OM606 NA vs Turbo Engine Differences – Blocks, Rods, Pistons and Camshafts Explained

OM606 NA vs turbo differences are fewer than most people expect but the ones that exist matter significantly for build planning. Today we cover every meaningful difference between naturally aspirated and turbocharged versions of the OM606 and OM605.

Pistons and Rods – The Primary Difference

The most important difference between OM606 NA and turbo engines is the connecting rods and pistons.

Wrist pin diameter:

• Turbo engines: 28mm wrist pin
• Naturally aspirated engines: 26mm wrist pin – always, regardless of version

This affects rod interchangeability directly. Turbo rods cannot be fitted to NA pistons and vice versa without machining. When upgrading an NA engine to forged rods you must source rods with 26mm wrist pins or machine the existing pistons.

F-tune Performance forged NA rods with 26mm wrist pins are available specifically for this application and drop directly into any NA OM606 or OM605 engine.

Oil Squirters – Both Have Them, Different Design

Both NA and turbo OM606 engines have oil squirters for piston cooling. This distinguishes the entire OM604 OM605 OM606 family from the older OM601 OM602 OM603 where only turbo versions have squirters.

The squirter design differs between NA and turbo versions because turbo pistons have an internal cavity that the squirter nozzle enters to spray oil directly inside the piston crown. NA pistons do not have this cavity so the squirter nozzle design is different. When fitting turbo pistons to an NA engine the oil squirters must also be changed to turbo specification.

Valve Size, Head and Springs – Identical

Valve sizes are the same between NA and turbo versions. The cylinder head is the same. Valve springs are the same. Everything above the deck surface is interchangeable.

The Block – Two Types

Early OM606 engines – those equipped with mechanical injection pumps from factory – have what is called a skeleton block. This is a slightly different construction than the later turbo block. However it is not weak. It is genuinely strong and nobody has ever broken one through normal high performance use. The difference is real but practically irrelevant for most builds.

Later OM606 engines equipped with EDC pumps from factory – such as those found in the W210 chassis – use the same block as the turbo engines. No difference in block specification between these NA EDC pump engines and factory turbo engines.

Camshafts – The Interesting Distinction

Early NA engines with mechanical injection pumps use NA specification camshafts. These produce maximum power at approximately 5400 RPM.

Later NA engines equipped with EDC pumps from factory use turbo specification camshafts. Mercedes apparently did not bother swapping the camshafts when they moved to EDC pump NA versions – they simply used the turbo cam specification in the NA application. This means these later NA engines already have a more aggressive camshaft profile than the early mechanical pump NA versions.

Why a Built NA Engine Beats a Stock Turbo Engine

With forged NA specification rods fitted the naturally aspirated OM606 becomes stronger than a stock turbo engine at equivalent power levels. The factory turbo rods are adequate for stock power but are not the limiting factor in a built NA engine with proper forged replacements.

A built NA OM606 with forged rods, correct head gasket and an appropriate turbo and injection pump can be cheaper to build, equally strong and just as fast as a factory turbo based build. The NA engine's lower purchase price offsets much of the upgrade cost.

Summary

• OM606 NA vs turbo: primary differences are wrist pin size and block specification
• Turbo engines: 28mm wrist pin, turbo block, turbo camshafts
• Early NA mechanical pump engines: 26mm wrist pin, skeleton block, NA camshafts
• Later NA EDC pump engines: 26mm wrist pin, turbo block, turbo camshafts
• Both NA and turbo versions have oil squirters – design differs between specifications
• Valve sizes, head and valve springs are identical between NA and turbo versions
• Forged NA rods with 26mm wrist pins drop directly into NA engines
• Built NA engine with forged rods is stronger than stock turbo engine at equivalent power

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