Twin Scroll Turbo System Design - Full-Race

Designing a high-performance twin-scroll tubular manifold like those available from top tuners like Full-Race is no simple task. Fitting equal-length primaries into the tight confines of a turbocharged car's engine bay while maintaining proper radius bends and strong exhaust gas flow characteristics is a serious design challenge. Determining the best length and diameter of the primaries and angle of the merge collector also requires a lot of R&D, as does choosing the best wall thickness and material for the tubing itself. That's where Full-Race's team of highly educated mechanical engineers and years of constant refinement of their designs comes into play. According to Geoff at Full-Race, "Because of the increased turbine efficiency found in twin-scroll systems, twin-scroll manifolds can often use a smaller runner than a single-scroll design. However, due to the complex shape of the runners and the requirement for a second wastegate and dumptube (one for each side of the divided turbine) there's more mass and more parts which adds expense and complexity. Plus, twin-scroll turbos are physically larger than their single-scroll equivalents, so it's more difficult to make them fit our cramped engine bays." Overcoming these challenges means developing extremely robust manifolds that make smart use of the available space, something Full-Race does with the help of computer programs like SolidWorks and other proprietary processes.

All this hard work does translate to serious performance gains in the power-delivery department, particularly at spool-up and peak torque where sophisticated tubular twin-scroll manifolds properly matched to a twin-scroll turbo deliver superior airflow to single-scroll or OE twin-scroll designs. According to Geoff, "Our twin-scroll turbo kits have a higher average cylinder pressure and turbine efficiency, while single-scroll systems tend to have a higher peak cylinder pressure and exhaust backpressure. We have found the twin-scroll systems have higher backpressure at low rpm (which is good for turbo spool-up) and lower backpressure at high rpm (which is good for top-end performance). On the other hand, single-scroll systems have lower backpressure at low rpm (bad for spool-up) and higher backpressure at high rpm (which hurts top-end performance)." In order to realize the full benefit of a top-shelf twin-scroll system like one of Full-Race's, the manifold design and A/R ratio of the turbo must be spot-on, so it's best to get the help of a professional when choosing a turbo for this type of system.

It's certainly possible to generate huge power and great high-rpm performance with a single-scroll turbo system. There are plenty of examples of very high-horsepower, single-scroll turbocharged engines out there, but with single-scroll systems spool-up and response are much slower than with a twin-scroll design, yet twin-scroll systems still provide excellent top end performance. Although switching from single-scroll to twin-scroll can be expensive, for hard-core boost junkies who want much faster throttle response without giving up any top end, there is no better solution. With the added benefits of higher turbine efficiency, lower cylinder temps and EGTs which allow more aggressive timing and fuel mapping, and the freedom to run more overlap,twin-scroll turbo system design is really a perfect match for the high specific output engines featured in many of our favorite sport compact machines.

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