Originally Posted by Josh@STILLEN

A grounding kit improves the electrical connections within specific points inside the engine bay. It improves the ground (hence grounding kit) connection at key points, and with the increasing complexity with ECU's and TCM's.. increasingly important to ensure everything is grounded properly.

On a brand new or newish vehicle, a typical grounding kit will in all likelihood not have a huge impact on horsepower, as everything is working as it should. But with every vehicle manufacturer, cost in every department is looked at and scrutinized, and wiring is especially typical in cost-cutting measures.

As the vehicle gets older, horsepower WILL be lost due to these connections, and a grounding kit will help prevent that, and bring power back to older vehicles once installed. This can happen within 1-2 years.. depending on condition, environment, etc.

That being said, for automatic transmission guys, there is an immediate improvement no matter what age of the vehicle, resulting in slightly sharper shifts, and increased transmission shift response time, and should be a no brainer when considering upgrades..