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Discussion Starter · #1 ·
My primary airbox (plenum chambre? the box sans filter that's also the air intake) has two holes drilled through at the bottom, around 10 mm in diameter. They appear to be drilled by a home mechanic and not from the thing left the factoru, but I'm not sure. Could anybody tell me if I should close them up or retain them?
 

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Air Box

My primary airbox (plenum chambre? the box sans filter that's also the air intake) has two holes drilled through at the bottom, around 10 mm in diameter. They appear to be drilled by a home mechanic and not from the thing left the factoru, but I'm not sure. Could anybody tell me if I should close them up or retain them?
No worries, they are also in my air box. Presume they are to secure the California emission kit which sits in this box on bikes sold new in that State.
They are very useful for securing an alternative engine breather filter, as I have done
 

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Discussion Starter · #3 ·
Pretty weird that tuners say there must be absolutely no leaks around the seams of the box when there two big holes on the box...
 

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No worries, they are also in my air box. Presume they are to secure the California emission kit which sits in this box on bikes sold new in that State.
Interesting thought - I just assumed they were drain holes to let water or dirt out (part of the box's function is to slow the air and drop large dirt particles)
 

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Discussion Starter · #5 ·
Drain holes usually comes with hoses attached to lead the mess away and down onto the ground. That, and finding the holes looking a bit homemade, made me wonder if the PO had drilled the holes himself to let more air in.
 

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Drain holes usually comes with hoses attached to lead the mess away and down onto the ground.
Only if the mess is - well - messy such as oil or gas, not usually for water or small amounts of dust / dirt
 

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Air Box

Pretty weird that tuners say there must be absolutely no leaks around the seams of the box when there two big holes on the box...
Any amount of holes in this particular 'secondary' airbox would make no difference to engine tune. In fact many have removed them or made tool storage capacity after disconnecting the joint between the two air boxes.
They are only there for asthetic reasons, like EU inlet noise restrictions and to hold the emission control equipment on California bound bikes.
 

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Any amount of holes in this particular 'secondary' airbox would make no difference to engine tune. In fact many have removed them or made tool storage capacity after disconnecting the joint between the two air boxes.
They are only there for asthetic reasons, like EU inlet noise restrictions and to hold the emission control equipment on California bound bikes.
This is not quite true - other than the fact many have removed them. The Tbird isnt very sensitive to this box being modified or leaking - unlike the other T3's where the secondary boxes make a lot of top end difference. This box does tune the intake length which will affect top end performance a little - though arguably opening up the filter box will have better positive affects. Just removing this box (and doing nothing else) will have a small negative affect on performance. It will also make the bike's intake louder and your filter will get a little more dirty. This box's prime functions are:

1. to tune the inlet length - affects performance curves.
2. to reduce inlet noise
3. to provide a reservoir of still air for the inlet which helps give reliable performance in all road conditions
4. allows inlet air to slow and drop larger dirt particles before heading to the filter.
 

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Secondary Air Box

This is not quite true - other than the fact many have removed them. The Tbird isnt very sensitive to this box being modified or leaking - unlike the other T3's where the secondary boxes make a lot of top end difference. This box does tune the intake length which will affect top end performance a little - though arguably opening up the filter box will have better positive affects. Just removing this box (and doing nothing else) will have a small negative affect on performance. It will also make the bike's intake louder and your filter will get a little more dirty. This box's prime functions are:

1. to tune the inlet length - affects performance curves.
2. to reduce inlet noise
3. to provide a reservoir of still air for the inlet which helps give reliable performance in all road conditions
4. allows inlet air to slow and drop larger dirt particles before heading to the filter.
1. Can't go with that one as it had no effect on my bike on a 300 mile run through some scenic South Island Country Roads. If anything, the machine performed better at higher cruising revs and was more throttle responsive. This was a trial before 'cutting' off the top of the box in preparation for conversion too a toobox. (Which I haven't got around too yet)!

2. Yes, fully concur.

3. When travelling at speed with high throttle openings there certainly would be no still air in that box. The three carbs would be sucking like schoolboys creating a vortex of air movement, which leads to-

4. that air movement, and very disturbed it would be, would not allow any object to find a place of rest. In a very short space of time it would be lodged in the air cleaner. One only has to place a hand over the exhaust and 'blip' the throttle just feel how much air we are talking about.

Because of a breather modification it is necessary for the air box to pulled apart often on my bike. To date have found no debris, bugs or otherwise inside.
 

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the performance differences will be in the mid range and not hugely noticeable with a lower tuned engine such as the T3, but they will be there. As I said, opening up the filter box can give gains across the range that cancel this out, just removing the secondary box though will have a small negative. For more info on this and how / why they work see here: http://motorcycleinfo.calsci.com/Airboxes.html

I have removed rocks from T3 airboxes on more than one occasion, but yes they dont often catch much debris.
 

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Resonant Airboxes

the performance differences will be in the mid range and not hugely noticeable with a lower tuned engine such as the T3, but they will be there. As I said, opening up the filter box can give gains across the range that cancel this out, just removing the secondary box though will have a small negative. For more info on this and how / why they work see here: http://motorcycleinfo.calsci.com/Airboxes.html

I have removed rocks from T3 airboxes on more than one occasion, but yes they dont often catch much debris.
Great article Mick, the math left me for dead! At the end of the day, they are talking main air box, that is, the one which contains the filter. I still do not believe our bikes would have a set up such as they have, i.e the 'primary' box unless it was for quieting down induction noise/fitting emission control.
 

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Great article Mick, the math left me for dead! At the end of the day, they are talking main air box, that is, the one which contains the filter. I still do not believe our bikes would have a set up such as they have, i.e the 'primary' box unless it was for quieting down induction noise/fitting emission control.
Its all part of the resonator, (ie although its split in two its all part of the airbox) but as I said before with these detuned bikes its not going to make huge differences just on the fringe. This is not true on the non-classic T3's though they suffer much more noticeably if there are problems with any part of the intake system.
 

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Its all part of the resonator, (ie although its split in two its all part of the airbox) but as I said before with these detuned bikes its not going to make huge differences just on the fringe. This is not true on the non-classic T3's though they suffer much more noticeably if there are problems with any part of the intake system.
So...

I'd assumed that you had to keep the whole airbox, or replace it completely via pods or similar. This is new to me. And the idea of reclaiming that space for a small toolkit or tire-repair pouch appeals...

Would a carb re-jetting make everything kosher again after removing this section, or is it an irreplacable loss at high revs that we're talking about? Or, am I misunderstanding the issue?

Also: on a bikebandit schematic, or reference to the Triumph service manual page, could you be clear about which part of the box can be ditched? It's not intuitive to me which part is being referred to. Or even a photo with an arrow pointing at it, frankly?
 

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Its actually mid range that is affected - arguable how much you would notice on these bikes when riding, though you would likely see it on a dyno.

If you were to open up another hole and rejet you would probably gain much more than you lost. Many of us have done this now (yes including me - I have killed my resonator too) without too many ill effects and a group of us have homed in on a setup that works quite nicely and adds a good amount of poke to the bike....

Roughly the base setup on keihin bikes is this:

Drilled 3x22mm holes in the right hand side of my new K&N equipped airbox. Fitted Thrux needles, 40 pilots and 115main jets, disconnected the aux airbox, set the mixture screws at 2.5 turns
I did consider the idea of doing the math and working out how to get a better flow through the original box while maintaining the resonator but it made my brain hurt too much! :D
 

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How much of this goes out the window if I still use the OEM filter?
probably not much if its fairly clean - though you might end up a bit rich. A K&N is only about $30 on ebay
 
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