Underdrive means to slow the rate of rotation in a system. Underdrive is achieved by either making the crank/main (drive) pulley smaller or the accessory (driven) pulley larger than the original diameter pulleys. Underdrive pulleys increase engine output by reducing the draw of the engine's accessories by slowing them down and reducing the HP they use. Horsepower gains from underdrive pulleys can vary by vehicle, engine, number of accessories and the amount of underdrive (Improvements of up to 5-15 HP at the wheels have been seen).
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The Inchtabokatables were formed on February 7, 1991 in a pub in Berlin called "Bärenschenke". The founding members were B. Breuler, B. Deutung, Herr Jeh, Franzi Underdrive and Kokolorus Mitnichten. Before joining The Inchtabokatables, B. Deutung and Herr Jeh played together with Subway to Sally singer Eric Fish in the band Catriona. Franzi Underdrive left the band shortly after the release of their debut album 'Inchtomanie'.
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The most commonly seen result is lighting may dim, or the stereo may cut out. Too much underdrive for a race car is not much of a concern due to the high RPMs they run at, but for daily driven vehicles it can lead to a dead battery if too much time is spent at idle or low RPM. Additionally, an underdrive pulley will not reduce the power consumed by the alternator, as the alternator's load is automatically adjusted by its control circuit to match the electrical load regardless of input speed. Changing the original crankshaft pulley can also have negative effects if the replacement pulley is not manufactured properly.
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In 2010 Sturmey-Archer launched a new range of duomatic 2-speed hubs, re-using the S2 name from the late 1960s, these hubs – designated S2 (freewheel), S2C (backpedal brake), and S2K (6 bolt disc brake) – share their general engineering principles with the original S2, but do not share any internal components. They offer a direct gear and an overdrive of 38%, a significant improvement for usability over the 'underdrive' gear of the original S2.
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Modifying the accessory drive system can increase fuel economy and performance to some extent.Better Business Bureau list of ineffective retrofit devices and glossary of terms Underdrive pulleys modify the amount of engine power that can be drawn by accessory devices. Such alterations to the drive systems for alternators or air conditioning compressors (rather than the power steering pump, for example) can be detrimental to vehicle usability (e.g., by not keeping the battery fully charged), but will not impair safety.
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Additional and significant performance improvements can be seen by reducing the weight of the pulley versus the original pulley. Gains can range from 3-6 HP per pound of weight reduced. Poorly engineered underdrive pulleys can cause unwanted side effects; this is due to not spinning the alternator, power steering, and/or air conditioning fast enough. This leads to low alternator voltage, weak/no power steering assist, and weak/no air conditioning effectiveness, especially at idle/low RPM.
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In general because of the way the CVT is set up, it is more efficient at a 1:1 ratio compared to maximum overdrive or underdrive positions. Independent test results have shown that at 1:1 it is actually more efficient than comparable bicycle internal gear hubs, while at the ratio extremes it is slightly lower. Torque inputs can be summed or divided, just as in a conventional planetary. Ratio control is stable, and can be actuated down the center line of the transmission, which again is similar to the proven planetary transmission.
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The transmission is monitored and regulated by Audi's "Dynamic Regulating Programme" (DRP), which tracks the driver's inputs (from how the driver applies the throttle pedal), driving conditions, and engine load - to compute the optimal gear ratio for fuel efficiency or maximum performance, as mandated by the user. The transmission can select pre- programmed underdrive to increase performance, or overdrive to improve economy. From 2004, Multitronic transmissions offered manual selection of a 'sport mode' to pre-select the performance mapping. The electronic system also includes sensors to detect whether the vehicle is traveling downhill, and provides additional engine braking in such circumstances.
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Two factors allow the NuVinci CVT to provide a continuously variable ratio range in a compact package: # The first is the geometric configuration of the drive, which is based on differing contact ratio of a sphere. Contacting a rotating sphere at two different locations relative to the sphere’s rotational axis will provide a “gear ratio”, which can range from underdrive to overdrive depending on the location of the contact points for input and output torque and speed. # The second factor is elastohydrodynamic lubrication (EHL). Transmissions that use EHL to transfer power are known as traction drives.
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In 2001, Ford partnered with Warner Bros. to offer a special version of its GT with the Bullitt nameplate, honoring the 1968 390 fastback model driven by Steve McQueen in the 1968 movie Bullitt which became famous for its high speed chase scene. The car was designed as a good handler so it was lowered 3/4 of an inch, received Tokico shocks, and short length sub-frame connectors. In addition, a new intake design, high-flow mufflers, and special underdrive pulleys helped increase the power to a conservative , though many owners report numbers closer to the 270-275 range.
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As the car utilizes a wet clutch, this condition could also occur in cold weather, when the thickened oil prevents the clutch discs from slipping freely. Power reaches the differential through a single universal joint attached to a torque tube which drives the rear axle; some models (typically trucks, but available for cars, as well) could be equipped with an optional two-speed Ruckstell rear axle shifted by a floor- mounted lever which provides an underdrive gear for easier hill climbing. The heavy-duty Model TT truck chassis came with a special worm gear rear differential with lower gearing than the normal car and truck, giving more pulling power but a lower top speed (the frame is also stronger; the cab and engine are the same). A Model TT is easily identifiable by the cylindrical housing for the worm-drive over the axle differential.
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The fluid drive fluid coupling was also used in conjunction with Chrysler's M6 Presto- Matic semi-automatic transmissions. The M6 was in reality a two-speed manual transmission with a conventional clutch mounted behind the same fluid coupling unit that was installed in straight Fluid Drive cars. The M4 Vacamatic had two forward speeds and reverse. There was a manual Pull-Cable to lock out the underdrive in the early models. From 1949–1952, Dodge models with the conventional 3-speed Fluid Drive carried front fender emblems that said “Fluid Drive.” The M6 Models had emblems that proudly proclaimed “Gyromatic.” In the 1941 brochure for Chrysler automobiles, a silhouette of the car's drivetrain was depicted against an outline of the car body, with the caption of an arrow pointing to the transmission: "Miracle Happens Here"! The transmission shown was an early variant (M4 "Vacamatic") of the later M6 transmission and was marketed to compete with the new Oldsmobile fully automatic, clutchless Hydramatic transmission, introduced in the fall of 1939 on 1940 Model year Oldsmobiles.
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Based in Pompano Beach, Florida, Dario Orlando founded Steeda Autosports (now known as Steeda) in 1988 using his years of experience repairing and racing cars. Steeda is one of the largest manufacturers of Ford aftermarket performance parts. Originally a simple Ford-based racing team, they introduced its Steeda GT in 1998. The Steeda GT was a low-production car with mostly handling and braking upgrades, including Steeda Ultralite (which were repackaged Konig Villains). A cold-air kit, underdrive pulleys, rear wing, Sidewinder custom side stripes, and some minor computer tuning added slightly over $5,500 to the price of a standard Mustang GT. 2002 Steeda Mustang GT In 2000, prior to the introduction of the Q400, the Steeda GT was given the front splitter, which helped keep the newer New Edge Mustangs planted on the ground, and became a popular aftermarket addition. This remained the only offering from Steeda through the 2002 model year. In 2003 Steeda introduced the Q400, based on the Mustang GT with an advertised 400 hp (298 kW). The 4.6L V8 in the Q400 was modified with a Vortech (or Paxton) centrifugal supercharger, K&N; Filter, Ford Racing Performance Parts (FRPP) throttle body, and an HD aluminum radiator.
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