If you’ve watched old movies, you may have seen drivers manually revving a hand throttle to accelerate their vintage car. While obsolete on modern vehicles, hand throttles allow controlling engine speed for unique situations.
Understanding how manual throttle mechanisms work illuminates automotive history. But a few specialty vehicle applications still benefit from installing a hand throttle today.
Let’s examine why hand throttles existed, how they work, and where niche applications remain useful.
Table of Contents
The Purpose of Old-Fashioned Hand Throttles
In early automobiles, controlling the engine speed was done manually via a hand throttle lever or twist grip. It provided a way to adjust rpm without using the main foot pedal. Hand throttles enabled:
- Maintaining constant speed while driving, rather than riding the accelerator.
- Increased control when engine braking downhill by regulating speed.
- Keeping rpm steady while idling without touching the pedal.
- Allowed “blipping” the throttle to match revs when shifting manual transmissions.
- It gives disabled people opportunity to drive.
Hand throttles provided flexibility absent from pedal-only throttle operation.
How Manual Throttle Mechanisms Function
Hand throttles use mechanical linkages to open the throttle butterfly valve in the carburetor or fuel injection throttle body. Here’s how they work:
- A lever or twist grip links to a cable that runs to the intake manifold.
- Actuating the hand control pulls the cable, opening the throttle valve.
- Valve plates allow air intake, raising engine rpm.
- Releasing tension closes the valve, lowering rpm.
This simple mechanical connection enables manual throttle modulation.
Modern Car Throttle Operation
Today’s cars rely on electronic throttle control for:
- Gas pedal position sensor signals the ECU to regulate engine power.
- Idle speed is controlled by the computerized idle air control valve.
- cruise control and traction systems modulate throttle automatically.
Without a mechanical throttle cable to actuate, hand throttles have been rendered obsolete for production vehicles.
Specialized Vehicles That Still Use Hand Throttles
Though rare, some unique vehicles still benefit from old-school hand throttle operation:
- Tractor pull trucks need precise rpm control to balance traction.
- Off-road rock crawlers allow steady low speed without riding pedal.
- Rally cars provide consistent acceleration through all surfaces.
- Drag racers can launch at optimal rpm.
For these niche applications, hand throttles remain useful modifications.
Installing Hand Throttles on Modern Cars
While most modern fuel injected engines lack mechanical throttle cables, hand throttles can still be added:
- Use a servo motor to actuate the electronic throttle.
- Tap into throttle position sensor circuits to control servo.
- Install lever or dial to operate servo motor.
- Program ECU accordingly to allow manual override.
With some fabrication, basic engineering knowledge and tuning, dual throttle control is achievable.
Important Safety Considerations
Adding a hand throttle requires thoughtful design and operation:
- Ensure fail-safe shutoff when released to prevent runaway acceleration.
- Select robust components to avoid failures and jamming open.
- Allow the ECU to maintain ultimate throttle authority if needed.
- Avoid use on public roads to prevent distraction hazards.
When done properly, hand throttles provide unique control – if used judiciously.
The Nostalgic Charm of Manual Throttle Operation
While limited in modern contexts, hand throttles harken back to an era of mechanical simplicity. The satisfying feel of manually revving the engine appeals to enthusiasts.
Just be sure to prioritize safety and smart operation if adding period-correct throttle controls. With care and common sense, hand throttles live on.
Long gone from mainstream vehicles, hand throttle recall a hands-on time, before electronic controls took over. But niche applications can still benefit from their precision. Whether for vintage charm or specialized control, understanding hand throttle mechanisms provides automotive insight. With prudent operation, they safely expand the flexibility of engine speed modulation.