4 into 1 exhast system for '77 kz650

G'day all, returning member from years ago. Doing a restoration on my '77 KZ 650. I already have done it once but it needs a touch up again, I intend to use it for historic racing here in Australia. I would like to know thoughts on a 4 into 1 exhaust system for it, are they still available and has anyone used one getting rid of the stock air filter system. I presume there would have to be some re-jetting required. Any info greatly appreciated Regards Neil

Welcome back. 

Might be taking out of my backside here but before you modify the bike I’d check with the racing sanctioning body to find out what mods allowed. 

I currently have a Delkevic 4 into 1 exhaust on my '78 kz650.
Stainless Steel, and the price is very competitive.
They have two muffler types; straight and megaphone.
I bough the straight, reminding me of the Yosh exhaust I use to have.
I'm currently using a stock air box, but have run pod filters way in the past, with a Kerker 4 > 1.

ZR7 ZR7S muffler system (1999-2005 ZR750 models).
It's ss & has crossover pipes between the 1-4 & 2-3 headers.


ZR-7 or ZR-7S. same exhaust as above.