Gripping Stuff - the ins and outs of clutches
If your mad nugget has a manual transmission and you're planning on owning it for a while, then you're probably going to have to change the clutch at some point, just like Moog did in the latest episode HERE.
But what is a clutch, how does it work, what upgrades can you do, and why does Moog put fish sauce on his ice cream? I'll aim to answer most of those questions below!
Basically a clutch is a mechanical linkage that transfers the power of your engine to the wheels, and is made up of three basic parts: the flywheel, the friction disc and the pressure plate. The engine's crankshaft spins around in a circular motion, getting faster as the RPM (revolutions per-minute) raise, and the flywheel is bolted directly to the crankshaft.
The flywheel is a thick steel disc, normally made very heavy to damp vibrations and make the clutch engagement smooth. You can buy "lightweight" flywheels (as Moog did), which helps performance by allowing the engine to rev faster through reducing parasitic loss.
Bolted directly to the flywheel is the clutch pressure plate, which most aftermarket companies paint a lovely bright colour because speed and performance is directly linked to how bright colours your parts are painted.
The pressure plate controls the clutch engagement as it pushes the friction disc onto the spinning flywheel as you let off the clutch pedal. The friction disc slides over the splined input shaft of the gearbox, so the clutch has to transfer the spinning motion of the flywheel and pressure plate to the friction disc without flying apart.
Upgraded pressure plates are often sold by advertised "clamping force", which is basically how hard it pushes the friction disc onto the flywheel - and that clamp force is important if you have hundreds of killerwasps spinning at thousands of RPM which need to be grabbed securely!
If the friction disc doesn't stick hard against the flywheel, or someone doesn't fully let off the pressure plate while revving the engine, you get clutch slip. Once a clutch is overheated and it is slipping you get that lovely "freight train full of poop on fire" smell all learner drivers get to experience at some point.
Thankfully, while nearly all clutch discs today are regarded as "organic" material, you can get friction discs made out of all sorts of fancy materials like ceramics and metals, which can handle the heat and pressure mad modded cars need.
In the above photo you can see the friction disc sitting inside the pressure plate. You'll also see four small coil springs. These springs help cushion vibrations and give you buttery smooth engagement as you let off the clutch pedal.
Some friction material discs are made in "puck" styles, which are a star, four- or three-pointed shape. These can have very aggressive engagement, so some clutch manufacturers make products with multiple friction discs. This is where you see "twin plate" or "triple plate" clutches (like what Marty fitted to his STi HERE), which have special pressure plates and friction discs to clamp massive horsepower loads but still give smooth engagement.
Now Moog's BRZ is ready for more power he can finally finish the Hyperdonga Megathrusta donk swap!