'80 KZ 750-E1 vs GPZ 750 Pistons

From the information supplied here and other sources online, I've noticed that the engines of these two bikes seem very identical. Both engines are the same size, bore and stroke, etc. The man difference seems to be the compression ratio; the KZ 750 is 9.0:1 rated at 74hp, and the 83 GPZ 750 is 10.5:1 rated at 92hp. My question is whether the GPZ's pistons would fit in the KZ. the parts are affordable and cheap but I don't want to tear the engine down and realize I've wasted my time chasing a pipe dream. What do you guys think?

Your question got me thinking as I also have a 1980 750 E1 so I went to kawasaki.com, owner info, parts diagrams, 1982 etc etc - check it out - and had a look. Once there it's possible to put the part # in a search box up top and see what other models it fits.

It looks like the piston pin and circlips are interchangeable with the 1980 E1 which would indicate same diameter but the piston itself looks a bit different. It takes 4 rings instead of 3 for the E1 piston and may have a bit more of a dome on it, perhaps for that extra compression.

Not the definitive answer you were looking for but I'm thinking maybe a fit with current head ........... and more than likely would fit if you had a GPZ cylinder head to accomodate the slightly different GPZ pistons.

Hopefully an expert will be along soon.


Cheers

I use these pistons on bored out KZ1300 and the pistons do interchange size wise. They are all three ring pistons. I have never seen a four ring piston myself. The difference is the dome shape. When you say that the parts are cheep, I am not so sure about that. It is actually cheaper to buy new pistons from Wiseco, than to buy stock pistons from Kawasaki, (If they are even still available)I buy all of my pistons used on eBay for my 1300 projects, because the stock piston is the largest I can go. If I go to Wiseco they would have to be oversize and I can't go that big.

I've a magazine page that says the GPZ550 are different to the KZ550 only in the compression, but is some differences between the exhaust valves. Also says that the GPZ pistons in KZ causes detonation :S
I think that this applies to the 750's....
Here is the article (look the pictures):

I'm going to check out the Kawasaki parts diagram and see if I can't find out more info on the engine differences. I know that they changed the GPZ quite a bit from 82 to 83. If it's not swapping KZ engine parts for GPZ parts, what other engine modifications can I do to shoot for the 100 hp range?

I looked at it a while ago and found that the cams, head, jugs were different from 82-83. But valves, cam sprockets, and several other parts were the same. My guess is compression is in the head and pistons (obviously), and the extra power has to do with the cams and compression. Otherwise there didn't seem to be enough different.