Transmission & Drive Train
It’s all torque
For the Jeremy Clarksons of the World who do not understand what torques are just think about a foot pushing down on a bicycle pedal and that effort going down the chain to the back wheel. The push of your leg at the end of the pedal crank makes torque. Your engine also produces torque and it is the job of the transmission to converts that into the force that the tyre applies to the road which pushes the car along. Maintaining speed requires this force to be constant as it overcomes air & rolling resistances which conspire to slow the car down, but what obviously interests us the most is how do we change the transmission to make the car go faster?
The Porsche is no different to any other car in that the transmission system is everything between the crankshaft of the engine and the wheels, namely the flywheel, clutch & clutch actuation, gearbox & gear selector mechanism, the final drive(s), differential(s), drive shafts, wheel hubs and wheel bearings. Any car will go faster by increasing the available force at the tyres, so even if the engine torque stays the same we can increase performance by re-engineering the transmission to make the most of the available torque by changing the gear ratios to Increase the wheel torque, maintaining optimal traction by controlling wheel slip or by reducing inertial or frictional losses.
Provided you have sufficient traction, all cars accelerate faster in lower gears, therefore it makes sense that lowering the gear ratios in the ‘box will make the car faster through each gear. There are two ways to achieve this, one by reducing the overall final drive ratio and the other by changing individual gears. If the gearbox has a good even set of ratios lowering the final drive (the ring/crown wheel and pinion) is a valid option that should be considered, however Ninemeister cannot recommend the option for road cars as most low ratio final drives are designed for motorsport and do not have the same lifespan as the standard Porsche parts. Obviously compromising reliability can never be a great idea.
Ninemeister rebuild 915, 930 and G50 gearboxes with revised ratios, steel syncros and heavy duty bearings, our usual approach is by lowering the maximum speed of top gear, lifting 1st gear and using a close set of intermediate ratios to reduce the engine rpm change between gears. Each gearbox is custom built to suit the requirements of the customer, car, engine and usage. Please speak to Colin to discuss options and prices.
When a car goes around a corner basic trigonometry confirms that the inside wheel must turn more slowly than the outside wheel and this speed difference is achieved by (not surprisingly) the differential mechanism which couples the final drive to the output flanges & drive shafts. Most Porsche gearboxes are fitted with an open differential which allows an unlimited speed difference between the two driven wheels, hence if one wheel loses traction the other wheel will start spinning until the torque is reduced or traction returns. Wasting power by losing traction is not the way to make your car faster, that’s why you need a limited slip differential.
Our recommended diff upgrade for G50 gearboxes is the 9m/Carbonetic unit which Ninemeister provide with custom ramp angles to suit all applications although we can also supply, service and repair all types of factory limited slip diffs. Please call for further information.
Inertia & Friction
The definition of inertia is the tendency of a body to resist acceleration, in relation to the drive train ; the relevance in relation to the drive train is the rotational inertia of the key components and first on that list is the flywheel and clutch assembly for which Ninemeister have lightweight RS & superlight flywheel & clutch solutions. Road wheels are another inertial part which are often overlooked, not so at Ninemeister as we supply the strong & very lightweight one-piece Rays wheels.
Reducing the friction in the transmission requires low friction oils and/or special finishing of the gears and final drive. We supply lower friction synthetic oils which comply with Porsche transmission oil standards. Micro finishing and low friction gear surface treatments are available through the 9m Technology centre, please ask for more information.
If you drive a Carrera 4 and are serious about going faster you should put serious consideration to a 2wd conversion. Not only are the C4 variants 50-100kg heavier than a C2, the additional friction and inertia in the C4 drive train will sap around 16% more power than the C2. Do the maths and give us a call!