Twin Charge Setup Guide – Supercharger and Turbo Combined on OM606 Diesel Engines

Twin charge setup combining a supercharger and turbocharger on the same engine is one of the most interesting performance configurations available for OM60x diesel builds. Today we cover the correct ways to do it, the wrong way that must be avoided and how to calibrate the supercharger boost level.

Supercharger Basics for Twin Charge Applications

The most common and affordable superchargers for twin charge setups are Eaton units – the M62, M90 and M112 found in Mercedes, Jaguar and Ford applications. These are widely available at scrapyards for very little money.

The critical limitation of Eaton roots style superchargers is one bar maximum boost. Beyond one bar the rotors start contacting each other under pressure, the air gets very hot and reliability drops rapidly. Set the supercharger to boost below one bar – 0.9 bar is a good target. At one bar and below these superchargers are efficient, cool and durable.

Screw style superchargers can handle two to two and a half bar and could theoretically replace the turbo entirely for moderate power builds. But today we are talking about combining both for the best of all worlds.

The Wrong Way – Do Not Do This

Do not route turbo boost through the supercharger. This creates a compound setup where turbo compressed air enters the supercharger and gets compressed again. The supercharger will consume more power than the additional compression provides. The system works against itself. Several failed builds have used this configuration. It does not work.

Correct Configuration 1 – Supercharger Into Turbo Inlet

The supercharger feeds compressed air into the turbo inlet. The turbo has two inlets – one from the supercharger and one open to atmosphere, closed by a flap valve.

At low RPM and boost the supercharger provides immediate boost response. The compressed air enters the turbo inlet and the turbo spools faster because it is already receiving pressurised air rather than atmospheric air.

When boost rises above the supercharger's effective range – approaching one bar – the flap valve on the atmospheric inlet opens. The turbo now draws unrestricted atmospheric air directly while the supercharger continues spinning without compounding. The turbo takes over boost duties entirely.

This configuration works well. Friends running this setup for years with excellent results. Simpler to implement than configuration two. The main consideration is ensuring the supercharger does not over-spin and that the flap valve is correctly calibrated for the transition point.

Correct Configuration 2 – Supercharger Into Intake Manifold

Standard turbo setup – turbo to intercooler to intake manifold. The intake manifold has two inlets. One inlet receives boost from the turbo via the intercooler. The other inlet receives boost from the supercharger through a small water to air charge cooler.

A flap valve closes the supercharger inlet when turbo boost arrives. When the turbo builds pressure the boost pushes the flap closed, sealing the supercharger inlet, and all boost comes from the turbo through the standard intercooler path.

This configuration is slightly more complex to execute correctly because the supercharger inlet must be fully sealed. Any boost leak at the flap valve when the turbo is running at two to three bar causes problems – the turbo loses pressure and the supercharger may over-spin. The sealing requirement demands higher quality fabrication than configuration one.

The advantage is that the turbo circuit remains completely standard and unaffected by the supercharger installation. The supercharger operates completely independently from the turbo.

Which Configuration to Choose

Configuration one is simpler to build and has proven reliability in real world use. Recommended unless there is a specific reason to separate the turbo and supercharger circuits completely.

Configuration two offers a cleaner turbo installation and is theoretically better but demands more precise fabrication. Choose this if packaging constraints make configuration one difficult or if you want the turbo system to remain completely standard.

Calibrating the Supercharger

The supercharger pulley ratio determines how much boost it produces. Start with the supercharger running alone – no turbo – and test different pulley sizes until the desired boost level is achieved. Target approximately 0.8-0.9 bar to stay safely below the one bar limit.

Once the supercharger is calibrated install the turbo and run the complete twin charge system. The supercharger provides immediate response from idle. The turbo builds and takes over at higher RPM. The transition should be seamless.

Why This Makes Older Engines Excellent

The OM601, OM602 and OM603 engines have less natural aspirated power than the four valve OM604, OM605 and OM606. This makes turbo spool harder to achieve on these older engines. A twin charge setup is particularly effective here – the supercharger provides the exhaust gas flow needed to spool the turbo much earlier than the naturally aspirated engine alone could manage.

For US builders working with OM601, OM602 and OM603 engines a bolt-on M90 bracket for these engine families would be an excellent product. The twin charge setup transforms these engines.

Summary

• Twin charge setup combines supercharger for immediate response with turbo for peak power
• Eaton M62 M90 M112 superchargers: maximum one bar boost, very affordable, widely available
• Wrong configuration: never boost turbo compressed air through the supercharger – compounding in this direction does not work
• Configuration one: supercharger feeds turbo inlet with atmospheric bypass flap – simpler to build
• Configuration two: supercharger and turbo feed intake manifold separately via flap valve – cleaner but requires sealed fabrication
• Calibrate supercharger with pulley changes running supercharger alone before installing turbo
• Twin charge is especially effective on older two valve OM601 OM602 OM603 engines with less NA power

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