Porting the engine

jaguar

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Nov 25, 2010
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These engines come with inadequate port durations for the exhaust and intake port. They limit both power and RPM. The transfer durations are OK. I recommend raising the exhaust port for at least a 150 degree duration for the 48cc and to at least 165 degrees for the 66cc. Go to this page to read the best way to figure out what your engine has: http://www.dragonfly75.com/motorbike/findduration.html
And go to http://www.dragonfly75.com/motorbike/blowdown.html to read more about the relation of port durations to peak RPM and to download my free porting calculator (an Excel spreadsheet).
The best all round port duration for the intake is 120 degrees which requires lowering the bottom edge of the port a bit. I use the Black&Decker RTX 3 speed rotary tool with cutting discs that is sold at Walmart. I also use a digital caliper which is also available at WalMart.
 
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jaguar

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these recommendations are not for racing but just to have better power for street use
 

Carl Walichnowski

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Jul 2, 2016
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I have absolutely no experience with porting so this thread and links are a big help. I would much rather try my hand at porting the cylinder then buying one someone else has done.
 

jaguar

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with a rotary tool and cutting discs it isn't hard to do.
If the disc is too wide to work in the corners of ports then just break off its edges so that it has a smaller diameter. That leaves it all jagged but still does the job.
I like to use calipers to measure how much to raise the ports. just mark the cylinder above the port up to where the caliper is with a marks-a-lot which makes it easy to not grind off more than you intend to.
 

butre

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I use the carbide bits. I'm not even sure how you'd use the disks effectively, they're far too fat and break easily.
 

Carl Walichnowski

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I use the carbide bits. I'm not even sure how you'd use the disks effectively, they're far too fat and break easily.
I was wondering that, due to the shape of the discs I'm sure it'd be difficult to get in there effectively. Do you prefer a certain type of burr? I have about 10 tungsten burrs but around 50 diamond burrs, are the diamond burrs effective?
 

jaguar

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I used the burr bits to make the boost channel when I installed a reed valve but I find the discs are all that's necessary on the ports.
The discs, since they are flat, are helpful to keep from making the tops of the ports jagged.
Carl, just click on my signature links and go to my CDI page if you want to buy a Performance CDI.
 
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