shift points (gears)

[SK17]

I'm changing from 3.55 gears in my 16 auto gt to 4.09 gears. I bracket race the car at the dragstrip. It has basic bolt ons and a dyno tune with the shift points around 7200rpm and rev limiter at 7800 rpm. I want to put off until the spring getting the dyno tune updated for the gearing change (shift points). I know the speedo isn't affected due to the placement of sensor on these newer mustang. I only have one race left and my question is:
where do you think the car is going to shift at rpm wise with the 4.09 gear before doing an updated dyno tune for the gear change? Before 7200 rpms or after 7200 rpms???????

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[Cory S]

What does a 4.09 gear do for you over the 3.55 for bracket racing?

 

[NGOT8R]

I'm changing from 3.55 gears in my 16 auto gt to 4.09 gears. I bracket race the car at the dragstrip. It has basic bolt ons and a dyno tune with the shift points around 7200rpm and rev limiter at 7800 rpm. I want to put off until the spring getting the dyno tune updated for the gearing change (shift points). I know the speedo isn't affected due to the placement of sensor on these newer mustang. I only have one race left and my question is:
where do you think the car is going to shift at rpm wise with the 4.09 gear before doing an updated dyno tune for the gear change? Before 7200 rpms or after 7200 rpms???????

Gears - Tire - RPM Calculators

http://www.wallaceracing.com/Calculators.htm

 

[WildHorse]

What does a 4.09 gear do for you over the 3.55 for bracket racing?

Nothing.

 

[Andy13186]

Pretty sure its almost always best to rev as high as possible without hitting the limiter, because you probably make more HP at 7800 RPM than the RPM you are at after the upshift.

 

[EFI]

I only have one race left and my question is:
where do you think the car is going to shift at rpm wise with the 4.09 gear before doing an updated dyno tune for the gear change? Before 7200 rpms or after 7200 rpms???????

The shiftpoint is going to be the same as before, changing gears does not change at what RPM the tune commands the shift. If it's commanded at 7200 before, it's going to be commanded at 7200 after.

Now what will change is the MPH that this shift will happen, which will be earlier. The only catch will be if there is a MPH parameter in the shift eg. the shift can only happen if the car meets a certain speed criteria and if it doesn't, then it won't shift even at 7200. If there's a speed parameter, then most likely you're going to go past 7200rpm and the shift won't take place until the MPH is met then it will shift.

It all really depends on how your tune is setup.

 

[SK17]

Changing gears will do nothing for me with regards to "Bracket" racing. I'm simply looking for a little quicker times from the 60' to the E.T. I'm also looking for a little more seat of the pants fun.

 

[Cory S]

Changing gears will do nothing for me with regards to "Bracket" racing. I'm simply looking for a little quicker times from the 60' to the E.T. I'm also looking for a little more seat of the pants fun.

A 3.55 gear with a 4.17:1 1st gear = A SLR of 14.8:1. Unless your car is over 4300lbs and/or revving to 9500rpm, going to a 4.09 rear gear will net you ZERO ET gain.

 

[WildHorse]

A 3.55 gear with a 4.17:1 1st gear = A SLR of 14.8:1. Unless your car is over 4300lbs and/or revving to 9500rpm, going to a 4.09 rear gear will net you ZERO ET gain.

Normally I agree with you. But there has to be some ET gain.
Although I didn't go 4.09, went 3.31 to 3.73, I picked up .3 in the 60' which translated into gains all the way down the 1/4.

 

[Cory S]

Normally I agree with you. But there has to be some ET gain.
Although I didn't go 4.09, went 3.31 to 3.73, I picked up .3 in the 60' which translated into gains all the way down the 1/4.

So many factors though. Picking up .3 in 60’ was probably not all from the gear swap, but how the tire planted itself in the first 5-15’ as well.

There’s a point where too much gear, creates a lower average torque to the tire before the 330’ mark.

If there’s plenty of gear (and on a 6R80/3.55 combo there is) to leave Ok for the first 60’, it’s normally the converter that is playing the majority of that role.

 

[WildHorse]

So many factors though. Picking up .3 in 60’ was probably not all from the gear swap, but how the tire planted itself in the first 5-15’ as well.

I would agree 100% if it was a one time thing. But it's consistently better. Comparing the 3.31 slips to the 3.73 slips. Average is .3 better.

 

[Cory S]

I would agree 100% if it was a one time thing. But it's consistently better. Comparing the 3.31 slips to the 3.73 slips. Average is .3 better.

In your scenario, the 3.31 swap to 3.73 is far more beneficial for the cars weight and being N/A then, or another N/A car going from 3.55 to 4.09.

 

[SK17]

I'm not hoping for night and day difference. I was hoping for maybe 0.2-0.3 tenths in the 1/4 mile with maybe a tenth in the 60'. I watched a couple videos from american muscle where they went with 4.10 gears on a 2014 gt auto and gained 0.3 tenths in the zero to 60. Roughly same hp/tq, same 6 spd auto, same trans gear ratios.

 

[SK17]

https://www.bing.com/videos/rivervi...004542C898BC644608C1004542C898BC&&FORM=VRDGAR

Here's the amercian muscle video.

 

[SK17]

Hey all. I finally did the change from 3.55 gears to 4.09 gears in my auto. Here's my results. I picked up a little in the 60 foot, 1/8ET and 1/4ET. Less than I had hoped but I'll take it. Here's what threw me. I picked up 2-3mph in my trap speed (114-115). This threw me because I thought I would lose top end mph with the lower gears.

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