Ok, 2.8, 5 speed.

Idles around 1250 but when running 60 turning 4500. It has the stock 3.42 rearend in it. Anyone know WHY this is?? Help greatly appreciated

 

First guess... speedometer is reading high. I had one that read the exact same thing. As they get old, they start reading high

 

This was my thought at first. so my friend drove beside me to test it and it was dead on. And i took a aftermarket tach from another buddy and it was reading the same 4500 at 60

 

Is it shifting into higher gears? Or are you going 60mph in secong gear?

 

Its a 5 speed.

 

What gear are you in? Is the clutch slipping?

 

3.42, and no the clutch works as it
should

 

i imagine your tach is bad...not uncommon, does it sound like its actually reving that high?

 

im not sure what a 2.8 should sound like at that high

 

the tach is broke or your not shifting the gear right and aren't in 5th.

 

I guess I could go take a short video of my car revving to 2500, which I think it what it runs at highway speeds (been a while since I drove it) and then I could rev up to 4500. you could compare the video to what you are experiencing

 

Well what gear are you in? if its already in 5th your clutch is slipping and you just dont know it. or does your car take a while to rev to high RPM'S when in nuetral? when in nuetral rev your car the faster it gets to the red line the better. the faster it drops in RPM's the better. so when you rev it as soon as it gets to the red line completely drop the gas pedal and see how fast it goes down. if it takes 5-7 seconds or more, your motor is WORE OUT. Thats the best way to test a motor in a car when buying one also. You want your RPM'
s to be redlin'ing from idle in about 2 seconds or less. and you want it to drop from redline to idle in 2-3 seconds. Hope this helped. LMK.

 

what size tires are on the rear of the car?

 

215 tire size and found out it was the tach. thanks guys

 

I was running 215's on my 89 RS and i switched to 205's on the back and 195's on the front and my car runs 3mph FASTER now.??????

 

This will help caculate tire changes.

http://www.miata.net/garage/tirecalcold.html

IM running 225/60s rear, 205/70s front.