ASK THE MXPERTS: COLD GAS VERSUS HOT GAS

Dear MXA,
I’ve always heard that cold gasoline makes more power than hot gasoline. Should I be putting my gas can in an ice chest?

The gasoline in your bike is hot. Not just when it burns, but as it sits. Exposed to direct sunlight, in a black gas tank or red gas can, fuel can reach temperatures in excess of 100-degrees. Even at its best, your gasoline will have the same temperature as the outside air (on a 95-degree day that means 95-degree gas). It has been proven that cold gas can produce more power than warm gas. But, science aside, in the real world, it’s not that simple.

Why not? The gain in horsepower, which is very small in any case, is caused by the cold gas being denser; however, on a warm 85-degree day, by the time you put 50-degree cold gas in your tank (which would require you to bring it to the track in an ice chest), ride to the starting line and sit there for 10 minutes waiting for your race to start, the 35-degree difference in fuel temperature will be greatly reduced, especially since the fuel tank sits directly over the Bunson Burner heat of a very hot four-stroke engine and exhaust pipe.

We dyno’ed cold gas and warm gas to see if the difference was measurable.

Here are the take-aways: (1) MXA ran a dyno test comparing 85-degree fuel and 50-degree fuel and found that peak horsepower was identical with both hot and cold gasoline. We did find a very small improvement at high rpm (after peak) with the colder fuel, but it was a very small percentage gain, in a very narrow rpm range, and disappeared in mere minutes as the fuel heated up. (2) Cold gasoline did stabilized the power at high rpm and maintained what it produced for longer than warm gas. Thus, keeping your gas as cold as feasible before the start of a moto will offer a small horsepower advantage on the start, but it will fade quickly. However, there is a slight uptick. (3) Unfortunately, because there is no such thing as a refrigerated gas tank, cold gas will return to ambient temperature within a few minutes (aided by the bunson burner heat generated below the tank from the top-end and exhaust pipe). The take-away is that keeping your gas as cold as feasible before the start of a moto will offer a small horsepower advantage on the start and for the first few laps, but one that is very difficult to achieve. And not worth the hassle for a local racer.