Originally Posted by
cardeyak
OK, I was just making a point that the lower the RPM usually means better gas mileage. I also agree that the rpm's can go too low. According to Randy's Ratio Calculator my current rpm's at 70 mph with a 3:07 ratio is 1825. With a 2:73 ratio 1623 rpm's about about a 200 rpm drop. According to this web page a small block Ford should be able to handle 1800 rpm's. Maybe a little low still thinking about it. I need to look at some more cam data. Crane is selling what they call a towing cam for trucks. Anybody ever try one?
I was probably overestimating the O/D gear ratio in my post above when I guessed 1600 rpm at 60 mph. Instead, you're at 1600 rpm at 70 mph. EPIC FAIL in a big van...might be able to handle a motorcycle application or a Cobra kit car. Even 1800 rpm's is not enough for a big van at 70 mph with a low torque motor like a 302.
No idea what you mean about "should be able to handle 1800 rpm's". How close is your torque and horsepower peak to 1600 rpm? Your engine probably puts out about 60 horsepower at that rpm...
George