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Alternator Underdrive Pulley For Honda K20 K24

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The T7Design Alternator Underdrive Pulley increases performance by reducing the force needed to overcome the inertia of the alternator during acceleration and gear changes; this will result in a snappier throttle response and more horsepower reaching the wheels.

Alternators, in general, have a broad generating power band, with the Honda K20 alternator producing a reasonable output from just 1,500 rpm, with the max output being made from 4,000 to 18,000 RPM, with this latter figure technically being the maximum warrantied rev limit.

In applications where the engine spends most of its time in the upper half of its rev range, you do not need to drive the alternator at such a high speed. However, the only issue you would potentially face is a lower output at idle. You may need to increase the idle speed to ensure the alternator is producing more current than is being consumed by the vehicle's electrical systems.

An underdrive pulley should also be considered if you have raised the rev limit of your engine; for example, if it is now 10% higher, we would recommend fitting a 10% underdrive alternator pulley and so on.


  • Underdrives the alternator pulley to free up additional Horsepower.
  • Hard anodised black for superior finish, corrosion resistance and wear resistance.
  • Precision machined to very tight tolerances.
  • Almost half the weight of the OEM steel pulley.
Specification Metric Imperial
Weight - 10% Underdrive 0.145 kg 0.319 lbs
Weight - 20% Underdrive 0.175 kg 0.385 lbs
Weight - Stock Steel Pulley 0.275 kg 0.605 lbs
Construction Billet 6061-T6 Aluminium
Finish Hard Anodised Black
Manufacturer T7Design


  • It is recommended to use an impact gun to remove the original alternator pulley.
  • Fits both models of Honda K20/K24 alternator.
  • For road applications, we would not recommend going less than the 10% underdrive pulley, any less, and you may find the OEM alternator cannot provide enough charge at idle with all electrical accessories turned on.