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Thread: deck hieght

  1. #1
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    what is the stock deck hight for a kz?


    i have set my piston to head clearance to .040". on my 1200cc 10.25:1J&E pistons.
    <DIV>do u think there is any real advantage to closing the deck hight on a KZ ? or does it depend on the aplication. i am hoping that it alows me more cousion , from pinging,while running pump gas. but i have no proof of this.</DIV>
    <DIV>from what i have read, it makes sence, so i do it.</DIV>
    <DIV>but i never seem to hear of anyone bothering with it.</DIV>
    <DIV>i have always been a pro less squish, but when mentioned on other forums it seem i am alone.</DIV>
    <DIV>what is your opinion.</DIV>Edited by: mark1135cc
    76kZ frame.raked 1.5*, & gusset work,1200CC.RS34 carbs,ported,1.5mm.over intakes, ,425cams,pods,kerker,backcut trany, billet 2nd,Dyna 2000,coils,ZRX12 rear end,and seat,170 tire,zx9front end.Ont.Can.

  2. #2
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    allways keep squish and cut the dome
    street cars kill bike racers

  3. #3
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    The reason .040" is used,ie head gasket and zero deck,is because G Bryce discovered the rods stretch .035". An overly large squish costs power but too low and the motor breaks the conrods.<div></div><div>You are street compression anyway so why chance it? Real compression the dome almost fills the entire chamber and is relieved to clear the spark plugs. Milling the head changes the cam timing due to the piston to valve clearance needed. First and easiest is to install some version of a race piston that has a dome on it.</div><div></div><div>You can run say .060" clearance to intake and say .080" to exhaust. So if you mill it say .020" they are now .040" and .060" at same cam timing. So to regain the clearance the cam timing is "adjusted" and may not be the optimum for the cams you have. This is also same version of installing larger intake valve 37.5mm into Z-1 head. The valves must be "sunk" to achieve .200" between them on the seat. Since usually hotter cams with a smaller base circle are used this gets the shim back into a buyable range. It all comes out in the wash but 10 to 1 is a street bike.</div>

  4. #4
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    Depends on the rods, some stretch more than others. Also depends on what's sitting on top of them (how much weight per piston/pin assembly), how much rpm you're turning, and how much stroke you've got.

    The problems start coming when you're modifying something hilariously outside of what it's designed for. A super tall dome can screw with the way the burn propogates, losing the power you were trying for. Sink the valves too far and they stop wanting to flow. And so on, and so on.

    Seems like a nice mild sort of combination for a streetbike, now put a big bottle on it and spray the balls offa it.




  5. #5
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    Thanks for the replies. sorry for the late responce.
    <DIV>do u think it is benaficial to run .040" squish on a street motor ? </DIV>
    <DIV>i was thinking it would help prevent detonasion at 10.5:1.</DIV>
    <DIV>what do u think, am i wasting money or does it do any good for the street?</DIV>Edited by: mark1135cc
    76kZ frame.raked 1.5*, & gusset work,1200CC.RS34 carbs,ported,1.5mm.over intakes, ,425cams,pods,kerker,backcut trany, billet 2nd,Dyna 2000,coils,ZRX12 rear end,and seat,170 tire,zx9front end.Ont.Can.

  6. #6
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    That is what the squish is for.<div></div><div>It basically acts like stirring the ashes on a fire.</div><div></div><div>You need .040,ie 0 deck and .040" head gasket.</div><div></div><div>If it is larger then you have this dead zone that cannot burn into so is mixture with no effect on the performance thus the loss in power that Bryce found.</div><div></div><div>The .040" goes to nil due to rod and crank stretch at RPM.</div><div></div><div>So the spark advanceat say 40 degrees BTDC starts the burn and the piston is quite far down the bore at this point. So right at TDC becomes nil and squishes out the trapped gases so point of maximum pressure is about 15 degrees ATDC. This effect is why you adjust the timing to achieve the point of maximum pressure just after TDC. Less and it acts straight down with no rod angle so the piston can move and more so the volume has grown so much to not get power.</div>

  7. #7
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    thank again sonicrete.
    <DIV>i do understand the theory. i jusy wondered if it was usefull on a street motor? i supose it must help to some degree. i supose u could tell if u were able to back the timming off. say u ran into a ping at 40* of advance then after u closed up the squish u may be able to run at say 38* of advance.</DIV>
    76kZ frame.raked 1.5*, & gusset work,1200CC.RS34 carbs,ported,1.5mm.over intakes, ,425cams,pods,kerker,backcut trany, billet 2nd,Dyna 2000,coils,ZRX12 rear end,and seat,170 tire,zx9front end.Ont.Can.

  8. #8
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    The squish is not related to the timing.<div></div><div>Less and is mechanical contact more is not beneficial to power,street or race.</div><div></div><div>The squish actually minimizes detonation because of creating turbulence. This why open chamber heads with low compresson can detonate.</div><div></div><div>The detonation is more related to the fuel octane.</div><div></div><div>You are trying to find the maximum point on a rounded shape. It is the interesection point of jetting,spark plug heat range,timing,compression,cam timing,etc. After you have built the motor you run as cold plug as the ignition can fire and jet down.The point of detonation is right next to the max power point,so if you rattle you back off the timing a bit till it stops. Sometimes maybe a bit richer to make it stop or next heat range colder. Finding that elusive peak with all combinations close to optimum.</div>

  9. #9
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    i thought that if u reduced the the squish u would remove the dead spots that were causeing the detonastion. therefore u would be able to start the burn later.
    <DIV>isnt it true that a chamber leass dead spots (faster burning), will require less timing?</DIV>
    76kZ frame.raked 1.5*, & gusset work,1200CC.RS34 carbs,ported,1.5mm.over intakes, ,425cams,pods,kerker,backcut trany, billet 2nd,Dyna 2000,coils,ZRX12 rear end,and seat,170 tire,zx9front end.Ont.Can.

  10. #10
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    There is no "gain" only right or wrong. Is that difficult to understand? Go back gobs of years to antique side valve flat head engines. That is where they discovered the effect of squish in the first place.<div></div><div>So go stupid and ignore history,then magically discover the effect and surpise makes more power. That is not a "gain" only preventing a loss.</div><div></div><div>I am not the best to ask since I tend to want to run timing. I have read and read how they retard timing to gain performance but I do not see it. Now maybe if they were running 50 degrees and backed up to 40 OK. Just because the spark ignites does not mean the burn begins. True CDI for ages would work well on 2 stroke but not on 4 stroke. The CDI had more voltage could jump a larger gap but was a wimpy spark vs regular inductive that was more like an arc welder. So starting a fire with little match or a blowtorch?</div><div></div><div>You go through all the motions of all the variables minimizing them,then is tuning from there.</div><div></div><div>The pump fuel is crap,might as well be kerosene. Even in a stock fuel class it did not come from the local BP station. In my case all my racing was done using Cam-2 standard purple or blue supreme. This removes the detonation as any variable so then can just move timing around to best performance. This effect even shows up in the XR200 dirt bike. It will run fine on pump gas but Cam-2 makes it so much better. Where you need to be a gear lower to climb hills,the Cam 2 is wind and go maybe the combustion just gets "unstable" and not detonation but definatly not as powerful.</div><div></div><div>Temperature and as to air density can require jetting changes just to maintain. As a rule for me first pass in the morning was quickest of the day,the one at noon the slowest,the one near 5 no matter the changes you made never was as quick as the am pass.</div><div></div><div>I get to repeat a line out of fast times magazine APE used to print. G Bryce got a motor from a customer that was down on power. Was assembled from good parts by some other shop. So they check it over and fine nothing wrong except the piston was .025" down in the hole. They do the work get zero deck and gained 17 hp. Used to be common if you did not gain enough valve to piston clearance at the cam timing you wanted just install another base gasket. This showed you were better off redegreeing cams or cutting piston relief since just this little fact wasthesingle largest power loss they had ever seen.</div><div></div><div>Detonation is an engine killer. It is exactly the same thing as beating on the piston and rings with a hammer. So where aquick pass on a drag strip is one thing where a4 hr ride on a hot day another. Then again you are just cruising along most of the time not putting any load on the engine and throttle almost closed.</div><div></div><div>What can I say ride the bike move the timing ride the bike leave it where it is best.</div>

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