UPRATED ACTUATORS

A factory actuator will be perfectly adequate for standard power, but if you’re planning to ask your car’s turbocharger to produce more boost, OEM parts can quickly become a limitation. In truth, an OEM actuator spring tends to be soft, which can result in a series of unwanted effects when it comes to tuning. In some cases, you may run into issues with exhaust back pressure, whereby the exhaust gases on the exit side of the wastegate overcome actuator spring load and force the wastegate open prematurely. As Gary Conway, Managing Director at London-based premium sports car tuning specialist, GCAP Performance, explains, “OEM wastegate actuators tend to use fairly soft springs, which can allow wastegates to start opening long before peak boost is reached. The risk is you lose out on much of the power your car is capable of producing. A stronger spring will provide faster spool-up, less boost drop at high rpm and a more stable, more responsive boost curve.”

Unsurprisingly, the spring inside a modern uprated actuator can be switched to meet the demands of the host engine and turbocharger. Additionally, modern actuators feature an increased surface area in the diaphragm housing (an important design consideration), which equates to more mechanical advantage over the actuator — your Porsche benefits from quicker peak boost and you’re able to control it fast due to the altered diaphragm surface area. This aspect of wastegate and actuator design is referred to as ‘control ratio’.

More often than not, uprated actuators offer improved reliability over OEM actuators thanks to high-performance fluorosilicone diaphragms with Nomex reinforcement. Additionally, most aftermarket performance actuators are configurable, allowing fine-tuning through selectable springs and preload adjustment.

As a case in point, Design 911 offers modern replacement actuators for the 993 Turbo, with spring pressures ranging from 5psi (spool-up) to 20psi (tuned running pressure).