Gears &Speedometer problem???

[arlander344]

I have a 2003 Mustang GT. I just recently changed the factory 327 gears to 373 gears. I know this throws the speedometer off so I bought a Diablo Predator tuner to correct that and get other performance gains. My problem is I have tuned my Mustang several times now, and yes I have changed the gear setting in the tuner to 373, but my speedometer is still 10 to 12 mph off at 60+. And yes the car still has the factory size of tires. I did not have this problem before I switched gears. Does anyone know what may be going on??? Should I use a different tuner??? Any help would be appreciated.

Thanks.

[chris098]

Which tires do you have? You might want to go to the manufacturers website and get the tire revs per mile from there. Sometimes the number is different than the one you may of calculated on your own

[2007STANG]

whats the web site

[chris098]

I dont know. Whatever brand name your tire is just google to find their site. Or go to google and put in the name, model, tire size and then add "tire revs per mile" and see what comes up. Or if you just find some sites that sells tires, try to search for your tire and they will usually have the tire revs per mile in the description somewhere

[SpectorV]

if its that far of the tuner isnt doing its job. Some do revolutions per miles~ or does yours just let you enter in the values. Make sure the overall tire height and such are correct in the entry as those might throw it off.

You can probably get a dallas speedcal unit and plug it in, worked great for my 01 v6, but the tuner should fix it.

[arlander344]

Yeah, I figured out it's the tuner after playing around with it yesterday. It lets you enter values for revs per mile on the tires and pre set gear ratios. I had both of those set for my vehicle but it was still off. The Diablo tuner I have came with two tunes, the "Diablo" tune and the "Factory HP" tune. In both you can set any parameters you want. At first I had the Diablo tune in and it worked but when I switched to the Factory HP tune the speedometer was off. Yesterday I switched back to the Diablo tune and its back on again. Apparently there is something wrong with their "Factory HP" tune.

[Scut95]

maybe the factory hp tune still reads the stock gear ratio and not the new 3.73.