Gears and incorrect speedo

[Deleted member 38176]

First of all, I just had my 4.10's installed and Im going to immediately say, "These should have been my FIRST mod". Good God.

Anyway, I know my speedo is now off (obviously) and I dont have a tuner *yet*. So typically, how much is the speedo off (in terms of MPH)? I need to keep track of it while Im driving.

Stock wheels/tires, 4R70W auto, just with 4.10's.

 

[007]

It will read 4.10/3.27 = 125% of your real speed (and also rack up those extra fakes miles too).

To correct it you need to multiply by 100/125 = 80%

Gears are fun huh!!! Hope you have nice big rear tires!

 

[SteedaGT9150]

when im going 65 speedo says 85, when im going like 73 speedo says 95. its not as bad at the lower speeds. like 35 says im going 50

 

[merc123]

I'd get a speedcal ASAP. I incorrectly set my speedcal so I was doing 30 MPH and it showed 150. I racked up 7 miles in like 2 real miles.

Ford Mustang: Mustang Tech: Calculators & Decoders: RPM Calculator

3.27: 50 is @ 1433 RPM
4.10: 50 is @ 1797 RPM

So now drive at 50 MPH in 5th gear @ 1797 RPM and see what your MPH is. Assuming you have a .67 5th gear ratio. Or @ 60 MPH you should be at 2157. This is with stock tires.

 

[EvilTurkey]

Stock wheels/tires, 4R70W auto, just with 4.10's.

Arent your shift points all messed up now? I was under the impression that you had to have a tuner in order to put the gears in or youd destroy your trans.

 

[Deleted member 38176]

Arent your shift points all messed up now? I was under the impression that you had to have a tuner in order to put the gears in or youd destroy your trans.

Well, I manually shift the auto (I know I know, its bad) about 90% of the time Im driving it so I really haven't noticed any problems with it. I'll definitely keep an eye out for that though.

The speedo is being a lot bigger problem then I anticipated it would be. The difference is between actual speed and indicated speed is more than I had thought. Going in, I thought that it would be a set number that I could easily keep track of while driving.....wrong.

Im buying a handheld tuner within the next few weeks for sure. The GT isn't my DD anyway, so its going to have to spend the majority of the time sitting

 

[Winters98GT]

Well, I manually shift the auto (I know I know, its bad) about 90% of the time Im driving it so I really haven't noticed any problems with it.

I really wouldn't do that. Dallas mustang had a speedcal many years ago, not sure who has them now.

 

[1991notchbackLX]

I have a diablosport predator handheld tuner for sale for next to nothing. It came with my car and my future mods are going to be WAY too extensive to use it. Let me know if it'd help you out.