Engine Porting - Gases out, Fuel Air in

E

Egor

Guest
The casting flash is the small edges were the mold was put together. and for us is really the webbing at the scavenging ports. It protrudes so far into the crankcase that it impedes the flow of gases. Some of the new two strokes eliminate the webbing all together, but for us just carve it as short as you like, and thin it out. Dremle works well. Have fun Dave
ibeenjammin said:
What the heck is casting flash?? and how did you remove it?
 
I

ibeenjammin

Guest
Is there a picture of this? Unfortunately I am not familiar with this. I would love a visual if you have one. :D

Thanks,
Ben
 
W

Wrench66

Guest
The port sizes for the exhaust and two transfers are passable.....but that intake is just a joke:eek:. Most mopeds have a least twice the area and 15cc less displacement.
I opened the intake ports sides by 1.5mm a side and lowered the floor by 1.75mm. The inlet manifold was also machined to match the cylinder's mount, it orig was just a hole that didn't even come close to matching the cyl opening shape, bad for flow:cry: The port is actually MUCH too high as cast, I've never seen a 2 stroke that has the port cast SO high up the cyl wall that at BDC the rings (BOTH!) are below the roof of the intake port. Chinese engineering is still a mystery :rolleyes: No way of solving THAT problem without casting up another (read BETTER) cylinder.
The exhaust port wasn't bad in shape BUT had very short timing, raised the roof 1.50mm and widened .5mm a side. Still in the mild tuned arena for sure but at least now the poor thing has a decent blowdown period.
The port mapping I used is near a Puch 50cc moped spec so it's not radical just better.
I also added some machining to the bushing type :sick: rod end and am working on a very inexpensively modded pocketbike pipe, look for the new threads on those. A new 18-20mm carb is slated to be used here as well.
I have not run this particular cyl yet but because the specs are from exsisting engines that do perform well it should be good.
 

Attachments

  • exhaust port mod.jpg
    exhaust port mod.jpg
    22.6 KB · Views: 1,903
  • intake port mod.jpg
    intake port mod.jpg
    21.9 KB · Views: 1,784
A

andyinchville1

Guest
Yes, I am also interested in all this porting work.....what results did you get with it?....Looks fairly easy to do but shaving off such small amounts would definately take patience and careful measuring!

Andrew
 
K

Klox

Guest
Awhile ago i downloaded a pdf document by A Graham Bell on 2-stroke tuning. It covers all you need to know about porting & tuning, even expansion boxes! I found it very informative......
Unfortunately i can't remember exactly where i got the link.....

Cheers,
Anthos
 
Q

quarkdude

Guest
A Graham Bell 2 stroke Tuning

Awhile ago i downloaded a pdf document by A Graham Bell on 2-stroke tuning. It covers all you need to know about porting & tuning, even expansion boxes! I found it very informative......
Unfortunately i can't remember exactly where i got the link.....

Cheers,
Anthos[/QUOTE

Hello Klox,
I was reading your porting inforamation and it sounds like something I would like to do - always trying to sqeeze more power from the 80cc chinese engine. I think I found the link you mentioned. Try this one:
http://www.kreidler.nl/artikelen/performance-tuning-graham-bell/performance-tuning-graham-bell.pdf
........Thanks a bunch for your porting pics......quarkdude
 
K

Klox

Guest
Yep! It was this article i was referring to. Years ago when i was in high school one of the motorbike magazines featured an article on the same topic. Well we tried and succeeded on "hotting" up our 50cc mopeds! The hardest part at that stage was the sheetmetal work involved to built the exhaust pipes.....it was lots of fun!
 
E

Egor

Guest
The Kridler was the bike to beat in the 60's, 70's they were always the one to reckon with. 50cc still holds the record at around 135mph. The matching of the ports is important as a last feature, the most important attempts are the exhaust and the intake timing. Remember as you lower the intake port you increase the port time (IE) the time the port is open. Don't worry about the rings showing at the top of the port, just make sure you can't see in the cylinder. Wider would go well with a larger carb, and it does need a new carb. Low RPM engines like these unlike the Kridler that will rev to 18,000 rpm, ours at 6000, flow is not an issue. If one of you are willing to make a reed box I will show you how to finish the port work. That would be the best intake for one of these slow revving engines. Look at the Russian engine it uses a rotary intake, Yamaha used a flat rotary valve, this gives you a positive, and on time intake. A reed valve is as good but has resistance. The balance of these engines is not intended for 10,000 so I think that is foolish, but a pipe tuned for 5 to 6,000 rpm will work well. Let me know what you find. Remember this engine is a piston port timed engine. Have fun Dave

PS: Make sure you round over the edges of the ports after you carve on them.
 
G

Ghost0

Guest
Wrench66, Egor,
Instead of lowering the intake port have you tried cutting the skirt on the piston?
 
Top