Velocity

Velocity (pronounced vuh-los-i-tee)

(1) Rapidity of motion or operation; swiftness; a certain measurement of speed.

(2) In mechanics and physics, a measure of the rate of motion of a body expressed as the rate of change of its position in a particular direction with time.  It is measured in metres per second, miles per hour etc.

(3) In casual, non technical use, a synonym for speed.

1540-1550: From the Middle French vélocité, from the Latin velocitatem (nominative vēlōcitās) (swiftness; speed), from vēlōx (genitive velocis) (swift, speedy, rapid, quick) of uncertain origin.  It may be related either to volō (I fly), volāre (to fly) or vehere (carry) from the primitive Indo-European weǵh- (to go, move, transport in a vehicle) although some etymologists prefer a link with the Proto-Italic weksloks from the primitive Indo-European weg-slo-, a suffixed form of the root weg- (to be strong, be lively).

Although in casual use, velocity and speed are often used interchangeably, their meanings differ.  Speed is a scalar quantity referring to how fast an object is moving; the rate at which an object covers distance.  Velocity is the rate at which an object changes position in a certain direction. It is calculated by the displacement of space per a unit of time in a certain direction. Velocity deals with direction, while speed does not.  In summary, velocity is speed with a direction, while speed does not have a direction.

The velocity stack

Velocity stacks (also informally known as trumpets or air horns) are trumpet-shaped devices, sometimes of differing lengths, fitted to the air entry of an engine's induction system, feeding carburetors or fuel injection.  Velocity stacks permit a smooth and even flow of air into the intake tract at high velocities with the air-stream adhering to the pipe walls, a process known as laminar flow.  They allow engineers to modify the dynamic tuning range of the intake tract by functioning as a resonating pipe which can adjust the frequency of pressure pulses based on its length within the tract.  Depending on the length and shape of the stack, the flow can be optimized for the desired power and torque characteristics, thus their popularity in competition where the quest is often for top-end power but the flow can also be tuned instead to produce enhanced low or mid-range performance for specialized use.

1973 McLaren M20C.

The 1968 McLaren M8A was built for the Canadian-American Challenge Cup (the Can-Am) and used a new aluminum version (later sold for street use as the ZL1) of the 427 cubic inch (7.0 litre) big-block Chevrolet V8.  Dry sumped and fuel injected, it was rated at 625 bhp.  A series for unlimited displacement sports cars, the wonderful thing about the Can-Am was the brevity of the rules which essentially were limited to (1) enclosed body work and (2) two seats.  With engines eventually growing beyond 490 cid (8.0 litres) and reaching close to 800 bhp, the McLarens dominated the series for five years, their era ended only by the arrival of the turbo-panzers, the turbocharged Porsche 917s.  The McLarens remained competitive however, the final race of the 1974 series won by a McLaren  M20.    

1970 Ferrari 512S.

Ferrari built 25 512S models in 1969-1970 to comply with the FIA’s homologation rules as a Group 5 sports car to contest the 1970 International Championship for Makes.  It used a five-litre V12 and was later modified to become the 512M which, other than modified road cars, was the last Ferrari built for sports car racing, the factory instead focusing on Formula One.

1965 Coventry Climax FWMW flat-16 prototype.

Coventry Climax developed their FWMW between 1963-1965, intending it for use in Formula One.  A 1.5 litre flat-16, both the Brabham and Lotus teams designed cars for this engine but it was never raced and the engines never proceeded beyond the prototype stage.  Like many of the exotic and elaborate designs to which engineers of the era were attracted, the disadvantages imposed by the sheer bulk and internal friction were never overcome and the promised power increases existed in such a narrow power band it’s usefulness in competition was negligible.  Even on the test-benches it was troublesome, the torsional vibrations of the long crankshaft once destroying an engine undergoing testing.  It was Coventry at its climax; after the débacle of the FWMW, the company withdrew from Formula One, never to return.

1970 Porsche flat-16 prototype.

Porsche developed their Flat-16 in the search for the power needed to compete with the big-capacity machines in the Can-Am series.  Unable further to enlarge their flat-12, their solution was to add a third more cylinders.  As an engine, it was a success and delivered the promised power but the additional length of the engine necessitated adding to the wheelbase of the cars and that upset their balance, drivers finding them unstable.  Porsche mothballed the flat-16 and resorted instead to forced-aspiration, the turbocharged flat-12 so effective that ultimately it was banned but not before it was tweaked to deliver a reputed 1500+ horsepower in Can-Am qualifying trim and, in 1975, at the Talladega raceway it was used to set the FIA closed course speed record at 221.160 mph (355.923 km/h); the mark stood for five years.

1966 Ford 289 V8 in GT40 Mk 1.

Not all the Ford GT40s had the photogenic cluster of eight velocity stacks.  When the Ford team arrived at Le Mans in 1966, their Mk II GT40s were fitted with a detuned version of the 427 cubic inch (7.0 litre) big-block FE engines used on the NASCAR circuits and instead of the multiple twin-choke carburetors with the velocity stacks familiar to the Europeans, it was fed by a single four barrel unit under a fairly agricultural looking air intake.  On the GT40s, the velocity stacks looked best on the 289 and 302 cubic inch (4.7 & 4.9 litre) small-block Windsor V8s, the ones built with the four downdraft Weber carburetors thought most charismatic.

1967 BRM H-16.

In typically English fashion, the 1949 BRM V16 is celebrated as a glorious failure.  In grand prix racing, it failed for many reasons but in one aspect, it was a great success: the supercharged 1.5 litre engine generated prodigious, if hard to handle, power.  Not discouraged, when a three litre formula was announced for 1966, BRM again found the lure of sixteen cylinders irresistible though this time, aspiration would be atmospheric.  It actually powered a Lotus to one grand prix victory in Formula One but that was its sole success.  Although nice and short, it was heavy and it was tall, the latter characteristic contributing to a high centre of gravity, exacerbated by the need to elevate the mounting of the block to make space for the exhaust system of the lower eight cylinders.  It was also too heavy and the additional power it produced was never enough to offset the many drawbacks.  Withdrawn from competition after two seasons and replaced by a more conventional V12, the FIA later changed the rules to protect BRM from themselves, banning sixteen cylinder engines.

1969 Ferrari 312P.

Build to comply with Group 6 regulations for prototype sports cars, the Ferrari 312 P was raced by the factory towards the end of the classic era for sports car racing which dated back to the early 1950s.  Fielded first with a three litre V12, it was re-powered with a flat-12 in 1971 and has often been described as the Ferrari Formula One car with bodywork and while a simplification, given the engineering differences between the two, that was the concept.  It appeared on the grid to contest the World Sportscar Championship in 1969, a return from a year of self-imposed exile after one of Enzo Ferrari's many arguments with the FIA.  Needing reliability for distance racing, the Formula One engine was slightly detuned and, as in the open wheeler on which it was based, acted as an integral load-bearing part of the structure.  Unlike Ferrari's earlier sports cars, this time the classic array of Webber carburetors was eschewed, the velocity stacks sitting atop Lucas mechanical fuel-injection.