There are as many as 4 rear axle ratios for the 1949 Kaiser Special, depending on which model in the K491 series you are talking about. Some Kaiser Travelers and the K4916 Taxicab were built with overdrive which would have a 4.55:1 ratio. The regular K4911 4-door sedan was only offered with 3-speed manual. According to page 191 of the 1947-49 Blue Cover factory shop manual, 3.73:1 could be special ordered by dealers and distributors for "flatlands". Same is true with a 3.91:1 ratio.
Regular rear end for 1949 Kaiser Specials was 4.09:1. There should be a small metal tag attached to the differential cover with numbers looking like "45/11" divide larger number by smaller number to get the ratio originally installed in the assembly.
If you do not have one of these shop manuals for your car, you should get one as soon as you can. It and the 1949 Kaiser and Frazer Illustrated Parts List will be invaluable support items.
1949 Kaiser Special engines were still the 100 bhp 7.3 to 1 compression ratio. It produced 100 bhp on the test stand at 3600 rpm. The dual-manifold 112 bhp motor was not offered in the 1949-50 model runs. The factory documents did not recommend "readlining" the motor as it was not built for high performance functions due to cooling issues at higher speeds.
