Other than the gearing, the problem you've got with an auto box is that controlling the torque to the transmission is out of your hands.
With a manual car you can rev the engine to about where it's generating peak torque during staging, and feed in the clutch as you pull away to transfer this torque to the wheels during the initial acceleration whist maintaining engine speed, until you're at the point where the speed of the car matches the speed of the engine whereby the clutch is fully engaged and you're off. This'll cause a little clutch wear but you'll get a quick start.
With an automatic, no torque is fed to the transmission at the instant you floor it. First you've got the reaction time for the engine to accelerate on full throttle, as it was previously idling. As the engine revs pick up, the torque converter starts to pass engine torque through to the transmission until it reaches its' stall speed, which will be lower than the speed at which the engine torque peaks - probably about 2200 RPM. As the car starts to pull away you are stuck in this situation where the engine is bogged down a little until the car speed has risen sufficiently to get the engine up into its' power band. The torque converter isn't as lossy as a clutch during this period but, because the engine is running slower than ideal, it's not generating as much power so the car is accelerating more slowly. Once the car is moving and the revs get into the engine's power band the automatic car is probably only limited by the fact that the gear ratios are taller and further apart than a manual car's equivalents. It's the initial start that's slow.
Drag racers on auto boxes normally change the torque converter for something that'll stall at a more optimal speed higher up the engine's rev range, and stage the car with the engine running well above idle and the brakes on, so the engine doesn't take as long to accelerate. The downside of this is that the torque converter will feel horribly slippy on the road and give poor fuel consumption. It's a compromise.
Revving it up and banging it into "D" might feel more like the manual option, above, in that the engine is already running at speed so perhaps you have gained by not waiting for the engine speed to rise. However, with a manual car you've got a nice big clutch to smoothly engage the drive and dissipate the energy that's lost in the process. In an automatic box you've got small, delicate clutches that are normally only actuated when the engine torque has been limited by the ECU. They're not designed to smoothly feed in a lot of power / torque so they will either do so with a bang or they will dissipate a lot of energy and burn out. If they engage with a bang the shock will get transferred elsewhere in the drivetrain. You had better hope that this is dissipated in the tyres as traction is broken because the other options are expensive. Lighting up the tyres isn't going to get you a good time. Neither is leaving bits of propshaft, gearbbox and diff all over the track.
OK. It's friday afternoon, I'm bored and I've probably just over-analysed the problem of drag racing with an autobox. Soon be home time
Kevin
Author
Topic: Ways to get better Acceleration with Auto V6? (Read 6536 times)