KZ1100 4INTO1 HEADER VS. STOCK how much hp. gain

on the kz1100 how much horse gain would you get from putting a good 4into1 VS stock 2into 1's when i say a good
4in1 what is a good 4in1,i know the carbs would need rejetting but how much horse is gained without putting a cam in or working on the heads

Hello Ted...if you are lucky, you might get a 5-7% increase in HP...as for 'good', everyone has their personal preferences...you may be quite limited for your bike on what is available. If you want new, then perhaps, V&H, MAC, or Kerker. If you want used, then the only thing limiting you is time and eBay

A lot of the improvement you feel is not so much from the extra horsepower you get but from the reduction of weight difference between a 4-1 and the stock exhaust. Depending of the bike, the weight savings can amount to quite a bit. You will get more improvement from a 4-1 on a modified motor then you will from a stocker. Some of the cheaper brand headers probably don't help much if at all. You get what you pay for. If you don't have to rejet the carbs, you probably aren't going to see much improvement. It can depend also on the baffle that comes with the header or one that you can upgrade to but baffles that improve power the most will also be louder...generally. I've read comparisons where most headers on a stock motor actually didn't increase HP much if at all while some actually lost HP. Try to buy a good quality header like a V&H or Kerker. Yea, they are more expensive but are generally better overall in fit, quality and for any performance increase.