What is a twin scroll turbo and is it always good thing


Pro Tuner
Staff member
2002 Clio 172
Read in one of @sleepers posts about a twin scroll manfiold on a turbo. What are these what are the benefits and are they always better than a standard turbo?
Twinscroll is the turbo type on latter Subaru STIs. I've taken a look at a few.
In the most basic terms it could be considered two turbines housed in one turbo unit. A small one that will spool quickly from low revs but will lose the will to live at, for example, 4k revs, and a big one that spools slower but sustains boost from, say, 4k revs through to red line.

The effect is quicker spool and boost sooner and longer. The payoff is increased cost; like most things.
Yes a sequential turbo works as above and could certainly be called twin schroll but thats not the what I was referring to

On an RB26 normal twin turbo set up cylinders 1,2 and 3 discharge into one manifold and to turbo 1 and 456 into the other . Pretty evenly balanced which is essential on a twin turbo RB26 style when they both come in together.
But now go single turbo - All exhausts discharge to the same place to drive one turbo . Sounds ok but it far from ideal because the pulses from the 6 cyliders all arrive at different times and this isnt efficient.
What a twin schroll manifold does is seperate the "unlike pulses" This means with equal lenght pipes the flow is much smother and way more efficient.
So twin schroll (rb26 style) isnt 123 into shcroll 1 and 456 into the other. This is why the twin schroll manifolds look far more complicated.
I have a Twin Scroll turbo on a split pulse /divided manifold and in a 4 cylinder no 1 & 4 enter 1 side of the divided turbine housing and meet up with cylinders 2 & 3 that feed the exhaust gasses into the other side of the turbine housing at the turbine wheel.

The single external wastegate on my car is fed from both sides of the divided manifold with the gasses separated until a few mm from the gate valve.

Ideally it is considered that there should be a gate on each side of the divided manifold for the best result but have been unable to find any direct comparison to prove any advantage that twins may have over my single set up.

It is important that the manifold has equal length pipes from each exhaust port for the best result.
hi guys new to this,well posted over a year ago,does anyone know what a peugeot rcz twinscoll 200 hp turbo can be taken upto by a re-map????as picking up the car tomm and already itching to get more hp 200 is fine but its not a small car and could do with 50 more horses.haha my names paul.nice meeting you guys.
The absolute 1st thing when searching for increased power in any turbo car is a free flowing larger diameter exhaust system that starts at the turbine outlet along with straight thru mufflers. THEN get it remapped.

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