Restrictor plate
From Wikipedia, the free encyclopedia
A Restrictor plate or air restrictor is a device installed at the intake of an engine to limit its power. This kind of system is occasionally used in road vehicles (e.g., motorcycles) for insurance purposes, but mainly in automobile racing, to limit top speed and thus provide more safety, to provide equal level of competition, and to lower costs.
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[edit] Racing series
A few top classes like Formula One limit only the displacement, while most others use additional air restrictors also (or limited boost pressure in turbo engines)
- Formula 3, 2000cc, 215 hp
- Deutsche Tourenwagen Masters, 4000cc, 470 hp
- "Le Mans"-like sports car racing according to ACO/ALMS rules, 400 to 600 hp in various classes
[edit] Rallying
After Group B cars were outlawed from rallying because they were too powerful (rumoured to have reached 600 HP), too fast and too dangerous, the FISA decided that rally cars should not have more than 300 HP. For a while no special restrictions were needed for that (e.g. the Group A Lancia_Delta HF 4WD had about 250 HP in 1987). But with development, in the 90s Group A] cars were rumoured to have reached 400 HP or more. So the FIA mandated restrictors for supercharged/turbochaged engine in all categories (World Rally Car, Group A and Group N).
This means that the rally version of a car like the Mitsubishi_Lancer_Evolution can have less power than the street version (the "280" HP Evo VII was believed to have more than 300 HP, and in some markets there were FQ-320, FQ-340, FQ-360, FQ-400 versions, with the number representing the power).
It also means that the torque and power curves of the engine are unusual. The engine produces peak torque and almost maximum power at a relatively low rpm, and from then to the rev limiter the torque drops and the power doesn't increase much. So the driver doesn't gain much from using high rpms and being in the right rpms is less critical than in other forms of racing.
In 1995 TTE used an illegal device to bypass the restrictor (allowing an estimated extra 50 HP). Due to this the team lost their results in the 1995 season and was banned from rallying until the end of 1996.
[edit] NASCAR
NASCAR NEXTEL Cup currently uses restrictor plates at Daytona International Speedway and Talladega Superspeedway.
The device limits the power output of the motor and hence slows both the acceleration and the overall top speeds obtainable on the tracks where the cars are so equipped. These restrictions are supposedly in the interest of driver and fan safety, although many members of both of these groups feel that the close packing of cars and their inability to achieve separation may actually make the racing at these tracks more dangerous, as there are often massive and frightening multi-car pileups during races (especially at Talladega). Such a crash is dubbed "the Big One" by drivers and fans. At Talladega, most races are marred by at least one occurance of such as the large packs rarely break up for very long (at Daytona such occurs less frequently, and usually just after restarts, due to the greater presence of handling that breaks the packs somewhat more). It certainly makes for a different style of racing at these events than that which occurs at the other speedways used by NASCAR, as reduced power makes it more difficult to pass other drivers.
Drivers often form long chains, which, due to the lessened group air resistance, typically travel faster than single cars. This type of racing is often referred to by fans, drivers, and crew members alike as restrictor plate racing or drafting. Occasionally, a car drafting behind another will touch, or bump, the car in front, pushing the front car even faster; This is called bump drafting.
[edit] Reason for restrictor plates
There have been three reasons that NASCAR used restrictor plates in its history.
The first use came in 1971 as part of NASCAR's plans to reduce the size of engines from 427 cubic inches (7.0 L) to 358 cubic inches (5.9 L). In order to allow teams with smaller budgets to race the larger engines, NASCAR made mandatory the use of a restrictor plate to be placed on larger engines to equalize performance with smaller engines. The transition ended in 1974, when NASCAR banned the larger engines, and went to the current 358 cubic inch (5.9 L) formula. This was a transitional process and, as not every car used restrictor plates, this is not what most fans call "restrictor plate racing."
The second use came following the terrifying crash of Bobby Allison at the 1987 Winston 500 at Talladega Superspeedway. Allison's Buick Regal flew tail-first into catchfencing early in the event, injuring spectators (although not actually entering into the grandstands). After a summer where the two subsequent superspeedway races were run with aids to prevent cars from flying, and smaller carburetors (390 cubic feet per minute instead of 750 cubic feet per minute), NASCAR imposed restrictor plates again, this time at the two fastest circuits, both superspeedways: Daytona for all NASCAR-sanctioned races and Talladega for Cup races. The Automobile Racing Club of America also enforced restrictor plates at their events at the two tracks. In 1992, when the Busch Series began racing at Talladega, the plates were implemented.
However, restrictor plates are not used for Craftsman Truck Series trucks. Rather, air intake, aerodynamic, and spacer restrictions were implemented for those races. Combined with the aerodynamic disadvantage of the trucks, this allows NASCAR to avoid the use of such equipment for the trucks.
The third use came in 2000. Following fatal crashes of Adam Petty and Kenny Irwin Jr.at the New Hampshire International Speedway during the May Busch Series and July Cup Series races, NASCAR imposed restrictor plates for Cup cars to slow the cars headed towards the tight turns as part of a series of reforms to alleviate stuck throttle problems which were alleged to have caused both fatal crashes. The plates, used for the Whelen Modified Tour events at the track, were used just once at the 2000 New Hampshire 300 event, allowing Jeff Burton to dominate by leading all 300 laps in the ensuing race. Due to the lack of passing (and by almost all fan's accounts, an extremely boring race at a track that already often produced boring racing) and the addition of an automatic kill switch in the case of a stuck throttle, the use of restrictor plates was discontinued at New Hampshire for the following race for Cup only. (Restrictor plates are still used for the Whelen Modified Tour.)
Rusty Wallace tested a car at Talladega Superspeedway without a restrictor plate in 2005, reaching a top speed of 235 MPH in the backstretch and a one-lap average of 228 MPH. Wallace subsequently described the experience as "out of control". [1].
