Nitromethane 101 by Dan Bethune

top fuel

If you have ever been lucky enough to be close to a nitro-burning engine while it was running, you certainly experienced the burning watery eyes and fiery nasal sensation that can only be associated with burning nitromethane. It is splendid suffering; and fans often take it all in, with a smile on their faces.

....but what is Nitromethane, Anyway?

Nitromethane (chemical name H3NO2) is a fuel that burns with far greater power than gasoline or alcohol, but it is also far more tempermental. Nitromethane can combust without any air at all. That’s why nitromethane was once used as a rocket fuel.

*German Development*

First experimentation with nitromethane began as far back an 1895, but the first documented use was in the mid-to-late-’30s Auto Union Grand Prix and land speed record cars designed by Ferdinand Porsche. They were running 85% nitro at that time, with the remaining 15% being acetone and castor oil.

Really.

The German lessons learned with nitro experimentation were lost with the fall of Germany in 1945.

*American Development*

American hot rodders reapplied the fuel technology in the late ’40s. According to most hot rod historians, nitro’s first competition use in America was by Vic Edelbrock Sr. Back in 1949, a racer came into the Edelbrock shop with 1 gallon of a nitromethane, but didn’t want any part of it because he had heard “it will blow up in your face.”

Edelbrock and friends added 10 percent of the nitromethane to the methanol in their flathead. With no tuning or familiarity with nitro, Vic Jr. recalls that the strange brew “just about broke the beam on Dad’s old 200 hp-capacity Clayton dyno. The spark plugs were so hot they turned into glow plugs. When they tried to shut it off, the engine kept running. They finally had to throw a towel on it to get it to quit.”

The engine was toast, but eventually they learned to add lots more fuel, colder spark plugs, and stronger internals to stand up to both the higher output as well as nitromethane’s corrosive effects. The Stromberg 81 carbs had to be nickel-plated, as did the fuel containers (hidden from prying eyes inside cardboard boxes). Eventually, Edelbrock settled on a 20 percent nitro/80 percent methanol mix that added 40 hp.

Edelbrock was able to keep the fuel a secret for a while, but with white flames coming out of the exhaust, fellow racers knew something was up. Vic disguised the distinctive odor by blending in a little orange oil. By 1952, an Edelbrock Ford flathead running 40 percent nitro had run 201 mph one way at Bonneville (before the exhaust valves got sucked into the ports).

*Power Increase with Nitro*

If you consider high-octane racing gasoline as the baseline fuel, replacing it with methanol-the best alcohol fuel-is worth a 5-10% power gain. But 80-90% nitro is worth two to three times the power of the alcohol.

*Hard to Start, Hard to Stop*

Initial start-up with high nitro concentrations is very tricky. You must get the engine cycling. It won’t start up spinning at 200 rpm like a gas engine would. You need to get some heat in the engine and spin it at 1,800 to 2,000 rpm.” The common practice is to start and warm up the engine on gas or alcohol.

High percentages of nitro required breakthroughs in ignition technology. Today’s top-of-the-line MSD units put out 50,000 volts and 44 amps on the top end. That’s about the output of an arc welder at each cylinder-and the Fuelers run two of them.

Once you get a nitro engine going, it may not want to stop. At 7,500 rpm on the top end, there’s so much heat in the engine it may keep running under auto-ignition even if you shut off the magnetos. Essentially, it becomes a diesel. Fuelers today shut down by turning off the fuel pumps as well as the ignition.

*How to keep all the parts together*

Everything gets built heavier and stronger in a nitro engine. Bigger piston bodies, wrist pins, big aluminum rods, and heavier cranks are standard equipment. Bearings, pistons, and everything has to have more clearance, and are run with heavy, single-weight 70W oil. This works better under nitro’s tremendous loads. There’s also a tremendous amount of blow-by; even when running good, due to the tremendous internal pressure and rich fuel mixtures.

*Timing*

Nitro is considered to be a “slow-burning” fuel. At the top end, only about 10% of the fuel in the chamber is vapor when the burn starts; the rest is liquid. The vapor burns first, which creates enough heat to vaporize the rest of the fuel. But it takes time to create that heat; hence, the great amount of lead needed: 38-50 degrees advance with a supercharger.

*Nitro is weird stuff*

You can strike a match next to a puddle of it and nothing will happen. But if you put a few drops of it on an anvil and hit it with a hammer, there will be a small explosion, like an old cap going off in a toy gun. More seriously, that means you don’t want to risk dropping barrels off a truck. The explosion chance is remote, but it is possible, especially on a hot day.

If spark fails early in the run, unburned nitro can build up and then explode with a force that can blow the heads off the block-or even tear the engine block in half.

Now you know.

Thanks for reading.

-Dan

(sources: Hot Rod Magazine, Gene Adams, Vic Edelbrock Jr., Jeff Prock, Bangshift , and a little urban legend here and there)