Sorry I meant to also ask, does changing the rear end gears void the warranty and require special tuning?

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Gear change will only void the rearend warranty and won't come into question unless Ford can prove the aftermarket shorter gear led to the death of the part that failed.

The only thing you need to tune for is your speedometer. If you have a hand-held tuner, you just set it to the new gear ratio and you're set.

I went with a 4.10 gear. On 26 inch DRs, I finish the 1/4 in 4th at about 5500 RPM or so. My redline is 6k. My best ET before the gears and DRs was 12.95. My best ET (in hot weather) with the DRs (before gear) was 12.98...I was bogging and never got the tire pressure right. My best ET after 4.10s has been 12.611 in perfect weather. It has 12.5s in it...I just need to practice launching and get the tire pressure perfect.

 

Auto 3.73 Manual 4.10 as a rule . I can say from exp. that the 4.10 with an auto are fun on the steet but 1st does not exist and blows 2nd away hard now keep in mind this was at 500 rwhp and 425rwtq and after2nd look out . At the track I ran better times with the 3.73 with my setup . Stock conv. 3.73 on 20 " wheels with the 17" wheels and dr inthe trunk I ran 11.90 at 118 with a slow 2.0 60 ft..

 

With a FI setup, 4.10 is too much gear for the auto...3.73s are perfect for a FI auto. N/A, however, 4.10sare great. You have a special setup.

 

I drive 500 miles then get on a helocopter for an hour (or boat for 6) and work for 14 days. After the 14, I get on the chopper to go back to my car and drive that 500 miles back home and screw off for 14 days or whatever else I feel like doing. So really I only work half the year. I think I'll keep this job.

TheDarkPath - you're making me want 4.10s again.

 

I installed 4.10 and then went with 4.30.

 

I have not checked the times at the track. But, I installed 3.73's and pulleys at the same time and it was definetely a noticable difference.

Automatic trans