Re: ultramatic out 3 spd o/d in

Posted by Tim Cole On 2021/9/30 17:49:46

I remember driving those Ultramatics and those motors were cranking hard with the 3.54. Of course that doesn't mean much without supporting numbers which I have in hand. At an actual 60 mph the typical Ultramatic car was turning over at around 2800 rpm. I had an old Dodge with an overdrive trans and it turned over less than 2400 at actual 60. And that was a near oversquare motor so the wear index was low. The Packard with it's long stroke undersquare has a sky high wear index at 2800 rpm. Probably close to twice that of the Dodge. I used to drive that Dodge from Philadelphia to Miami non-stop. On the Indian Nation and the Will Rogers Turnpikes in Oklahoma I ran the crap out it. That car was the ultimate on a long trip.

So the R-11 ( correct me if that's wrong) with the .72 overdrive and 3.54 brings that 2800 down to around 2000 at true 60 mph, with the 4.10 you get 2300 which is a lot more relaxed but still a high wear index. However, the conventional trans ratio with an overdrive has the motor cranking around 2200. So the main benefit of the 4.10 ratio is faster acceleration because the internal transmission ratios don't change. The overdrive is strictly an add on.

The earlier overdrives were .61 and puts the rpm down to 1708 with the 3.54 ratio at true sixty which is probably tall for a 288 motor, except I'd rather wind gears in exchange for the higher axle ratio. With the 3.9 the result is 1900, and 2000 for the 4.1 ratio. Packard claimed 2078 for the 4.1 ratio in a 22nd series Super so these numbers should be reasonable.