Vitamin Bottle Airbox

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Inspired by legends like JBOT, I build this shorty airbox. It seems to rip, but is this .8L setup giving me the same benefits as a tube and larger bottle. 64cc, single Reed, 17.5mm carb all polini.

I sanded out the mouth of the bottle and hacked off the threading to give a better clamp surface. I ended up cracking the bottle and taping it closed.

It lost some revs with this setup, but has a little more torque down low per butt dyno.

It seems to rip and is slightly quieter than just running a UNI foam filter.

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Early pic with an unnecessary hose on the carb.

I went this direction because the carb faces straight out. This is a little more tidy than a long bending hose, but it seems likely to get knocked off. The carb is mounted with a flexible connector, so I am not too worried about damage to the carb. (edited)

Re: Vitamin Bottle Airbox

Nice, I've been thinking that a Nutella jar might make a good airbox but my girlfriend's vitamin bottle looks pretty similar to yours so I'll have to give that a shot too

Re: Vitamin Bottle Airbox

🇮🇹💦 Of the Loin /

I've gone full rabbit hole and now use various plumbing bits for airboxes

Looks goofy, rides great

Re: Vitamin Bottle Airbox

Totally normal JBOT /

Few things.

You need a dome at the terminal end. That really reflects the wave back into the intake.

Then the tubes you’re using are no good.

Use irrigation tubing. It’s very thin and pliable. You can flare the end for a Venturi effect. Really helps pull air in.

Re: Vitamin Bottle Airbox

Totally normal JBOT /

And if you use the extension hose, try to make it as short as possible but don’t 90deg it too close to the carb. That will fuck up your flow.

I use springs and string to hold the tube towards the frame in a flexible but secure position

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Re: Vitamin Bottle Airbox

The trick to a good air box is to calm down the air before entering the motor making the air more dense and less turbulent!

Re: Vitamin Bottle Airbox

This bottle comes with a hydrodynamic nozzle that could be moved to the side. The neck is flexible for mounting.

Anyone have some laying around they could mail me? It looks like some next gen stuff.

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Re: Vitamin Bottle Airbox

🇮🇹💦 Of the Loin /

Plumbing bits are great because they already figured out fluid dynamics

Re: Vitamin Bottle Airbox

I use that irrigation tubing for all kinds of dumb shit, got piles laying around the farm if anyone needs a foot or two.

You can heat it with a heat gun and it's like modeling clay, you can make it into anything and when it cools it stays put, so handy... Halloween costumes, forms, just any weird lightweight shapes or structure.

Re: Vitamin Bottle Airbox

Bryan Teeuwen /

This would really lend it's self well to 3d printing.

Re: Vitamin Bottle Airbox

I like Graham's irrigation tubing . Working with what you have . ;)

Re: Vitamin Bottle Airbox

Dirty30 Dillon /

I would normally comment on how it could double as a one-sided legshield, but I am more interested in the banjo string fuel line and completely unhinged cabling.

JBOt is of course correct, you preferably want a conical/rounded end to bounce the wave back. This is a first iteration, but if it were me I would remote mount to get that vibrating weight off the end of that intake and stop it from sticking 12" off the bike.

Re: Vitamin Bottle Airbox

Kevin Bishop /

Is this science for PP setups? All of the reading I’ve done for larger displacement (250) have all called for 90 boot air filters. I don’t use plastic 90’s anymore just rubber to absorb the wave effects. It has worked for me.

But then I never use an air box

Re: Vitamin Bottle Airbox

Totally normal JBOT /

I’ve used air boxes on piston port and it worked ok, not as good as it works on reed but it does capture blowback.... One can have issues if there’s too much and pooling occurs

Re: Vitamin Bottle Airbox

What pulse are we talking about here? I always thought that as crankcase pressure becomes positive relative to atmosphere the reeds closed, which would reduce / eliminate this sort of thing? Like how folks convert PP cylinders to reeds partially to reduce the amount of gas that gets sprayed out of the carb.

I'm clearly missing something; what's the deal?

Re: Vitamin Bottle Airbox

Whether is reeds shutting or a piston, when the intake port shuts there’s still inertia to the column of air proceeding.

When that flow hits the reed/piston it creates a reflected wave. Another opportunity for 2 stroke optimization. Give that something to reflect off of in the airbox, and it is similar to an exhaust chamber.

I think a lot of people leave this power laying on the table because it has to be matched with other rpm related tuning and can make carbs harder to tune.

Shifty bikes don’t need as broad of a power band. I assume reeds and variators are more compatible. PP?

I would like to try it for shits and giggles

Re: Vitamin Bottle Airbox

That totally makes sense; just like an impedance discontinuity in a transmission line.

Thanks!

Re: Vitamin Bottle Airbox

Dirty30 Dillon /

The resonant wave is sound, just like an expansion chamber. Whether it's reeds or PP, matching that to your tune helps push blowback back into the cylinder just like a return wave on the exhaust pushes back unspent charge into the combustion chamber.

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Alan Jackson /

ive just realised i spend ages working out pulse speeds gas temps and lengths to reflect pulses at the right rpm for exhausts yet totally ignore the inlet side. im thinking you want a stuffing pulse to return to the reed right on thr point of closing at peak power rpm. or lower rpm if you want more spread. i knew intake tuning was a thing having read jennings book nearly 40 years ago. just never tried implementing it

Re: Vitamin Bottle Airbox

There’s a reason not many people do it.

This isn’t 1:1 comparison to exhaust chambers. The gasses in the exhaust are high pressure. Good density means efficient and fast wave travel.

The intake is being evacuated constantly. Very low pressure. And the wave isn’t the exploding mixture of fuel, just that very low pressure column of air bumping into a closed reed or piston skirt.

I think the greatest good of a tuned intake length is to, at a min, not let that weak ass return get OUT of the intake before the next signal pulse pulls the air and fuel back in. And, If I understand it correctly, that’s mostly at low rpm where most of use tune our clutches to stay clear of.

Top it off with the majority of people on mopeds tuning with butt dynos, and it’s hard to get an accurate picture.

I will throw something together this weekend and share too. Can’t go wrong if it’s all for fun.

Re: Vitamin Bottle Airbox

🇮🇹💦 Of the Loin /

Piston ports don't give AF they need to breathe mostly

Reed is like half way in-between

Constant Velocity carbs solve most all intake problems except they need to warm up more than most as air temperature makes a big difference in the Velocity of air

Try and make a Reed air box like a CV carb box, but you don't need to go so crazy with tuning

Re: Vitamin Bottle Airbox

Totally normal JBOT /

I’ve played with many different lengths of an airbox hose length and shorter is usually better

What seems to be most important is bottle ID.

Too small a diameter and it just doesn’t work right. I’ve found that these fat shampoo bottles are basically the perfect size.

Re: Vitamin Bottle Airbox

🇮🇹💦 Of the Loin /
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This is what peak performance looks like

Re: Vitamin Bottle Airbox

Maitland, please ride this next time you ride in Sacramento. I wanna see it in action!

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Alan Jackson /

would an old motul 710 or 800 2stroke oil bottle do? or is it best to have a round bottle.

i have a few empties kicking about in the garage.

Re: Vitamin Bottle Airbox

Alan Jackson /

im sure i read a long time ago (jennings?) that much of the benefits of intake tuning is lost on reed valve motors.

but i remember seeing formula to work out the desired tuned length.

much like with exhaust pipes. get it right and its free power. im gonna read up on jennings and bell. (cant understand blair)

Re: Vitamin Bottle Airbox

🇮🇹💦 Of the Loin /

Straight tube:

Good for low end throttle response and power and noise cancelling. Also good for temperature

Bad for top end (starves it too much, bike only does a solid 35-40)

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