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Street Twin Airbox

25K views 32 replies 16 participants last post by  smoove7410 
#1 ·
Last night I was bored so I got down to trying to remove and clean out my Airfilter. After my trip to Utah earlier this year I was certain it would be caked with dust and need a little attention.
For anyone that hasn't done this yet, you only need a t20 star wrench.

Remove the breather hose and its bracket from the airbox plate, then the remaining four screws holding the plate on should be easy to access. The air filter slides right out of this hole (you may need some needlenose pliers to "encourage" it out of place)

Here's the interesting part: while I had the filter out and the airbox open I started up the bike just to see how it behaved with an "unrestricted" intake. As expected, much different (I hesitate to say better without proper testing) performance. Throttle response was excellent. Exhaust note out the V&H pipes was louder with a bit of extra "bark" to it when blipping the throttle. I took it for a quick ride around the block like this and the bike just felt more alive. The stock airbox and filter serve an important function day-to-day of course but surely there has to be some intake mods in the works to get a little more character out of these machines. In the meantime, I may fool around with this further to see if there can be some sort of "bolt-on/off" intake improvements.

As always, chime in on the topic lads.
 

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#2 · (Edited)
Seeing the small size of the intake snorkel as visible in the second photo, I'm not surprised it ran better. Huge increase in air intake capacity. I'd imagine it'll be the first thing future tuners tackle.

I am dismayed however to see that the filter lid holding screw holes are not fitted with metal inserts. In time these holes will wear out. In a less penny-pinching World they would be fitted with this sort of thing:



Some quick-release thumb screws could then be added for tool-free filter inspection :):

 
#3 ·
I contacted K&N the other day to see if they are in the works of developing a high-flow air filter for the ST and T120 (they share the same OEM filter). Unfortunately, its a no go at this time. So instead I took measurements of the stock filter pictured above and tried to see if they make a filter for another bike with similar dimensions and this was the closest I could find:
http://www.knfilters.com/search/product.aspx?prod=YA-1602-U&pkid=3784265&rw=1
This is the replacement filter for a 2005 Yamaha xv1700 Road Warrior. The rubber/plastic would need just a slight amount of trimming to fit the stock Triumph filter cartridge, and this filter is about .5" thinner which shouldn't be an issue. Any danger in trying to make this work?
 
#11 ·
Ok, so this thread is almost a year old and K&N is now making a filter for the ST and T100/120

https://www.knfilters.com/search/ap...017&make=TRIUMPH&model=Street Twin&engine=900

This will increase flow through the filter to the throttle body. Gains could be found however (and without looking at the situation) and increase the odds of gains with the X pipes and slip on cans and with a proper tune if there are smooth transitions at the airbox opening and specially the airbox to throttle body transition.

food for thought...someone reach in there and feel out the situation.

The easier it is to fill the airbox with air and get it into the engine, the better a freer flowing exhaust will get the spent gasses out of the engine and complete the system.
 
#5 ·
DNA makes one:

https://www.e-dnafilters.com/produc...et-Twin-900-(2016)-DNA-Air-Filter-P-TR9N16-01

Also, in photo 2 from @Xtoff, Forchetto may be mistaking the breather hose with the snorkel. Or maybe not, if anyone knows the difference it would be him. Anyway the snorkel is visible in photo 2 but it is rearward (to the right) of the breather hose and much larger in diameter. The snorkel probably is not an air restrictor, but more of a sound baffle.
 
#9 · (Edited)
#16 · (Edited)
It will make a real difference, but it will be a pretty small one. I did the air filter after I did the cat delete, so for me, the difference was pretty tame in comparison to the exhaust change.

The reusable aspect of that filter is probably more of a factor than the performance gain. It should last the life of the motorcycle with routine cleaning.
 
#18 ·
All excellent observations here.
I have mucked about with A/F mixtures since, well many years ago lets say, most recently on a Yamaha MT07, (my first ECU equipped FI bike). With that bike I tried several approaches. My first approach was to install a Leo Vince under body CAT delete full system, opened up the complicated air box, deleted a snorkel ETC. and of course running a little lean got a lot of decel popping on the headers. My next step was to add a Booster Plug chip, and these really work, they have an air temp sensor that adjusts the A/F about 6% richer across the entire rev range and is compensated for ambient air temp. It is a good quick fix. I ultimately had the ECU flashed as I upgraded to a DNA Stage 2 filter and airbox cover.
Given you don't remove the CAT and we can't flash the ECU on the twin, I think using the booster plug+ DNA filter+ a more open pipe or not, would be a very reasonable solution to ensure a sufficiently rich mixture.
I noticed a big difference with the Booster plug in smoothness mid range power, and decel popping on the MT07. They are a relatively cheap initial fix compared to A piggy back fuel controller, which in my opinion, having done this before, and now riding A street Twin, would be a waste of money, UNLESS you go the route of a CAT delete and performance pipes, and Intake mods.
 
#19 ·
Just a thought....

If the cubic feet per minute intake flow using the same snorkle (T2201014) and Air filter (T2201057) shared between models has been considered sufficient by Triumph to meet the needs of a 1200cc engine, shouldn't it be surplus to requirements when it only has to deal with 900cc?


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#20 · (Edited)
Just a thought....

If the cubic feet per minute intake flow using the same snorkle (T2201014) and Air filter (T2201057) shared between models has been considered sufficient by Triumph to meet the needs of a 1200cc engine, shouldn't it be surplus to requirements when it only has to deal with 900cc?
CFM can remain the same on two different flow systems, each having a different intake shape. The shape of the intake and flow path affects the velocity and turbulence of the fluid, but not necessarily the CFM. The velocity and turbulence factors contribute to noise (among other things).

Kind of like how you can blow out a lung full of air, in one second. Then you can do it again, but shape your mouth differently, resulting in a whistle. Same amount of air moved during the same duration of time, just one had a different shape, and therefore sound.

As to why removing the snorkel results in additional power, that may have more to do with how certain velocities and turbulences affect the AF mixture, and how that changes the flame propagation during combustion. I don't fully understand all the physics behind that part of it, at least not well enough to explain it.
 
#21 ·
Thanks, perhaps someone will soon manufacture something along the lines of TTPs BREATH to replace the air box intake seal that grips the snorkel to assist intake flow. If a water spray guard is included to prevent unwanted ingress I cant see any negatives.


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#22 ·
Thanks, perhaps someone will soon manufacture something along the lines of TTPs BREATH to replace the air box intake seal that grips the snorkel to assist intake flow. If a water spray guard is included to prevent unwanted ingress I cant see any negatives.
I just removed the intake seal altogether when the snorkel came off. It serves no purpose once the snorkel is out.

https://www.triumphtwinpower.com/bo...ter-intake-cover-bellmouth-velocity-stack.php

As for the above linked bellmouth cover, color me skeptical that such a short length of intake accessory has any affect on power. We can't have it both ways: either the snorkel is the longest velocity stack you can get (and is therefore beneficial to making power) or it is better to just leave the airbox as open as possible, meaning that a bellmouth cover is counterproductive.

Most of the dyno testing I've seen suggest that airbox modifications, up to and including complete removal, do not make significant power gains.
 
#24 · (Edited)
FWIW, I lost peak HP after installing a DNA air filter.

I was typically around 54-55bhp with the stock filter and associated mods and now I’m peaking at 53.xx.

That number hasn’t risen with a PCV, whether using Auto Tune or custom maps. I can’t explain it, could be the weather or any other number of factors, but the Dyno has been consistent.

Doesn’t mean the bikes not running better. The curve is smooth all the way to redline, which it wasn’t before.
 
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