Stock Air Box Vs Open Filter Discussion

[Zino]

Open Filter Vs Stock Air Box
Here is my experience 

Stock Air Box 
Easier Tuning Start big work my way down till the main Jet runs right .
Less variation with weather 
Better gas mpg
Ok to good  power

Open Filter 
Harder to tune 
very finicky to weather 
lower gas mpg
great power to crappy power

I feel most tuners should max every part of there build first and then look at open filters when they are at the mid race and race level builds .

[geoffh]

I use a chinarelli copy of the Yamaha OE air box,if it,s a daily rider my vote is for the stock box just opened up a little.

Geoff

[oldgeek]

Apr 12, 2020 8:45:43 GMT -5 Zino said:

Open Filter Vs Stock Air Box
Here is my experience 

Stock Air Box 
Easier Tuning Start big work my way down till the main Jet runs right .
Less variation with weather 
Better gas mpg
Ok to good  power

Open Filter 
Harder to tune 
very finicky to weather 
lower gas mpg
great power to crappy power

I feel most tuners should max every part of there build first and then look at open filters when they are at the mid race and race level builds .

I completely agree with your reasoning, and would add noise to your list. If you want as much noise coming through your carb as you have coming from the pipe, by all means use a pod or even no filter.

Removing the stock airbox on a 2T or even 4T is likely the #1 mistake across the board for new "tuners".

[harleyracer59]

if you ride in any kind of moisture, a stock style air box is a must. the internal baffles also keep moisture out of your motor. a pod filter with a holy cover doesn't help much especially if filter location is near rear tire.

[jackrides]

Stock airboxes that are designed for limiting top speed or for quiet can be opened up for better flow. Hopefully, carefully done.

[SMALL CC TEK]

Stock stock stock . Open elements are a little easier to run if you stick a prefilter over the filter and oil with heavy or lite oil just depends on your weather and environment ie elevation humidity etc.. They will run awesome but one day you come out for a quick pass and it's acting up check the filter oil ! lol Stay stock just modify it race only for open element type my opinion ..

[Zino]

bump

[theredmouse]

I'm going through this debate myself right now.

my stock air box is distorted and made the jog bog down like crazy from sucking in all that unfiltered air. To verify the problem i removed the filter element and zip tied it around the intake tube. bogging went away, the scoot sounded great but i am unsure if getting an open filter or a stock box.

I absolutely love the open filter sound, and it seems to run great, but the engine changes pitch like its gonna bog but never does. Do i need to up the stock carb jet?

I haven't actually ridden this thing more than a mile at a time because i don't want to be stranded by it.

Is there any in between so i can get the sound but not worry about blowing this thing up?

any recommendations would be great!

[Zino]

Open filters need bigger jets sometime 20% bigger .
You want to go big enough to get gurgly rich and then go down a couple jets .
And do a proper wot plug chop to see if you have a good smoke ring.

Just be prepared to listen for a zingy sound which means your lean
Temp and humidity changes effect open filters faster .

You want sound get a good pipe My yasuni r my neighbors can here from a 1/2 block away when I am really on it .

[theredmouse]

so i decided to get a stock box, mainly because i wanna get some miles under me first before i start messing with fuel mixtures. Also the stock airbox is cheaper than a quality open air filter setup.

if i plan on modding to a bbk later on and tuning/upgrading the carb, would you recomend getting an expansion muffler or just a street one?

7.0.3

[Zino]

Depends on Goals
Expansion pipe
none of them are quiet they give the best top speed because they move power band in higher a higher range and raise the rpms you need to up jet carb from 0-10% usually You also have to get stiffer clutch springs so you take off in the power band you need lighter weights in the variator so your transmission stays in the power band .

Street pipes
Quieter similar to stock sound may still need to up jet 0-10% The powerband starts at a similar place just ends later so you have better take off and top speed so may not need to change clutch springs or weights much at all.

[ThaiGyro]

I will always love this topic. Stock versus pod filter. Most know I am an air-box guy, but there is no one answer, really. I draw the line, just as in cam and valve selection on a 4T at application. What do you want it to do?

Yes you can make a bit more top end with pods. I said...a bit. Five % per 50cc would maybe max at WOT, maybe. However what you lose at the bottom end and mid range may not be worth it.

I do not have a real good 2T example, yet. Just starting to develop a flow bench for 4T's.

Here is what I have learned- Build for your needs. If you want good low to mid to high end? Buy a rocket. If you want to ride city and country with some short blasting? Work-able, but costs. Just top end? Pay me...can do!

When you go from a 49cc to a 70cc, you still need an airbox. Maybe you need a longer snorkel or slightly wider. The air pressure you seek for "breathing" in backed up in that box. Picture this: Outside a pod filter you have +/-14.7 pounds. Inside an air-box your pressure cannot fully escape...so maybe 15.1 or more. Isn't that more air? Hahahaha...cut holes to "let" more air in? Hey, it is already in there! Now you are lowering that box pressure towards ambient. Wrong way.

Hard to explain, but try this: You want the vacuum wave (piston draw) to be higher that the air-box pressure, if possible. That is where torque happens. You want air molecules to be pissed of that the reeds are closed. They are ready and backed up by more! More under higher, not lower pressure.

The only deviation where we have seen results was a few years back, when we were using OEM boxes for 49cc to 70cc mods, buy putting a pod filter at the outboard end of the snorkel. We found that the box needed some sized orifice where the OEM filter was. (Or other way to induce turbulence) This produced good low-to mid range torque and great mid to high end, but not quite the same top end. About 2-3% less. My favorite engine.

[matlock]

if you put a sealed airbox the size of an suv you can achieve more power than any open filter

[ThaiGyro]

Matlock, the airflow dynamics are not that simple, nor linear. That is THE problem. On any engine, you want the best flow possible. Whether 2T or 4T, that cannot happen with no air-box. Think big engines...supercharged or turbo's. They add gobs of air into an air-box.

Even most of todays MX'ers use a "sub" box to trap air as much as possible, though they run WOT 90% of the time.

Some engineers have that shite down...Look at the OEM box for a Rotax 125 MAX. Not much bigger air-box than my 80cc Yamaha 2T, but that Rotax, with a baffled chamber makes 34 HP out of the box.

Defies most imaginations...steal their math.

[matlock]

if i put my scooter in my house and fire it up with no filter its a airbox the size of my house and it runs wide open