Perfect Power Application Notes.


Application Note - AN 10

This note describes the principle, wiring, and set-up of the LAUNCH control feature in the XMS4 system. A wiring diagram is included.



A turbo exhibits a "delayed" action. At low RPM the turbo is not spinning, and the result is no boost. Because the engine is decompressed, it is very lazy. When starting from a dead stop, one has to "tease" the engine, to get the turbo spinning. This helps, but it is not the solution. The LAUNCH control was invented (not by us) to overcome the turbo lag.

Turbo Launch Control

A TURBO LAUNCH CONTROL RPM setting is specified, let's say 4000 RPM. Then a switch input (switch#2) is activated, which tells the XMS4 unit that LAUNCH is active. At this point the ignition retards to the max retard that was entered into the Parameters map (shiftF1). Then the throttle is pressed, which increases the RPM. Once the RPM reaches the entered Launch RPM, the ignition is RETARDED to a point where the RPM increases no further. Now the turbo is spinning, and it produces boost. At the time when the clutch is released, the S2 switch opens, and the ignition JUMPS to the map advance. The result is that the car takes off, with the turbo spinning. The turbo lag has been eliminated.



Bad Points

The above operation results in extreme exhaust temperatures, because unburnt gas is leaving the ports. The exhaust valves, manifold, and turbo are subjected to very high temperatures. This should only be done for seconds, and for racing applications only. The turbo launch control is not recommended for street use.


XMS4 Stand Alone Unit - Launch Control Wiring


It works! But at a price! It works better if the turbo is a fair distance from the ports, and if the branches are made from high temperature material. A variation of the turbo launch control has been tried on a tack racing engine, but I can't report on the success.