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Old September 4th, 2018, 12:50 PM   #1
memphisninja
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Stock 2-2 into 2-1?

Can I just remove one exhaust and cap that side? I see that there is a pipe that interconnects the 2 headers. What would be the downside to just running 1 stock exhaust with the other side capped? Would it be to restrictive or cause one cylinder to run richer (or leaner?) than the other? Would I have to cut off the one header side and weld it into just the one pipe? I have an 06 ninja 250. Thanks
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Old September 4th, 2018, 01:34 PM   #2
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Nope, won't work. Exhausts rely on very specific pulse velocities and pressure waves as dictated by pipe-length and diameter. Optimum header-length before merge is 46-56cm (based upon speed-of-sound). Pipe diameter should match displacement & volume flow.

Stock exhaust is highly optimized for stock engine. Changing any parameter will lower/raise HP/TQ level and their peak RPM-points. Racers adjust these in tiny increments to optimize performance in exact RPM-ranges they use.

What you are doing is stuffing 2-cylinders worth of flow into passages designed for 1. Not to mention non-laminar flow caused by capping and sharp transitions through H-pipe. What you want to do to make this work effectively (maintains existing performance or improve it), is:

1. examine and measure pipe-diameters & lengths of OEM new-gen exhaust, note length of header to merge. Measure pipe-diameters after merge. Cut open new-gen muffler and measure internal pipe-diameter

2. examine and measure same with aftermarket 2-1 new-gen exhausts from Tyga and AreaP.


After doing #1 & #2, you'll get good idea of what design parameters, such as lengths and diameters of various sections are required to get good performance out of 2-1 exhaust. Here's link to similar procedure you're thinking of that didn't work: https://www.ninjette.org/forums/showthread.php?t=322941 . Header-lengths way too short before merge, and pipe-diameters not large enough after merge for 2-cylinder's worth of flow.

You'll want to optimize design for maximum-flow in RPM-range you want to use, then adjust carbs for max-power AFR in that range (13.5:1 is target for NA engines). Then slowly advance ignition to achieve MBT. Best done on dyno with fully-programmable EFI system with 3D mapping of fuel & ignition.
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Old September 4th, 2018, 02:37 PM   #3
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You would need a proper collector to join the 2 header pipes into 1 exit pipe (of the correct size).

No good way to modify the stock 2-into-2 to a 2-into-1.
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Old September 4th, 2018, 03:44 PM   #4
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dude. This bike has been on the market since 1988 and you still see the need to ask a question that has been answered 10,000 times over.

Do some googling. Damn.
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Old September 4th, 2018, 06:04 PM   #5
memphisninja
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Quote:
Originally Posted by choneofakind View Post
dude. This bike has been on the market since 1988 and you still see the need to ask a question that has been answered 10,000 times over.

Do some googling. Damn.
Well why the hell isn't a 2-1 exhaust available? I've owned bikes from the 70's and they still make exhausts for them... For such a common bike, it annoys me that there is only pipes available for the newgen.
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Old September 4th, 2018, 07:06 PM   #6
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here's a post from last week or so with a little insight. (and pics)
https://www.ninjette.org/forums/showthread.php?t=322941
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Old September 4th, 2018, 07:18 PM   #7
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Quote:
Originally Posted by memphisninja View Post
Well why the hell isn't a 2-1 exhaust available? I've owned bikes from the 70's and they still make exhausts for them... For such a common bike, it annoys me that there is only pipes available for the newgen.
I suspect there's not much market for such upgrades. The ones buying these upgrades are racers and pre-gens have stopped being raced long time ago. Even new-gens are on their last legs with 300s and 400s becoming more popular.
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Old September 5th, 2018, 02:18 AM   #8
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Here's an example of how to do it right so there's performance gain. Note larger diameter of pipe aftrr merge collector to deal with twice flow volume.

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