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Speedo HELP!!


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So I have been wondering why people are not doing the speed limit. I was on base the other day and driving and noticed every one was doing ten under the speed-limit no problem I go around them and even a cop. They followed me until I got to where I was going. After I got out they said very nice car oh by the way do you know the speed-limit? I said sure its 35. Well he was clocking me doing 45. He didnt give me a ticket and was nice but this has me puzzled. I am trying to figure out if the tune I have doesn't take in the 331 rear end or tire ratio. I called Lethal and they told me the tire rev/ mile is 750. So I did that and still not sure if its right? I found a website and it says 724. What should I do? Can anyone tell me @ 45 MPH in 4th gear what they RPM should read.

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I can go do it tomorrow and see on the actual car what it is and let you know. But I think 45 in 4th is a little under 2k. Because I shift at 2k and I shift to 5th around 45 mph so it should be a little under 2k if not 2k.

Edited by svt13
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Well I am turning just over 2000 rpm @ 40 mph. I am not sure what I need to do to fix this?


do you have an iphone?? if you do go download a gps app and check your speed with it... ive done this before on my super duty cause they dont have a programmer for the 2011 that does 37' and above tires...

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What should I do?



Your sig has 6 different cars listed so I'm not sure what year you're talking about. Here's something for you, or not;




My FRPP Whipple 2.9L Supercharger kit included a Pro-Cal tuner and which allows me to change parameters for both tire size and gear ratio changes.


There is also a aftermarket unit that allows you the same, plus change the RPM rev limit and the Vehicle Speed limiter. I think it sells for 2 or 3 hundred dollars.




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