CO2: Drag Racer's Life-Giving Gas
CO2 is a nearly odorless, colorless gas that is formed by the
combustion of carbon. It is a product of most living organisms and is
used by plants as a source of carbon. Bored yet? Sounds like a lecture
from my ninth grade science teacher, which, of course, would do
wonders to put me right to sleep. Seriously though, as far as drag
racers are concerned, it's definitely the gas of life. This gas powers
more items in a race car than the motor itself. Air shifters, throttle
stops, clutches and some parachute mechanisms would all cease to work
if that little silver bottle were to go empty.
It didn't all start with air shifters, as CO2 has been used and tryed for years on some race car systems, but most sportsman racers got introduced to it when the air shifters came into to play. Back then, that notorious little thing had people as up in arms as today's delay boxes do. A tiny round cylinder attached to the back of a shifter, whose plunger would push the shifter handle into the next gear when told to by a black RPM controlled box. Initially, two speed cars were first to be outfitted with them, but today we have controls that shift all three speed equipped vehicles as well.
Then along came the "super" racers with a need to throttle stop their vehicles. CO2 cylinders were perfect and the rest is history. Nowadays, some bracket racers have abandoned the two-step box used on the starting line to control starting line rpm and have switched over to using CO2 cylinders that directly pull the carb linkage back to a preset rpm. Advantages to that style are many. When the trans brake is released, the amount of air forced into the CO2 cylinder can be controlled to allow the throttle to go wide open at a preset amount rather than just slamming it open, which can have a tendency to spin the tires on slippery tracks. Some have argued over the years that running an engine on a two step at 3000-4000 rpm for a while can have a adverse effect on bearings and rods. Some of this is unfounded, but using the CO2 does away completely with that; for lack of a better term; myth, by allowing the racer to control the actual carburetor butterflies while still maintaining a constant "foot on the floor".
Let's go into some discussion now of the various parts of a properly used CO2 system along with some no-no's and troubleshooting tips.
The liquid boiling point of CO2 is -80 degrees Celsius, which transfers to roughly 112 degrees Fahrenheit, which in the case that you failed ninth grade science, is pretty #%*@ing cold. Because of it's extremely low boiling point, the liquid that is filled into your bottle is boiling, which when inside the closed confines of the bottle, forms a gas that gives you pressure. CO2 is commonly used by the soda or beer industry to charge the liquid to come out of a dispenser. It's also used in some fire extinguishers and by some plant growers to add carbon dioxide - that's what CO2 is - to plants. Now I'm no scientist or chemical engineer, and there might be some of you out there that know more about CO2 than me, but with all due respect to my ninth grade science teacher, that's about all a racer needs to know as to how and why we use CO2.
The first and most obvious part of the system is, of course, the CO2 bottle. Bottles are available in a variety of sizes, but the most commonly used ones are the 10 oz and 2.5 pound units. The most common of the two is the 10 oz. and it is that one that is 2" in diameter, roughly 16" long. This is the smallest bottle a drag racer should ever think of using since even with it, if you happen to have a small leak, it doesn't take very long to empty. That little bottle will however, usually last for a year's worth of runs if you only use it for the air shifter. Using it in conjunction with a throttle stop, will tend to empty it faster, depending on a number of variables, such as, the amount of actuating cylinder displacement and of course, with more lines and fittings, comes the possibility of more leaks. Some racers have gone to using the larger 2.5 pound bottle because of this. In any event, having a spare filled bottle is an almost necessity. Those of us that used to shift ourselves and converted over to an air shifter, will find that it's near impossible to go back to shifting, should you have to because you ran out of air. It's like that part of our brain was whisked away with the wind.
Bottles are filled by weight, the weight of the liquid we pump into it. It's the only way to guarantee that one doesn't get overfilled. Most welding supplies or fire extinguisher houses that fill bottles have the equipment to fill one, although some might not have the proper scale to accurately weigh a small 10 oz. bottle.
When I refill bottles at our Service Support Trailer, the most common asked question is "how much pressure do I put in it?". Generally, I don't have a clue. The amount of pressure a bottle has is directly related to the amount of liquid and the temperature of the outside, or ambient, air. A full bottle installed in a car during the heat of the summer, will register roughly 1200 to 1500psi. Take that same bottle during the cold in November, and you'll end up with 800psi if you're lucky.
Temperature plays that important role. That's why if you take a bottle to be refilled at a shop that can't accurately weigh it, you end up with usually one of two problems. Either it's been severely underfilled, which then tends to have you running out sooner. Or, it's been overfilled, which if left in the hot sun somewhere, will leave you with a bottle that will blow the safety blowoff valve located in the side of the shutoff valve. In addition, it will scare the ever living daylights out of you, if you're close by when it blows.
One more word of caution here. The 10 oz. bottles are the only ones exempt from DOT certification. NHRA mandates that a CO2 bottle be stamped with a DOT-1800. In addition, any bottle larger than the 10 oz. ones must be recertified every five years. Legally, I can't fill any bottle larger than the small 10 oz. ones that is out of date. Recertification is not a big deal and involves sending your bottle to a supply house that does that sort of work. It's pressurized beyond it's allowable limit and check for cracks. Every time a bottle is filled and emptied, it tends to expand and contract the metal slightly. In time, this can cause stress cracks. Aluminum bottles are notorious for that because of the type of metal used, however, it doesn't occur that often that should have you concerned about getting your bottle recert-ed. Something to keep in mind if you happen to be buying a used bottle.
Let's talk about leaks now. Most people plumb their systems with the popular 1/4" air brake line, either black or clear. Care should be taken to be sure the fittings used are fairly new and even at that, you should perform a simple leak check of your system by spraying it down with Windex or the equivalent. If you've got a leak, this will show it. While you're spraying, spray down around the valve area of the bottle, as sometimes the o-rings on the valve do go bad. Air shifter cylinders and solenoids usually tend to be pretty leak proof, however, that's not the case with throttle stop components. Most throttle stop cylinders on the market today have rubber cup rings on the actuating piston. CO2 is a relatively cold, dry gas, which means that it can tend to dry out any lubrication that may be on the sealing rings. A little dirt or dust entering the system, and you've got an annoying leak. I tend to tell my customers that every so often, a squirt of a little WD-40 or the equivalent into the air inlet side of the cylinder will go a long way toward alleviating leaks and allowing the piston to glide effortlessly in and out.
One thing you need to remember is that, leaks are a part of the game. Unless you manage to take very good care of your CO2 system; lines, fittings, etc.; leaks will occur. That's why, DRC Race Car Products, (609) 397-4455, recently introduced their CO2 Bottle Shutoff. This high pressure solenoid mounts directly on the bottle between the shutoff valve and regulator and wires into the ignition switch so that the only time gas flows is when the switch is on.
Most racers know that after a day's racing, it's wise to reach over and shutoff the CO2 bottle valve. Some even shut it off between rounds, because their system leaks so bad. How many races have you lost because you either forgot to turn the bottle on or left it on and it's empty? With this new valve, those problems become a thing of the past. It's perfectly acceptable to leave the bottle on constantly and allow the 12 volt shutoff solenoid do the work for you. This is also excellent for cars, especially dragsters, where the bottle is mounted in a rather tough place to have to be shutting it off constantly.
Chapter two, regulators. The ideal regulator to own is one with two gauges on it. One gauge will measure bottle pressure and the other monitors output pressure. Air shifters need at least 50 psi of output pressure to shift properly and can run on pressures as high as 100 psi. Throttle controls are very similar, only picture this. If you're using the throttle control to close the carb throttle blades either to slow the car down or as a starting line rpm controller, the speed that the air actually enters the cylinder will adversely affect the duration it takes for the throttle to either close or open. Oh, now I'm starting to sound like my ninth grade science teacher. The speed at which the air enters the cylinder is a direct result of pressure. More pressure and the air enters faster, less pressure and you can guess the rest. We've already said that CO2 pressure is a result of the ambient air temperature, so it stands to reason that the output pressure from the regulator can significantly change enough to affect the aforementioned air speed. Read this twice, as there'll be a quiz after..., whoa, this is really strange.
On an air shifter, if the pressure should change twenty or thirty pounds, it's only going to hit the shifter handle harder or softer. But should the pressure change that much on a throttle control cylinder, it can greatly affect the speed at which it travels. Which means that the throttle blades are either opening faster or slower, which as you can suspect, will either speed up or slow down your car. If this pressure change happens from one run to the next, you don't stand a snowball's chance in hell of running consistent.
Single gauge regulators are preset for the output, or low side pressure and because the only gauge on them reads tank pressure, you don't have any idea what the output pressure might be. Most regulators will do a good job of regulating the output pressure with regards to the amount of tank pressure, meaning that if you set them for 75 psi, they'll stay set there regardless of tank pressure. But what about the 47 miles of hose you've got running throughout your car. Temperature will affect that hose and can backfeed to show an either higher or lower pressure if you had a two gauge regulator to read it. That's why it's important to be able to monitor the low side pressure. We all know how important consistency is and it's little things like that that can throw you for a loop when you least expect it.
That's about it, CO2, class 101. The only way you'll know that you've passed is if you see win lights in your lane. In years to come, we might find a better alternative to using CO2, but for the forseeable future, it's here to stay. Making yourself aware of it's pitfalls and benefits, along with a small understanding of how it works, can go a long way towards insuring those aforementioned win lights.