I installed a Sunpro 85mm tach yesterday. I'm afraid it might be reading too low, or that I drive like a -----. my idle is at 700, and the highest I've ever taken my engine was 5000 (looking at the speedo, then at both speedo and tach). I tapped the blue tach wire just behind where it clips into the gauge, I plugged the positive wire into a slot labeled 1 on my fuse box thing, the ground is to a grounding bolt under the dash on the driver's side up against the outside wall. the light souce is the dimer switch for the gauges. could any of this cause a wrong reading?

 

I think it's reading just dandy, I revved to about 6.3 and my engine didn't explode.

 

you hooked it up right so it shouldnt read wrong..the only way it would read wrong is if the calibration of the tach

lewis

 

not if the idle is at 700.. its working fine.. just press your pedal down farther

 

Ground problem, poor connections.
Thats what can make a stock one start to jump around. (among other things)

 

ya, when I had the ground loosely connected it jumped around, but I'm pretty sure it's reading accurately because I've gone over 6000 and no rev limiter or engine exploding.

 

take the car for a spin... read of the MPH and the RPM... also remember what gear you are in.

go home and yank out the big calculator... figure what RPM the motor should be turning at the given MPH... rember you gota figure what the gearing is from both the gear you are in and the final drive

mark

 

nah, forget that..

3000rpm in 5th gear at 60mph, on a d16a6 w/ Si Tranny.

but if u dont have that engine/tranny.. what do u have??

 

dx tranny, I hit about 2500 at 60

my second gear seems to match my mph: at 25 its 2500, at 40 its 4500 at 60 its 6000.