Flywheels, Pressure Plates and Clutches

[Richardnew]

Here's an article I wrote for Vintage Motorsport magazine a few months back. It's a very basic look at the options you have available.



Richard Newton

[chris_seven]

This basically follows on from Richard's comments and I always think it is helpful to light the darkness with a few numbers and would like to consider two cases.

The first is a 901 engine with a stock and lightened steel flywheel similar to the one we recently shipped to Merv in Australia.

Stock Flywheel: 12.05lb Inertia 0.154kgm^2
Light Flywheel: 7.1lbs Inertia 0.091kgm^2

Using 6” wheels and 185 x 70 profile tyres with 1967 911S Gear ratios the equivalent flywheel masses calculate as follows;



This isn’t quite the full picture as these simple calculations assume acceleration from zero rpm in a single gear.

To gain a better understanding we need to think about the ‘Constant Equivalent Mass’ which accounts for free flywheel energy and the recovery of energy between gear shifts – this makes the math a bit more complex but to contrast is interesting. It also assumes a specific 'launch' rpm and we used 2500 as an average value.



It is also worth looking at the 911 engine with the larger diameter (225mm) but lighter flywheel and the RSR Flywheel.

Stock Flywheel: 8.36lbs Inertia 0.117kgm^2
RSR Flywheel 6.3lbs Inertia 0.076kgm^2 (Assumes RSR Style scalloped edges)

Basic Equivalent Flywheel Mass as follows:



Constant Equivalent Mass case:



A more complete analysis with lightened clutches, wheels, brake rotors etc can be carried out to show where weight saving and hence 'bang for your buck' can be carried out with a relatively straightforward spreadsheet.

[Merv]

Very nice article Richard. Good timing as well. It almost seems a shame to hide the flywheel from Chris in the bell housing ...