How it works
In the cockpit the driver will pull the shift lever to the rear (see Figure 1) in order to upshift the transmission. This is done without lifting from the accelerator. To downshift the transmission the driver will push the shift lever forward and blip the throttle to assist in the gear change by relieving load on the drivetrain.  The clutch is not used on downshifts either.

The shift-without-lift process starts when the driver moves the shift lever and triggers a series of electrical events. Attached to the shift lever is a spring loaded micro-switch that responds to the drivers inputs and sends a signal to a sensor located on the transmission. The sensor rides on a cam inside the transmission that allows it to identify which gear the transmission is in (see Figure 2). 

Simultaneously a signal is then sent to the vehicles Electronic Control Unit (ECU - see Figure 3) that will in turn momentarily interrupt the engines ignition and fuel system to one or more cylinders (sorry we can't say how many - manufacturers secret). The gears in the transmission are momentarily unloaded enabling the synchronizers to lock a different gear to the transmission's main shaft. In a street car the load is removed from the transmission by depressing the clutch pedal and momentarily disconnecting the engine from the transmission's input shaft. The driver then can change gears and release the clutch, thereby reconnecting the engine to the transmission.  In a Champ Car the clutch mechanism is used only when moving from a standstill. 

The Electronic Control Unit shown below in Figure 3 will interrupt the engines ignition system for 30 to 50 milliseconds allowing for the upshift or downshift to take place. The amount of delay and other system parameters are programmed differently depending on the type of track the car will be used on and the gear ratios chosen. This is one of the reasons you will see the engineers toting their laptops around the garage area and connecting them to the cars ECU's at various times. 

From the drivers seat the transition between gears occurs in rapid succession with little notice of the systems intricacies. From the engineers standpoint the gear change must be made in the shortest possible time. To give you an example of the importance of this, consider that combustion takes place in each of the engines cylinders in 3 milliseconds or less. When this burn time is interrupted there is loss of power from that cylinder. Combustion pressure is lost and can only be regained when the piston arrives to complete it's next compression and power strokes. When the engineers deal with this system the relevance of 50 milliseconds of ignition and/or fuel system interruption means power is lost in the interrupted cylinders for as many as 3 'combustion' cycles each (assuming around 16,000 rpm). The trade-off of lifting off the throttle, however, is even worse.

One benefit of the shift-without-lift technology is that we no longer see engines ruined due to over-revving on upshifts when a driver misses a gear.  Unless the shift mechanism fails, it simply no longer happens due to driver error. That means less blown engines and money saved.  All over-revs you hear about today are done on downshifts.

While all of this high tech hardware might provide for faster lap times than the old clutch and shift method the driver must still properly time the upshifts and downshifts to optimize power output. No easy task on some of the big road and street courses at the speeds Champ Cars run and the vibration and g-force loading they are experiencing.  A healthy dose of respect is given to the drivers and engineers that prepare and drive these cars on race day.

Go to our forums to discuss this article