Inaccurate Tachometer?

Rotary#10 · 07-20-2010, 12:09 AM

Have a gtus with a vert wheels with tires of 205/55/15 my MPH is off by 4-5 mph. So 70mph on the gauge is about 65-67 mph according to my GPS. LOL. grr I need 16's ! I would agree when the car was completely stock the rpms would be off give or take a few 100. As long as its in spec of the FSM it should be alright if not. Happy hunting for the problem.

infernosg · 07-20-2010, 06:50 AM

I went through and cleaned some electrical connections a while back and that seemed to help slightly (maybe 50 RPM?). One of my trailing coils is pretty crispy so it is being replaced and maybe that will amount to something. I'm pretty sure this is a combination of the accuracy of the stock speedometer/tachometer and the poor charging system in the RX-7. The latter is fixable, the former, probably not so much unless you switch out for aftermarket.

07-20-2010, 06:50 AM	#2
infernosg IT'S ALIVE! Join Date: Dec 2009 Location: Richmond, VA Posts: 811 Rep Power: 16	I went through and cleaned some electrical connections a while back and that seemed to help slightly (maybe 50 RPM?). One of my trailing coils is pretty crispy so it is being replaced and maybe that will amount to something. I'm pretty sure this is a combination of the accuracy of the stock speedometer/tachometer and the poor charging system in the RX-7. The latter is fixable, the former, probably not so much unless you switch out for aftermarket. __________________ '86 Mazda RX-7 Base '79 Mazda RX-7 GS

07-20-2010, 12:09 AM	#1
Rotary#10 Rotorhead Join Date: Sep 2008 Location: "the town " Oakland Posts: 219 Rep Power: 17	Have a gtus with a vert wheels with tires of 205/55/15 my MPH is off by 4-5 mph. So 70mph on the gauge is about 65-67 mph according to my GPS. LOL. grr I need 16's ! I would agree when the car was completely stock the rpms would be off give or take a few 100. As long as its in spec of the FSM it should be alright if not. Happy hunting for the problem. __________________ Currently running: 90 GTUs converted to S5 TurboII. Track car. 90 N/A GTUs.. Running project car 89 N/A GTUs in Black #2 10/6/18 Blown coolant seal undergoing rebuild and restomod.