A good design is sum of great engineering choices resulting a satisfactory compromise.
The goal has been to design street drivable, 120hp per litre M60 engine with smooth power delivery, and reasonably good idle characteristics. Is it possible without Vanos? Please read on!
First, I recommend you to read my previous articles in order to shed some light on: Why to build custom 4,4 litres BMW M60B44 engine? and Building tips for high performance M60B44 engine with over 130% volumetric efficiency.
Design limitations:
This design is based on the dynoed, and extensively tested engine. As you know from the previous articles, the engine is 4,4 litres BMW M60B44 frankenmotor. Currently it has 294 CFM cylinder heads, hollow billet cams and custom built 4 to 1 headers among other mods, such as Motec M150. From this baseline, the following changes has been designed for the engine:
A) Bimmerblog.org designed, secret sauce camshafts,
These camshafts:
- provide better idle and part throttle drivability than aftermarket cams,
- are exceptionally good at reducing parasitic losses,
- are suitable for up to 120hp per litre configuration,
- No rollercoaster in power curve,
- No risk of knocking in high compression engine.
B) Bimmerblog.org designed, individual throttle bodies (ITBs) with bellmouths:
- Tapered intake runners,
- 55mm butterflies,
- Effective runner length is 216mm,
- Effective runner diameter is 53,4mm,
- Relatively easy to DIY from aftermarket or OEM parts.
Other remarks:
- The low end torque was not a design parameter: only the smoothness of power curve,
- 41mm header primaries can be deemed undersized by many,
- Collectors are seen restrictive in layman’s terms, yet the negative supercharging is substantially high at 8000rpm,
- ITBs and aggressive idle ignition control by Motec further improves idle quality,
- Amount of scavenging for the engine has been found by trial and error, and;
- This works across different cams,
- Engine lifespan will be severely reduced with mean piston speed of 26,2 m/s @9500rpm,
- Short stroke crankshaft is highly recommended for the application.
Bottom line:
Yes, 120hp per litre, naturally aspirated M6x engine is doable on the street. Cams, cylinder heads, headers and intake manifold have to be carefully matched together.
More information about performance upgrades can be found on my other articles:
BimmerBlog.org 