Ok everybody with AUTO"S...which gear do you have and what do you think? I am leaning towards a gear swap and would like to get it right first time.I was thinking 3.73's. Check my sig for my mods. Thanks!

 

3.73s or 3.90s if you dont mind not using a Ford part. 4.10s are too much for the auto.

-Dan

 

I asked the same thing a while back, and most of the guys here suggested the 3.73's for the auto.

 

I personally am very pleased with my 4.10s. I had originally purchased 3.73s but exchanged them for 4.10s prior to installation. 3.73s are a 12.7% change. 4.10s are 23.9% change. I felt the 3.73s wouldn't make enough of a difference for the money spent so I opted for the 4.10s. Most of my driving is around town and gas mileage really hasn't suffered.

As someone else put it "Don't fear the gear"

 

I am waiting for my 4.10's to be installed. I had a hard time deciding between the 3.73 and 4.10, but I didn't think the difference from 3.31 to 3.73 would make that much difference. I will let you know how it runs the second week of July.

 

These guys have done more testing with the auto that anyone else that I have seen. Here is what they have to say about the subject:

"This was achieved with the stock final drive ratio in the rear end. Our car has a 3.55 in the axle, not the stock 3.31. But the 3.55s are a total wash because all they do is make up for the 1.5� taller rear tire we run on a 20� rim. Plus our 12 second ET’s came with the regular rear tires on the 20 rims. Not a drag radial! As I suspected and predicted, the automatics will only need a very subtle gear change for some good quarter mile performance."


Alternative Auto

 

I'm still up in the air about this. I installed 4.10's in my '05 within days of having it. While the fun factor is there with the lower gears, it is not translating into any better times at the track, at least not in my case. In fact, I think the lower gearing is actually hurting my 1/4 mile times, by not allowing the engine to make the use of its broad torque curve.

Case in point. This past weekend I had a chance to run side by side with a fellow ’05 auto owner on the local 1/8th mile track. My driveline mods are 4.10’s and a JLT CAI w/DTP (SCT) premium fuel tune. His car has the stock 3.31 gearing, and the Steeda CAI w/ DynoSpeed tune (SCT). Our times were almost identical throughout the day. In fact, said cars 60ft times were averaging 2.1x while mine were in the 2.0x area with street radials. Given the same 60ft times, history dictates that he should have been running 1-1.5 tenths faster through the 1/8th than I would.

It is my opinion that the 4.10s move the engine too quickly through the powerband, and by going with a taller (numerically higher) gear such as the 3.55/3.73, the car will stay in its torque band longer, thus providing a little better performance. I am going to switch the gears out at some point in the near future and put my theory to the test. I’ll let you know how that works out.

 

I'm using Motive 3.90 in my 05 GT automatic.

I'm fairly happy about it except the noise it makes at around 60 mph - which I understand is fairly normal.

 

I was going to say... don't forget about the 3.90 gears as well. I am leaning more towards them over the 4.10's at this point. But I still have some time before I do this, so I'll make a decision then based on the experiences here up to that point. I sent Bryan (2005RedGT) a PM a couple days ago asking how he liked his 4.10's with the auto. He must be on vacation and hopefully will respond to this thread too when he gets back on. I think he was very pleased with the results.