v80z Posted December 13, 2004 Share Posted December 13, 2004 Can you determine rear diff ratio by a casting number? My car is a 77 it has an r200 but I want to make sure of the ratio. Also Is anyone running a Muncie? What is the top end like with a SBC at 6500 rpm 16" wheels approximately? Thanks. Oh I have been searching the forums Quote Link to comment Share on other sites More sharing options...
johnc Posted December 13, 2004 Share Posted December 13, 2004 Can you determine rear diff ratio by a casting number? No. Pull the rear cover and check the tooth count numbers stamped in the ring gear. Do a little math and you've got your ratio. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted December 13, 2004 Share Posted December 13, 2004 If it is a stock R200 from that car it would be a 3.54. Casting numbers don't tell you the ratio AFAIK. You can pull the rear cover if it is out of the car and on the edge of the ring gear the ratio will be stamped. Your 3.54 should have 39:11 stamped on it. Divide the 39 by 11 and you get 3.5454545454. 3.70 is 37:10, 3.90 is 39:10, a 4.11 is 37:9, etc. If it is still in the car, mark the pinion flange and mark one of the wheels. Hold the other wheel to prevent it from rotating, then spin the pinion until your mark on the wheel comes all the way around. Then multiply the number of turns you made on the pinion by 2. So if you spin the pinion a little less than two times and the wheel comes around once, then you've got a 3.90. A 3.54 would be about approximately 1.75 pinion revolutions. A 4.11 would be just a hair over 2 revolutions. Or just spin the flange until the wheel goes around twice and count the pinion revolutions. Quote Link to comment Share on other sites More sharing options...
jbc3 Posted December 13, 2004 Share Posted December 13, 2004 Try a gear/speed calculator like this http://pw1.netcom.com/~sgalaba/mph.htm Quote Link to comment Share on other sites More sharing options...
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