Question..... Speedo accuracy OE & ring pinion change, new calibration needed

[HOOKED ON GT]

In the midst of 3:90 change and wondering about the current speedo and what we know about its accuracy and how "off" mine will look after the new final drive gets plonked in.
I think GT's read too slow at low "gated community" speeds but maybe pretty accurate at high (at the track) speed?

Stuart

 

[DakotaGT]

You can change this pretty easily with a handheld tuner, typically an SCT tuner (see link below)

lower final drive ratio

I was looking at the Stillen web site and noticed that they are listing a Ricardo 390 final drive for the GT. Does anybody know about this?

www.fordgtforum.com

 

[HOOKED ON GT]

I think Torrie can do it?

 

[HOOKED ON GT]

Hers a cool calculator www.blocklayer.com/rpm-gear.aspx

 

[HOOKED ON GT]

Jason Heffner did the reinstall of the trans and did the adjustment on the 3:90 and Bridgestones speed calibration and now Id say that my speedo shows say 60mph and my phones "speedo" shows about 63-64mph.
I better make sure I remember this (assuming the phones accurate) as most cars read the other way.

 

[Nafod]

The old fashion way.. Mile marker and stop watch. or your local police neighborhood radar(your driving to fast).
Phone GPS can be close, but then , who makes the phone, how old is it, how many satellites does it see.
I use a new iPad for various utilities, one being worldwide charts and approach plates in a aircraft that cruises at altitude (30k's) and for long periods(2-16 hrs). Most of the time the gps isn't accurate enough to display known location on the iPad. Just depends.
Gear ratios/ final drive/ rear tire measurement and RPM. But you would need an accurate RPM, and my guess is the speedo in the GT with known issues is not that accurate.
I say the dyno setup should be fairly accurate. Jason I'm sure has a dialed in dyno.