Twin Charge Setup Guide – Supercharger and Turbo Combined for Maximum Response

Twin charge setup guide – episode five and the final instalment of the five part boosting series. Today we cover the Holy Grail of diesel boost configurations: combining a supercharger and turbocharger for immediate response with unrestricted peak power.

The Five Boosting Methods Recap

This series has covered sequential turbo, single turbo, compound turbo, VNT and now twin charge. Each involves trade-offs. Twin charge uniquely minimises those trade-offs by combining two fundamentally different boosting technologies.

Why Twin Charge is the Holy Grail

Sequential requires complex plumbing and a compromised exhaust manifold. The small turbo and large turbo share the exhaust path creating packaging and efficiency constraints.

Compound is simpler to set up but relies on the small turbo as a critical component. Both turbos are connected and must work together continuously.

Twin charge – supercharger plus turbocharger – eliminates these connections. The turbocharger sits on a full tubular exhaust manifold with no restrictions, sized purely for peak power. The supercharger operates independently, connected only to the intake side. These two devices do not share any gas path. They are genuinely separate systems that happen to both feed the same engine.

This means you can build the most efficient single turbo setup possible and add a supercharger alongside it. Maximum efficiency from both components with no compromise to either.

Two Ways to Set Up Twin Charge

Method One – Supercharger boosting through the turbo

A diverter valve with two inlets and one outlet sits before the turbo inlet. One inlet comes from the supercharger, the other is open to atmosphere. A flap inside the valve moves freely – it opens whichever inlet is providing more airflow.

At low RPM the supercharger pushes air through the diverter valve into the turbo inlet. The turbo uses this pre-compressed air to spool faster. When the turbo reaches full boost it draws far more air than the supercharger can supply. The flap automatically moves to open the atmospheric inlet and the supercharger is effectively bypassed.

Simple construction, automatic transition, works well. The limitation is that the charge air passes through the turbo compressor regardless of which device is boosting.

Method Two – Supercharger boosting directly to intake

Standard single turbo setup – turbo, intercooler, intake manifold – completely unchanged. The intake manifold has an additional inlet port with a diverter valve. The supercharger connects to this port and boosts directly into the intake.

When the supercharger is boosting the diverter valve seals the turbo side to prevent boost from escaping back through the turbo circuit. When the turbo reaches boost pressure it pushes the diverter flap over and seals the supercharger inlet. The turbo takes over completely.

This requires a properly sealed diverter valve – it must seal in both directions under pressure. More engineering work than method one but the result is completely clean separation of the two systems. Open the bonnet and it looks exactly like a standard single turbo installation. The supercharger is an addition, not a fundamental change to the turbo system.

A small water to air intercooler between the supercharger outlet and the intake manifold is recommended when running this configuration. It removes heat from the supercharged air before it enters the engine.

The Transformation Half a Bar Provides

Half a bar – seven PSI – of boost from the supercharger completely transforms how an OM606 feels to drive. To demonstrate this on an automatic transmission: hold the brake fully, press the throttle until the boost gauge reads seven PSI, release the brake. The car launches on boost rather than building boost from a standstill.

This is what diesel engines lack – they only deliver full power once boost arrives. Adding even a small amount of boost from idle changes the character of the engine completely. One bar of supercharger boost effectively doubles the engine's displacement in terms of available exhaust gas to spool the turbocharger.

A three litre OM606 with one bar of supercharger boost is feeding the turbocharger as if it were a six litre engine. The turbo spools as though it is mounted on a much larger engine. The result is a large, efficient turbo that spools quickly and flows freely at high RPM – the combination that a single turbo can never achieve alone.

Lag vs Boost Response – The Distinction

Lag is when you are stationary or at very low speed, press the throttle and nothing happens while the turbo spools up from rest.

Boost response is when you are cruising at 60-80 mph with the turbo already partially spooled and you press the throttle – how quickly does boost build from that point.

Twin charge addresses lag specifically. The supercharger provides immediate boost from idle eliminating the period where the engine is unresponsive. Boost response at speed is determined primarily by turbo selection and is separate from what the supercharger provides at low speed.

Summary

• Twin charge setup guide: supercharger for immediate response, turbocharger for peak power, no shared gas path between them
• Method one: supercharger through turbo inlet with automatic diverter flap – simpler but less separated
• Method two: supercharger direct to intake with sealed bidirectional diverter – cleaner separation, more engineering required
• Small water to air intercooler between supercharger and intake recommended for method two
• Half a bar of supercharger boost transforms diesel engine character completely
• One bar of supercharger boost effectively doubles engine size for turbo spool purposes
• Lag is eliminated by supercharger boost from idle – boost response at speed is a separate characteristic
• Twin charge allows maximum efficiency from both turbo and supercharger simultaneously

That is all five ways to boost your engine. Happy boosting. Stay safe. Bye!