4cyl 750 heads

hey guys, been awhile. been having too much fun with the ninja;) but i may FINALLY get back to my 810cc KZ650 project this season. Im looking for info on combustion chamber size, valve size and port designs on the gpz750 heads. the turbo and na versions, aswell as the kz750. Im looking for the one with the biggest ports, valves and combustion chambers. yup you guessed it, im going turbo so i need to drop cr a bit with larger combustion chambers, and big valves and ports just work better for top end na or turbo:) it will be a megasquirt project using gpz1100 TBs. should be a fun learning curve.
thx!

Glad you are having fun:) and I'm looking forward to seeing the project materialize...take plenty of photos:)

In the erly 90s kawasaki made the ZR750 "Zephyr" I believe this head should drop on any of the erlier 6 & 750s. This head also provides more cooling fins. I know the cams interchange for sure.

how do the zephyr ports compare to the gpz? anyone have valve sizes and combustion chamber sizes??

yes ill be doing a full write up with pics when i get to itB)

I have one in the garage, I will get the #s tomorrow and let you know. I do know that the bike was rated at a quite high horse power. I can also take a picture or two.

otakar wrote:

I have one in the garage, I will get the #s tomorrow and let you know. I do know that the bike was rated at a quite high horse power. I can also take a picture or two.

cool!
was the zephyr stronger than the na gpz750?

My brother has the ZR750 Zephyr and he could pretty much keep up with a stock GPz1100. Actually he has a better off the line. I think the Zephyr engine, even though very close to the original 750, is much better. If you could find an entire ZR motor, that would be the way to go.

otakar wrote:

If you could find an entire ZR motor, that would be the way to go.

What about a ZR-7S head from a 2001 ZR-7?
The 2001-2003 ZR heads were very close to the Zephyr's/ GPZ's if I am not mistaken.

Hmm. Turbo eh! If you're gonna change the head then I'd look out for GPz750 head. I believe these have the largest combustion chamber of all the 750's albeit not by much. The ports are pretty much the same on all the 750's including the Zephyr. You can always get the dremel out and enlarge them a bit if you want. Valves sizes are the same on all 750's as well.
Use the stock Kz650 cams. This is what the GPz750 turbo used and they are fine. Std 750 and GPz750 cams have too much duration for a turbo.

What were you gonna do regarding pistons?
You know you can't use Wiseco's 810 turbo kit as the pin size is different to std 750's, they are intended purely for the GPz turbo as they run different rods with a larger piston pin.

You could probably drop the CR somewhat by machining some material out of the chambers and using stock 750 pistons. That would possibly net you with 8.5-9.0CR which you could run say 10psi boost with on pump fuel.

....Just looked up the CR's The 83-85 GPz has 25.9cc chambers, 82 GPz has 24.9cc, KZ750H has 24.8 KZ750L has 25.3. Dunno about the Zephyr or later stuff.

Im using the regular version of the 810 pistons(have a new set on the shelf allong with a freshly bored out 750 block) so finding the largest combustion chambers is top priority to lower the static cr as much as possible. im hoping to get it down to about 10:1 vs the advertised 10.25:1 with combustion chamber work and piston prep.(i have expirience doing this to my 12R to prep for a big shot of nitrous) it will be a low boost setup. 6-7 psi. i dont want to stress the stock crank and rods too much. im probly going to double the hp of the motor. i dont want to go more than that on stock 650 stuff.
thanks for the info on the heads, ill keep my eyes peeled for 83-85 gpz heads this summer

You could always use several base gaskets underneath the barrels. Kawasakis latest base gaskets are made of metal and are about 0.45mm thick if I recall correctly.
Could be worth a try.

using a spacer is the wrong way to lower compression. it increases squish to the point its not effective. i know its done been done, and does work ok, but its not the best way. im happy with a low boost setup anyway. like i said, i dont really want to stress the stock 650 bottom end. its not as well designed as the 750 turbo. and my 12 will be around 300hp on nitrous this season....