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  #161  
Old 02-28-2015, 12:26 PM
Desertduler Desertduler is offline
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I have been busy with other things lately but now it is time to get back to my kart engine modifications,I machined a jig for my cylinders so that I could cut some rear boost ports in some cylinders and try them out. This cylinder pictured needs to be bored out and I used it first to get the correct booster port angle as to have the booster ports converge near the spark plug in the roof of the combustion chamber which is located off center in the combustion chamber towards the intake side of the cylinder,here one can see where the two ports will converge in the roof of the combustion chamber just at the spark plug and I have timed the rear boosters about three degrees after the main transfer ports have started to open to help achieve a wider power delivery.The rear booster ports are fed by the windows in the skirt of the piston that I have machined. Next I will remove my cylinder from my kart and proceed with this next modification.These ports will need to be dressed up after I bore this cylinder oversize. Also the booster ports will be squared at the timing edge when I finish them.
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  #162  
Old 03-01-2015, 07:19 PM
Desertduler Desertduler is offline
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Here are some photos of my engine as I tore it down today for inspection and modifications.
One can see the destruction of the corners of the reed valve petals that are hitting the outer edge of the reed valve stops on the corners,I did not feel the engine go away but I would have in time,these reeds are not going to cut 9000 rpm engine speeds all day long so I will switch to Boyesen reeds without reed stops.Both sides of the piston look great for what it has gone through,the moly coating is starting to get ate away but that is nothing new to me as my KTM 300 will eat the coating off on one hard desert race,I think the coating is more of a marketing ploy but as long as I can still see the oil retention lines on the piston skirts I am good with still running the pistons that have the coating worn away.Here is the timing line for this cylinder that I am going to add booster ports to,this cylinder will have narrower booster ports in it and I will experiment with different cylinder boost ports and come up with the one that I want.One nice thing about this little Rotax is that the cylinder liner can be replaced and one can alter the porting without scrapping the cylinder.Notice the dome in the combustion chamber by the spark plug that is where we want to aim the rear booster ports as to get the intake charge gases rolling and in turn loop charging the engine more than it is already is so there is a so called glob of combustible gases there ready to ignite.I will cut the rear boosters to this timing line as set with my degree wheel.
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  #163  
Old 03-01-2015, 08:32 PM
kawicat kawicat is offline
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i have a snowmobile with a 503 rotax. i believe the 503 and 277 use the same bore(72mm) could this conversion be done to a 503?
  #164  
Old 03-01-2015, 08:41 PM
Desertduler Desertduler is offline
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Quote:
Originally Posted by kawicat View Post
i have a snowmobile with a 503 rotax. i believe the 503 and 277 use the same bore(72mm) could this conversion be done to a 503?
Your engine uses the same piston as mine,and along with the 247cc Rotax engine, they use the same piston.Indeed your engine can be modified this way.
  #165  
Old 03-01-2015, 08:48 PM
kawicat kawicat is offline
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how much $ is it to be done? i am looking at a max 8500 rpms before my clutch blows up. does the reed valves allow for higher rpm operation?
  #166  
Old 03-01-2015, 09:11 PM
Desertduler Desertduler is offline
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Originally Posted by kawicat View Post
how much $ is it to be done? i am looking at a max 8500 rpms before my clutch blows up. does the reed valves allow for higher rpm operation?
There is no need to surpass your stock engine RPM.This mod will indeed make more power through out the RPM range of the engine and it will indeed make a ton of more low end power.I have done a few more things to my engine in order to get it to achieve the RPM levels that I am obtaining but I only have one gear ratio that I am dealing with,your sled has a CVT and the only thing that I would do after this mod was done to your clutching would be to lower the engagement speed of the primary clutch as a starting point and take advantage of the increased low end power that is on tap and then maybe a different secondary helix and spring.I had to jet my carburetor way rich compared to what it was because now with the reed valve set up acting like a one way valve the engine just pulls air through the carburetor to mix with the fuel instead of a back washed air fuel mixture charge that had been spit back out of the intake port that would load up at low RPM's.
If you read back through this thread you will see that I went from a 180 main jet to a 260 main jet and a richer needle setting.I am a very busy person and I would have to really think about a cost that I would charge to do this modification for you and I would have to make you some custom reed valve housings in order to house the reed valves that I would use for you engine but that is not a big deal.
  #167  
Old 03-01-2015, 09:18 PM
yanbolduc yanbolduc is offline
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hey kawicat, you could simply put some rotax 550 pistons and cylinder on your motor, they are 4mm bigger and are already reed valves cylinders. Easy swap I think
  #168  
Old 03-01-2015, 09:33 PM
Desertduler Desertduler is offline
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Quote:
Originally Posted by yanbolduc View Post
hey kawicat, you could simply put some rotax 550 pistons and cylinder on your motor, they are 4mm bigger and are already reed valves cylinders. Easy swap I think
They both have a 61mm stroke the same as a 247,I don't think the cylinders from a 550 reed will work on a piston ported 503 crankcase.The 550 has a rear booster port that leads to the crankcase and the crankcase has a port in the case that leads to the booster port.
http://www.skidoopartshouse.com/oemp.../crankcase-503
http://www.skidoopartshouse.com/oemp...aa41/crankcase
  #169  
Old 03-01-2015, 09:50 PM
yanbolduc yanbolduc is offline
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Oops, I think youre right. Sorry for the bad information.
  #170  
Old 03-01-2015, 09:51 PM
Desertduler Desertduler is offline
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Also remember in order to get the maximum benefits of the rear booster ports the engine will need a whole different expansion chamber to achieve the best results of this modification.Welcome to the not so simple two stroke world!
  #171  
Old 03-01-2015, 09:55 PM
Desertduler Desertduler is offline
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Quote:
Originally Posted by yanbolduc View Post
Oops, I think youre right. Sorry for the bad information.
Hey, That is not bad information at all! That shows that you are thinking
I say to myself sometimes that a wise man knows that he is not!
I can not tell you how many times I thought something was going to work and it did not!
  #172  
Old 03-03-2015, 04:32 PM
kawicat kawicat is offline
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so correct me if im wrong, but since its reed valved could you turbo it? or is that only with case reeds?
  #173  
Old 03-03-2015, 05:44 PM
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Originally Posted by kawicat View Post
so correct me if im wrong, but since its reed valved could you turbo it? or is that only with case reeds?
Yes it could be turbocharged,but at BDC you would not get the flow like you would with case reeds and that can be both good and not as good at some RPM levels with turbocharging.
  #174  
Old 03-03-2015, 06:04 PM
Desertduler Desertduler is offline
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kawicat,this is how you can make some reed valve housings for your engine,buy two of these reed spacers which are for a KX250 Kawasaki and shear some .072 aluminum sheet to fit the reed spacer blocks which are aluminum and heli arc it all together to house the reed valves for the KX250 but keep them as small as possibile and then you will need a base mount to fit your cylinder after you machine the intake down.Make some templates out of paper to get the four sides of each housing that will need to be made.
http://www.ebay.com/itm/Kawasaki-Ree...=Model%3AKX250
  #175  
Old 03-03-2015, 09:17 PM
kawicat kawicat is offline
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ok. what reeds worked best for you? what is the deal with the 6/6 nylon spacer? is it needed with the reed spacers you listed above? what intake flange did you use?
  #176  
Old 03-03-2015, 10:55 PM
Desertduler Desertduler is offline
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Quote:
Originally Posted by kawicat View Post
ok. what reeds worked best for you? what is the deal with the 6/6 nylon spacer? is it needed with the reed spacers you listed above? what intake flange did you use?
The carbon fiber reeds with the reed stops are getting ate away at the corners on my engine so I am switching to Boyesen Power Pro reeds and they are dual stage and they have no reed stops.You will not need the nylon spacer that I made to make up the space that I needed with the use of the KR-1 reed valve housing.I made my own intake base flange and yours will have to be different than mine but easier to make.When you get ready to do this post some pictures and I can explain what to do if you want or you could send me one of your cylinders and I could lay the design out for you if you like or I could cut out some paper templates as a rough draft to show you how to do this and or you could just heli arc the whole made up reed valve housing right to the cylinder after they have been milled down thus eliminating any intake flange.
  #177  
Old 03-04-2015, 03:22 PM
kawicat kawicat is offline
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ok when i get all the components ill post pictures. what do i do for reed cages? im not 100% familiar with reed valve engines as i dont own any, but ive helped service my friends dirt bike and that had reeds
  #178  
Old 03-04-2015, 05:55 PM
Desertduler Desertduler is offline
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Quote:
Originally Posted by kawicat View Post
ok when i get all the components ill post pictures. what do i do for reed cages? im not 100% familiar with reed valve engines as i dont own any, but ive helped service my friends dirt bike and that had reeds
Just like these.
http://www.ebay.com/itm/2002-Kawasak...dd6b07&vxp=mtr
  #179  
Old 03-04-2015, 05:59 PM
Desertduler Desertduler is offline
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kawicat,are you going to just use your 503 for your snowmobile or do you have something else in mind for your engine?
  #180  
Old 03-04-2015, 06:05 PM
kawicat kawicat is offline
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its going in my sled. the sled is a custom modsled with the chassis and hood from a 1972 arctic cat panther, using the skidframe, track, chaincase, and clutches from a 1990 skidoo safari; using the front suspension from a yamaha or skidoo tundra pogo sticks and some c&a pro skis. why do you ask?
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