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@Duckman there is that little triangle opening made up between the frame and radiator at the front. There's no obstruction (or very little) in that area from the fairings...at least with the Norton GP fairings I have, I don't remember how it was with the Armour Bodies. This is not a good angle, but I designed my airbox to have the inlet just in front of that area so that air goes directly into it. I also made a "heat shield" out of Kydex that sits between the air box and the engine, but I honestly don't think it makes any difference. I know Spears claimed an increase in power from the one he sells, but I'm not sure I believe that. Or maybe it's just because of the way my airbox is made that it already keeps hot air out and there's no need for an additional shield? The one I made is about twice as big as the Spears one and doesn't fit with the stock airbox, only with mine.

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@Duckman there is that little triangle opening made up between the frame and radiator at the front. There's no obstruction (or very little) in that area from the fairings...at least with the Norton GP fairings I have, I don't remember how it was with the Armour Bodies. This is not a good angle, but I designed my airbox to have the inlet just in front of that area so that air goes directly into it. I also made a "heat shield" out of Kydex that sits between the air box and the engine, but I honestly don't think it makes any difference. I know Spears claimed an increase in power from the one he sells, but I'm not sure I believe that. Or maybe it's just because of the way my airbox is made that it already keeps hot air out and there's no need for an additional shield? The one I made is about twice as big as the Spears one and doesn't fit with the stock airbox, only with mine.

View attachment 21075
That little heat shield is I think, one of those good ideas but probably amounts to about 0.1 hp. :)
 

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Can I remove the front snorkels with out a tune? View attachment 21042
Yes you can change with out a tune good question though what are you going for. Some small changes would be if you go with a full exhaust mod the air box and get some velocity stacks. Go with a high Flow air filter. Get a ecu flash you can gain some hp. For the bike about 10 to 15 percent gain. It is nice. I have a extra air box not used just so I could mod one. And I have a full after market exhaust too. I was waiting to tune the back or get a aracer ecu with autotune. But the ecu flash is way cheaper and same results. Now I have a zx10r also and upgraded that and held back on the 400. So now I have the exhaust airbox just sitting in my room. But only have 200$ into it so might sell might upgrade.
 

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Guys,
Attached are photos of my air box modification that I did on my 2021 Ninja 400 "street bike".
I kept the longer velocity stacks. If you are not racing the bike, the longer stack will work better on a street bike where you are in the 4,000 / 7,500 rpm range.
If you open up the air box, you do need to reflash the bike. I also have a full titanium exhaust system on the bike.
On the flow bench, there is no air flow gain by changing to any other air filter, the stock air filter is so large, compared to the fuel injection internal ID that it's a no gain.
Yes, it will be louder!
BMHS
View attachment 21060 View attachment 21061 View attachment 21062
Hey bud. I’ve just bought a 400, and plan on buying a second one for track. So out of my 2 air boxes it would be wise to put the 2 long stacks in the street bike and the 2 short stacks in the track bike?
 

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Hey bud. I’ve just bought a 400, and plan on buying a second one for track. So out of my 2 air boxes it would be wise to put the 2 long stacks in the street bike and the 2 short stacks in the track bike?
For the street if you want economy don't change a thing one long one short as the ecu is already setup for that. For the track two short velocity stacks. A high performance airfilter and flash and weather or not you do a full exhaust.
 

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I’ve tried all the different combinations. I have one air box stock and one cut out. I’ve tried both long, both short, one of each, and now Spear’s super short stacks.

Even if you keep the box stock and use the short stacks you really need the ECU tuned to take advantage of it. Stock the ECU is tuned very different between the short stack cylinder and the long stack cylinder. Not only is the fueling different between the two cylinders but also ignition timing.
 
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