As l write this, a suffocating blanket of snow clouds looms on the horizon while thousands of tanker trucks with winter gas roll inexorably toward gas stations in the Northeast and Midwest. In spite of the fact that I'm not a meteorologist, I know exactly what the clouds and cold weather will bring. Yet though I am an automotive journalist, I don't have the foggiest idea of what chemical grog fills those shiny stainless-steel tanks. It's surely got to be bad, no?

And as winter's pall approaches New Jersey once again, the CSK office grumblings about winter gas resurface. While joining the ritual chorus of nay-sayers, I found myself thinking, What the hell do I really know about winter gas? Or for that matter, what do I know about fuel? Nothing.

Funny how we're all experts on making horsepower, but nobody knows anything about fuel other than pour magic juice in, engine go boom-boom. Considering that horsepower comes from the fuel and not the high-dollar parts, wouldn't you say there's a pretty big gap in the information super highway? The realisation made me feel awkward, like a heart surgeon who doesn't know basic first aid.

To satisfy my curiosity about fuel in general and winter gas in particular, I put in a call to Thomas Hart, a fuel chemist with a master's degree from Georgia State University. He's designed many spec fuels for racing, including Formula One, NASCAR, NHRA Pro Stock and motorcycles, and has previously owned his own race fuel company, Turbo Racing Gasoline.

Thomas explained that gasoline is made up of many different chemicals, or components, not just one uniform molecule. Smaller, lighter components have a high volatility (they evaporate easily) and boil at a lower temperature, whereas heavier, more complex components don't evaporate as easily and boil at a higher temperature.

Each fuel has its own unique signature, called a distillation curve; think of it as a recipe. The distillation curve tells the chemist which components are in the fuel and what their weights (e.g., their boiling points) and quantities are in relation to each other. A simplistic way of looking at the distillation curve would be to list all the fuel's components on a sheet of paper with the heaviest ones at the bottom and the lightest ones on the top.

The trick is to have the right fuel for the right time of year. In the summer, when the temperature is high, the presence of too many light components will cause the fuel to evaporate too readily. This can result in vapour lock, an over-rich mixture and excessive evaporative emissions. In the winter, too many heavy components keep the fuel from evaporating, causing hard starting, a lean mixture, heavy hydrocarbon emissions and poor converter light-off.

Obviously, since we can't change the weather, we have to use a fuel that will optimize performance and emissions for a particular climate. To do this, fuel manufacturers use heavier components in the summer and lighter components in the winter. This is a simplification of things, but it's close enough for government work.

For reformulated winter gas, lighter, low-boiling-point components are added to the gasoline to increase volatility. This makes your car easier to start and accelerates converter light-off, thus lowering emissions. That's the official line on reformulated gas.

And now for the teaser. According to Thomas, one of the most popular compounds gasoline refiners used to pump up the brew is called methyl tertiary butyl ether (MTBE).

"'MTBE has several good things about it" says Thomas. "One, it boils in a range where the components have a fairly poor octane value. MTBE enhances the octane in the distillation curve. It fills in a good hole there around normal hexane and normal heptane. MTBE has an extremely high octane number, over 108. You've normally got some real junk [in the distillation curve]. [MTBE also] helps on acceleration and cold starting. On a carbureted car, it helps on fuel distribution." Gearhead translation: MTBE is a big check in the horsepower column.

With a little fuel chemistry under my belt, I called Mitch Markusich, the proprietor and head brewmaster of PRO Racing Fuels in Mississauga, Ont., Canada.

"The essential difference between summer fuels and winter fuels is the vapor pressure," says Mitch. "Manufacturers do this by pumping up the mixture with light-end components like butane, propane and isobutane." The caveat, according to Mark is that these components all have high octane values as well.

Shoring up the positive aspects of additives like MTBE, which Thomas earlier asserted, Mark said, "Another major property in [reformulated winter gasoline] is the use of oxygen-bearing ether compounds like MTBE, ETBE (ethyl tertiary butyl ether) and ethanol. It's like pouring liquid oxygen into the combustion chamber. The engine doesn't have to draw the oxygen in because it's already available in the fuel."

To illustrate his point, Mark pointed out that in Canada, where his racing fuels are made and used, the government doesn't allow the use of lead in racing fuels. Instead, PRO uses (among other components) MTBE to increase the oxygen content and octane of its fuels. Mark also pointed out that oxygen-bearing compounds like propylene oxide (a fuel additive outlawed in many racing organizations) and nitromethane have a considerable amount of oxygen in their makeup, over 5O percent in the case of nitromethane (By comparison, a 14-15 percent constitution of MTBE would give pump gas around a 2 8 percent oxygen content.)

So what does all this mean? Obviously winter gas can't be compared to race fuel; the recipes are too dissimilar. Pump gas must adhere to ASTM specification D4814, which puts specific limits on the composition of highway fuel. But within these limits, there is some blending flexibility. And in many Northern states, there is also the requirement for reformulated fuels.

Here's the poop: As specified by state law, reformulated winter gas contains any number of lighter, lower-boiling-point hydrocarbons (butane, propane, etc.) that just so happen to have an excellent octane value. Added to this may be any number of oxygen-bearing ether compounds (MTBE, ETBE, ethanol) that improve emissions and also have a relatively high octane blending value.

So what's all the bad hype for? Price, for one thing "It's actually more expensive to make reformulated winter gas than normal, summer fuel, ' says Thomas Hart. Lower fuel economy is another concern.

"The oxygen-bearing compounds displace fuel components, so it takes more fuel to get the job done. Normal gasoline has a stoichiometric ratio of 14.7:1, reformulated winter fuel runs between 14.3 and 14.4:1," says Mitch Markusich.

And the complaints about poor performance? Mitch says, "When people bitch about the fuel, it's not really the fuel's fault. The weather is largely responsible; after all, it is winter. Low cranking voltage in the battery, increased oil viscosity, atmospheric condensation in underground fuel tanks and so forth."

The bottom line is that when it's cold, winter gas seems to be the hot ticket for performance enthusiasts. Not only is the dense winter air good for horsepower, but the higher oxygen content and octane value of winter gas make the pot sweeter And as for fuel economy and price? When did that ever get in the way of having a good time behind the wheel? It s just too bad we have to deal with all that snow and ice".