Alright I have a 4.44 rear end in my s. My speedo seems to be about 7% off. What is the best calibration box to get, the yellow jacket or the yellow box? The yellow box has been around longer, but looks very complicated to install, and the on-line instructions really focus on motorcycles. The yellow jacket is about $40 cheaper, but I hear of problems with them too-constantly reading 0 mph. All opinions welcome. Thanks in advance.

 

i helped a friend install the yellow box and have had no problems. It's not as hard and intimidating as the instructions make it out to be. The yellow jacket, on my other friends, however, had the problem reading 0 for a while... took me two days to figure it out :-/, so i kinda have bad impressions about it, but once it got working, it was fine.

BTW, how long did it take u to calculate that you were 7% off? lol.

 

I've been using the Modifry Yellow Jacket since I installed my 4.57-R final drive and it hasn't missed a beat yet (and I won't, I'm sure)
Its all about the proper connections (goes for both yellow's )

Get the shifter beeper from Modifry too
Very helpfull tool, you will never miss a shift again.
Beep...beep...beep...BEEEEEP (=shift)

 

Modifry Yellow Jacket, you can adjust it as you drive the car You do not have to pull over or stop the car to set it.

 

Absolutely. Not having to power-cycle the device in order to pickup adjustments makes the yellow jacket far easier to dial-in. I went out on the interstate, set the cruise for 70mph and turned the dials on the YJ until my speedometer and my gps had the same number. It took less than 5 minutes, no dip switches, and no thinking about how much correction to make.

 

The 7% error was fairly easy to pick up on. Living in a college town, most people travel at 35 on the city streets, when following them I would be doing about 37; when trailing my buddies on the interstate doing 70, my speedo would say 75. Infact, Rick's.com uses the 4.44 gear ratio as an example saying it is 7-8% inaccurate.