What power gains with 4 into 1?

As OMR is pointing out, it is really about balance. That is, having all the parts working in concert. Just installing a low restriction exhaust, or just some massive carburetors, or just some wicked cams alone will not make a really big difference in actual performance.
When the carbs, head, cams and exhaust are properly balanced and working together, you get the most bang for your bucks.
Yes, the engineers at Kawasaki spent a great deal of time and money designing these systems to provide the best balance of smooth, reliable performance, low maintenance and reasonable (legal) noise levels, taking into consideration the different laws in each country and the ever more stringent ones in the U.S. in particular. Besting them requires knowledge, careful planning and a goodly number of shekles.

650ed wrote:

Old Man Rock wrote: Case in point, street racer Toyota, Nissan etc... with Cherry bomb exhaust... Eeeewww, sounds bad ass but still a dog turd in acceleration, torque, power..... .

Amen! Some folks believe dB = hp, but they are only fooling themselves. Ed

This also describes a large subdivision of the HD community and many of the sport bike squids.

TexasKZ wrote:

650ed wrote:

Old Man Rock wrote: Case in point, street racer Toyota, Nissan etc... with Cherry bomb exhaust... Eeeewww, sounds bad ass but still a dog turd in acceleration, torque, power..... .

Amen! Some folks believe dB = hp, but they are only fooling themselves. Ed

This also describes a large subdivision of the HD community and many of the sport bike squids.

The HD's and Cruisers are probably the best example of how the loud pipe argument is deeply flawed. Here in UT it seems obligatory to have pretty much straight through pipes and make a lot of excessive noise. But while that noise is very loud when they pass you standing at the roadside or for the brief moment you are behind them, once you are in front you really don't hear it and on the rare occasion someone is going fast enough to pass you, you really don't hear them until they are right on top of you, so thinking all that noise will provide protection from the average moron driving a car who is thinking about everything other than driving, is just deluding yourself IMO.

The visibility issue is similar too, although I believe in making some efforts to be visible, we always here "I didn't see him" after someone takes a motorcycle out, but I find in normal driving it appears that people can't see my F350 Crewcab 4x4 pickup either, the only difference is if this did result in an accident, it would likely not make the news because it would only be a fender bender (for me anyway), whereas the same incident would result in serious injury or death if I was riding one of my bikes. The only way to ride or drive is to assume every other driver is an idiot, who hasn't seen you and will do the stupidest thing, at a moments notice, only by closely watching other drivers to see if they have seen you and are looking what they are doing can you remain safe, no matter how loud your pipes are, or how bright your lights and fluorescent your jacket may be.

I had a great example just a few days ago, I was pulling my travel trailer behind my truck which gives you a massive frontal area to make you visible and I had my headlights on, it was daylight with perfect visibility. Someone came up to a stop sign to my left, almost stopped and then drove right across in front of me, made worse by the fact I was driving on solid ice and packed snow, luckily I wasn't going very fast and managed to scrub off enough speed to avoid hitting them. The woman drivers response, once realizing her mistake, was to just stare at me and not continue to accelerate and get out of the way. You can't fix stupid, even with JB Weld and Duct Tape.

As for the extra power from a 4-1 exhaust, I think that alone is marginal at best in most applications, the amount you have to rejet to have it run the same is a clue to how much freer flowing it might be. The manufacturers of the bikes put a lot of time into designing their systems. i know period testing of 4-1's in the day showed many systems dramatically reducing power. Too often more noise fools the "Butt Dyno"' in to thinking you are going faster.

Some bike make great gains, not sure the KZ is a model that benefits enough to warrant the expense. On my FI 1500 Vulcan getting rid of the air box, reed valves and using aftermarket pipes, thunder side winder intake and an FI controller was a transformation. The bike runs cooler and gained 8hp over the stock 64. the difference is the tune of motors. With inline four power being at the top of RPM range, i just don't think it makes that big of change and the drive ability at low RPMs usually suffers. The Vulcan being nearly square on HP/TQ and the power band in the low to mid range 2000-5000 rpm was very impactful where ya do the most rinding. Also improved gas mileage. Every inline four I have driven has the sensation of being pulled, the big V-Twins have a sensation of being pushed. My 0.02$ R

rrsmsw9999 wrote: Some bike make great gains, not sure the KZ is a model that benefits enough to warrant the expense. On my FI 1500 Vulcan getting rid of the air box, reed valves and using aftermarket pipes, thunder side winder intake and an FI controller was a transformation. The bike runs cooler and gained 8hp over the stock 64. the difference is the tune of motors. With inline four power being at the top of RPM range, i just don't think it makes that big of change and the drive ability at low RPMs usually suffers.

That's what I noticed on the 2-1 that I put on my 750 twin. It was well designed and worked really well with going one size up on carb jets. There was definitely more power come on above about 3k RPM, but low end pull was basically gone and the stock 750 pulls like a freight train at low end. I read the explanation about why taking away the dual pipe with crossover hurts the low end, it was posted a while back.

Seems to me to be a pretty reasonable tradeoff unless I'm missing something? Unless you are pulling a trailer or pulling an F150 out of a ditch wouldn't one rather have power in the 2.5k to 4k range where most riding goes on?

The 1100 Spectre has really nice low and midrange power, I guess I would like a little more arm stretching top end now and then, maybe a pipe would help there then.
My thoughts about a little more exhaust sound are not hoping when passing cars but when trapped among a group of them, at least make the ones that dont see you look in their mirrors and know I guess.

Bowman wrote: Seems to me to be a pretty reasonable tradeoff unless I'm missing something? Unless you are pulling a trailer or pulling an F150 out of a ditch wouldn't one rather have power in the 2.5k to 4k range where most riding goes on?

In my case it's not. The 750 twin is geared to chug around in the 2400 -2800 range in high gear for most city driving (35 - 45 mph range) and the stock setup had a lot of pull in that range. The aftermarket pipe was very soft there, had to downshift to accelerate. Power didn't kick in until above 3k.

High gear as in 5th? In the city? How come not just leave it in 4th?

Please LOOK !!! under filebase at the top then click on "General" and look for the 2 part article 1978 Cycle mag 4 into 1 article for the KZ1000.

One of the best articles on headers of all time !!!!!! Have the mag somewhere but I'll be damned if I can find it and I thank you for putting it on here !!

Bowman wrote: High gear as in 5th? In the city? How come not just leave it in 4th?

Because it cruises smoother in top gear. The stock 750 twin has so much low end torque you can easily cruise 30 mph in 5th gear which is 2000 RPM.

Actually a Tri Y header makes more midrange torque and the top end does not suffer at all. Would be well suited for the inline fours on these bikes. we used them in professional racing on V8 engines, both flat plane crank and 90 degree crank types and either were great.