When I purchased my Rubicon back in October at a dealer it already had mods from the previous owner (lift, tires, gibson headers, exhaust etc..) Is there anyway I can find out if the Jeep has already been programmed. Its a 6sp and the speedo is accurate. At 70mph i'm at 2600 rpm in 6th which is telling me it might have been regeared also, but not sure. Thought it might have 456's or 488's. I just don't want to invest in a programmer if its already been done. Thanks for your input.

 

Don't know if you have a Superchips Programmer installed, but you atleast you have the Procal installed to reset your speedo. My 09JKU at 70mph does the same 2600 rpm in 6th , I have 255/75R17 with 3.73 gear's

 

You can always match your MPH with those on a GPS if you have one when checking accuracy. If you are regeared, they have to be 4:11 or 4:56 with 2600 RPM at 70 MPH...too low for 4:88's. If you want to test gearing just jack your rear wheels off the ground and count your driveshaft rotation in relationship with your wheel revolution., 4:11 turns of shaft should equal one revolution of wheel. Please safety support your vehicle when checking (i.e. jackstands, wheel cocks etc.) and check it in NEUTRAL.

 

The dealership can't calibrate for 35's. (at least they couldn't the last I heard). If the previous owner calibrated and left the tune on your JK, their tuner is now useless to them, since it is locked to your vehicle. Assuming there is a calibration on it now, you may run into a situation with the dealership overwriting it and putting you back to stock. Anyway, regardless of whether it is or isn't calibrated, you should get one of your own.

Start by figuring out exactly which gears you have. (lift a corner, etc).

 

From the numbers you've posted I can tell you your gear ratio...

Final Gear Ratio=(RPM)*(Tire Diameter)/(Tranny Ratio)*(336)*(MPH)
Final Gear Ratio =((2600)*(34.4))/((0.84)*(336)*(70))
Final Gear Ratio =89440/19756.8
Final Gear Ratio = 4.53:1
I will guess that one of your numbers is off by only 6/10ths of a percent (pretty damn good on your part) and that you have 4.56:1 gears.

 

^ rain man.

 

Thanks for all the help on this. I jacked up the Rubicon today, rotated the driveshaft (4.5 turns per one revolution of tire) 456 it is!! You dont normally hear much about 456's. Usually the jump is from 410's to 488's or 513's.

 

LOL

 

That's exactly what I was thinking. If the dealer didn't give you a tuner, you are not in a good spot. The aftermarket tuners are VIN locked so you and your buddies can't buy one tuner and use it on 3 or 4 vehicles.

 

Sorry to revive this but I have a question along these lines as I bought a used Jeep with mods already done, but no tuner/programmer. My speedo seems close when checked with the radar signs along the road but who knows. My question is - if my Jeep has an aftermarket programmer installed on it now and I get a new one - will the new one just overwrite the old one - no issues?

Thanks.