No change in 1/4 mile ET after gear change

[Fx4cobrawing]

I have a 2006 Ford Mustang GT with an automatic transmission tuned by Lito that I changed the gears from the 3.31 to a 4.10 over the winter. The car is running identical Et's, 60 fts and mph as if I never even changed the gears. Still running the same tune, and nothing else has been changed on the car. I corrected the gear ratio and revs per mile on the tuner and car seems to be running good. My question is do I need to get a new tune for the gear change because by rights the car should run a little quicker?If the car doesn't need a new tune then what could be holding the car back?

 

[Dino Dino Bambino]

People forget that while a numerically higher axle gear ratio increases torque multiplication in each gear thereby providing stronger acceleration, it also reduces the top speed in each gear and you'll almost certainly have at least one extra gearchange on the way to the 1/4 mile.
Depending on the shape of the torque curve and the transmission gear ratios, the results of swapping in higher ratio axle gears will vary. Generally speaking, cars with engines that are more biased towards horsepower rather than torque (and typically higher revving) will benefit more from a higher ratio axle gear.
In your case, you need a higher stall rpm (e.g. 3000) torque converter to properly reap the benefits of the 4.10 gears.

 

[Fx4cobrawing]

Car is going through the traps at about 5500 RPMs

 

[JimC]

Looking at the 60 foot information there isn't any change there. Are you getting a lot of spin at launch?

 

[Juice]

View attachment 83087
Car is going through the traps at about 5500 RPMs

In what gear?
There is no way you are running the same mph at the same rpms.

 

[Fx4cobrawing]

No tire spin, 4th gear with the overdrive off,, and I'm not sure what rpms the car was going through the traps with the 3.31 gear

 

[Midlife Crises]

You are not getting off the line. I like Dino’s suggestion that a torque converter would benefit ET. Along with sticky tires if traction has been a problem.

 

[Dino Dino Bambino]

I'm not sure what rpms the car was going through the traps with the 3.31 gear

The math is easy; it was just under 4500rpm.

Like I said, you'll need a higher rpm stall torque converter. This will help you to launch faster and improve that 60' time. The car may then become traction limited so a pair of aftermarket rear lower control arms (I recommend BMR) would help reduce wheel hop, and stickier tires would reduce wheelspin.

 

[Daniel Roberson]

I have a 2006 Ford Mustang GT with an automatic transmission tuned by Lito that I changed the gears from the 3.31 to a 4.10 over the winter. The car is running identical Et's, 60 fts and mph as if I never even changed the gears. Still running the same tune, and nothing else has been changed on the car. I corrected the gear ratio and revs per mile on the tuner and car seems to be running good. My question is do I need to get a new tune for the gear change because by rights the car should run a little quicker?If the car doesn't need a new tune then what could be holding the car back?[/QUOTE Looking at your 1/4 mile times I say you are pretty fast being you have no mods but gears. The cheapest thing you can do to improve is making sure you have some healthy tires on the back and with the traction mods like lower controls arms, lowering springs etc.

 

[86GT351]

Looking at the 60 foot information there isn't any change there. Are you getting a lot of spin at launch?

Also what tire are you running?

 

[86GT351]

No tire spin, 4th gear with the overdrive off,, and I'm not sure what rpms the car was going through the traps with the 3.31 gear

Just a suggestion. Keep a log book of everything. Outside Temp, Humidity etc. Launch RPM, Finish LIne RPM, Shift Points and more.

 

[Fx4cobrawing]

I'm not trying to be a smart ass but evidently some people cannot read. The car is not spinning and everything done to the car is irrelevant to my question and all I did was change the gear.....nothing else was changed....I foot brake the car to about 2200 rpms the same with the 3.31 and the 4.10 gears.

 

[BullittSS]

Variable weather conditions can significantly affect 1/4 mile times. A density altitude calculator is a good tool for removing weather variables when comparing time slips:

https://www.dragtimes.com/da-density-altitude-calculator.php

 

[Midlife Crises]

Again, you are not getting off the line. You did not add power and you are not spinning the tires. What is holding the car back. If I was a smart ass I would tell you to turn the traction control off. Convention would suggest launching at a higher RPM to take advantage of the gear change.

 

[Juice]

Those time slips are practically identical. Based on that info only, the car did not get gears installed.
With that much of a supposed gear change, 60' time must drop and it did not.

 

[Fx4cobrawing]

Totally agree....I tell people maybe someone snuck into my garage at night and took the gears out. I installed them myself so I know what I did

 

[Pentalab]

What is your rpm, when cruising at 50 mph... (OD OFF).

On my 2010 GT auto, with 3.31 rear gear, it's 2000 rpm at 50 mph. And 4000 rpm at 100 mph. 6000 rpm at 150 mph. (This is all in 4th gear in the 5r55s, OD shut OFF).

With a 4:10 rear gear, it should be just 120 mph @ 6000 rpm....and 5000 rpm at 100 mph.

 

[Juice]

Totally agree....I tell people maybe someone snuck into my garage at night and took the gears out. I installed them myself so I know what I did

Time to jack up the rear, count driveshaft revolutions to confirm 4.10.

 

[OX1]

Variable weather conditions can significantly affect 1/4 mile times. A density altitude calculator is a good tool for removing weather variables when comparing time slips:

https://www.dragtimes.com/da-density-altitude-calculator.php

This is a good point, 3.31 run was in Sept, 4.10 run was in June. Was the DA significantly different
from both of those days?

 

[RED09GT]

Launch it up higher. Go up until you spin the tires, then back off a bit.
With 4.10 gears, your wheel speed at 2200rpms is slower than it is with 3.31 gears (17mph vs 13mph) so you are completely knee-capping your launch by following the same formula. Then you are playing catch-up for the rest of the run.

2800rpms would give you about the same wheel speed as you had with the 3.31 gears at 2200rpms.