I saw an ad in Super Street for a ground cable. They are selling a #4 gauge ground cable for the engine ground. The ad says "less resistance will reduce constant power loss." Any truth in this? I am sure it will be a minimal .5hp gain if anything.

 

Thicker guage wire is mostly only needed for running longer lengths. Thats why you see people with sound systems that run a 4 guage + wire to the battery and use a 8-12 guage wire for the ground since its usually less then 4 feet. If the engine ground is a long cable, then yeah a bigger guage could help, if its not long then anything 12 guage or less would be sufficient.