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Discussion Starter #1 (Edited)
This job is not something you can easily tackle if you don't have access to an engineering workshop or a similar set up at home. Ideally you need a lathe (not essential though) and a welder, preferably of the TIG type if you want a neat job.

Regardless of that, here's a little how-to:

Remove the slip on and then the header pipe once you have uncliped the connection for the O2 sensor. Easily accessed on the RH side once fairings are removed. The nuts that hold the header pipe flanges on take a 12mm socket and are not tight because there is a compressible washer between the exhaust ports of the head and the two pipes.

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Score a line at 90 degrees across the weld that joins the rear piece of the header (the bit that goes to the muffler) onto the main body that houses the CAT. You will use this line as a reference for when you go to weld the assembly back together again. Now cut through the weld with a hack saw or even better use a 1mm wide cut-off disc in an angle grinder if you have one.

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At this stage you can now try and remove the CAT material but I found it too difficult so cut the front part of the header off from the main body as well:

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This enabled me to hold the canister in the chuck of a lathe and drill a 1" hole through it:

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That gave me enough room to get a boring bar in there and bore the rest of the CAT material out:

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By using a lathe you end up with a nice clean job. There are actually two CATs in there, separated by a 3/4 inch gap. I turned the body around in the lathe to get at each end.

P1000148.JPG

Then I spot welded the front header section back to the main body and fitted it to the bike. The slip on was next fitted to the bike with the rear section of the header slipped inside it. This allowed me to line everything up before finally putting a couple of careful spot welds on the rear join of the body. I used a gas welding plant for this so there were no sparks but you need to be real careful where you wave that torch! Have a fire extinguisher sitting right beside you.

Lastly I removed the whole assembly as one piece again ready to be fully TIG welded. I will get a mate of mine to do this as he's neater at it than me :)

P1000150.JPG

There is bang on one lb (450 grams) of CAT material in there.

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Is there any particular reason that you cannot just cut the pipe in two spots, and weld in an open section of tubing, disposing of the cat entirely?

As a side note, I also usually like to have new exhaust gaskets on hand...just in case there is an issue. I have seen some pretty gnarled up ones, from new.
 

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Discussion Starter #4
Is there any particular reason that you cannot just cut the pipe in two spots, and weld in an open section of tubing, disposing of the cat entirely?
Yep, good idea if you can get your hands on the right diameter pipe. I live in a small town with no steel and tube shop.

Can you explain what this does pros and cons? Might have a shop do it
I'm no expert but for me weight is a big one and also less restriction to the exhaust flow. Once I get a freer flowing slip on and a tune to match then I will reap the benefits of this job.
 

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Just my 2 tech-cts...

The first statement must be: A naturally aspirated engine needs a certain back pressure because otherwise it can lose a lot of torque in the lower and medium rpm range.
But we might as well say: The less back pressure, the more power can be achieved in the high(er) rpm range - in principle.

When removing the catalytic converter, it behaves similarly to other changes in the intake and exhaust area that change the gas dynamics (generally speaking).
As a rule, a different flow velocity of the exhaust gas is required to ensure that the delivery rate of the engine remains optimal. The flow velocity and thus the engine rpm must normally be increased for this purpose.
In practice this can mean (and will in most cases, but not necessarily - depending on the engine) loss of torque in the low and medium rpm range. As opposite, however, it has more torque (in direct comparison per rpm, not absolute) in the upper rpm range, which ultimately means more power.
However, the engine must also overall be tuned to higher rpm's, otherwise the potential is wasted because - simply put - the intake side of the engine "seals off" and does not allow these high speeds at all (remember: widened Throttle body, etc.).

Therefore - those who have already done rpm tuning will benefit from optimizing the catalytic converter from a performance point of view (removal is permitted for road operation).
With the standard engine, you won't feel the horsepower you get from the top, but subjectively feel the disadvantages in the low to medium rpm range more.

Important: We are talking here about a cat replacement, i.e. a specially adapted replacement pipe or several replacement pipes instead of the catalytic converter(s). These statements must not apply for removed ceramic catalytic converters or other wild dummy constructions (the flow behaviour of the gas in most cases is different).

Read the quote from what @Warp12 said here http://www.ninja400riders.com/forum/9-ninja-400-general-discussion-forum/1497-throttle-bodies-ex400-vs-400r.html#post13459
"Port design, valves, taper, cams, etc...all contribute. Everything functions as a system. As any modern cylinder head porting company will tell you, a bigger port (or TB) is not always better. Now, if you are porting the head, changing the cams, exhaust, rpm limit, etc...well, then all bets are off."
I was thinking it might work better by replacing the cat with a smaller diameter pipe. The cat is pretty large, and it looks well-designed to have a minimal effect on flow. Most of the after market pipes have very gradual increments in pipe diameter. For example this Spark system for my gf's 300:



But, in the end, the proof is in the pudding...interested to see the results. :)
 

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Discussion Starter #6
I was thinking it might work better by replacing the cat with a smaller diameter pipe. The cat is pretty large, and it looks well-designed to have a minimal effect on flow. Most of the after market pipes have very gradual increments in pipe diameter.
Yeah I was thinking same, you would possibly get better velocity of flow from the smaller constant diameter pipe rather than the (now) empty bomb?.
Someone with more knowledge of exhaust tuning may be able to offer input.
 

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Discussion Starter #7
@Kiwi Rider, I've thought that the 'master of always quoting me' would by himself come up with the tip that you could replace the O2-Sensor with an eliminator since it's quite worthless now and therefore also doesn't interfere with the ECU any longer.
You can read about that here: http://www.powercommander.com/downloads/211/install/optimizer/eng76423007.01.pdf
This sensor is also responsible for unstable driving in the closed loop circuit and must be replaced when you remap the fuel-maps in the ECU (without the resistor the ECU is throwing an error).
And what you also should be looking for already, if you really have the plan to reflash the ECU of your bike, is a replacement for the 'K-CAS' Kawasaki-Clean-Air-System, because this must be done also for not giving wrong measurements with the secondary air injection into the exhaust.

So now let's wait for his quote here.
Why is the O2 sensor worthless now that I have removed the CAT?

Also: Being a Ninja noob I have never heard of the Kawasaki Clean Air System. Is this the same as the PAIR valve I mentioned in my 'weight reduction' thread as yes, I am thinking of removing this. Will add a picture I took on the wkd just to check we are talking about the same thing. Any thoughts on removing this?

Lastly, If someone is quoting you then that means you have said something thought provoking or noteworthy rather than something meaningless. :)

P1000166.JPG
 

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Why is the O2 sensor worthless now that I have removed the CAT?

Also: Being a Ninja noob I have never heard of the Kawasaki Clean Air System. Is this the same as the PAIR valve I mentioned in my 'weight reduction' thread as yes, I am thinking of removing this. Will add a picture I took on the wkd just to check we are talking about the same thing. Any thoughts on removing this?

Lastly, If someone is quoting you then that means you have said something thought provoking or noteworthy rather than something meaningless. :)

View attachment 1325
As for the PAIR valve, here is a good explanation (although on a different bike):


Brock is a pretty sharp guy, with years and years of racing/tuning experience. He breaks it down in layman's terms, I think.

It will throw a code upon removal, almost 100% assured. You can get this to go away, again, through the ecu. :)

It used to be called Kleen on the Kaws...but same function, basically, whatever they call it.
 

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Discussion Starter #9
As for the PAIR valve, here is a good explanation (although on a different bike):

https://www.youtube.com/watch?v=_xMykbzJWiQ

Brock is a pretty sharp guy, with years and years of racing/tuning experience. He breaks it down in layman's terms, I think.

It will throw a code upon removal, almost 100% assured. You can get this to go away, again, through the ecu. :)

It used to be called Kleen on the Kaws...but same function, basically, whatever they call it.
Yes this is a good clip, have seen it before. Good to have it posted up for others though.

Not so sure if you can clear out error codes with an ECU reflash as the problem still remains. I would have thought fitting an in-line resistor could be a better option?
For example I have an error code from removing my EVAP canister. It reads
3A Purge valve malfunction, wiring open or short .
In my case it is wiring open because I have removed the purge valve solenoid. If I was to bridge out the wiring at the connector or just cut the connector off and join the two wires together it would be a wiring short but, (and I'm only guessing) if I was to fit an in-line resistor the ECU would possibly think the purge valve was still connected and the error code would be gone.

Any thoughts?
 

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Yes this is a good clip, have seen it before. Good to have it posted up for others though.

Not so sure if you can clear out error codes with an ECU reflash as the problem still remains. I would have thought fitting an in-line resistor could be a better option?
For example I have an error code from removing my EVAP canister. It reads
3A Purge valve malfunction, wiring open or short .
In my case it is wiring open because I have removed the purge valve solenoid. If I was to bridge out the wiring at the connector or just cut the connector off and join the two wires together it would be a wiring short but, (and I'm only guessing) if I was to fit an in-line resistor the ECU would possibly think the purge valve was still connected and the error code would be gone.

Any thoughts?
Yes, the ECU can be flashed to ignore the issue with removing the valve. Check 8:30 in the video I referenced. For my 14R, I ordered a resistor plug to make it "think" the valve is there...now if I could only figure out where I put that part, since we moved, lol! :)

Oh, forgot to add...be sure to verify with the ecu flashing service...not all features are available early in development, from my experience. But this one is pretty basic, I think.
 

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From my experience, anyway:

Whether you use a block-off plate(s), plug the hose, remove the valve and plug the stock cap(s)...it's all the same, performance-wise. You are blocking the ability to inject air.

I have block-off's on some bikes, and plugs on others...all the same, minus the weight savings, and any ecu codes you may encounter. :)

Also nice to get that clutter out of the way, on top of the engine!
 

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Discussion Starter #12
... the Block Off Plate really blocks the secondary air into the exhaust and here's a link: https://www.sportbiketrackgear.com/driven-block-off-plates-kawasaki-ninja-400-2018/
Thanks for the link. The plate is $26.99 which is OK but the thieving sods want another $43 for postage to NZ! :eek:
So I wont be paying $70 for a plate that I already have on the bike except mine has a short pipe on it for a hose to slide over, which I can easily cap off.

For those not sure what we are referring to its the silver plate with two bolts in this photo:

P1000166.JPG
 

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So im thinking of doing the same as you Kiwi, mainly due to being pulled over all the time, so doing it your way will allow it to at least seem like the cat is still there even tho its hollow :) Im just thinking will the part of the pipe be to open? will there be to much airflow and not enough back pressure? I know the aftermarket headers are actually bigger than the stock headers so im thinking it should be fine but im not sure, hows the throttle response? better or worse? is the torque lower ?
 

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Discussion Starter #14
So im thinking of doing the same as you Kiwi, mainly due to being pulled over all the time, so doing it your way will allow it to at least seem like the cat is still there even tho its hollow :) Im just thinking will the part of the pipe be to open? will there be to much airflow and not enough back pressure? I know the aftermarket headers are actually bigger than the stock headers so im thinking it should be fine but im not sure, hows the throttle response? better or worse? is the torque lower ?
I felt the throttle response was slightly better and that it was pulling better through low and midrange but it was negligible.
The main reason I did it was for a weight saving of nearly half a kilo.
The two cats are a bit of a $hit to get out as they dont slip out and then getting correct alignment when you tack it all back together before fully welding is important and a bit fiddly too .
 

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I felt the throttle response was slightly better and that it was pulling better through low and midrange but it was negligible.
The main reason I did it was for a weight saving of nearly half a kilo.
The two cats are a bit of a $hit to get out as they dont slip out and then getting correct alignment when you tack it all back together before fully welding is important and a bit fiddly too .
to late lol tore the CAT apart and ripped everything out, will weld back together at work in a few hours, at half a kilo loss and at least a 5% performance gain im sure it will be nice :) just waiting for front sprocket and chain to arrive to install, wont be able to ride bike for at least 7 days until all the rain stops, either way when I do I will be able to test the sprockets and full exhaust system all at once :) this will now put me at 10kgs of weight saving as well hehe Just helped a mate install a full system on a R3 and im glad the 400 uses a CAT which is basically like a thicker pipe because that R3 cat is just stupid haha.
 

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Discussion Starter #16
to late lol tore the CAT apart and ripped everything out, will weld back together at work in a few hours, at half a kilo loss and at least a 5% performance gain im sure it will be nice :) just waiting for front sprocket and chain to arrive to install, wont be able to ride bike for at least 7 days until all the rain stops, either way when I do I will be able to test the sprockets and full exhaust system all at once :) this will now put me at 10kgs of weight saving as well hehe Just helped a mate install a full system on a R3 and im glad the 400 uses a CAT which is basically like a thicker pipe because that R3 cat is just stupid haha.
Sounds like a plan, what will you be running for back half of exhaust system?
You do realise your bike will never be as light as mine Lol :devil:
Radiator fan is 3/4 kilo for a start.
 

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Sounds like a plan, what will you be running for back half of exhaust system?
Kiwi, did you find the actual cat only occupied about 3 inches on the O2 sensor side of the larger diameter section of the pipe?

I cut mine on the mid-pipe side first, with plans to cut on the weld at both ends, and noticed it was buried closer to the 02 sensor and header down pipes, so I cut on the weld near the o2 sensor......and found, using my 14" chop saw with a metal blade, that it was much harder to cut through than the other side(is the housing for the actual cat screen/disc titanium), as if I was cutting through titanium or something much harder than the steel header, requiring a slow cut speed.

Unless I truly dulled the blade that much quicker running it at a higher RPM then they call for, since my saw runs higher RPM and using a router router speed control dial will burn up the motor running at a lower RPM.
I did make the first cut without any cutting oil.........which running higher RPM I should have......shame on me, might have killed a $80 blade on one cut.....lol hopefully not.....

Anyway, I cut it open and found the actual honeycomb cat was about a 3 inch thick disc.
I was fortunate enough that exactly where I cut that front weld it cut into the welds for the cat inside the pipe and I taped it out in about 10 seconds with a large square punch.
I pushed it straight out the opposite side of the header pipe (so slip on/mid pipe) side as one solid part.

No honing, turning, drilling, cutting, hacking etc. to get it out.......was so darn easy I felt discouraged that cleaning up the cuts, welds and chamfering/beveling the edges of the cuts, to weld it back together will be the hardest part.......so I took a break from it for a few days.....lol

So a tip to others would be, if you cut it on the front weld, cut it on the weld but closer to the back side of the weld, you might also cut the weld for the inner cat screen and can just push it right out the other end ;)
 

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Discussion Starter #19 (Edited)
Kiwi, did you find the actual cat only occupied about 3 inches on the O2 sensor side of the larger diameter section of the pipe?

I cut mine on the mid-pipe side first, with plans to cut on the weld at both ends, and noticed it was buried closer to the 02 sensor and header down pipes, so I cut on the weld near the o2 sensor......and found, using my 14" chop saw with a metal blade, that it was much harder to cut through than the other side(is the housing for the actual cat screen/disc titanium), as if I was cutting through titanium or something much harder than the steel header, requiring a slow cut speed.

Unless I truly dulled the blade that much quicker running it at a higher RPM then they call for, since my saw runs higher RPM and using a router router speed control dial will burn up the motor running at a lower RPM.
I did make the first cut without any cutting oil.........which running higher RPM I should have......shame on me, might have killed a $80 blade on one cut.....lol hopefully not.....

Anyway, I cut it open and found the actual honeycomb cat was about a 3 inch thick disc.
I was fortunate enough that exactly where I cut that front weld it cut into the welds for the cat inside the pipe and I taped it out in about 10 seconds with a large square punch.
I pushed it straight out the opposite side of the header pipe (so slip on/mid pipe) side as one solid part.

No honing, turning, drilling, cutting, hacking etc. to get it out.......was so darn easy I felt discouraged that cleaning up the cuts, welds and chamfering/beveling the edges of the cuts, to weld it back together will be the hardest part.......so I took a break from it for a few days.....lol

So a tip to others would be, if you cut it on the front weld, cut it on the weld but closer to the back side of the weld, you might also cut the weld for the inner cat screen and can just push it right out the other end ;)
Good tip. From my original post:
"There are actually two CATs in there, separated by a 3/4 inch gap."
 

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God tip. From my original post:
"There are actually two CATs in there, separated by a 3/4 inch gap."
Dang....sorry I missed that.........mine must have been the lightweight racing edition.........there was only one cat inside mine :)

I grabbed a spare header pipe off eBay for cheap and used it as the donor....was never cut open or modified, so its odd it only had one in it.......off a 2019 N400
 
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