TOPIC:

I know its probably obvious if I looked at them on the inside.

Is there any difference between a head from a 78 650 and a 80 750? Physically they are the same size correct? I know the 80 750 uses a hi-vo cam chain but Id be interested in using my 750 cams, I just want to use the actual head from the 650 if possible, without major (or minor) machine work. Or are the cam journals (correct thingy??) different between the 2 also? Valves would probably be different sizes also.

Not worth doing just to avoid a few bad holes that were badly retapped where the carb holders attach right?

Thanks
DanO

Yes, a 650 head will bolt on a 750 motor with no problem. You will probably have to use the 750 cam cover because of the different cam chains. You will losw some hp though, the 650 head has smaller ports and valves than the 750. I have a spare KZ750 head that I was going to use on a GPz750 motor, but I might let it go. U2 me if you are interested.

I'm not sure about the power loss. The KZ650 head has a smaller combustion chamber which should lead to higher effective compression rations. I know Steve Darlington on another list used a stock 650 head to pretty good effect. The best thing would be to fit larger valves in the 650 head, but the higher compression might make up for differences in port and valve sizes. It would be interesting to take compression readings on the same motor with both heads and see what the difference would be.

If I were to do this what can I myself do to improve the 650 head?

If you look in the database files for the 1980 KZ750, you will find some 1980 magazine articles that discuss the "new" four cylinder KZ750. They discuss, in detail, all of the many tech changes from the KZ650 to the KZ750. While many parts are interchangeble (with a little modification) it is clear that the KZ750 cam, pistons and head were redesigned and re-engineered to work together to produce substantially more power than the 650 produces. While you will certainly have a functioning bike with the 650 head on the 750 engine, I believe you are missing the benefit of the Kawasaki re-engineering that went into the 650 engine when it was remade into a 750. It was a lot more than just a bigger bore and more displacement.

I think it will be fine, hell if I had a 650 head and a 750 engine I would put it on. Remember that the smaller the intake runners the faster the flow.
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