TY 175 airbox

[trialsrfun]

Am assisting with the restoration of a pretty standard Yamaha TY 175 into a bike that will be ridden in trials, is the air cleaner/airbox perfectly ok as is or are there performance improvements to be gained by changes or even replacing with a different set up?

[feetupfun]

If the motor, carby and exhaust is standard then the standard air box is fine. If you increase the engine capacity or improve the breathing then you may benefit from a freer breathing airbox

[sbest]

I've done some work on Yamaha Blasters, KTM and other 2 strokes and found there is much more than air restriction going on with the airbox. I've found many high flow aftermarket intake airboxs lose power, as do many of the "common sense" mods that are suggested on the internet. One guy does it without testing, reports on it or posts cool pictures and it takes off like wild fire. 

As a rule, intake systems should maintain a steady cross sectional area from port to filterbox with some gradual decrease as it approaches the port. A slight coning (or trumpeting) as the intake port enters the airbox is preferable to broaden the affected rpm range. Longer favours lower rpm, shorter favours higher rpm. There are formulas (read up Gordon Jennings, Gordon Blair, A Graham Bell)  but experimentation is still needed, especially with harmonics and Helmholtz box factors. The box volume itself is important also, and the same, bigger favours lower rpm.

Often where you gain power at one end, you lose it at another. I have made long intakes that gave tractor like low rpm power but hurt top rpm output. Most of the time I was looking for mid-range to max, which I gather may not be what a Trials needs? 

All this said, to my eye the TY175 airbox does not look too bad, and the filter has ample area for the carb. An airbox lid is important for resonance, but if you feel it is restrictive, test with it removed. 

Ah, testing! That is the rub. Without a dynometer, I find speed testing on a hill the most repeatable. Fit a speedometer, digital bicycle speedos are cheap, accurate and easily adapted. Find a long steep hill and establish 2 markers on it. Pick a gear, enter at a fixed low rpm and give it WOT at the first marker. Record your speed at the top marker. This is you baseline. Now you will know if any mod you do makes more power or less.

[trialsrfun]

Thanks for your valuable information, we got the bike running much better today well enough to ride in a forthcoming local trial. 

[bestrcpilot]

the biggest gain with the TY intake track is gained by maker the connection  to the air-box the straight as possible. As most of the trouble with the intake is a pinched intake rubber hose between the carby and the air-box. If you ride it like a modern bike.IE.. lots of revs and using the clutch, then opening the top of the air box up will help it to rev better. Now if you are running a short header pipe and after market exhaust and porting then a bigger air-box and a straighter intake track dos help. IE. using a Yamaha RD 350 intake (from the reed plate to the carby.) And make sure the reed are sealing as after  35 years they are know the lift and not seal. The use a new carby as the stock one are also know the wear and and not run right.

Hope this helps