Boost Controllers

The simplest form of engine management to extract more power is a manual boost controller. As its name implies, the boost controller maintains stock or higher levels of turbo boost. As in a "Stage I" application (Exhaust and intake) the boost controller overrides and adjusts turbo boost levels over the engine's entire rpm range. A manual or "solid response" boost controller, however, does NOT adjust/change other engine parameters such as timing or the air/fuel mixture. You will need a boost gauge (factory or aftermarket) to initially set the boost controller. 15 psi peak boost (up from 13.2 stock) seems to be the magical stage I number (Note that the factory ECU cuts fuel at 17 psi) for good power and reliable performance.

Fuel Controller/Computer

The factory ECU tends to make the engine run rich above 4000 rpm. Running too much fuel, especially with increased boost, decreases combustion (not enough air to combust all the fuel) and hence?less power.

A fuel controller/meter adjusts the fuel mapping, allowing the engine to increase its power output. This can be significant?in the magnitude of 15-25 hp for a properly tuned/matched fuel controller combined with a manual boost controller. An example of a fuel computer is the ApexI S-AFC.

For crusing down the highway, an air/fuel ratio of 14.5-14.7 is ideal for fuel economy and emissions. However, for big power (18+ psi boost), safe power (little or no detonation) the target AFR is 10.6-11.2.

Piggyback ECU & Full ECU Replacement

The next step up in engine management is either a "Piggyback" ECU or a full ECU replacement engine management system. These computer systems typically incorporate boost control, fuel controller, and add to the mix things like ignition/timing.

With more parameters than just boost pressure, a properly tuned engine management system can have a greater impact on mid-range torque and throttle response with little or no effect on reliability. This is because they have greater control over how the engine performs as a whole and do not need to resort to dangerously high boost levels as the sole method to make more power.

"Piggyback" ECU's (like the "UTEC" & "UNICHIP") typically add functionality to the factory ECU. The benefit of "Piggyback" ECU's is that the factory ECU typically retains control over the vehicle's vitals. In other words, the factory ECU still reads and uses all factory engine sensors (such as O2) and performs as the factory intended. Therefore, a "Piggy-Back" system usually only influence the "performance" parameters (such as turbo boost, fuel mixture, timing, etc.). It does this by intercepting the factory ECU signal, sending preprogrammed performance parameters (i.e. higher boost), and then "lying" to the factory ECU when sensor information is sent back (no?I am only running 13.2 psi?not 15 psi :^).

The downside to "Piggyback" ECU's is that they typically need to be installed and tuned by a shop (standard/base maps are available that work fairly well). The key here is "tuned". Since every car that leaves the factory slightly different, new engine management needs to be adjusted to your car's parameters to maximize its potential. Some tuners (Vishnu used to do this before the ECUTEK reflash was available) will use a piggyback ECU along with a manual boost controller.

A full replacement or stand-alone engine management system (Link, AEM, TEC-II, etc.) allows even greater flexibility. With that flexibility comes complexity, custom fitting, and cost (expect to pay $600-1,200 over a "Piggy-Back" ECU). As you progress further down the power path (monster turbo, custom cams, new fuel systems, etc.) a replacement ECU becomes necessary.