2 Speed Vs 3 Speed - Drag racing Print
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Tuesday, 02 February 2010 00:39

There is a common belief that the more gears a transmission has, the better the car will perform over the ¼ mile. It is also generally accepted that any time savings in the 1st 60 feet can have double the effect over the entire track.

Torque Converters (efficient ones) multiply torque. Whilst they cost hp to run and create heat, this generated torque is what actually accelerates the car down the track.

3 Speeds

Recently in the USA, some teams have been playing with the GM TH400 3 speed transmission. It has 2.48:1 1st gear ratio, 1.48:1 2nd gear ratio and 1:1 in 3rd.

The problem was with all this leverage (1st gear ratio and the torque converter) they found they couldn’t get the car to hook up. These were big tyred, chassis cars with plenty of torque and the crews were no dummies.

A simple calculation showed that a leverage ratio of nearly 9:1 was being realised. They then experimented with reducing 1st gear ratio and eventually settled on a 2.1:1 1st gear ratio. A later change to a Powerglide with a 1st gear ratio of 1.8:1 made virtually no difference to the cars ET or MPH.

Turbo Charged Cars with Small Capacity Engines

Turbo charged engines don’t produce the torque of big capacity or supercharged engines. Here the 3 speed can perform well. An advantage of turbo charged engines is the ability to control boost (hence hp). If traction were an issue then some ECU adjustments to the Waste Gate can rectify this situation.

Road Cars used on the Drag Strip

Generally a 11 sec and slower road driven car with minimal tyre/chassis modifications and nominal hp and will benefit from a 3 speed. The car will remain on the torque converter for shorter periods of time in start stop traffic.
Increase the engine hp and traction becomes an issue. Add a transbrake and tyre shock on transbrake release is considerable.

2 Speed (Powerglide)

Advantages-      Proven ¼ mile performer
Performance parts readily available
Strongest transmission on the market
Reduced tyre shock on transbrake release
Disadvantages- Diff Ratio becomes a compromise between 60ft time and end speed (MPH)

3 Speed

Advantages- Still gaining market acceptance
Performance parts now becoming available
Design flaws limit torque rating
Diff Ratio suits both street and strip driving
Disadvantages-  Requires either boost control or tyre/chassis mods on big hp cars
Parts can be expensive

Last Updated on Tuesday, 02 February 2010 00:47