compression ratio

Discussion in 'Performance Mods' started by Bikeuser, Jul 28, 2008.

  1. Bikeuser

    Bikeuser Member

    compression ratio increases power and fuel economy at the same time. I read that the HT motor only has a static 6:1 compression ratio. I have also measured the combustion chamber volume to be 9.18cc this ratio really sucks. I calculated that by decreasing the volume or increasing the piston height you can bump this up to an optimum 9:1 by adding or removing 3cc's. I think that the real ratio is alot less maybe 12:1 may work well.
    I will be brazing some pistons to decrease the chamber volume at TDC. I will let you guys on how it goes. my only worry is being able to start it.

  2. skipu

    skipu Member

    Cool They Definately Need More Compressioneven A Very Thin Copper Base Gasket Can Improve Compression Some !!!
  3. BSA

    BSA Guest

    You can grind 10 thous./inch of the cylinder head safely.

  4. Bikeuser

    Bikeuser Member

    You guys are dead wrong on that. such a small change will only get you to 6.1:1
    that chamber is huge. you will need to take off .100 to get any kind of meaningful results. this is for the cylinder head itself. the deeper you go the faster your head volume changes. the head is just too thin to do any sort of machine work and still keep integrity. I have also considered brazing some material on to the chamber but I feel that Pot metals melting point is just to close to the brazing rods usefull teperature. So i will be brave and either solder or have a guy MIG weld some aluminum on the top.
  5. jonboy2five

    jonboy2five Member


    you guys remind the newbies that an increase in compression needs increased octane fuel. i learned that the hard way on an mx bike about 10 years ago...
  6. BSA

    BSA Guest

    I didn't say 10 thous./in. was gonna make a big difference, but from what I've read thats the maximum amount you can take off safely.

  7. Bikeuser

    Bikeuser Member

    you can get away with 89 octane. I believe that the real compression ratio is way less if you measure the swept volume from the top of the exhaust port to TDC. any body know for sure?
  8. skipu

    skipu Member

    i think this brings to me a new project yes !!!!! im going to mill a after market head on my bridgeport with interchangeable compression domes and added cooling this should be an easy 1 ill pick up the stock this friday and get started thanx guys for turning on my light switch to this i feel there is great improvement to be made throughout these happy time motors ive got a buddy of mine in chicago im going to talk to and see if he has some spare time to give me a hand on this also !!!! in chicago that
  9. Ozi

    Ozi Member

    DONT introduce different materials/metals inside the combustion chamber.

    you'll regret it.

  10. skipu

    skipu Member

    ya i cant see adding anything to the piston being good . if anything you would want to lighten your pison "my idea is going off of a (pro design) cool head using high grade aluminum ive used them in the past on my banshee and my cr 250 thay work very nice
  11. Simon_A

    Simon_A Member

    Wanger, a member here in the forums, bumped his compression up by replacing the cylinder gasket with a cut up coke can.