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Another long term passion is cars, and my current garage consists of a BMW Z4 E85 3.0i and an Alfa Romeo 4C Spider.


I do not like the over-the-top styling you see many car enthusiasts deploy, but I believe subtle styling modifications can improve the visual appeal. Mechanical and electronic mods are also welcome!   fsdf

BLCK Z4 Side 01.jpg
Z4 Suspension 02.jpg

Q: Theoretically, how high can my engine rev?

Engine RPM is limited by various factors. One problem with high RPM in a DOHC engine is valve lift, where the springs literally cannot pull the valve closed fast enough and the piston hits it. This is only ever a bad thing and leads to a severe engine failure!

Another limitation is determined by the bore and stroke of your cylinders, in particular the stroke. Engines can only move the cylinders at a max speed of approx 25 m/s. Doesn't matter if it is a road car or a Formula 1 engine, this limit is constant. With this in mind, and kowning your cylinder stroke in mm, the cylinder speed can be calculated for various RPM.

Piston Speed = 2 x stroke length x RPM / 60

My BMW Z4 E85 3.0i

Bore 84mm Stroke 89.6mm

Piston Speed

2 x 0.0896 x 6500 / 60 = 19.4 m/s

So in theory if the M54B30 engine could reach 8,000rpm

2 x 0.0896 x 8000 / 60 = 23.9 m/s

This is quite close to 25 m/s so for reliability allowance let's assume a red line of 7,500

2 x 0.0896 x 7500 / 60 = 22.4 m/s

My Alfa Romeo 4C Spider

Bore 83mm Stroke 80.5mm

Piston Speed

2 x 0.0805 x 6500 / 60 = 17.4 m/s

So in theory if the 1750 TBi engine could reach 8,000rpm

2 x 0.0805 x 8000 / 60 = 21.5 m/s

This is still well below 25 m/s so let's try raising the RPM even further to 9,000

2 x 0.0805 x 9000 / 60 = 24.2 m/s

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