running a j head on a kz900

i have a kz 900 that i am putting back together and adding a 1045-1075 kit.and was thinking that putting on a j head could help breathing. i know the ape chain tower and the compression loss. so if i wanna run street gas do i go with the 10.25 with the lower compression or run a kz head on it and get the higher compression? meaning would the higher compression be more benificial than the bigger valve size and cc's with the lower compression. also i heard something about the jheads not having a tach hook up? is that true or only on some years...etc...?

i dont how clear my questions are but i don't know what else to say - thanks guys

Go with the Wisco 1075 12:1 kit part #R1075. You will than retain 10:1 compression and can get the extra benefits of the J head. You can also use the pistons made for the J engine with the 17mm wrist pins but you must insert a spacer or multiple base gaskets under the cylindr block to make up for the shift in the wrist pin positioning on the pistons. This would be a better choice because you will have a better squish band inside the combustion chamber due to the more even piston dome. Than you can use kit #K1076.

Post edited by: otakar, at: 2007/11/18 09:36

otakar wrote:

Go with the Wisco 1075 12:1 kit part #R1075. You will than retain 10:1 compression and can get the extra benefits of the J head. You can also use the pistons made for the J engine with the 17mm wrist pins but you must insert a spacer or multiple base gaskets under the cylindr block to make up for the shift in the wrist pin positioning on the pistons. This would be a better choice because you will have a better squish band inside the combustion chamber due to the more even piston dome. Than you can use kit #K1076.<br><br>Post edited by: otakar, at: 2007/11/18 09:36

You can never have too much squish! Can you?
Seriously though, what do you want to do with this bike? Daily rider? Road burner? Turbo? Vintage race project? Anyway, the J-head has better airflow and will develop more power. How much? I dunno anyone who's done a dyno run and compared it to stock figures.(you could be a pioneer here!)

For dependability stick close to stock. Use the 10.25:1 with the j-head and you'll be at about 8.5:1. I read that this combo drops copmression about 2 full points. (close to stock). With some carb tuning, a quiet aftermarket 4into1 pipe and you'll have a fine machine. Pods will increase peak power, but the stock airbox will give broader torque curve and be more fun to drive.

The cam chain and its bits are a weak link on older bike. It'll be worth it to replace cam chain guides and rubber bits to prevent grief down the road. Make sure your cam chain tensioner is in working order too.

If it'll help your decision: my own bike has APE studs in the crank case and cylinders. The block is enroute to APE for their 8.5:1 1075cc upgrade. I've replaced the cam chain and am replaceing the old bits with new liska pieces(new stock where liska isn't available).

Slotted cam sprockets will give some free power, this takes a little know how on your part, but isn't impossible.

hope this helps...Sam

i just had my head milled a little.
.20 you can see where it did hit the intakes a little.
i also had the boss drilled for the tach.

Most of the j heads have no tach drive like on a KZ1000. The only ones I know of are the heads off a 81-82 CSR model j motor. Not sure exactly which years the CSR was made that used the tach drive but I'm sure it was at least the early years...just be sure to check before you buy one.

the early j-heads did have the tach drive but are not the real desirable ones.
here is a picture of the front of my j-head after the shop drilled the boss for me.
it really was not to much of a problum for a quality machine shop to do.
nothing i would try on my own though.
i wanted to run my oe tach so i opted to have it drilled.
you can always run an electronic tach.