Please help need advice!!!

Discussion in 'General Questions' started by Andres, Oct 2, 2016.

  1. Andres

    Andres Member

    So I am very concerned about port matching the GT80 cylinder with my stock crank transfer ports.My concern is I am running stock cdi and a 6cc high compression head.Do you think it will start if it does will it run without a problem.Do you recomend I upgrade to this cdi below??? gt80-engine-only-720_78b64022-7b2a-41a8-a526-2480dc58d5a8_large.jpg 4138_large_e9bb40f2-b3cb-41a5-a26c-94810ed46f94_large.jpg
     

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  2. crassius

    crassius Well-Known Member

    it is stroke and rod length that will need to be matched - ignition timing won't change
     
  3. jaguar

    jaguar Well-Known Member

    any good engine builder will tell you that when you increase the compression you need to retard the ignition.
    The Lightning is more retarded than standard but not as much as the Jaguar CDI.
    These engines need a 7.5cc head. Anything less gives too much compression which will cause the cylinder plating to flake off and the bearings to have a short life.
     
    Timbone likes this.
  4. Andres

    Andres Member

    W
    Were can I by a jaguar cdi and a 7.5cc head
     
  5. jaguar

    jaguar Well-Known Member

    Click on my signature link to go to my site and go to the CDI page.
    I don't think anyone makes a 7.5cc head which is one reason I stay mad at all of the parts suppliers.
    If anyone knows of one then please inform us.
    If there is none then you can sandpaper down the stock head about .8mm or buy a 7cc head and dremel out more space in the combustion bowl. Either way you'll need a pressure gauge to make sure you don't exceed 130psi.
     
  6. Andres

    Andres Member

    Thanks
     
  7. gary55

    gary55 Well-Known Member

    These heads do not increase compression unless replacing a stock straight plug head. Left to right stock straight plug head = 10.1cc, stock slant plug head = 6cc, pancake performance head = 7.9cc, rounded fin performance head = 8cc, flat fin performance head = 8cc. The head on the far right is the head sent with the GT 80 engines. I am not real smart on the various performance gains achieved through the differing chamber designs. I can tell you that the gains are not due to increased compression. The slant plug head has the highest compression of all the heads below.
    [​IMG]
     
  8. sp1ke

    sp1ke Member

    nothing to bad in port matching apart from changing the volume of the crank case

    removing material weakens your compression in your crank and thusly at your head so reducing the force thrusting up the transfers

    so you may get away with that head making up the loss in theory wouldnt run just that head on standard bike jag is right could put compression to high he knows his stuff dont exceed 130 psi

    but with a weakened initial compression its possible id definatly do some compression tests
     
  9. gary55

    gary55 Well-Known Member

    Surely by now you have completed this build. I would love to hear what your compression was. If you didn't remove any material from the head or cylinder it should be around 90 lbs.. I have built 5 of these engines so far. They need around .030 decked from the jug to get to 125lbs. comp.. This is all assuming that the bottom end you are putting it on is type B with 40mm stroke. If you are putting it on a type A bottom end you will have problems. So how did the build go?
     
  10. Andres

    Andres Member

    It went really good but i cant get the engine to pass 45mph
     
  11. Street Ryderz

    Street Ryderz Well-Known Member

    What did you expect to get? what gearing are you using? what size wheels do you have on it? If you have a stock 44t and a 26" wheel the engine is turning 10,500 rpm at 45 mph !
     
  12. Andres

    Andres Member

    32t sprocket wheel size 26"
     
  13. Street Ryderz

    Street Ryderz Well-Known Member

    Ok so 7700 rpm what pipe are you running?
     
  14. Andres

    Andres Member

    Spanchon champer mz
     
  15. Street Ryderz

    Street Ryderz Well-Known Member

    Do you notice the pipe effect? if not the a/f mix might need to be adjusted by jetting differently to get the most from it!Or the engine is not making the power to over come the gearing!
     
  16. Andres

    Andres Member

    Thanks
     
  17. Thanks Doc, wasn't sure.
     
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