Whats reason for the reducer pipe welded inside the end of the collector? Anyone know?

 

Can you post photo?

Depending on exact location and dimensions, it can serve couple purposes.

 

The reduced section is tack welded inside end of collector from factory.

 

It's on my 2016 cbr1000rr. My 2012 1k headers did not have this.

 

TLDR;
That neck-down ring is to create lip on wall of pipe to prevent backpressure pulse from flowing back in through exhaust-valve and pushing out fresh intake charge back out intake valve.

real info
1. In simple one-way flow like garden-hose, flow velocity is highest at centre of tube. It gets slower as you approach edge of tube due to friction against stationary wall.



2. Exhaust flow is not as simple as garden hose due to flow only occuring when exhaust valves are open. Since flow has certain velocity, it takes time to reach end of muffler and you may have multiple exhaust-valve opening pulses in pipe. Along with vacuum pulses in between when exhaust may actually be flowing backwards in pipe.



When pressure pulse reaches end of muffler, it reflects a backpressure pulse. This encountres outgoing exhaust flow and opposes it. Due to larger flow-volume of exhaust going out, backpressure pulse takes path of least resistance. It’s squeezed out to edges along wall of pipe where exhaust flow is slowest and weakest.

So lip at end of collector is to prevent this backpressure pulse creeping back along outside edges of pipe from flowing back into cylinders through exhaust valve. This would oppose incoming fresh air and may even push it backwards into airbox. Thus causing less efficient cylinder filling.

Another way of providing barrier lip to backpressure pulse is at exhaust port-to-pipe junction. Measure exhaust-port diameter on 2012 engine and you may find that it has smaller ID than 2012 exhaust-pipe flange. Honda probably found that single lip after 2016 collector may work better than individual lips on each header-pipe at exhaust port.

Too much of anything will hinder performance. You may find having dual-lips at 2012 exhaust port and after 2016 collector may not work as well. Should really measure exhaust port ID of 2016 engine and compare to header flange diameter. You may find that Honda has tuned 2016 headers to match 2016 engine specifically. To get optimum performance from 2016 headers, you’ll want to install 2016 engine. Using 2016 header on 2012 engine may result in lower performance than 2012 header.

Look up Helmholz resonance. Exhaust operates more like pipe organ than garden hose.

 

If I'm looking for more low- mid range torque just keep these then?
your saying the 08-11 stock headers without the reducer may not be any better?
just wondering if this reducer piece is reducing performance in any way because it's a little more restrictive?

 

Restriction isn’t a factor in exhausts because they’re not constant flow devices like garden hose. If you want more low-end torque, then many tuning variables need to be adjusted, not just exhaust:

- exhaust valve operational.
- 4-2-1 tri-Y header
- camshafts designed for torque with higher lift, less duration, less overlap than current ones with earlier intake-valve closing
- adjustable cam gears to fine-tune
- smaller valves to increase mid-range air-velocity and cylinder filling
- longer intake trumpets on intake manifold
- longer, smaller diameter runners on intake manifold
- dyno-tuning to optimise all of the above

 

Ok, im talking all stock motor, intake and exhaust with just a slip on.
Sounds like my best option for me is prob slip on muffler and just keep stock headers with reducer and dyno tune?
In your opinion the 08-11 header without the reducer will prob be a waste of time?

I wonder why all bike manufacturers don't use this reducer?
is it just on this gen cbr 1k (12-16) to go with the engine design is why? Hmm?

 

Thanks for all your replies, very informative.
I'm not planning on building the engine or anything major. I just wanted to make sure this reducer on the header (which I've never seen before on other headers and thought might could reduce performance because it's there for emissions,ect)..would not hinder performance with a slip on and tune. Thank you