Question.

Good Folk.
Pardon my ignorance but I have an '85 GPZ550.
What is the difference between a GPZ and a Z 550....other than the GP bit.
I sound stupid I know but....
Many thanks
Hog.

From a Motorcyclist magazine article about the GPz550:

Kawasaki got all this impressive performance by heavily tweaking the base KZ550 platform. To the KZ’s already stout, 553cc four, engineers added hotter camshafts with more duration and lift. The GPz received domed pistons for increased compression. As a whole package to increase power, Kawasaki also gave the GPz reshaped ports, electronic ignition, a less-restrictive airbox and exhaust, and larger main jets. Output jumped from a claimed 53 to 57 hp at 9,500 rpm (the redline), yet the bike retained much of its prodigious (for a middleweight) midrange power, which is so appreciated on the KZ.

The chassis got a host of upgrades, too, the biggest of which were triple discs in place of the KZ’s solo front disc/rear drum combo. Kawasaki also added a neat cockpit fairing, rearset footpegs, an air-adjustable fork, (rebound) damping-adjustable shocks, a low handlebar, a fuel gauge and oil cooler, all topped off with Firecracker Red paint and black-painted engine and wheels. And while the GPz retailed for $300 more than the KZ ($2,599 versus $2,299), you’d be hard-pressed to buy all those upgrades for three bills. All in all, the GPz550 was packed with good stuff, and everyone who cared about sporty bikes noticed.
....

I think just the styling, pretty much. Maybe due to the age difference.

Woah! I didnt see MartinCSRs reply when I posted mine.There you go. All you need to know.

Very informative, thank you.
Hog.

For more info,this is a pretty good site;
www.motorcyclespecs.co.za/bikes/Kawasaki.htm

and for parts for your bike,try here;
www.z-power.co.uk/

The main difference on the engine is the jetting, compression, camshafts, and oil coolers.

The Gpz550's come in 3 types. The first is dual-shock Kz550. Second is mono-shock Kz550. Then the third is your mono-shock Zx550.

The "Z550" is the European name for the non-Gpz Kz550.

Here is more than you ever wanted to know about the camshaft differences and a few other internal differences and similarities.
s3.amazonaws.com/gpzweb/CamsKZZXZR550500...KZZXZR550500400.html

Gentlemen, many thanks for the information, gratefully recieved.
Hog.