Basically, a clutch is a mechanical device that engages and disengages the power to the transmission, especially from a driving shaft to driven shaft (in the case of automotive, this is from a crankshaft to a driveshaft or driveaxle).
Clutches are used whenever the transmission of power or motion must be regulated or controlled either in amount or over time (e.g., clutches control whether an automobile transmits engine power to the wheels or not, and allows for optional engagement or disengagement of the driveline from the engine to change between gears/gear ratios in the transmission as needed).
In the simplest application, clutches connect and disconnect two rotating shafts (crankshaft and driveshaft). In these devices, one shaft is typically attached to a motor or other power unit (the driving member-engine) while the other shaft (the driven member-wheels) provides output power for work.
The vast majority of clutches are “friction” clutches and ultimately rely on frictional forces for their operation and transfer of power. The purpose of friction clutches is to connect a moving member to another that is moving at a different speed or is stationary, often to synchronize the speeds, and/or to transmit power. Usually, the least amount of slippage (difference in speeds) as possible between the two members is desired.
Various materials have been used over the years for automotive clutch disc-friction facings, including organic (carbon), ceramic, Kevlar, brass, sintered iron, etc. Modern performance clutches typically use either a compound organic material with copper wire inlay or a ceramic/ceramic-metallic material. A typical coefficient of friction used on a friction disc surface is 0.35 for organic and 0.25 for ceramic. Organic materials are usually used where possible on stock to moderate horsepower/torque applications to provide smoother clutch engagement. Ceramic materials are typically used in higher horsepower/torque and heavy-duty applications such as racing or hauling, and are a great choice for this although the harder ceramic materials can increase flywheel and pressure plate wear.
A clutch damper is a device that softens the response of the clutch engagement/disengagement. In automotive applications, this is often provided by one or more mechanisms in the clutch disc centers (hubs) like coil springs, dual-dampened coil springs and/or marcel plates that help make a clutch more drivable and reduce chatter. In addition to the damped (sprung) disc centers/hubs, which reduce driveline vibration and ease engagement, pre-dampers may be used to reduce gear-rattle at idle by changing the natural frequency of the disc. These weaker springs are compressed solely by the radial vibrations of an idling engine and are fully compressed and no longer in use once the main damper springs take up drive.
A pressure plate's job is basically to apply a clamp load to squeeze the clutch disc firmly between the pressure plate and the flywheel. In the performance world, there are basically three types of pressure plates: the Long style, the Borg & Beck, and the diaphragm. Of these three, the diaphragm is the best plate for street use, but all three offer certain advantages. The Long style pressure plate is easily identified by the three thin fingers that engage the release bearing in the center. Under the pressure plate cover is a series of coil springs. In order to release the clutch, you must compress these springs. The lever arrangement allows the clutch tuner to add small weights to increase centrifugal loading on the pressure plate as engine speed increases. The Long style is mainly used for drag race applications where the static load (established by the stand height) can be adjusted separately from centrifugal load.
The Borg & Beck style is similar to the Long style and is basically a street version of the Long style pressure plate. It can be identified by the somewhat wider three fingers that release plate pressure by compressing the coil springs found under the pressure plate "hat". Certain applications of the Borg & Beck also offer centrifugal assist for high-rpm, high-horsepower applications. The Borg & Beck uses rollers inside the cover that are forced to the outside under centrifugal force to increase the plate load with rpm.
The diaphragm pressure plate uses a single, large Bellville-style spring to load the pressure plate. There are several advantages to this style of spring. First, it loads the pressure plate evenly since the pressure is equally applied to the entire plate assembly. Second, and more importantly, as the Bellville spring is compressed (clutch released), it reaches a point where the pedal effort decreases when the spring over-centers. This makes holding the clutch pedal in at a stoplight much easier than a coil spring type pressure plate.
Friction-disc clutches generally are classified as push type or pull type depending on the location of the pressure plate fulcrum points. In a pull-type clutch, the action of pressing the pedal pulls the release bearing, pulling on the diaphragm spring and disengaging the vehicle drive. The opposite is true with a push type clutch where the release bearing is pushed into the clutch disengaging the vehicle drive. In this instance, the release bearing can be known as a thrust bearing.
Clamp load is the measurement of the clamping force applied to the clutch disc when engaged (squeezed) between the flywheel and clutch pressure plate. The clamp load is generated by the springs, diaphragm, etc. that are housed in the pressure plate. Clamp load can also be effected by the clamping distance or clearance between the flywheel friction surface and the pressure plate friction surface and can be adjusted on many race style clutches. Clamp load has a direct feedback to pedal pressure or pedal force required to disengage the clutch. In general, the higher the clamp load, the stiffer a clutch pedal will feel. This effectively limits the drivability of high clamp load style clutches on street cars as the high pedal pressures can make them uncomfortable to drive, especially in traffic. All Fidanza Performance V-Series clutches are designed to deliver 15-25% increase in clamp load over the stock clutch application in order to provide optimum performance increases while still allowing for great drivability.
A flywheel at its most basic is a device to store energy. In the case of a flywheel used in automotive applications, it actually serves several purposes. First, it does store energy to help smooth out the torque and power flow of the engine as it runs through its combustion cycles. The flywheel gains energy as the engine accelerates, and stores it as rotational kinetic energy. It then gives some of that energy back to the system to help create momentum to carry the crank and pistons through the compression cycle and help optimize power delivery. Secondly, the flywheel also helps deliver rotational and torsional stability and balance to the engine’s rotating assembly (crank, rods pistons, etc.) in order to help the engine run smoother and reduce wear.
Next, most flywheels today also provide the power and torque transfer point between the engine and the vehicle’s driveline (clutch, transmission, driveshaft, axles, etc.). The flywheel bolts directly to the engine’s crankshaft and rotates at the same RPM as the engine. When the clutch is engaged, that rotation and accompanying power and torque are then transferred through the gears of the transmission (adjusted by the transmission’s gear ratios), to the driveshaft, then axles, then the wheels and eventually to the ground to move the vehicle. This of course is a simplified description, but it covers the basics.
In addition, most flywheels used in internal combustion engines also provide the mounting location for the starter ring gear, which creates the interface to initiate the rotation of the engine’s internals and start the combustion cycle (get the engine started).
The idea of changing engine performance by changing the timing of valve-train components and how they interact has been around since the first hot-rodders started modifying their internal combustion engines. Opening intake or exhaust valves a little sooner or a little later, or changing their orientation to the piston position or their overlap and duration have been staples of adding power to cars for decades. For conventional V configuration engines; this was most often done by changing the actual camshaft profile, putting in a “performance” camshaft or possibly switching to different ratio rocker arms. Controlling the valve-train timing means controlling how the air and fuel move through the engine and to an extent, how efficiently the mixture is burned/used to make power.
With the advent of overhead cam engines and movement to external mounted cam gears to provide the location for a timing belt or chain to connect and coordinate the timing between the crankshaft and camshaft(s), engine builders and tuners found another spot that would allow them to more easily adjust valve-train timing, without needing to change the actual camshaft(s); the cam gears. These cam gears could most often be easily accessed and did not require actually opening up the engine, and since they were bolt-on external parts, they were much easier to adjust and less expensive to modify than a hardened camshaft. The first “cam gear pioneers” simply modified their stock cam gears to try and get a few degrees of adjustment and improve performance, but with mixed results, as modified cam gears were often not accurate enough to provide precise timing or would sometimes break when not machined correctly. As this practice gained popularity, manufacturers like Fidanza saw the potential for specially designed “adjustable cam gears” that were stronger, lighter, looked better and had a greater / more precise range of adjustment to allow tuners to seek out the optimum in power and performance from the engines they worked on. The easy adjustability also meant that as other items were added or subtracted from the vehicle: headers, nitrous, turbo, etc. the timing could be easily re-adjusted to get the most out of the new configuration.
Some of the effects of altering camshaft timing include being able to increase overall horsepower and even adjust the engine’s torque curve and power band. So if you’re looking for an easy and economical way to get some additional power out of your car’s engine, try some Fidanza Performance adjustable cam gears!
NOTE: For optimum performance gains and to protect your engine, we recommend having your cam gear timing professionally set by a reputable tuner / dyno facility.
Fidanza performance adjustable cam gears are CNC machined from high quality 6061 T6 aluminum and are all designed to deliver timing adjustment up to +/- 12 degrees.