A lot of racing takes place under controlled conditions. The pavement or dirt is a known factor. The weather conditions are similar to those of previous races. The location is easily accessible and relatively comfortable to work in.
But what about racing in cold climates where there is rough terrain, snow or ice, and unpredictable outdoor conditions? Recently someone reached out to us to ask about our weather calculations when using temperatures in the negative numbers. It was a surprising question because we never thought of racers using our site for colder climates. It got us thinking. While we can’t write much about rough and unpredictable terrain, we can write about racing methanol engines in colder weather.
Engine Power Affected By Air Density
Cold temperatures raise the air density. Really cold temperatures really raise air density. We use temperature to measure the amount of heat in the atmosphere, but what it is really measuring is the amount of movement of molecules in the atmosphere. The more the molecules are moving, the more heat is generated. When they are moving a lot more, there is more space in the atmosphere for moisture, pollution, and other molecules. Conversely, when it is cold, molecules are not moving as much and there is less space for other molecules. This makes colder air denser than warmer air.
A common measurement of air density among racers is density altitude. This is meant to compare a measure of air density at a given location with that value if it were at sea level. Higher elevations indicated by higher density altitude equate to less air density. An elevation of 0 feet, or sea level, is equivalent to a standard in motorsports of 60 deg F, 29.9 inHG and 0% humidity. When it gets colder than 60 degrees, density altitude values end up being negative. They end up being some value that would occur for an elevation that is below sea level.
System setups for warm vs cold
If the fuel system is set up for the proper amount of fuel for the air density that prevails, higher air density raises horsepower. If the fuel system is not adjusted properly for the change in air density, power may not necessarily go up with colder temperatures. If the air/fuel ratio of the fuel system in warmer weather is on the marginal lean side, that may make good power in warmer weather. However, without a proper increase in fuel for colder weather, it may be too lean in colder weather. Power may be less causing a ‘head-scratching’ tuning dilemma.
For low altitude locations such as with 50% humidity, and 29.9 in HG uncorrected barometer, here are some motorsports examples of ambient temperature and the air density & density altitude values commonly used for tuning fuel systems:
Note that the temperature is the only change in this illustration, and it dramatically affects air density and density altitude.
Racing Engine Performance in Different Conditions
Below is an analysis of 2 different engines on a summer day and a winter day: a typical naturally aspirated sprint car engine on methanol with 600 HP and a typical blown methanol drag racing engine with 1,800 HP.
For either racing engine, the amount of horsepower that increases at 0 deg F temperature over the amount at 80 deg F is the question. Horsepower calculators on the internet can be unreliable when compared to each other. A different way to indicate how much horsepower increases from cold weather would be to look at the amount of fuel at the two different temperatures. We used our online engine tuning calculator, ProCalc to determine fuel needs.
Sprint Car Engine Analysis at an 80 Deg F Summer Day
For the sprint car engine at 95% air density, an optimum amount of fuel to the engine is 1.5 GPM at 8000 RPM.
This is fuel injection jetting setup is for a 360 ci sprint car engine on a summer day. It shows a lot of data for tuning. It is done with a smaller combination of nozzles and main bypass that increases fuel pressure and atomization. That is optimal for great response coming out of a turn. For the tuner, setting the high-speed bypass to open at about 90 psi will flat line the fuel curve at about 600 RPM over the torque peak. That is a typical optimum setup for this category of racing engine.
Sprint Car Engine Analysis at a 0 Deg F Bitter Winter Day
At 0 deg temp with the proper adjustments to the fuel system to maintain the same air/fuel ratio and fuel pressure, the optimal amount of fuel to the engine is 1.8 GPM.
The fuel system was adjusted for approximately the same air/fuel ratio in both the summer and winter setups. That resulted in the following:
• engine fuel demand for summer: 1.5 GPM
• engine fuel demand for winter: 1.78 GPM.
Maintaining the air/fuel ratio and fuel pressure, the calculator determined larger nozzles and a smaller main bypass combination for bitter cold weather. That puts more fuel to the engine for the increase in air density. Engine response would be similar to the summer setup. However, horsepower would be a lot more. For engine builders, the high speed bypass opening and size would remain the same for both setups.
That is a 19% increase in fuel at the cold temperature with proper adjustment of the fuel system for the same tune-up used in the warm temperature. The same tune-up includes all of the following:
• the same air/fuel ratio for horsepower and torque
• the same fuel pressure for response
• the same fuel enrichment for cooling
• the same fuel enrichment for the ‘accelerator-pump-shot-of-extra fuel’ for coming out of the turns when the throttle plates are slammed open
• the same high speed bypass opening pressure
• The same high speed bypass jet size.
The question is, how much power is increased from this greater amount of fuel?
Although a 19% power increase may be a stretch, that would be over 700 HP if that is the effect.
600 HP in summer x 1.19 = 714 HP in bitter cold weather.
Actual Sprint Car Engine Power Output
While the power from the rotating assembly may be up by 19%, other factors such as engine friction tend to dampen the final output. In addition, intake tuning characteristics may affect a change to the power in cold weather, down or up. All of the thermodynamic characteristics of the air columns moving through the intake system can change with temperature. It is possible to have an intake system that is marginal at warm weather and really wakes up in colder, higher density weather; or vice versa. Ram tube volume and length may favor one air density over the other. Intake system delivery plenums may favor one air density over the other.
Tuning characteristics from the intake design, in this case, depend on the length of the intake air column and the intake volume. The weight of the air from air density could have an effect on the ramming characteristic of these intake dimensions, especially in extreme setups.
As a result, a power increase from cold weather may be somewhat different than that theoretical value from a proper fuel system change. However, the potential power change is illustrated.
Blown Methanol Engine Analysis on an 80 Deg F Summer Day
For the blown methanol engine at 95% air density such as on a summer day near sea level, an optimum amount of fuel to the engine is 9.5 GPM.
This setup shows blower hat nozzles from 50s in the front down to 44s in the rear. That is a typical blower hat setup. Port nozzles are smaller 36s in the second row. This combination puts more fuel above the blower for intake cooling and blower lubrication, again a typical overall setup. The result with a 95 main bypass and this 12.5 GPM fuel pump make an air/fuel ratio of 3.2 to 1. That is typical of a good running blown methanol racing engine.
Blown Methanol Engine Analysis on a 0 Deg F Bitter Winter Day
For the blown methanol engine at 95% air density such as on a summer day near sea level, an optimum amount of fuel to the engine is 9.5 GPM.
At 0 deg temp with the proper adjustments to the fuel system to maintain the same air/fuel ratio and fuel pressure, the optimum amount of fuel to the engine is 10.7 GPM.
This setup for a bitter winter day is revised to maintain the same air/fuel ratio and fuel pressure. That resulted in the following:
• blown engine fuel demand for summer: 9.46 GPM
• blown engine fuel demand for winter: 11.32 GPM.
Maintaining the air/fuel ratio and fuel pressure, the calculator determined larger nozzles and a smaller main bypass combination for bitter cold weather. That puts more fuel to the engine for the increase in air density. Engine response would be similar to the summer setup. However, horsepower would be a lot more.
That is a 20% increase in fuel at the cold temperature adjusting the fuel system for the same tune-up. The same tune-up includes the same air/fuel ratio for horsepower and torque, the same fuel pressure for response, and the same fuel enrichment for retarding detonation as well as the same ‘accelerator-pump-shot-of-fuel’ on the hit.
Although a 20% increase may be a stretch, that would be over 2,100 HP if that is the effect.
1,800 HP summer x 1.20 = 2,160 HP in bitter cold weather
Frosting on the Intake Indicates a Power Increase
While racing at 0 deg ambient temperature may be rare, the actual temperature of the air/fuel going into the engine may approach a much colder value, even in warmer ambient conditions. The intake temperature is the driving factor.
At 80 deg ambient temperature, for example, methanol vaporizes in the intake. Methanol has a very high heat of vaporization. That is, it absorbs heat when it vaporizes into the intake system. Often the intake throttle bodies & housings of methanol fuel racing engines frost over under certain conditions. This is common in the evenings and high humidity air. Frost occurs from the humidity in the air when that temperature is 32 deg F or colder.
It may be more common than perceived. Actual air temperatures going into a methanol racing engine may be a lot lower than the ambient temperature. And calculated power level changes may be more significant from a colder intake temperature than what is expected from ambient, warmer values.
Factors to Watch for in Colder Temperatures
COLD WEATHER POWER: Monitoring power increases from cold weather can be complicated. Some motorsports vehicles with more power may spin the tires causing a reduction in elapse time even though power is up. That is a typical problem that is tough to sort out. As previously mentioned, the proper amount of fuel is needed for best power. That proper amount changes with air density. In effect, the proper amount of fuel or air/fuel ratio goes up or down with air density in the same proportion. However, the power may not be in proportion.
COLD WEATHER STARTING: Starting a racing engine in cold weather may be problematic. It is common practice to warm up a racing engine before going into competition. One objective is to get the engine oil warm for proper circulation. However, getting good vaporization in the intake from engine heat is important as well.
OTHER ENGINES IN COLD WEATHER: Air density affects most all engines the same as it does for popular V-8s. That would include engines with different numbers of cylinders and rotary engine configurations.
Conclusion
While it is rather rare to race in colder conditions, interesting things happen to the engine’s power as the temperatures drop. It can be a pleasant surprise to realize you have a huge bump in horsepower. As long as other parts of the setup are accounted for in the colder weather, racing in winter can be a spectacular experience from a power-generating vantage point!
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