Delasangre4231 Posted January 13, 2010 Share Posted January 13, 2010 (1983 280zx NA 5 speed) I recently replaced my entire dash cluster because I bought the car without a working speedo or fuel gauge. So I now believe the speedo is off. I went into town one day with my parents following, I was doing (according to the speedo) about 80-90 the whole way, my parents pulled in behind me about 30 seconds later and said they did about 60. So my question for those of you with GPS units with speed readouts is what RPM are you at in what gear doing 45-50, and then just for fun what speed are you getting at about 4k RPM in 5th gear? Quote Link to comment Share on other sites More sharing options...
Guest Rolling Parts Posted January 14, 2010 Share Posted January 14, 2010 GPS? Get a pencil, paper, and a watch. Drive at 3 different rpm's and note the time it takes to drive between mile markers. Obviously 1 minute = 60mph (less is faster, longer is slower). Convert seconds to MPH and use the 3 data points to plot it. You're done. Quote Link to comment Share on other sites More sharing options...
Sonethirty Posted January 14, 2010 Share Posted January 14, 2010 Search button! I'm fairly certain there was a thread on this not too long ago in this same forum. (280zx) Quote Link to comment Share on other sites More sharing options...
abc_was_here Posted January 14, 2010 Share Posted January 14, 2010 Well doesnt your car have offsize tires than stock? My z naturally already reads faster than what im going any about one mile per hour for every ten miles an hour of speed 10 means im going 9 20 means im going 18 ..... 70 means im going 63 And at 4k in 5th gear my z reads over the 85mph mark, dang 85mph speedos Quote Link to comment Share on other sites More sharing options...
BluDestiny Posted January 14, 2010 Share Posted January 14, 2010 Well does your car have offsize tires than stock? More factors depend on the readout of your speedo, including what diff you are using and the tranny, along with the tire size compared to stock. If its just a matter of tire size, google "tire size calculator" and you'll find one that tell you the percent your speedo is off by. Quote Link to comment Share on other sites More sharing options...
(goldfish) Posted January 15, 2010 Share Posted January 15, 2010 http://webspace.webring.com/people/cz/z_design_studio/transmission.html Quote Link to comment Share on other sites More sharing options...
BluDestiny Posted January 16, 2010 Share Posted January 16, 2010 That calculator is amazing. Quote Link to comment Share on other sites More sharing options...
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