I recently purchased an 88 iroc-z 5.7 TPI. Amongst modifications made by previous owner are 3:27 gears. I notice that the speedo is reading about 20mph higher than actual speed. Is this a result of the modified gears? and if so what can be done - or is it just a busted speedo? appreciate your help

 

Speedometers can be calibrated, but you need the right equipment - ie a rolling road.

 

the tires may be a different size from stock. although 20 mph seems a little high a little too much for just different size tires. i would think the difference would have to be a couple of inches for it to be that different.

your speedo may just be busted. good luck either way.

 

Thanks your replies - I did find some info on checking and adjusting the speedometer at

http://www.speedometershop.com/ratio.html#ADAPT