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TOPIC: Abandoning KZP Project, need some advice

Abandoning KZP Project, need some advice 08 Sep 2019 18:59 #810552

  • Lordzacharious
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So, I had the intentions of rebuilding my KZP, but with school taking up much of my time, and having a 76 KZ900 to work on, as well as two 78 KZ1000s, I really do not see the point in continuing on with the build.

Since I have my sights on one of my 78 KZ1000s, I am considering using what I can from the abandoned project, or selling what I can to help fund the 78

With that said, I had the


  • frame and all parts powdercoated,
  • cylinder head built by Cavanaugh (larger exhaust valves put in, new guides, valve job, etc),
    APE K410 cams,
  • Cylinders bored for the new Wiseco 1075 pistons


  • I also have a new set of of wiseco 73mm pistons with bored out cylinder for the earlier engines.

    So my question is, since the J head will technically fit the earlier engines, is it worth it to keep the cylinder head for my 78? Or just sell what I have and start fresh?
    I know the J style cylinder head will drop the compression, but I am not sure if the 73mm pistons I have would raise the compression enough to make it worthwhile. Im also curious if the K410 cams would be a feasible option with that combination. I would definitely have to get some new carbs if the J cylinder head would work.

    Thanks guys!
    1976 KZ900 (current project)
    1994 KZ1000 Police
    1983 KZ750L3
    (Non KZs)
    1981 Honda CB750K
    1981 Yamaha XJ650H Maxim
    1975 Honda XL250

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    Abandoning KZP Project, need some advice 09 Sep 2019 11:05 #810587

    • zed1015
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    The J head would be worth keeping with all that work done but the compression will still be down 2 points to around 8.25 to 1 no matter what bore size as the pistons comp ratio is configured to the smaller volume of the early KZ heads.
    For your info the early head is 36cc and the later J and GPZ are 40cc so that 4cc difference equates to the 2 point compression drop.
    On 1015cc engine each 1mm of the bore = 3.84cc and on a 1105cc = 4.1cc so a head skim (or combination of barrel decking and head skim etc ) of 1mm will get the compression back up close to the original 10.25 - 1 of the 73mm Wiseco piston.
    There is enough meat to take more than 1mm off the head and still clear the valve seats as I have done this myself but with the larger valve and 410 cams I would check the piston to valve clearance first although there should be no problems as the J valves sit higher in the head and is why J valves have shorter stems.

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    Last edit: by zed1015.

    Abandoning KZP Project, need some advice 09 Sep 2019 13:18 #810593

    • Scirocco
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    zed1015 is right about the compression drop!!! I am in the same situation of a 8,25 to 1 compression scenario with my 903 ccm cyl. /Piston bottom end. IMO i am wasting 20 HP at the moment with this Setup but a 1100UT engine swap is next on my to do list.
    So if you swap to your J head you need a CCIA to use your APE K410 cams.



    I am runing GPZ110UT cams in my J head now with APE sprockets for the Z1 cam chain.

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    Abandoning KZP Project, need some advice 11 Sep 2019 17:19 #810724

    • Lordzacharious
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    Thanks guys!!

    So with all that in mind, do I use the earlier cam chain and guides ?

    Also, any recommendations for carburetors? All I can think of at the moment is RS34s. Of course, I have a set of BS34s, but I imagine an airbox scenario isnt going to be super practical vs a mechanical slide set with pods
    1976 KZ900 (current project)
    1994 KZ1000 Police
    1983 KZ750L3
    (Non KZs)
    1981 Honda CB750K
    1981 Yamaha XJ650H Maxim
    1975 Honda XL250

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    Abandoning KZP Project, need some advice 11 Sep 2019 20:52 #810732

    • Scirocco
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    Lordzacharious wrote:
    So with all that in mind, do I use the earlier cam chain and guides ?


    Yes, that´s the reason you need the CCIA (roller chain) on HYVO chain J/GPZ Modell heads.

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