During the last two weeks I was asked three times about compatibility of Kawasaki KZ650 and stainless steel exhaust header made by Black Widow (UK) for Kawasaki ZR750 Zephyr. It looks like a good reason to write a short post with illustration. There are three points, or call them potential bottlenecks.
First of them is simplest to solve: KZ750 (inline four) and therefore Zephyr 750 are direct descendants of Kawasaki KZ650, so exhaust port spacing is similar for KZ650, KZ750 (inline four) and Zephyr 750 cylinder heads. So Zephyr 750 Black Widow downpipes fit KZ650 and KZ750 cylinder heads without issues and might be installed using their original exhaust holders, while with Zephyr 750 exhaust collars.
The third, and the last point is if Zephyr 750 stainless steel downpipes are compatible with KZ650 mufflers. Since original KZ650 mufflers are factory welded to header pipes it means that those who ask the question are already running aftermarket mufflers, or are ready to do so. And here Zephyr Black Widow exhaust has a feature which everyone who wishes to install it on KZ650 has to consider for himself. The thing is outputs of downpipes have a pretty large outward sweep. To show what exactly I mean I fitted an aluminum pipe to the downpipes, so it’s a direct prolongation of the downpipes’ output pipe. The length of the aluminum pipe is around 640mm. Thus, you may see where straight mufflers would be pointed if you use them along with Black Widow exhaust header.
And considering that there is not much of a choice of exhaust headers for KZ650 downpipes, my opinion on this question is as follows: since Zephyr 750 downpipes are made of stainless steel, their outputs might be modified without losses for exterior.