance. This system may very well wind up being great for street cars or sport racing but that doesn't mean it will win at the highest levels. Everyone thought AAC was the next big thing but good old ABC just won the worlds.
Personally, if I was an engineer working on all out high tech race motor design, I think I would be working on some sort of slide valve with electro-mechanical actuation. I certainly wouldn't be wasting my time on any form of crank driven rotary valves. Even if someone gets them to work, mine has more potential on a strictly theoretical standpoint.
08-23-2009 | 06:08 PM
#34
One thing to keep in mind when debating all types of rotary valves is this:
Everyone assumes the valves turn at a constant rate. There is a very easy way to vary the speed of the valve, making it open and close MUCH faster, yet slow down when it's closed.
You can speculate all you want, and even when you can plainly see the valve mechanism, you may not know exactly how it operates.
Gear driven rotary parts can turn slow for half-a revolution and fast for the other half when the gears are offset (not centered) on their shafts.
Everyone assumes the valves turn at a constant rate. There is a very easy way to vary the speed of the valve, making it open and close MUCH faster, yet slow down when it's closed.
You can speculate all you want, and even when you can plainly see the valve mechanism, you may not know exactly how it operates.
Gear driven rotary parts can turn slow for half-a revolution and fast for the other half when the gears are offset (not centered) on their shafts.
08-23-2009 | 06:17 PM
#35
By their own website, it is a spherical rotary valve driven by chain, belt, or gears off of the crankshaft. Such a design, regardless of the details will have certain advantages and certain disadvantages to a conventional valve system. This is engineering FACT, not speculation. Now whether or not they have managed to get the advantages to outweigh the disadvantages and result in a truly superior system is unknown. My guess is that they have not but I would be very happy to be wrong.
I am not skeptical because I fear new technology, I love new stuff. But you have to understand that people have been trying to come up with better valve systems for 4 stroke motors for over a hundred years (including similar rotary systems) and ALL have failed to replace poppets in high end performance. This system may very well wind up being great for street cars or sport racing but that doesn't mean it will win at the highest levels. Everyone thought AAC was the next big thing but good old ABC just won the worlds.
Personally, if I was an engineer working on all out high tech race motor design, I think I would be working on some sort of slide valve with electro-mechanical actuation. I certainly wouldn't be wasting my time on any form of crank driven rotary valves. Even if someone gets them to work, mine has more potential on a strictly theoretical standpoint.
I am not skeptical because I fear new technology, I love new stuff. But you have to understand that people have been trying to come up with better valve systems for 4 stroke motors for over a hundred years (including similar rotary systems) and ALL have failed to replace poppets in high end performance. This system may very well wind up being great for street cars or sport racing but that doesn't mean it will win at the highest levels. Everyone thought AAC was the next big thing but good old ABC just won the worlds.
Personally, if I was an engineer working on all out high tech race motor design, I think I would be working on some sort of slide valve with electro-mechanical actuation. I certainly wouldn't be wasting my time on any form of crank driven rotary valves. Even if someone gets them to work, mine has more potential on a strictly theoretical standpoint.
I honestly don't know enough to even begin speculating on what they can or can't do ...However they did show some good results on a stock engine...whether they can be used on a top level race engine is something I have no clue about.... Also without them showing the dyno curve its impossible to know what kind of power curve they achieved...their peak numbers sound impressive, but who knows the full story without a dyno curve..... Apparently another type of rotatry valve was being designed but its use was banned by formula 1....So even if they do find a new technology there is a strong proponent to protect the status qua, so even if something beter is out there we may never see it.... top level racing has been known to restrict technology to keep the playing field equal....So wether top level racing uses a certain technology or not really is no measure of whether the technology is good or not....... I am by no means an expert on the subject, I just found the Coates system pretty cool is all...I just didn't like all the armchair engineers being soo skeptical of something they really haven't analyzed first hand..... There is so much information missing from the website and tests, such as flowbench results and dyno curves that really we know very little about the system one way or the other...Hell the system may be great for making extremely economical engines, who knows....I certainly do not, and chances are the only people who have all the answers are the people from Coates themselves.....
08-23-2009 | 06:26 PM
#36
One thing to keep in mind when debating all types of rotary valves is this:
Everyone assumes the valves turn at a constant rate. There is a very easy way to vary the speed of the valve, making it open and close MUCH faster, yet slow down when it's closed.
You can speculate all you want, and even when you can plainly see the valve mechanism, you may not know exactly how it operates.
Gear driven rotary parts can turn slow for half-a revolution and fast for the other half when the gears are offset (not centered) on their shafts.
Everyone assumes the valves turn at a constant rate. There is a very easy way to vary the speed of the valve, making it open and close MUCH faster, yet slow down when it's closed.
You can speculate all you want, and even when you can plainly see the valve mechanism, you may not know exactly how it operates.
Gear driven rotary parts can turn slow for half-a revolution and fast for the other half when the gears are offset (not centered) on their shafts.
Now, I'm not an expert on off center gears so I will admit that it very well may be possible to design a complex set of multiple off center gears to achieve the desired result. It is making my head hurt just thinking about how to do it right but there are smarter people than me out there that might be able to figure out. I sure would like to see such a system. It would definitely be an engineering masterpiece whether it worked well or not.
08-23-2009 | 06:46 PM
#37
Joined: Jun 2008
Posts: 3,301
From: Conducting aggressive board meetings at my local track
Is everyone assuming the shape of the rotary valve is a constant symmetrical shape?
What if it wasn't symmetrical? I.E. the valve would have a tear drop shaped opening (like a camshaft lobe) vs a square shaped opening.
Instead of the camshaft supplying the non linear opening and closing of the valve, the valve itself could supply the non linear opening and closing.
I'm no engineer, but the idea just popped into my head.
What if it wasn't symmetrical? I.E. the valve would have a tear drop shaped opening (like a camshaft lobe) vs a square shaped opening.
Instead of the camshaft supplying the non linear opening and closing of the valve, the valve itself could supply the non linear opening and closing.
I'm no engineer, but the idea just popped into my head.
08-23-2009 | 06:57 PM
#38
Actually, I think you would want more of an hourglass type shape. Sort of a double teardrop. You would want the leading edge of the port to be very wide so it will flow well even though most of the port is still closed. Then get more narrow so the port doesn't get huge and kill your velocity. Once the leading edge starts to close you would then want the trailing edge to start getting wider to make up for the area being lost at the leading edge.
08-23-2009 | 07:16 PM
#40
Damnit, it wont post my diagram right.
Let me put the idea into an RC perspective. Imagine looking down the carb opening on one of our motors to see the intake port on the crankshaft (which is a rotary valve). Instead of the normal rectangular shape you would see something more like this:
BACKPLATE
l l
l l
l l
l"-. .-"l
l . l
l l <------Hourglass shaped crank intake port
l . l
l_-" "-_l
c
r
a
n
k
The overall length of the port would be much longer than normal but you wouldn't want a port that big at full open (it would reduce the velocity of the air/fuel mix killing bottom end torque) so it narrows down as it opens and then widens out as it closes.
I like this idea, I wonder how long before someone steals it
Let me put the idea into an RC perspective. Imagine looking down the carb opening on one of our motors to see the intake port on the crankshaft (which is a rotary valve). Instead of the normal rectangular shape you would see something more like this:
BACKPLATE
l l
l l
l l
l"-. .-"l
l . l
l l <------Hourglass shaped crank intake port
l . l
l_-" "-_l
c
r
a
n
k
The overall length of the port would be much longer than normal but you wouldn't want a port that big at full open (it would reduce the velocity of the air/fuel mix killing bottom end torque) so it narrows down as it opens and then widens out as it closes.
I like this idea, I wonder how long before someone steals it
08-24-2009 | 07:40 AM
#43
I had to look that one up too... Once I saw it, I realized I've seen a design that used it before. I think they used them on some old motorcycle engines. It seems like the little pin and slots would wear pretty quickly, but it might work if it were part geneva mechanism, part normal gear..... it looks weird in my head and is probably not even possible, but now I want to draw one.
The idea is for it to work like a 4-position geneva mechanism for exhaust and intake, but use a normal gear to turn through the compression and power strokes. The way my valve is situated, the pressure from compression and power will make it seal more tightly, and also make it more difficult to turn during those strokes. So, it would be 1 position per stroke, but only for half of them... a half-linear gear of sorts.
You guys just keep making my brain go off on these nice mental exercises, and I think in the end it will result in very good things.
The idea is for it to work like a 4-position geneva mechanism for exhaust and intake, but use a normal gear to turn through the compression and power strokes. The way my valve is situated, the pressure from compression and power will make it seal more tightly, and also make it more difficult to turn during those strokes. So, it would be 1 position per stroke, but only for half of them... a half-linear gear of sorts.
You guys just keep making my brain go off on these nice mental exercises, and I think in the end it will result in very good things.
08-24-2009 | 09:31 AM
#44
Tech Initiate
Joined: Jul 2009
Posts: 31
I've seen "gears" that were part geneva mechanism and part gear. Before the advent of stepper and servo motors manufacturing machines used cams and gears to do the movements that are now done electronically. Everything was done mechanically. Oval gears, square gears, rotary to linear mechs, linear to rotary, all kinds of ideas that got the job done.
http://www.dself.dsl.pipex.com/MUSEU...alveIC.htm#mel
http://www.dself.dsl.pipex.com/MUSEU...alveIC.htm#mel
08-24-2009 | 09:41 AM
#45
Good reading there. When I did some digging on various types of unusual valve mechanisms I came across a fascinating overview of different types of mechanisms for steam engines. Absolutely amazing combination of mechanical complexity and in a way simplicity as well. Those guys were geniuses.