I found one...and bought it..Bath tube head

wrote:

My engine is a 81 GPZ1100, so it has the 17mm wrist pins.   Here's where things get a little fuzzy for me on the specifics.   From what I understand from researching:

Because they are 17mm and the later model engines are 18mm, there is a .5mm delta some where.   If all they did was increase the hole size why would anything change length wise?
Somebody smarter than me needs to clarify.  Is the rod the same length between the early and later engines?  if the rods are longer on the earlier models then you would want to shim the base of the cylinders so that there would not be any interference.  I'm just guessing here....

577nitro.

It's just the pin size that 1mm bigger.
Rod length is the same on all J/GPZ type ( no kickstart) engines .
Center height from the crank pin is the same so no deck height changes or block spacers needed.
The combustion chamber volume of the bathtub is also the same as the earlier J/gpz at 40cc but the exhaust valve angle is 1 degree steeper and the valves are bigger.
Depending on your chosen pistons the exhaust pocket angle may need machining and the pockets enlarging.
Other than that it's just the normal valve to piston and head clearances etc you have to be aware of.

My engine is a 81 GPZ1100, so it has the 17mm wrist pins.   Here's where things get a little fuzzy for me on the specifics.   From what I understand from researching:

Because they are 17mm and the later model engines are 18mm, there is a .5mm delta some where.   If all they did was increase the hole size why would anything change length wise?
Somebody smarter than me needs to clarify.  Is the rod the same length between the early and later engines?  if the rods are longer on the earlier models then you would want to shim the base of the cylinders so that there would not be any interference.  I'm just guessing here....

577nitro.

The distance length of the small end piston pin center and the big end crank bearing center of the crank rod is the same on 17 or 18 mm = no delta 0,50 mm!!! You have 66 mm lift on both piston pin size and the same deck high. AFAIK the J engine piston pin is located 0,50 mm closer to the piston dome to lower the displacement from 1015 ccm to 998 ccm.

Some info, but not enough...
www.aperaceparts.com/tech/techkz1000.html

wrote:

Ok, so I finally just bit the bullet and bought one..searching and searching for a good deal just never happened.   So now I have another piece of the performance
puzzle.  I realized that my 81 head just ain't worth putting any money into, as it will never really perform.  It's fine for burning up miles and doing stock restoration not much more. 

I have the 34mm FS Mic, Dyna2000 Ign, Kerker4into1...but not sure on the cam and pistons.  I want about 130hp, not sure the parts combo that will make that.  I'm sending the head straight to Cavanaugh for a full rebuild, port and polish.  Since its an 81, it burns oil from the bad bore job from the factory, so maybe do a 1170 or 1200 something big bore. 

Thoughts welcomed.

577nitro---proud owner of a hyper rare bath tub head.



 

A 1200cc street motor should put out about 115HP to the rear wheel (dyno results : J head 3X cams 36RS) Your carbs seem a bit small, should be 36's as a minimum to support the head flow. Once you go above 1200 everything needs to get bigger. If you want that "130HP" you will need more CC's bigger still carbs etc. might have to go to 1327cc.
 

wrote:

Some info, but not enough...

www.aperaceparts.com/tech/techkz1000 .

Thank you….I read the above page about four times, and it appears all is good.   No need to worry about the crank pin size, as I am using the same crank, cases…etc

If I go larger on displacement then it’s just the standard deck height checking.   All of my confusion on the pin size only relates to using parts from 80 and down with 81 and up engine combo’s, which I’m not.   

If I go larger, then I just need to be sure the pistons have the 17mm pin size and not 18mm…that’s pretty much it.   

Wheeeewww, glad I got that all straightened out…thanks to all for your ideas and info.   Now I just need to figure out a cam/ piston/compression ratio  that will work together for my HP target.  One issue I’m fighting is that I’m at a density altitude of ~6000 to 7500’ so I don’t get much in the way of compression.  

Thanks!

577nitro-

wrote:

... that will work together for my HP target.  One issue I’m fighting is that I’m at a density altitude of ~6000 to 7500’ so I don’t get much in the way of compression.  

Turbo? Did I hear you say turbo? I'm pretty sure you just said turbo.

wrote:

wrote:

... that will work together for my HP target.  One issue I’m fighting is that I’m at a density altitude of ~6000 to 7500’ so I don’t get much in the way of compression.  

 

Turbo? Did I hear you say turbo? I'm pretty sure you just said turbo.

I heard it too!!!!    Better to be blown than injected
 

wrote:

... that will work together for my HP target.  One issue I’m fighting is that I’m at a density altitude of ~6000 to 7500’ so I don’t get much in the way of compression.  


 

Turbo? Did I hear you say turbo? I'm pretty sure you just said turbo.

I heard it too!!!!    Better to be blown than injected How much does a turbo kit cost these days and which is the best?   I have three turbo charged vehicles because of the altitude, and pulling over the mountains hauling dirt bikes, trailer, hunting gear….   I looked for a long time for a 750 turbo, but never found anything I could afford…or they were total clappers.

A used kit would be fine if there is one around.   

wrote:

 How much does a turbo kit cost these days and which is the best?   .   

Unfortunately, I don't think anybody is making kits anymore. They do show up on eBay every once in a while.  I'm guessing you're not going to find one for less than $2,500.  And often they're not complete.  
It's certainly a more complicated option now that the kits are out of production.

ebay.com/itm/353987883537
 

wrote:

wrote:

... that will work together for my HP target.  One issue I’m fighting is that I’m at a density altitude of ~6000 to 7500’ so I don’t get much in the way of compression.  







 

Turbo? Did I hear you say turbo? I'm pretty sure you just said turbo.

I heard it too!!!!    Better to be blown than injected How much does a turbo kit cost these days and which is the best?   I have three turbo charged vehicles because of the altitude, and pulling over the mountains hauling dirt bikes, trailer, hunting gear….   I looked for a long time for a 750 turbo, but never found anything I could afford…or they were total clappers.

A used kit would be fine if there is one around.   




 

You should have mentioned the altitude in the first place. Pretty easy to make 130HP with a stock GPZ1100 motor using a turbo charger and some RS34 carbs. Some examples on here of blow through carb setups, one comes to mind is a green KZ650SR with a similar build not done from a bolt on kit using modern turbo unit mounted at the front of the motor.

www.kzrider.com/forum/11-projects/423436...-turbo-kz650?start=0

Hardest part of it is setting up a reliable oil scavenge system to feed the turbo bearings.

That head is not necessary on a turbo build, you could use the stock head and put 1 mm oversize exhaust valves in it and call it a day, no porting necessary. That head you bought is more for a big CC motor build.


 

Since we are talking power here...I highly recommend swapping out your ancient ignition system for a Dyna2000, it made a world of difference on the old GPZ1100.  I bet I picked up 3 to 5 HP just from it.  Smooth power now everywhere, no more stumbles off idle just power...like harley torque.  I can wheelie now on power alone...it could never do that before, with a full tank too.

I did blow a 20amp fuse though, which I think is due to the increase in load, but that fuse was 41 years old, and ready to pop anyhow.   New, rule, replace all old fuses.  

577nitro

Who really needs a turbo anyway?   

I was pleased with the 1984 ZN head work when It was done last Christmastime, and am so-much more-so now...