Twin-scroll and twin-turbo are different hardware. A twin-scroll turbo is one turbocharger with a divided turbine housing that keeps exhaust pulses from paired cylinders apart. A twin-turbo engine uses two complete turbochargers. This guide explains the difference, how a twin-scroll system is built, and where it is used.
Quick answer
Twin-scroll means one turbo with two exhaust passages feeding its turbine. Twin-turbo means two turbos. An engine can even have both, with two turbos that each use a twin-scroll housing.
Twin turbo vs twin scroll at a glance
| Feature | Twin-scroll | Twin-turbo |
|---|---|---|
| Number of turbochargers | One | Two |
| What is “twin” | Two exhaust passages (scrolls) in the turbine housing | Two complete turbos |
| Main aim | Preserve exhaust pulse energy for earlier boost | Split the workload (parallel) or cover low and high rpm (sequential) |
| Needs | Divided manifold that keeps cylinder groups apart | Extra plumbing, space and cooling |
How a twin-scroll turbo works
A single-scroll turbo collects all exhaust into one path. Pulses from different cylinders can interfere with each other before they reach the turbine. A twin-scroll turbo groups cylinders so consecutive exhaust events stay in separate passages up to the turbine wheel.
BMW describes the four-cylinder layout as cylinders 1 and 4 on one path and cylinders 2 and 3 on the other. Six-cylinder engines can use the idea too: BorgWarner has described a BMW 3.0-litre inline-six system with three cylinders feeding each scroll.
The turbine housing alone is not enough. The exhaust manifold must keep the groups separate, as Garrett and BorgWarner both explain in their technical notes.
Benefits and limits
- Earlier turbine response at low and medium rpm, where pulses are still distinct.
- Less pulse interference and better scavenging, depending on valve timing and manifold design.
- One turbo keeps packaging simpler than two.
- More complex exhaust: a divided manifold and matching housing are required.
- Smaller benefit at high rpm, where exhaust flow behaves more like a steady stream.
Gains are not a fixed percentage. One 2025 SAE paper on a direct-injection gasoline engine reported higher low-end torque with twin-scroll but slightly higher average part-load fuel consumption, so better response does not always mean better economy.
Where twin-scroll turbos are used
Mitsubishi’s own history lists a twin-scroll turbocharger on the 1989 Minica Dangan-4 and on the 1996 Lancer Evolution IV. BMW has used it on four- and six-cylinder engines. The original Toyota GT86 is not an example, because Toyota describes it as naturally aspirated.
For a plain-language walkthrough of the mechanism, read our twin-scroll turbo explainer. If you are weighing turbo trims on a compact car, see the Mazda 3 Turbo AWD specs.
Twin-scroll vs single-scroll: what to check before choosing
- Confirm the engine’s exact turbo type in the manufacturer’s documentation.
- For a modification, plan for a matching divided manifold, housing and ECU tune.
- Remember turbine A/R: a smaller A/R generally improves low-speed response but can restrict high-rpm flow, per Garrett.
- Do not expect a twin-scroll label alone to add peak horsepower.
Frequently asked questions
What is the difference between twin-scroll and twin-turbo?
A twin-scroll system is one turbocharger with two exhaust passages in its turbine housing. A twin-turbo engine uses two complete turbochargers.
Is a twin-scroll turbo better than a single-scroll turbo?
It can be when low- and mid-rpm response matters, because it preserves exhaust pulse energy. A single-scroll turbo is simpler, and either can perform well when properly matched to the engine.
Does a twin-scroll turbo remove turbo lag?
No. It can reduce response delay, but turbine size, rotating inertia, gearing and engine calibration still affect lag.
What are the downsides of twin-scroll turbos?
They need a divided manifold and turbine housing, which adds complexity and cost. The response advantage also shrinks as engine speed rises.
Can an engine be twin-turbo and twin-scroll?
Yes. An engine with two turbochargers can use twin-scroll turbine housings on each one.
Is a twincharger the same as a twin-scroll turbo?
No. A twincharger combines a turbocharger with a mechanically driven supercharger, as in Volkswagen’s 1.4 TSI Twincharger. It is a separate concept.
[…] Twin-scroll and twin-turbo are different things. For a closer look at the naming confusion, see our guide to twin-turbo vs twin-scroll. […]