Cruzzar Posted October 3, 2020 Share Posted October 3, 2020 I have recently purchased a stock 1975 280Z and would like to replace the 4 speed with a 5 speed from a 240sx with the .76 5th gear final drive ratio. With the overdrive it would seem to me that I should replace the rear end gears with something lower such as 3.70 or 3.90. Any recommendations? I have done some of the tire diameter/gear ration calculations and it appears that I can get close to about 2600 rpm at 65 mph with the 3.90s. Is this about right ? If I go with the 3.70s the rpms would be down to about 2356 rpm at 65mph, would this be overdriving the stock l28 too much? Quote Link to comment Share on other sites More sharing options...
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