Engine Porting - Gases out, Fuel Air in

Discussion in 'Performance Mods' started by Egor, Jun 14, 2007.

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  1. Egor

    Egor Guest

    Anyone out there doing any porting? This is a biggie, although you have to manage the throttle with some discretion this was the biggest boost for my China engine. If I were to put an expansion chamber with the carb and ports I don't think the rest of the parts would hold up. I will not even bring up 4th and 5th ports. I wanna hear what you are doing. Have fun, Dave

  2. JosephGarcia

    JosephGarcia Guest

    I really beleive you have taken these engines farther than any of us ever have. I've only heard of carb modifications, and expansion chambers.
  3. Guest

    Guest Guest

    Dave, you got pictures?
  4. Egor

    Egor Guest

    I can put up some pic's. Ill also get all the mesurments for you so you can replicate them. I want to hear from one of you after you do it, now that will be fun. I started porting Hodaka's back in the day, you could do the same thing to this engine but it would never hold up to the pressure. I think we were getting 15 HP out of 100cc. 10,000 rpm so you can see what around 80cc could do. Have fun Dave
  5. Guest

    Guest Guest

    Nah, not gonna port mine, I want it to last awhile.
  6. Egor

    Egor Guest

    The porting is like this. You can take it to the limit or anywhere in between. I have a mild port and it gets the engine running cooler and idles perfect, when you twist the throttle it has considerable more power, but[​IMG] if you were to abuse it, it would not last long, but if treated proper it should last just as long. If you have no will power then you should not go there. My example to HP is to show what a 80cc engine is capable of. Have fun, Dave

    PS: The pic is a mild port, notice the intake is just covered see how much exhaust is showing, Bad air out, Good air in.
  7. Guest

    Guest Guest

    So you're saying just grind the exhaust port so it's a little bit higher?
    I have a bunch of different files around here somewhere and a Dremel.

    Looks too easy. I do have a gentle throttle hand.
  8. dave1490

    dave1490 Guest

    i port matched the exhast to the pipe the best i could{1 retanguler the other is round}removing all the casting flash and opening it up right to the bracket also in the pipe i 45 degreed the holes and slighty enlarged them,it helped a fair amount.am going to build an intake from scratch using play-do to get the right shape then fiberglassing it with resin{got to decide if i want low rpm{long and thin}or max power{short and thick}.and might use a 20-25mm carb.
  9. SlicerDicer

    SlicerDicer Guest

    I may mess with the Dax motor like this once I convert to the Tecumseh :) I think it would be neat to mess with it if nothing else.
  10. ibeenjammin

    ibeenjammin Guest

    What the heck is casting flash?? and how did you remove it?
  11. Egor

    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
  12. ibeenjammin

    ibeenjammin Guest

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

  13. Wrench66

    Wrench66 Guest

    The port sizes for the exhaust and two transfers are passable.....but that intake is just a joke:shock:. 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 :puke: 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.

    Attached Files:

  14. ourhearts

    ourhearts Guest

    did either of you notice a gain in top end speed?
  15. 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!

  16. Klox

    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.....

  17. quarkdude

    quarkdude Guest

    A Graham Bell 2 stroke Tuning

  18. Klox

    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!
  19. Egor

    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.
  20. Ghost0

    Ghost0 Guest

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