1973 340, want more power.

Richard McLaughlin said
Right. So putting in 3.73 or 3.91 I would notice a massive improvement correct??

Also should I change it to sure grip as well??

if your making any kind of power, im thinking the sure grip will net a better result then the higher gear BECAUSE a higher gear will burn one tire quicker then you do now BUT a sure grip will distribute the load and actually get your car moving