The Dynaflow was kind of the precursor to the switch pitch transmissions used in 65-67 Buicks, Cadillacs Oldsmobiles, and some Rolls Royces. I have one in my 70 GS. You can switch stall speeds (3200/1800) at the flick of a switch. Best street transmission ever. They work great.
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98 Riviera SC3800 All stock except gutted air box.
1970 Buick GS455 Stage1, TSP built 470BBB, 602HP/589TQ
Best MPH, 116.06 MPH, Best ET, 11.54
https://www.youtube.com/watch?v=UHCda-t_Jls
https://www.youtube.com/watch?v=sfT2tEO4XcU