Smokin 5000HP+ Posting Maniac
Join Date: Feb 2009
Better Fuel Mileage At Higher Speeds Than At Lower Speeds
After installing my TH700R4 I found my '71 would only get 12 mpg at 55 mph but 16 mpg at 70-75 mph which didn't make a bit of sense. I knew my engine loped clear up to 1300 rpm because of it's marine cam but I never thought much about it until I realized I was running around 1300 rpm at 55 mph. Hmm.
So I installed a set of 3.70's and that brought my 55 mph cruising rpm up about 300 rpm and that did the trick as I now get 14-1/2 mpg at 55 mph and the same 16 mpg at 70-75 mph. So it was just a matter of my components being mismatched. And with the 17% lower gears my car is much more responsive in all gears and at all road speeds.