I need a straight answer

Ok Here goes this is the desiding factor for my engine and what will I do. I can get a running 1981 KZ750H for $80 bucks from a bone yard.
I have the opertunity to purchace a gpz 750 engine parts. I asked for the rotating assembly with pistons, a complete head with '83 cams, cam cover, oil cooler base for engine and cooler itself, and jugs. I figure the rotating assembly cause of the hyvo cam chain. The block is broken at the pickup side, and shipping the complete engine will be expensive. So we agreed on parting the engine.
My question is will all this gpz stuff fit in a KZ750 block, or do I have to modify somthing? The other question is will I end up with the same stock HP out put as the gpz wich is 84HP or will it be less?
Thanks in advance guys, What do you guys think.

BTW a zr7 engine, I found one but they said your not going to touch one for less then $950. Way out of my leage. Thats without carbs. WOW!!1:blink:

If the Boneyard 750H engine is decent you could just swap the GPZ head, cams, etc. to get the same result. As far as getting the GPZs original HP, that would depend on the carbs you are going to use.

It would be cheaper to just get the pistons, head and cams, and really a better idea would be to use the KZ750 head so you could keep the tach drive (although you would have to use the KZ750 exhaust cam for the tach drive gear), it has a little smaller combustion chamber volume (for higher compression) but is otherwise identical (valves and ports). The GPz pistons will give you higher compression (9.5:1 vs 9.0:1) and the GPz and KZ both use a HyVo chain.

What I would do:
Get the KZ750 motor and spend $360 for the 810 kit, use the GPz cams (bolt in, but no tach drive), shave .025 off the cylinder head (have to elongate the cam sprocket mounting bolt holes), and use the GPz (or even better RFS if you have the $$) carbs.

The only difference (power producing wise) between the GPz750 and the KZ750 motors are the cams, carbs, and higher compression pistons.

Actually, I would use fuel injection instead of carbs, but most people are more comfortable dealing with carbs.

I am assembling a GPz750 motor for another member at the moment, 810 kit, shaved head, and GPz550 six speed transmission, (almost have him talked into EFI) he is looking foward to riding it

Just to be clear, I'm not advertising, I don't want anyone asking me to work on their bikes, he's local and seldomly posts here (plus I still feel guilty about flipping his KZ750E, even though I bought the parts to fix it)

So unless I have crashed your bike, don't even ask :evil:

Post edited by: steell, at: 2006/02/17 17:25

Wana ride my bike?

So the 750 head has a smaller combustion chamber then the gpz head?
If so then shaving the z750 head and using the gpz pistons I could get about 10:1 comp?

Post edited by: Snakebyte, at: 2006/02/18 01:43

I have not run the numbers, but I'm guessing ~10:1
I have a new set of .020 oversize GPz750 pistons that I am going to use (still have to buy the rings), and I'm going to cut the head as far as I can (waiting on warm weather so I can get my mill here). I have read that you can cut it .035, but the head I am working on has been cut .025 and it don't look like it could go much farther. I have a KZ head in addition to the GPz heads, and I may use it, the KZ head is supposed to have a combustion chamber about 10% smaller (~2.5 cc) and I think that should equate to around a 10.2: compression ratio, maybe a little more. The numbers may be off a little because I don't have them in front of me and my memory is not as good as it was

I ran across a University Research Study on port flow a while back, and it indicated a 10-20% increase in port flow with some simple modifications, I'm going to give it a try and see how it works, I have spares so it don't matter if I screw up a head or two
If it works, it should deliver over 100 hp at the crank (and enable me to beat my Nephew's GPz750 motored 79 KZ650SR with my 83 GPz750).

If you are not in a big hurry, you could wait till I measure the cc's on the different heads for more accurate info.

Post edited by: steell, at: 2006/02/18 02:33

Yup, take your time. my engine project isnt till next year. I'm still working on getting my zx9 swing arm on:P

Hey Steve...will you work on my bike? I know you wanna, you can't help yourself man...besides, I know you have all that free time and no other projects of your own to be working on:laugh: