The TH-2004R is a great overdrive transmission that has received a lot of attention. While some disagree, it is basically as strong as a 700-R4 and will bolt to virtually any Chevy, Pontiac, Buick or Olds Motor with few modifications. The TH-2004R has a 2.74 ratio in first gear, which is 10% lower than most transmissions. The overdrive will give a 22 to 33% increase in gas mileage for highway driving and better cruise-ability. The TH-2004R is a popular transmission swap for muscle car restorations to add the overdrive option & to update to a modern transmission.