Larger Airbox For Ty 175

[pschrauber]

Hi,

I' am rebuilding my twinshock TY, this is a long time project, whenever I have time I do something for the bike .... Anyway the airbox of the TY 125 / 175 is very tiny it has more likely the size of a can of sprats then a airbox for a 175 to 200cc motor. A larger one should improve power output.

Can any one tell me where I may get a larger capacity airbox for my TY, also some stories / how to ... for custom made air boxes would be very nice too.

Many Thanks

Patrik

[cleaner]

Just cut the top off. Leave the part with the four screws and the criss cross to hold down the filter.

[woody]

A larger one should improve power output.

I don't understand why? I could if the engine was struggling to get air due to the airbox restricting airflow, but it doesn't. The TY175 engine doesn't have flat spots and it will rev out cleanly so it must get enough air. A larger airbox won't allow it to draw more air than it needs? The airbox on my KT250 was smaller than a TY airbox but still provided the 250 motor with enough air.

I've ridden a 300 Fantic with a large volume airbox and flatslide carburettor and it was no more powerful than a standard bike. The standard bike actually felt better...

[pschrauber]

That is one good idea. I believe it will work very good when I also take out all the restricting plastic tubes inside the air box where the intake is located.

But the bike will snorkle like hell and the noise will increase a lot, that is not so nice for my and others ears. I personal like quite and good sounding bikes.

With a cover / panel the airbox keeps the bike also quite, something I don't want to miss.

Photos of self build airboxes would be nice ..

[woody]

This is one I made for a 320 Majesty using a modern airfilter but 175 could be done the same. I did it not for performance but for the ease of removing the airbox for maintenance because the original airbox is a lot of work to remove. Also it was broken.

There was no difference with performance.

[pschrauber]

@woody: Thank you for the pictures.

To the question is air flow a task and why bigger airbox can be an improvement,

here some math:

engine capacity: 175cc

rpm: 1.250 (just above idling)

rpm: 3.000 (lower mid range)

(engine capacity) 17 5cc x rpm = air volume per minute

0,0175 m³ * 3000rpm = 52,5l/min

with a diameter of 22mm the air has an speed of 23,0m/sec or 138,11 m/min which is a speed of around 83km/h.

0,0175m³ 1250rpm = 21,9l/min

with a diameter of 22mm the air has an speed of 1,0m/sec or 57,61 m/min which is a speed of around 35km/h

In this speed range any edge, ridge in the air flow and yes also the capacity of the airbox makes a difference.

For comparison:

Drive your car just 35km/h and hold out one hand and turn the hand surface against the airstream and you will see.

I think this pictures very well the dynamics you have inside the intake carb and airbox as it is easy for you to try out

how much influence a proper design intake system has.

Sorry for the math I tried to make it as easy as possible I will not bore anyone here more with the physics then I did already ... correction see bold

Edited April 1, 2013 by pschrauber

[feetupfun]

Patrik, there are some errors in your explanation. I noticed the following straight up and stopped checking the rest:

175cc is 0.175 litres, not 0.0175 litres

2.3 m/sec is 8.3 km/h, not 83 km/h

I also think that the proof of the design of the TY175 airbox lies in the fact that the standard competition version of the TY175 has a wonderful free-revving characteristic.

From what I understand of what you are saying about your bike, there is a rubber snorkel on the airbox. Please be aware that the standard competition TY175 as sold around the world as model 525-xxxxxxxx, did not come with that snorkel, but road-going Ty175 models such as the 1N4-xxxx did have the snorkel, and the snorkel probably does cause a bit of additional drag to the airstream.

[feetupfun]

I know that some people modify their TY airbox by removing the lid and fitting a flat piece of foam across the top instead of the foam sock-on-core that is standard. One weakness with this is that the velocity (and pressure drop) of the air through the foam is increased by the reduction in surface area of the media. Another consideration is that the smaller a filter is, the quicker it becomes clogged with dust, in dry conditions (very important where I ride).

The modern trials bike filter in Woody's Majesty photos is a basin shape which increases the surface area compared with a flat piece of foam

[woody]

Patrick, I can't argue with your physics as I have no qualifications in that subject. I can only speak from experience.

The 300 Fantic I tried with specifically designed large volume airbox to boost performance was no better than a standard bike. When I've run my Ossa with no airbox, just a piece of gauze across the carb intake, there was no difference in performance and you can't get a better airflow than straight into the carburettor with no airbox in the way?

The engine can only draw as much air as it needs and if the stock airbox doesn't stop it drawing that air it's difficult to see how a bigger one will make any difference - like the 300 Fantic example, or my 320 Majesty?

[mattylad]

We punch out the restriction at the bottom of the air box which is spot welded on by using a large socket and hammer from the under side.

then we fit a Montesa 315, or Yam mono filter.

Finally fabricate an alloy plate which just covers the perimeter of the air box lid and screw down.

[pschrauber]

Patrik, there are some errors in your explanation. I noticed the following straight up and stopped checking the rest:

175cc is 0.175 litres, not 0.0175 litres

2.3 m/sec is 8.3 km/h, not 83 km/h

I also think that the proof of the design of the TY175 airbox lies in the fact that the standard competition version of the TY175 has a wonderful free-revving characteristic.

From what I understand of what you are saying about your bike, there is a rubber snorkel on the airbox. Please be aware that the standard competition TY175 as sold around the world as model 525-xxxxxxxx, did not come with that snorkel, but road-going Ty175 models such as the 1N4-xxxx did have the snorkel, and the snorkel probably does cause a bit of additional drag to the airstream.

No errors I believe, but sadly I mixed up the units. Air flow is calculated in m/s or m/min and I had to transform the ccm in m³: 175cc are 0,0175 m³ or 174 x 10^-4 but m³ is difficult to imagine so I recalculated it in Liter. I see it's not wise to combine translate and math ... too much tasks at once ... The output of 23 would right here I skipped the internal calculation about the medium flow rate thought first to show up with digits behind the comma but then messed with the comma ... anyway. 23m/s is the right outcome ! I will correct it. And there is another problem my RETURN button doesn't work when I use the editor here ???

Edited April 1, 2013 by pschrauber

[pschrauber]

To the size of the airbox, as more room you have as less bad influence from the pulsating airflow you will have inside the airbox, if you have a tiny airbox you might use resonators to deal with them as the airbox is a resonance/volume chamber so you can even adjust an engine with the size and geometry of an airbox. In short: as less complicated ways the air has to flow towards the cylinder as easier it is for the engine to get the right amount of mixture ... (The return button doesn't work in this forum ...)

[andy.t]

I made one several years ago out of fibreglass, I thought it was an improvement on the original, I found the old link for when I posted it here some time back. If your interested its here http://www.trialscentral.com/forums/topic/21102-ty175/

[tee_why]

We punch out the restriction at the bottom of the air box which is spot welded on by using a large socket and hammer from the under side.

then we fit a Montesa 315, or Yam mono filter.

Finally fabricate an alloy plate which just covers the perimeter of the air box lid and screw down.

Pretty much my version also removing center, used Beta EVO filter, cut out inside original lid the spider arrangement inside top of lid, drill a couple of large holes on the sides of the lid, trying to maintain at least some water resistance!

[jc2]

I'm a bit of a skeptic about the value of larger airboxes on Ty175s too. I've often wondered if its any more than placebo effect.

So long as the airfilter area & inlet pipe (carb mouth to airbox) are sufficient to flow freely at max rpm, its difficult to see how airbox volume would have much effect unless the airbox lid/inlet is quite restricted

Patrik, you haven't accounted for volumetric efficiency in yr calcs, which is way below 100% in a 2T, especially one set up for trials with a small carb, small ports & little/no suction pulse from the exhaust. And its even lower at part load, part throttle opening & below peak torque rpm (or above it for that matter).

So airspeed will be much lower than you calculate

Also, I'm not convinced of the relevance of air speed at the carb throat/venturi anyway, even if you could calculate it accurately. I'd have tho't it more relevant in the inlet pipe, which has cross-sectional area 3.7 times that of carb venturi, or at the bottom plate/restrictor in the airbox which has cross section about 2.7 times that of the venturi. Air speed is much reduced at those points compared to carb throat (since its inversely proportional to area).

And as I understand it resonance effects come more from the inlet system volume on the other side of the carb mouth - ie crankcase volume + inlet tract volume (to the carb inlet/mouth).

I'd have tho't the main pressure drop (& hence performance loss) in the inlet system upstream of the throttle (carb slide) is normally the air-filter element. In the TY175 that bottom plate in the airbox may also contibute, so some slight advantage may be gained from improving those 2 areas, tho I suspect it'd mostly be at hi rpm. If there was any improvement in throttle response at low rpm, you'd nearly have to be Magic Mick to notice it.