Goat Herder
Gutter Rider
I have been studying the posts , and have wounder d if it is possible to use reed valves successfully on a 2 cycle motor. I love the CH its the coolest one. Oh lets put a blower in one lets?
blower
- Thread starter Goat Herder
- Start date
Clotho
Member
The problem with supercharging or turbo charging a chengine is mostly on the exhaust side. The increase in pressure on the intake side is enough to ensure that the flow goes in the right direction. The real problem lies on the exhaust side. Without having some way to keep the boost pressure in the cylinder it just flows out through the open exhaust port which equals a no boost condition. A reed valve isn't going to change that since it only lets flow happen in one direction. The exhaust is still open. If you reversed the reed the engine wouldn't run at all as the exhaust couldn't escape. A rotary valve might work but would be a great deal of work to implement. A tuned expansion chamber might work too but it would only make boost in the range it was tuned for. This would make the engine extremely peaky. ie. it would make lots of power in a very small part of the rpm range.
Goat Herder
Gutter Rider
Ahh rotary valve still do not grasp enough of a plan on that to try it. Nice incite Clotho . It sure would be cool to pull something like this off though!!!!!!
Clotho
Member
Rotary valve: Imagine a disk spinning at 1:1 with the crankshaft and sandwiched between the exhaust port and the muffler inlet. On half of the disk a series of overlapping holes are punched so that the exhaust port is open to the muffler inlet half of the rotation and closed the other half (covered by the disk). The disc actually looks like the happy face below but without the eyes.
Considering the degree of modification required and the benefit in terms of hp I think the best answer is a Morini engine.
We already get considerable hp gains with the chengines after proper porting, expansion chamber and carb adjustments. By the time you do all the mods that we have found to work you really are pushing the envelope on these little engines. Even if you could provide funtional forced induction to one of these motors I doubt that it would last very long.
Your idea of using a reed valve seems like a good one at first. After all it is called a valve and a valve is needed on the exhaust side. The truth is that valve timing is what is really called for. ie. the need to keep the boost in the chamber but only half the time. (The other half the time it is burnt and you want to let it out). Reed valves are probably miss named. They really work more like a diode. They only allow flow to happen in one direction.
If you have done all the mods and you still feel the need for more power then the Morini is the way to go. The good news is that a Morini motor is going to force you to rethink your installation and hopefully you will come to the conclusion that the rest of your parts are probably not up to snuff to handle the extra hp. These bikes are a complete system and the weakest link always breaks first. Usually with us on it! A good example of this progression is the evolution of Easy Rider's bikes. He went from Chengine to Morini to Custom framed Morini for a reason. As his hp progressed the quality and durability of the rest of the bike increased as well to handle the increased load.
So there is balance to all of this.
Considering the degree of modification required and the benefit in terms of hp I think the best answer is a Morini engine.
We already get considerable hp gains with the chengines after proper porting, expansion chamber and carb adjustments. By the time you do all the mods that we have found to work you really are pushing the envelope on these little engines. Even if you could provide funtional forced induction to one of these motors I doubt that it would last very long. Your idea of using a reed valve seems like a good one at first. After all it is called a valve and a valve is needed on the exhaust side. The truth is that valve timing is what is really called for. ie. the need to keep the boost in the chamber but only half the time. (The other half the time it is burnt and you want to let it out). Reed valves are probably miss named. They really work more like a diode. They only allow flow to happen in one direction.
If you have done all the mods and you still feel the need for more power then the Morini is the way to go. The good news is that a Morini motor is going to force you to rethink your installation and hopefully you will come to the conclusion that the rest of your parts are probably not up to snuff to handle the extra hp. These bikes are a complete system and the weakest link always breaks first. Usually with us on it! A good example of this progression is the evolution of Easy Rider's bikes. He went from Chengine to Morini to Custom framed Morini for a reason. As his hp progressed the quality and durability of the rest of the bike increased as well to handle the increased load.
So there is balance to all of this.
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runslikeapenguin
New Member
as mentioned turbo charging a 2 stroke is not a simple task, even with a disk valved engine its a whole new world of tuning.
this is the engine from the current 50cc world record holder. its a Kreidler, and its turbo charged.
however it is possible to run a piston ported 2 stroke on boost, it does however get extremely complicated. i talked to a guy once who ran a snow mobile set up like this and just listening to him try to explain it made my head want to explode.
you basically have to run a specially designed expansion chamber, for starters, one that will create a great amount of back pressure and very low amount of flow. you then run the rest of your turbo plumbing as usual however you need to install one more link. in the intake stream you have to run a reversion pump, like a reverse blower. what this does is it creates two high pressure areas, the exhaust and the intake. you have to calculate it so that the turbo pressure is still enough to blow past the reversion pump. so in theory you pressurize the exhaust and the intake so when the piston is on its power stroke it becomes the low pressure area and the intake pressure fills the new low pressure area as the exhaust leaves the cylinder.
its a tuning nightmare to say the least. the turbo has to be ratioed exactly so that it builds more boost off of less exhaust pressure to make sure that it fills the cylinder with the intake charge and not just equalize with the exhaust and the intake. the guy started going into how you had to run the engine extra lean to make sure your exhaust go really hot to make sure that you could build boost because the flow was so restrictive. i stopped him there
i was getting a headache.
this is the engine from the current 50cc world record holder. its a Kreidler, and its turbo charged.
however it is possible to run a piston ported 2 stroke on boost, it does however get extremely complicated. i talked to a guy once who ran a snow mobile set up like this and just listening to him try to explain it made my head want to explode.
you basically have to run a specially designed expansion chamber, for starters, one that will create a great amount of back pressure and very low amount of flow. you then run the rest of your turbo plumbing as usual however you need to install one more link. in the intake stream you have to run a reversion pump, like a reverse blower. what this does is it creates two high pressure areas, the exhaust and the intake. you have to calculate it so that the turbo pressure is still enough to blow past the reversion pump. so in theory you pressurize the exhaust and the intake so when the piston is on its power stroke it becomes the low pressure area and the intake pressure fills the new low pressure area as the exhaust leaves the cylinder.
its a tuning nightmare to say the least. the turbo has to be ratioed exactly so that it builds more boost off of less exhaust pressure to make sure that it fills the cylinder with the intake charge and not just equalize with the exhaust and the intake. the guy started going into how you had to run the engine extra lean to make sure your exhaust go really hot to make sure that you could build boost because the flow was so restrictive. i stopped him there
i was getting a headache.
Norman
LORD VADER Moderator
that looks like a tuners night mare that engine looks like it has a spot for a carb on the case side for say a rotary valve? I wonder how the turbo is lubed ? looks cool but I'll say I think it would not work on the street only on the track and then make you pull your hair out and that would put Ilikeabikea out of business. I like these kind of pictures it get the idle mind to working.
Norman
Norman
eDJ
Member
Yeah, I agree. Photos like that are stimulating. I used to enjoy looking at
the earlier Japanese Racing cars power plants which looked like the N'th degree of R&D
had been reached in producing the them. Then one turns to look at American
"big iron" of that day and finds a more cost effective solution to the same problem.
It looks like a Rubiks Cube for engineers to spin their wheels on to me.
The point regarding lubing the Turbo Shaft bearing makes the other eye candy pale
in comparison. Wouldn't a larger, simpler, less expensive power plant do the same.
the earlier Japanese Racing cars power plants which looked like the N'th degree of R&D
had been reached in producing the them. Then one turns to look at American
"big iron" of that day and finds a more cost effective solution to the same problem.
It looks like a Rubiks Cube for engineers to spin their wheels on to me.
The point regarding lubing the Turbo Shaft bearing makes the other eye candy pale
in comparison. Wouldn't a larger, simpler, less expensive power plant do the same.
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tylerlough
New Member
Clotho
Member
Very cool!
Thank you very much for posting both the picture and the video. I thought it might be possible to use a tuned pipe but I figured that the result would be a very peaky since it could only make boost in the range the pipe was tuned for. My thoughts were confirmed when Mr. Buddenbaum (in the article linked to) describes this turboed Kriedler as having a super peaky power band. Norman is right. This motor is so specialized that it would never be practical for the street.
Some other things to note are how robust the block is and the fact that it is water cooled.
It is going to take me some time to wrap my head around the idea of a reversion pump but the 2 high pressure areas make sense. I don't see a reversion pump on this Kriedler tho.
The next time someone mentions that they want to put a blower on their Chinese bicycle engine we can just point them at that picture and say. This is what it takes.
Thank you very much for posting both the picture and the video. I thought it might be possible to use a tuned pipe but I figured that the result would be a very peaky since it could only make boost in the range the pipe was tuned for. My thoughts were confirmed when Mr. Buddenbaum (in the article linked to) describes this turboed Kriedler as having a super peaky power band. Norman is right. This motor is so specialized that it would never be practical for the street.
Some other things to note are how robust the block is and the fact that it is water cooled.
It is going to take me some time to wrap my head around the idea of a reversion pump but the 2 high pressure areas make sense. I don't see a reversion pump on this Kriedler tho.
The next time someone mentions that they want to put a blower on their Chinese bicycle engine we can just point them at that picture and say. This is what it takes.
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Goat Herder
Gutter Rider
Cool my head hurts now! Looks about way!! too hard. I thought it was possible.
runslikeapenguin
New Member
the kriedler is a disk valved engine, no need for the special tuning, you only need the reversion pump system with piston port engines.
Clotho
Member
Ok, The disc valve is on the intake side then. I don't see anything on the exhaust side that looks like a valve.