Transfer port correction and duration mods

M

mech_engineer

New Member
I'm new here, my name is Hector, i live in puerto rico. I have taken all courses of mechanical engineer and i'm currently finishing my minor in aerospace. I have a 74 schwinn with a "80cc" i have made a few cool mods to it and i will like to share them.

1- Port my exhaust port to 60% of piston diameter or 28mm, gasket match and also port the exhaust pipe flange for less restriction.

2- First i ported the entire tranfer port and corrected the transfer ports area with jb weld close almost .20 inch of the area most close to exhaust. note you need to use jb weld inside the transfer port to make the air change direction to desire angle of attack "to the rear of cylinder, intake side"

3- Ported intake, mached runner and gasket, also i port a little inside the runner.

note: i don't change any duration in the cylinder...

4- take of 5mm of piston skirt in intake side to increase intake duration. this will increase rpm

5- Piston top notch in exhaust part to increase duration it will increase rpm

6- Piston Top notch in transfer part to increase duration it will increase rpm

to increase power you will need to increase time area in intake and exhaust and decrease transfer time area. this will narrow your power band but produce more power at top rpm....

this mods make my engine develop more power and rev higher also change the idle a lot. now you can hear the engine breathing air.
Parts changed
1-banana expansion chamber i need to tune the length
2- 54 tooth rear sprocket (20-30mph) i live in the center of the island needed for hills ( i have the 36 tooth 40mph+)
3- resistor tipe spark plug cap ngk

fuel oil Blendzall racing castor 1 ounce per liter of 87, 91 and 100 octane gas. i will use 100 octane with high compresion head

Future modifications
1- carb 19 or 21 mm
2- stuffed crank case
3- balanced crank
4- reed valves
5- new cylinder a good one not the stock one
6- high compresion head
7- High quality bearing
8- "brake pads clutch" ceramic ones?



Sorry if I write something wrong this is not my language.
 
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1974 Schwinn
e79p.jpg

transfer port reduced area
cvhd.jpg

Blendzall racing castor
fqzn.jpg

The Banana expansion chamber
ev3y.jpg

Ported exhaust note: gasket have been replaced
zpmx.jpg


Like 30mins ago i buy the 21mm carburetor the dellorto black. i have read that i need to reduce the main and idle jets because my bicycle will run very rich "if starts"


I have been reading of port timing and i have made a excel program for port timing, you only need to input the mean area and stock duration, and it give back the needed duration for each port and how much you need to cut in mm for increase duration for very high time area for intake and exhaust and reduced time area for transfer.the program is made for 8k rpm.
 
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I have been reading of port timing and i have made a excel program for port timing, you only need to input the mean area and stock duration, and it give back the needed duration for each port and how much you need to cut in mm for increase duration for very high time area for intake and exhaust and reduced time area for transfer.the program is made for 8k rpm.[/QUOTE]

Would you share the excel file with us ?
 
Old post and I hadn't heard from mech engineer in almost a year, the guy had some really good ideas but I'm not sure if he's still playing with these engines...
I don't remember if he ever made his spreadsheet public but it seems like I may have got a copy of it from him back then, I will check if it's on my pc or one of my flash drives later.
 
Dave, Id love to see the engineers formula as well!

But wouldn't 60% of piston diameter equate to 29mm?

Ive played around with different 2 strokes for a long time, and have yet to find a "one size fits all" solution, but who knows! Im sure it would be interesting!
 
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