boosting compression? ideas?

Discussion in 'Motorized Bicycle General Discussion' started by Thunderhead289, Oct 30, 2013.

  1. Thunderhead289

    Thunderhead289 New Member

    Joined:
    Jul 2, 2013
    Messages:
    49
    Likes Received:
    0
    so I shaved my head down a bit and was curious on everyones opinion on doing so.

    I also drilled a few extra holes in the baffling of the exhaust due to the higher compression.

    can anyone tell me the adverse effects of lessoning the back pressure. what negative effects will it have? obviously with less back pressure there will be more heat in the chamber, but is there anything more than that?

    bear with the video a bit as I made it to get views on youtube since I get paid through ads.
    https://www.youtube.com/watch?v=ZMMbWtStkTY
     
  2. dodge dude94

    dodge dude94 New Member

    Joined:
    Jun 8, 2012
    Messages:
    1,017
    Likes Received:
    0
    Get an expansion pipe, less back pressure where it's unneeded, back pressure where it is needed.
     
  3. Thunderhead289

    Thunderhead289 New Member

    Joined:
    Jul 2, 2013
    Messages:
    49
    Likes Received:
    0
    explain that too me, where is the back pressure needed?

    I cant bring myself to get one over a shift kit, I just do not care for the look of them even if they are such an improvement. id love to build a motor for best power, though I seriously doubt the bottom end integrity of these motors.
     
    #3 Thunderhead289, Oct 30, 2013
    Last edited: Oct 30, 2013
  4. Nashville Kat

    Nashville Kat Active Member

    Joined:
    Apr 20, 2009
    Messages:
    1,427
    Likes Received:
    1
    I file the head down flat- I take all the ridge away that fits down onto the head gasket-
    the normal ridge actually makes the head gasket have a smaller area of contact, and usually bends the head gasket onto two different planes

    anyway, filing that ridge away takes a little bit of top cylinder space away, and with the same bore and stroke otherwise, increases compression- I could really feel the pop when I first did it

    the head gasket is not compromised either in volume or squashed into two different planes, so in theory and probability at least, it should last longer and seal better.

    I just got an odd extra 50 cc engine dirt cheap on ebay- the straight verticle plug head is ALREADY flat with no ridge- so I'm curious as to when it could have been made, and have no way to find out.
     
    #4 Nashville Kat, Oct 31, 2013
    Last edited: Oct 31, 2013
  5. mapbike

    mapbike Active Member

    Joined:
    Mar 14, 2010
    Messages:
    5,380
    Likes Received:
    1
    Actually the bottom of these engines does pretty good, the wrist pin/upper bearing is normally the weak spot on these engines when bearing fails its usually that one, sanding the head down flush wont hurt a thing, I've done it multiple times, it will increase compression and give your engine a bit more grunt power and help power even on top end, a well tuned carb and a free flowing exhaust is where to biggest improvement is on a basically stock engine, I will include links to upper bearing which is very good quality.

    http://www.pocketbikeparts.com/Piston_Wrist_Pin_Bearing_p/cgpr302450.htm

    https://www.treatland.tv/malossi-needle-bearing-p/malossi-needle-bearing-663209b.htm

    Map
     
    #5 mapbike, Oct 31, 2013
    Last edited: Oct 31, 2013
  6. Thunderhead289

    Thunderhead289 New Member

    Joined:
    Jul 2, 2013
    Messages:
    49
    Likes Received:
    0
    so if I run it richer to keep the combustion temps down I should be alright with less back pressure? im sure it will use more fuel due to better flow, but im not all too worried about fuel mileage with what these get!
     
  7. dodge dude94

    dodge dude94 New Member

    Joined:
    Jun 8, 2012
    Messages:
    1,017
    Likes Received:
    0
    You'll need to jet it richer because more air in/out means you'll need more fuel.

    Simple engine dynamics.
     
  8. Huffydavidson

    Huffydavidson STREETRACER/MANUFACTURER

    Joined:
    Jan 29, 2012
    Messages:
    1,075
    Likes Received:
    0
    So, what saying is, that if I shoot some holes in the can I'll have higher compression ?
    Dang , after all the money and machine work I've done and spent , NOW you tell me.
    LMAO
     

Share This Page