3 2005 GT Driving Impressions And Initial Findings

After driving around the automatic 2005 GT at length now, I’ve learned that the new 5-speed automatic defiantly puts the available 300 HP to very good use. This is without a doubt, the fastest automatic trans equipped Mustang ever produced by the factory. First gear in the new 5-speed auto is an unbelievable 3.22 ratio where as the old 4R70W was a 2.84. This low 3.22 ratio first in the new GT makes good use of 3.30 ratio in the 8.8 rear axle.

I’ve already established an opinion that 4.10’s like we always installed on 2004 and older automatic Mustangs will probably be way to steep if stock or near stock tire height is retained. Even 3.73’s could potentially prove to be to steep and make the engine run out of, or accelerate out of its torque curve too quickly in first gear. I believe that 3.55’s coupled with a properly chosen and moderately looser torque converter would be just right for a ’05 Mustang looking to extract more acceleration from a standing start. Possibly even leaving the stock 3.31’s in the axle with just a slightly looser converter could prove to work very well.  This car, when punched from a dead stop will burn the tires easier then any other automatic trans equipped mustang in prior years. We will be trying a few different things with gears and converters very soon.

 

I felt that the ’03 and ’04 automatic Mach-1’s where very respectable automatic 4-valve Mustangs. But because the ’05 motor produces more low-end torque than the older Mach-1 with the 4-speed auto, and because the ’05’s automatic has more forward gears with better ratios – It’s very obvious that an automatic 05 GT stock, will run 3 – 4 tenths better than an automatic ’04 Mach-1 stock.

As a performance tuner/enthusiast, one of the most noticeable tuning drawbacks the automatic ’05 Mustang has is what is known as “Torque-Reduction” during up-shifts and down-shifts. Ford calibration people actually pull as much as 10 to 30 percent or more power from the motor during shifts so that the trans will last longer, feel better and some what softer when shifting. This can really be felt especially at wide open throttle, and even the tone of the engine changes as the power is briefly reduced during the shifts.

 

Our custom tune for the automatic ’05 GT has already made a significant difference in how the car feels and performs during the shifts. Our tune actually chirps the tires very hard during the 1-2 shift and now shifts very positively during the rest of the shifts from part throttle to WOT. I still feel that with the TQ reduction turned off, these automatics will still last a long time with stock and moderately increased power levels. We’re still not sure though what they’ll take long term with big power adders as it’s in its infancy right now, but we intend to find out.

This spring we will take the car to drag strips and start to see what a good custom tune will do along with gears, air Intake kits, pulleys etc. Our totally stock 2005 GT has base-lined 250 HP at the rear wheels.