Books from Racecarbook.comFree articles about racingBobs Blog!

NA Racing Engine Intake Design vs Cylinder Volume

Normally aspirated (NA) racing engines are popular throughout the world, both in land and water motorsports.  When the intake valve opens in this design, the piston changes direction from exhaust evacuation to intake inlet.  As the piston goes down the cylinder, air pressure drops.  Atmospheric pressure that is higher is outside of the engine.  That higher pressure feeds air through the intake system into the cylinder.

FYI: Fuel is introduced in the intake system for an air to fuel ratio for subsequent combustion.

The amount of air that enters the cylinder is a function of the intake system that feeds the intake valve.  Most NA engines have an intake port and manifold pathway that feeds the cylinder.  For example, in a stack type fuel injection system, the intake pathway is normally a combination of segments.  These are:

  • the intake port in the cylinder head
  • a casting or billet throttle assembly
  • a ram tube.

For example, a V-8 racing engine would have 8 of these pathways.

There is a strong relationship between the volume of air in the intake pathway and the cylinder volume.

When the intake valve opens, the volume of air in the intake pathway port, throttle assembly, and ram tube fill the cylinder.  Keep in mind that racing engines normally operate at high RPM.  So the time to file the cylinder with 60+ events per second is quite short.  The intake event is terminated by the cylinder going to the end of its stroke and the intake valve closing.  If the volume of the intake pathway is smaller than the cylinder volume, then air is pulled from above the ram tube.  It may be open air such as in a nostalgia dragster, or it may be from a plenum feed by an air cleaner such as in a sprint car.  Here are some examples of a brief study from intake dimensions from various racing engines:

  • record holding nostagia dragster with a small block GM engine with a tunnel ram manifold and hat injection — intake-to-cylinder volume ratio 1.1 to 1
  • formula one engine from 2001 from published data in “Racecar Engineering” magazine — intake-to-cylinder volume ratio range from 1.05 to 1 to 1.1 to 1.
  • drag racing ProStock carbureted engine from the 1990 era — intake-to-cylinder volume ratio 0.8 to 1 for quickest elapse time; higher ratio for highest horsepower.

More information in our “5000 HP on Methanol” book.

Drag Racing FC Chaos, Texas Motorplex, 2022 World Finals Recap

We enjoyed entertainment of the FC Chaos world finals at Texas Motorplex, in October, 2022.  The racing facilities are quite first class.  Our thanks to Homer Doherty who met us at the entrance for the facility.  Homer transported us (and many others) around the pits in his electric cart, where-ever we needed to go.  This service was provided as a free courtesy to the spectators.

We met the FC Chaos race director, Chris Graves.  Chris and his wife, Tera, put on quite a show of supercharged alcohol and nitro powered drag racers. Continue reading

HP Gain from Small Opening in Roots Blower Case

Roots blowers are popular in motorsports for making more power. They are made up of a simple blower case with two rotors inside. The rotors spin from an engine driven blower drive. This pumps extra air into the engine. With extra air and the appropriate extra fuel, extra power!

The blower case design was changed in later years to improve performance. One of these areas is the size of the blower case discharge opening.

Original Roots blowers ran on industrial engines. They were simple mass flow devices running at atmospheric pressure. In the mid 19th century, motorsports racers put them on racing engines. They pumped a lot more air into the engine causing boost. This became an easy way to make more power.

However, because they were originally designed to operate at atmospheric pressure, they were inefficient with boost. While they made more power, it was not that much more for the amount of increased air into the engine.

One of the design areas affecting efficiency is the blower case discharge opening. That is discussed in several of our publications. Here are two examples: Continue reading