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You should just get a J/GPZ head ( not an 83/85 Unitrack or spectre bathtub head) and fit an APE idler. 
There's plenty about, they are cheaper and you are starting ahead of the game with the bigger stock valves.
You just need to either skim ( around 1.3mm ) to correct the compression or go for some pistons to do the same.

I thought about a j/gpz head but I'm running mtc 13.5to1 pistons that are cut out for the valves in the early style head if I switch to a gpz do you think I'd have to clearance the pistons? Even with the compression loss if I run big cams I think I'd have problems....my next motor will have gpz head but it will be built for it ..if I ever get the small tire together we gonna do a big tire build 

wrote:

I thought about a j/gpz head but I'm running mtc 13.5to1 pistons that are cut out for the valves in the early style head if I switch to a gpz do you think I'd have to clearance the pistons? Even with the compression loss if I run big cams I think I'd have problems....my next motor will have gpz head but it will be built for it ..if I ever get the small tire together we gonna do a big tire build 

 

The  J/GPZ1100B heads have the same valve angles as the early heads and they are also recessed 1mm ( along with 1mm shorter valve stems) to maintain sufficient valve to valve clearance for the larger stock valves and a skim of approx 1.3mm  will correct the compression.
Its the 83-85 GPZ1100/1100R/1100 Spectre twin swirl bathtub head you need to avoid as this has a 1 degree steeper exhaust valve which won't match the piston valve pockets.

So the 83-85 gpz is what's called the bathtub head ? ....I think on this bike I'm going with a early kz head been ported and under bucket shims ..can't remember valve size but cams are 460/480 I think ....may not be best match for me but I found it and it's ready to go I have missed almost all season so I just want to get my small tire bike back together making passes ....so I can spend the winter building a car tire bike ...brings me to my next question .. Looks like there is several very knowledgeable guys on this post so instead of starting a new one I'll just ask you guys that are already here

....if I'm building a motor with zero parts to start with what is the best combo ? ...just start with a J motor and buy a big block and pistons ? Or is any part from early pre 80 kzs better like cases ..and no crazy, hard to find, or super expensive aftermarket parts...just the best parts combo for a big cc drag bike. Keep in mind I'm on a Ret. ARMY income ..I know I ask alot of questions but I've realized if I don't learn how to build and repair my own stuff I can't afford to race..lol ..I ordered a Clymer manual for the 73to81 kzs and after I read it a few times I'll order one that covers J and gpz bikes ....one last question please give your input on best trans I'm sure I'll use a slider clutch like is in my small tire bike 
.....thanks to anyone that took time to read this and extra Thanks to anyone who reply 
JC

Yes! the 83-85 GPZ1100 injection Unitrack (same engine in the Z1100R but with carbs and the same head but with shim over on the 1100 spectres) uses the "Bathtub head".. Biggest valves, Steeper exhaust valve, etc.
There's lots of combos you could use from a ground up build all depending on your preferences.
Personally i prefer the early style ( kickstart) motors. Parts are plentiyfull and most performance parts for the later J/GPZ's are just adapted from the early stuff where needed anyway so lock-up's and cams etc are early fittment with adaptors to fit the later engines.
The MK2 big crank pin motor would be a good base with stock welded crank, stock gearbox undercut ( Murdoc racing procut ) ,billet 2nd gear and lock-up clutch.
Normally aspirated i'd use a J head as the base, If turboed then an early head will do the job.
Use lisker/PMC type solid camchain idlers ( or modify your originals) and APE/TSUBAKI HD camchain and manual tensioner.



 

As the foundation of your new library, I recommend the factory service manuals over any of the aftermarket ones like Haynes, Clymer, et cetera. The factory manuals and supplements are much more model and year specific. You can start your collection for free.

www.kzrider.com/service-manuals

APE also provides a wealth of information based on many years of experience.

www.aperaceparts.com/tech.html

Ya I have checked out apes article about the different motors ....the free manuals will definitely save me a few bucks ....I need to find and old school drag bike shop that will let me come do a apprenticeship ....lol    I'm about threw the manual I got just figured I'd read it and I'd be a bit familiar with  Whatever section I need to reference next ...probably be putting the head, cams , and chain back on 

Then I can use pre 80s cases ( don't they have an extra mounting bolt or something?) and a mkII crank... then just get the rest of the parts for J motor like block and pistons then can I use a gpz bathtub head ?...Without a loss in compression or clearance issues? Or would I need to order gpz pistons for the different valve angle in the gpz head ? .......this is about what I had in mind and if I'm ordering new block and pistons the rest of the parts should be easy to find used I hope anyways !
thanks again guys for answering questions and helping me out .... Believe it or not I do try pretty hard to research this stuff on my own... Every time I search  something  it's not that there's no information...... there's actually too much ..you find 15 different answers online for every question lol...!

So you're saying that if I get a J head not the GPZ then all I have to do is have it milled 1.33mm ( I think that was the number you said ) ... And the compression loss that everybody says makes the J head swap pointless or not worth it is taken care of ? ....all the parts on my bike I have now are early kz from head to oil pan ...mill a bit off slap on that ape chain adapter part and I'm g2g ? Sounds good 

So many options and configurations on these cool KZ motors .... They need to open a franchise store like a 
"build a bike workshop"
Like the kids do for stuffed bears but we go there pick each part and they put our custom "build a bike workshop" KZ motor..lololololol

This is my bike with Z1 engine and J-head swap.