How To/Formula for Making Your Own Boost Tube

OK, let's get right down to it. This can't be hard and to me isn't worth trying to profit off of my fellow members. Here's the skinny:

As per what I conclude from this link: www.2-stroke-porting.com/bbottle.htm

The boost bottle needs not be larger than a single cylinder, and if you have twin or triple carbs, then you can 1/2 or 1/3 the size of the boost bottle. So, if my interpretation is correct, since we only have 1 cylinder and 1 carb, then the boost bottle needs not have a size (volume) larger than the size of our cylinder (43cc/49cc/52cc/55cc) or whatever. Based on this, I don't know what good it would do for us to have multiple boost bottles, or if it would be worth the efforts $ wise. I'm sure someone will purchase them and enlighten us though."

OK, so here it is, all we need to know is the volume of the cylinder (boost bottle) that we are building. We know what it should be, our cylinder size or slightly smaller. Enter the formula for the volume of a cylinder V=pi x radius squared x height. Bear in mind that you don't want to exceed the volume of your cylinder, as that will not create the pressure in the boost bottle that we are looking for.

So here is what I used, and I have converted it to SAE measurements to make life simple. 1 cu. in. = 16.3871 cc which means that 49cc = 2.99 cu. in., 43cc = 2.62 cu. in., and so on, just divide your cc by 16.3871.

In my case, I have the 49cc X1. I decided to use 1" Schedule 40 PVC (plumbing or electrical, I found they both had the same inside diameter at my local HomeDepot). The inside diameter is 1" or so close, who cares. This gives us the radius of 1/2" or .50". Therefore, the radius squared is .25" is one variable in our equation.

We know that pi = 3.141579....etc., but I stopped there. Multiply that by .25" and we are almost there, 3.141579 x .25 = .785

Take and divide the equivalent cu. in. of your cylinder by .785, and you will get the length of pipe that you need. In this case, since I used 1" PVC, and the inside diameter is actually 1", then the length of pipe I needed is 3.81". That came from 2.99 / .785 = 3.80, which is slightly over 3 3/4".

So here is what I did, I took:

2 1" PVC Pipe Caps (no threads, glue on) $.36 ea.

1 Piece of 1" Schedule 40 PVC, 3 9/16" long (I allowed for the fact that the
caps are arched, and the tubing. $3.xx for 10'

2 1/8 NPT x 3/16 Hose Barbs (these are the nipples that the hoses attach
to) $2.45 ea. but you can probably find them cheaper

1pkg of the small hose clamps, and however much 3/16 fuel line you need to
reach where you want to put your bottle $2.00 + price of hose

1 1/8 - 27 Tap & (1) 11/32" Drill Bit for drilling and tapping 1 PVC cap &
the manifold $10

1 Teflon Tape $1.00
1 PVC Primer & PVC Glue $4.00
1 Small Tube Silicone $3.00

Total project about $30, and much less if you already have the drill bit and tap, and if you are making more than 1, this will really bring the price down. Another good idea, if you live near or pass by a construction site, is to ask a plumber or an electrician for a scrap piece of 1" PVC, or look around if they will allow you.

Basically, just drill and tap one of the PVC caps, and the manifold. It helps if you use smaller bits and graduate up to the 11/32" hole. Wrap the pipe threads on the nipples with at least 2 wraps of teflon tape. Primer the pipe on both ends and the 2 caps, glue it all together. I used silicone around all the threaded entries, and over the glue bead as a safety net. Install.

I have attached a pic with the 2 I just made. I will be going out of town in the morning, until Sunday. I won't be able to install these until Sunday or Monday, along with new pipes, carbs, v-stacks and filters. I just couldn't wait to post this info, and hopefully save some people some $$$$$$. Anyone can feel free to make one and post results before I get back and do so. If 3-4+ guys go in on the supplies, it's really not bad, still beats $50 for one.

This post is not meant to mislead anyone, but simply to give the mathematical approach to building the boost bottle. Anyone having any improvements is encouraged to post them here for the good of all. Thank you.

I have a much easier way!!!! ML =cc Buy a cap and some pvc attach one end with a cap dont use glue yet and using a ML(milaliter scale same as you use to give babys there medicine. Fill the boost bottle with water using the ML tool till you get the correct size.Remember when you glue the caps the glue does take up some space. If you drill your hole first you can put it all together fill the bottle to be sure you have the correct volumn and then using a small extention or a screw driver and a vice you can knock the caps back off. Hope this helped some of you that have problems with all those math equations. mogyver69(boostbottleman)

Very useful guide but there are a few things worth mentioning. First I would recommend using a metal casing rather than PVC as PVC has a tendency to breakdown aftertime when exposed to caustic substances like gasoline. Another comment is that the expansion chamber does not have to be exactly the same size as the displacement of the motor or even slightly less. In fact using a slightly larger chamber is often found to perform better. The last comment I have is that when installing your boost chamber you want to use the shortest length of hose possible and always mount the chamber above the intake manifold with the opening pointing down. This is so that as the condensation from the mixed air and fuel vapors gradually form it will drain back into the intake instead of accumulating in the bottom of the expansion chamber.

I had a question in regards to the volumn of the boost bottle. There seams to be much debate about. When your making the bottle do you take into account the length and size of the hose. For instance a piece of 1/4 hose 14" long is approx 9.5cc. Do you deduct 9.5cc from the boost bottle to compensate for the length of the hose. Why or why not? Please if your a non believer save your comments for another thread. Oh and by the way the construction of PVC isnt much different then a gas can, Most gas cans these days are made from plastic as well as fuel line you find in cars of today!!! I have several friends with boost bottles made of pvc there engines are still going strong yrs later.

I used two used co2 canisters from my paintball gun and drilled out the tops with a 3/16" drill bit slipped over some 4 stroke racing fuel line 10" each tube,got the fittings from fish store,total it cost me 15 bucks.Thats even with buying the tap.And yes tube length- volume is a factor.I took a bone stock x1 with 5 hrs on it,topped out at 25-27 mph.Got rev-pipe,rocket key,ported out intake manifold,drilled out purgevalve hole to 1/8" and added dual boost valve,readjusted carburetor cable and now it goes 35-37 mph.Saturday im adding a velocity stack w/built-in choke,90 degree bend airfilter,38 tooth rear sprocket for 5/16 chainset,20 tooth front sprocket.Next week a cvt trans and future plans include a hp carb and bigbore kit.ride hard-ride safe peace.

hmm cams way is quite interesting

The first pic is the double co2 setup.....

The second pic is a single boost bottle made out of a personal size can of axe

third and fourth picture is Zerk fittings[grease fittings] drilled out and two propane gas tank fuel level floats..........Peace

Damm dude tone those pic's down some it hurt my eyes looking at them. If those are those small CO2 canisters you need like 3' hose to get the right volume. You need a total volume of 52cc plus the nipples should be pointing down not up.

those zerks are too small, the fittings should between 3/16 and 1/4" for 52cc engine..

Yeah im kinda new to this stuff, this might sound kinda dumb but what ever. What fuel do you use in the axe bottle and what do the hoses attach to.

You don't put fuel in any boost bottle, the boost bottle attaches to the intake manifold and when the piston is on the downward stroke it forces excess fuel/air mixture back out the intake, the boost bottle helps capture some of that mixture and releases it back into the engine on the intake stroke...There is no fuel, fuel additive, nitrous or anything else in the bottles...

Here is ones I build...The decal is for looks only, No Nitrous

If you still have the engine ill buy it from you

Okay I Built A Boost Tube Out Of A Pvc Type Material .75" Dia X 6" Long And It Comes Out To About 43 Cc Will This Work With A 49cc Engine? Or Do I Need To Build A 1" X 4" Tube?