I just got a 93 Z28. As far as i know its stock. It has white face gauges in it with a 150 mph speedo. Its an auto and has the stupid 2:73 gear. When I'm doing 30mph the car shows 35. Its correct at 50mph. At 65mph the car shows 60. Thats as far as i've tested it so far. Could it have come with the 115mph speedo and when they changed the gauges maybe not reprogrammed the computer? Thanks for any help

 

what u are explaining sounds like someone put lowwer gears in it and did not reprogam the speedo. thats really odd that its on at 50. what rpms are u at 60 on the speedo.

 

Ok i just followed my girlfriend again to make sure and I had one of them wrong. Here's how it came out. These are + or - 1 mph. Real speed- 30, my speedo- 25. Real speed- 40, speedo- 35. Real speed- 50, speedo- 48. Real speed- 60, speedo- 64. Thats as far as we got. In drive (so in the 1:1 gear) at 60mph was 2150rpm. I need help with this one for sure!

 

in overdrive at 60 on your speedo at 2150rpm should be 343 or a 373 gears (a good thing) so you have gears/trany like my old 93, the one i have now has higher gears or higher geared trany and is at 1800rpms at 60 on the speedo in overdrive. it could be (when getting to the 50mph) the speedo pointer is hanging up on the white face plastic plate that is placed over the stock speedo face. thats if its like the one i put on mine where u slide the faceplate over the needles through the holes. im pretty sure u can have the speedo reprogramed if u want it to read right. the only other thing i can think of is the converter or trany. is the trany slipping? if not it doesnt really sound like a big deal so dont get down about it.

 

pictures..pictures and more pictures. lets see this beauty.

 

Actually that rpm was in drive. In overdrive at 60mph it is only showing about 1600 rpms. I'll get some pics fo it when i get it cleaned up some. It sat on a farm for a while so its still dirty

 

bummer then i would say 273s and or u have the high geared auto trans like me. what size of tires do u have that will have a small effect on the speedo to. still not a big deal. keep an eye out for a rear end with some 343s. u can find out the ratio by lifting the rear (support correctly and block tires) and with the car in nutural (mark tire and driveline)spin the tire one revolution and count the times the driveline goes around. if a little less than 3 its the 273s, a little over 3 then 323s, if about 3 1/2 then 342. if u look in the glove box there are a bunch of numbers and letters. its called service parts id and tells u option and process codes. if u have a GU2 your car came stock with 273s if you have GU5 then it came stock with 323s. i dont know why but i was thinking i had 342s but i have the 323s. in any case i think the needle is hanging up and your car is fine, the speedo is just off. least u noticed it right off, i drove around for a year before i figured out i was 5mph under what i thought.

 

How sure are you that your girlfriends speedo isn't off? I'd make sure you know that before you start worrying about it.

 

yep that sure could be to. i noticed it when i see one of those radar machines (tells how fast ur goin) along the road and looked down. i then remembered the couple times i thought for sure i was getting a ticket (10 over) and the state'r didnt look twice.

 

That's why you use the surefire way of telling how fast you're going. Get on a highway where they have mile markers, start at a mile marker, time until the next mile and do the math to calculate your average speed (of course you want to do this where you can try and keep the same speed the whole time).