OM606 Stroke and Bore Guide – Why Camshafts Control Power Not Stroke Length

OM606 stroke and bore misconceptions are everywhere online. Today we correct the most common one – the idea that short stroke causes the high revving nature of these engines. It doesn't. Camshafts do.

Stroke is Stroke

The claim that the OM606 revs high because of its short stroke is wrong. Stroke length does not determine where an engine makes its power. Camshaft profiles do.

Here is the proof. A 2.9 litre OM605 stroker build uses a 92.4 millimetre stroke – significantly longer than the standard 84 millimetre stroke. That engine still revs happily to 7000 RPM and beyond. The CDI diesel engines use an 88.3 millimetre stroke and they produce all their torque at low RPM and fall flat at high RPM.

The difference between these engines is not stroke length. It is camshaft profile.

Bore and Stroke Specifications

Standard OM601, OM602, OM603, OM605 and OM606 engines:

• Bore: 87mm
• Stroke: 84mm
• Displacement: 2.0, 2.5 and 3.0 litres respectively

OM604:

• Bore: 89mm
• Stroke: 86.6mm
• Displacement: 2.2 litres

CDI engines:

• Bore: 88mm
• Stroke: 88.3mm

The difference between OM604 stroke and CDI stroke is approximately 1.76mm. Fitting a CDI crank to an OM604 does not transform it into a torquey low RPM engine. 1.76mm of additional stroke changes almost nothing about the power delivery character.

Camshafts Control Everything

The camshafts determine where torque peaks and where maximum power occurs. This is not adjustable by changing boost or turbo selection – those force the engine to produce power differently but the fundamental character comes from the cams.

Standard turbo camshafts on an OM606 produce maximum power at around 5400 RPM. NA camshafts raise this slightly. Stage 1 camshafts push maximum power to around 6500 RPM. Stage 2 camshafts reach around 7000 RPM.

If you want your OM606 to behave like a CDI engine with maximum torque at 1500-2000 RPM the solution is to have a cam grinder regrind your camshafts to CDI profile. Your engine will then produce maximum power at around 3900 RPM. It will be sluggish and boring at high RPM – even worse than a CDI because indirect injection is less efficient than direct injection at low RPM. That is not what anyone building a performance engine wants.

Be grateful for what these engines are. High revving, responsive and capable of serious power when pushed hard.

Stroker Builds – The Correct Displacements

For builders wanting more displacement and more low end torque the correct approach is a proper stroker build using readily available parts:

• OM604: 2.2 litre → 2.3 litre
• OM605: 2.5 litre → 2.9 litre
• OM606: 3.0 litre → 3.5 litre

These conversions use more or less standard parts that are combined correctly. They are simpler and more financially viable than the 2.7 litre or 3.2 litre CDI-based hacks that require extensive machining and do not produce significantly better results.

A 2.9 litre OM605 stroker is a completely different animal from a standard 2.5 litre engine. The additional displacement transforms low end torque and throttle response while maintaining the high revving character these engines are known for because the camshafts remain unchanged.

Watch the Videos Before Asking Questions

The same questions come in every day on Facebook and Instagram. Questions about stroke, camshafts, displacement and power delivery that are answered in detail across these videos. Watch the videos first. The answers are here. If you still have questions after watching then ask – that is absolutely fine. But asking the same question that was covered three days ago wastes everyone's time.

Summary

• OM606 stroke and bore does not determine high revving character – camshafts do
• Standard stroke is 84mm on OM605 and OM606, 86.6mm on OM604, 88.3mm on CDI
• A 2.9 litre stroker OM605 with 92.4mm stroke still revs to 7000 RPM – proving stroke is not the limiting factor
• CDI camshaft profile on an OM606 produces maximum power at 3900 RPM – slow and boring
• Correct stroker displacements: OM604 to 2.3L, OM605 to 2.9L, OM606 to 3.5L
• Stage 1 and Stage 2 camshafts are the correct way to move the power band higher

See you in three days. Bye!