zardoz337 Posted February 19, 2008 Share Posted February 19, 2008 Hello all! I have a question that my search of posts on this subject has not yelded a satisfactory answer to. I have a 1983 280zx GL Turbo with the digital dash (and speedo) that is limited to 85mph. I see there is a mod to change to KPH reading to increase beyond the 85 MPH limit but, to me anyway this is a "cludged" solutation at best. I like my digital dash and would like to mod the speedometer to read past 85 MPH AND retain the KPH function as well (with a similar increase) It would seem to me that as the signal generated is digital there should be a way to modify the signal electronically to get an accurate speedometer reading above 85 mph and retain the stock display (or if not replace the display or the whole speedometer unit with one that LOOKS like the stock unit). I recognize this my be an extensive mod but to me at least it would be worth it. At some point I plan to do a V8 conversion so this probably will add even more complexity to the project. If anyone has any thoughts, ideas, comments or even flames(!) on how I might approach this please let me know. I understand the circut uses a wheel and light sensor to convert the analog cable motion to an electronic signal but does anyone know what component(s) in the system limit that signal to 85 MPH? I assume the wheel spinning faster than 85 MPH still will produce an accurate signal but something else in the circut does simply not register beyond 85... can anyone tell me if this is accurate? Thanks! Lee Quote Link to comment Share on other sites More sharing options...
roger.svoboda Posted February 27, 2008 Share Posted February 27, 2008 if you have a degree in electrical engineering you might be able to redo the circuit but other than that I haven't found anything. (and I have a degree in electrical engineering.) the speedo circuit is designed to only read 85 mph once a setpoint is reached regardless of the input voltage. the other choice is analog speedo from 79 or 80. Quote Link to comment Share on other sites More sharing options...
Guest terrymac22 Posted September 15, 2008 Share Posted September 15, 2008 zardoz337... The reason your digital dash's speedo only displays 85-mph, is because the speedo microprocessor has a speed loop in its program. The loop is simply than 85 then display 85-mph > What not inside the processor memory programs, is the speedo wheel which is the primary speed indicator. The faster your Z goes, the faster the wheel rotates. Their are 26 slots in the wheel. Why i don't know; but the light sensor is turned-Off for x-amount of time (the wheel is between the Light Emitter and the Receiver Detector). There is a formula for Speed Distance divided by time.. well, if the z is moving some distance then the amont it moves also mooves the Speed wheel. Now, if you have high speed clock source and during a fixed time period and you use counter to store the counts which are incremented to by the clock whle the wheel blocks the light surce, you have a digital value relative to distance X, for Y-time Period...result value in counter is the vehicles speed relative to the Time Period set by the Clock. So if you have a varible Clock which is accurate, the you have a Speedometer. I am not a degree'd engineer, but I have designed an interface which is simple, 2-wires plus an external circuit which is the input to my Speedometer. My 280zx Speedo Schematic is on photobucket. com.... you can build your own speedo using the schematic. Mine version works great. Heres one of the drive tests I made with a friend doing the camera work. hope the above helps and you conntinue to enjoy your Z's digital dash. terrymac22 Quote Link to comment Share on other sites More sharing options...
TrumpetRhapsody Posted September 15, 2008 Share Posted September 15, 2008 That looks very Back-to-the-future... where's the flux capacitor? Please please please take a pic with it reading 88mph! Quote Link to comment Share on other sites More sharing options...
roger.svoboda Posted September 21, 2008 Share Posted September 21, 2008 well that is a solution if you like uglly on the dash Quote Link to comment Share on other sites More sharing options...
zardoz337 Posted January 31, 2009 Author Share Posted January 31, 2009 Terrymac22, You said "The reason your digital dash's speedo only displays 85-mph, is because the speedo microprocessor has a speed loop in its program. The loop is simply than 85 then display 85-mph >" That is sort of what I was thinking....now to find a way to dump the processor and reload it onto an eprom...with some modifications to the "speed loop" portion of the program. Then replace the processor with the modified eprom... What do you think? (I am also thinking that a modded speedo eprom would be a big hit in the z-car community) And thank you all for your input! Lee Quote Link to comment Share on other sites More sharing options...
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