Yesterday my son and I did something I have wanted to do for some time. We replaced the 9" rear 3.7:1 differential with a 3:00:1 differential. I was a little concerned about the big change and how the truck would perform.

Since many of you are new, my truck has a rebuilt 292 with ECZ-C heads (bigger valves), 4 bbl Edlebrock street carb, an improved street cam from John Mummert and dual ram horn exhaust. Estimated HP is about 210 (the original was 175hp if I remember correctly). I figured with the few extra horses, we could change the ratio without to much loss of performance.

Results: I now have a true 4 speed (T98). The granny gear is actually a usable gear now. In fact starting out in first takes the truck to nearly 20 mph. 35 mph is easily achieved in 2nd and you can cruse at 45 mph in 3rd at only about 2500 RPM's. Now the best part, on the highway cruising at 65 MP is achieved at 2800 RPM, it was about 4000 RPM's with the 3.7 and the engine noise was quite loud. Now you can go 65+ and conversation and listening to the radio is quite easy. I am sure gas mileage is improved.

All-in-all I am quite happy and so is the truck, so I thought I would share the good results.