Ihave been doing some 0-60 runs in my 94 z28with a stop watch.I have a g-tech but didnt use ituntil earlier today(brother in-law borrowed it). i was getting 6.6-6.8 0-60with the stopwatch.
what got me wondering was i did a 0-30 run and got 2.9 seconds with the stopwatch and i know i should be going a little faster than that(it felt faster than that). my wifes explorer will do better than that. So i got the G-tech backand when my speedo hits about 52-53ish mph it blinks out the 0-60 time. I did two runs with it the first i got 6.1sec and the second(a little less tire slippage)5.9sec.
At cruising speed it doesnt feel like im going faster than the speedo says.
i just let my brother in-law use the g-tech in his '07 Ford Mudstain and he got 5.3 seconds with the gtech and that is about what it is supposed to run more or less.
just wondering if anyone has ever had a problem with the speedo laggin or just off?? I dont know?I need someone to ride beside of me or something.

 

I also just had a new performancetransmission put in. Will this possibly have something to do with it?I dont know what the car ran beforeI put the tranny in. Inever timed it because I just bought the car and it wouldnt shift from 1st to 2nd under wide open throttle.

 

Do you have bigger than stock tires? I don't mean wider, I mean taller profile or bigger rims.

 

If the transmission has different gear ratios than a stock one, then yes it would have something to do with the speedo error. Although, whoever installed it should have had enough forethought to install something to compensate for the new gearing. You could always borrow somebody's GPS, and compare that speed w/ the speedo.

FYI-While accelerating like that, there may be a slight lag in the speedo.

 

It has the stock 16" wheels.
I got my brother in-law to ride beside me and at 30-35mph it was off onlyabout 2mph with is car. It is kinda strange b/c it seems as if it is lagging. Like the car is moving faster than the speedometer. The G-tech reads 60mph when the speedometer on the car is at about 52mph but atcruising speed its not off by that much?
Im not sure about the ratios in the transmission i will have to find out about that.
I just got my car back today from installing 3.73 gears. They recalibrated the speedometerbut i dont know if that will help. I cantgag on it for a couple hundred miles so i wont know for a while.

 

find a friend with a GPS unit. Most of them tell MPH.

 

speedo was fixed with the reprogram fromthe gear change i checked it with the g-tech and it matched.
blinked 0-60 time when needle hit 60mph rather than 52mph.

 

Cheap speedometer test. Drive down the highway at a steady 60 MPHexactlyas shown on your speedometer. Look for the highway mile markers, they are exactly 1 mile apart. Start your stopwatch as you go by one marker, stop the stopwatch as you go by the next marker. If your speedometer was correct, it should have taken exactly60 seconds. If it took longer the speedometer is reading fast, if it took less the speedometer is reading slow. You can do some math & find out the exact amount of error.

 

The G-tech isnt that for 1/4 mile times? If so, the 0- 60 is your 60 foot time, not 60mph. Then there the 0-100 foot time, 1/4 mile time......

 

It will tell you the 60ft time,0-60mph time, 0-100mph time, 1/8mile time,1/4mile, horsepower, handling g's. go to gtechpro.com and read all about it.