kevinlock3333

i have a 2003 GT and in fourth i hit 130mph redline. 5th i get about 132mph.
i have 18" rims with 295/35zr18 kumho ecstas, mag exhaust, and short shifter.

why only 132? i held the peddal to the floor in 5th for maybe 5 seconds and it went from 130 to 132.

what could the problem be? or am i not staying in 5th long enough?

thanks

avlon06

that sounds safe, why are you trying reach your top speed?

Z28KLR

You're just not in 5th long enough. It's a slow climb. I'm not sure what our cars' top speed is, it seems like if you gave it long enough that you could bury the speedo (which I've been told is not that accurate over 100mph or so). The fastest I've ever done in mine was 135 while trying to race a 6-series BMW, and it had more to go (I didn't); when I had my '96 GT I once reached an indicated speed of about 143mph. Again, not sure how accurate the speedo's are, but I think if you give the car enough room you could send it to the 150 mark.

WannaBeGearHead

Wow way make 2 threads asking the same dumb question.

cliffyk

You don't mention what performance mods you have, if none then that's about right--in 5th at 3600 rpm or so you're probably only putting 150-155 HP to the wheels (click here for my "How much HP does it take to go how fast?" calculator).

In 4th you're banging up against the redline. Also, the speedometer really isn't accurate enough at 130 MPH to be trusted, explicitly, probably +/- 5% at best, meaning that if your true speed were 130 the readout could be 123.5 to 136.5.

Here's my "How fast can I go in each gear?" calculator that will let you sort out what gears you might have.

Those tires are slightly larger (796 vs. 810 revs/mile) than the OEM tires which will make the speedometer read 1.5% or so slower than actual speed unless it's been corrected.

cliffyk

One other possibility...

Although I have never personally seen this, the Red Book states that some lower cost GTs were not equipped from the factory with "Z" speed-rated tires--and that these cars had a 125-128 MPH speed-limiter set in the tune.

As I said I have never observed this myself, but check the tag on the driver's side B-post to see what tires you car left the factory with--if they were not "Z" rated that could be the issue.

avlon06

you could also do the trick from mustangworld.com and have a digital reading of your speed...

http://www.mustangworld.com/ourpics/fcar/dtcodes.htm

0440thgt

I agree 100%

cliffyk

The diag mode will tell you if the speedometer needle is incorectly placed, however the digital disply will still be affected by gears and tire diameter.

One other thing that has always bothered me about that MW article is that they have never added a notice that there's a bug in oil pressure monitoring that will on most cars cause it to read 0, and throw DTC 5284 claiming the o/p sending unit is bad--this sends many in to a tizzy when they try the "secret" test mode.

In the last as a "head's-up", the DTCs displayed by the cluster test mode are with one exception all Body and Chassis codes, having nothing to do with the powertrain...

Read more about the HEC (Hybrid Electronic Cluster) self-diag mode here...