particles that would otherwise be released into the atmosphere; it greatly obstructs exhaust flow and can sap almost as much power as a small air conditioning compressor. Two-stroke engines Engine braking in a premix two-stroke engine can be extremely harmful to the engine, because cylinder and piston lubricant is delivered to each cylinder mixed with fuel. Consequently, during engine braking, the engine starves not only of fuel but also lubricant, causing accelerated wear. Many old two-stroke cars (Saab Automobile, Wartburg 353, etc.) had a freewheel device on the transmission to make engine braking optional. Most two-stroke motorcycle engines since the 1970s have had lubrication by an oil pump, independent of the throttle and fuel system, such as Suzuki's Posi-Force system. Applications As soon as the accelerator is released enough to slow the engine, engine braking comes into effect as long as the wheels remain connected via the transmission to the engine. A slipping or disengaged clutch, or a torque converter, would disengage the wheels or absorb braking energy. The braking force varies depending on the engine, and the gear the transmission is in. The lower the gear, the higher the braking effect due to higher rpm and the torque transferred through the transmission (higher torque is delivered from the engine in lower gears). Engine braking avoids wear on brakes, and can help a driver maintain control of the vehicle. Active use of engine braking by shifting into a lower gear can help control speed while driving down very steep and long slopes, saving the brakes from overheating or excessive wear. If it is applied before the brakes have been used, it can leave the brakes available to make emergency stops. The desired speed is maintained by using engine braking to counteract gravitational acceleration. Potential transmission wear caused by engine braking can be mitigated by certain techniques. Slipping the clutch to complete a downshift wears the clutch plate as it slows the vehicle, doing the job of the brake pads or shoes. A well-executed rev-match in the same setting minimizes stresses on transmission components, so engine braking does the work of slowing the vehicle. Improper engine braking technique can cause the wheels to skid (also called shift-locking), especially on slippery surfaces, as a result of too much deceleration. As in a skid caused by overbraking, the vehicle will not regain traction until the wheels are allowed to turn more quickly. If