Optimum Gear Ratio For Road Racing

[Black Pony]

I have a Base 2016 Mustang GT. I am considering doing some road racing on weekends. What would the optimum gear ratio if I kept it NA?

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[Grintch]

Depends on the track, your redline, etc.

I often wish for taller gearing with the stock 7000 redline and PP 3.73 gears.

Also, remember the gearing is quite different for 2018+ cars, so ignore any you need a 4.09 or more advice as it doesn't apply to a 2016.

PS - with a base GT, gearing changes would be very low on my list of useful mods. High on the list, brake upgrade.

 

[AlbertD]

There isn't a one size fits all answer. It will be dependent on the track, your tire size, your rev limit (and usable power), etc...There are some tracks I visit were I wish the gearing was a bit shorter and other tracks were I want it a bit longer.

I agree with Grintch...for a base GT, proper brakes would certainly be my main focus.

 

[Black Pony]

I have a Base 2016 Mustang GT. I am considering doing some road racing on weekends. What would the optimum gear ratio if I kept it NA?

I will be changing out the standard brakes for the six piston Brembos. Regarding potential track locations, since I live the the Atlanta area, it would be Road Atlanta and Atlanta Motorsports Park. I am also considering installing either the Power Pack 2 or Power Pack 3, so the rev limit will vary. A suspension upgrade is currently in the works. Based on the tracks listed above, and in particular Road Atlanta, which Power Pack would you recommend?

 

[BmacIL]

Power Pack 3 if you're going to do power mods (should be furthest down the list for the track, but I get having it for dual purpose) and 3.73 w/ the torsen diff. Don't just do gears. The diff is way, way better for track use. You can do a full assembled pumpkin swap.

 

[Black Pony]

Thanks for everyone's advice. I agree, the pumpkin swap is the best way to go.

 

[Grintch]

Remember tire size is also a factor, shorter tires effectively shorten the gearing. 6th gear is not something you want to use on track, the big gap between 5th & 6th will drop you out of the power band. The 3.73 costs you ~20 mph on the top end of 5th verses the 3.31. You might want some of that on the long back straight at Road Atlanta. At AMP I would be surprised if you even get into 5th.

 

[ddozier]

For Road Atlanta or any of the bigger tracks you have a couple of options and the shorter tracks really need the 3.73. For me the deciding factor is RPM, If you are wanting to keep the engine between 5000 and 7200 as much as possible then you will need to shift more with the 3.73 and that can make you slower. If you are willing to spin the RPMs to 7800-8200 you will be faster with the 3.73 because you get the advantage of staying in a lower gear longer and having fewer shifts. Once you get to carrying more speed in the corners and cant take advantage of the lower gear TQ out of the corner then a 3.55 or even a 3.31 with the Torsen rear end will start to make more since.

I started with a PP car so having used the 3.73 setup for several years I am ready to move to the 3.55. I am looking to reduce the total number of shifts needed to complete the lap, up-shifts cost you time, downshifts complicate the lap. Ideally being able to run Road Atlanta in 3rd and 4th would be perfect but that is not really possible given the higher terminal speeds of the main straight and the back straight. You will need some data mainly looking at top speed, and RPM for a given track. Use that data to decide.

Here are a few data points I used to make my decision to move from 3.73 to 3.55, these numbers are from a 2015 PP GT with 2018 intake manifold and bolt-ons, otherwise stock engine, on 305/680/18 26.7" tall tire at Road Atalanta

Terminal MPH Speeds at:
Front Straight = 129.7
Up the hill From 1 to 2 = 101.6
Entry to the Esses = 84.8
Top speed in the Esses = 103.6
Between 5 and 6 = 114.5
Back Straight = 149.7

What this tells me is that if I am looking to shift at 7200 I will need 5th gear on the main straight and the back straight, but I also need to make a shift from 3rd to 4th at the entry into the esses and the end of the short straight just before turn 6. If I am willing to spin the motor to 7900 rpm I can stay in 4th on the main straight, 3rd up the hill out of turn 1, through the Esses and up the hill through turn 6. This alone gets rid of 4 up shifts and 4 down shifts, 8 total shift events in less than 1/3 of the track. It also allows me to drive into the Esses harder and not have to short shift to 4th just before the entry. It also gets rid of the down shift from 4th gear to 3rd while braking for turn 5 when you really need to be 100% focused on proper entry and exit and not performing a down shift. That is just playing with the RPM side of the equation but there are big gains to be found in this part of the track. If you are like me and are looking for ways to be faster while being gentler to your equipment them you take these numbers and look for a way to reduce shifts and RPMs by changing the final drive gear to a 3.55 or even a 3.31.

The 3.55 gear will allow me to run less than 7500 rpm (I prefer to shift at 7200-7400 max) and stay in 4th on the main straight, use 3rd up the hill through 2 and into the esses, through the esses and up the hill out of turn 5, shift to 4th by the end of the straight before turn 6 and downshift to 3rd while braking for turn 7. Making almost 1/2 of the track end up at 3 shift events. As long as I can carry the same terminal speeds I will be faster, and the reality is I will likely be faster and after some time running the 3.55 gear I will have to decide again on pushing RPMs higher or moving to a 3.31 as the speeds increase. The downside to this is if you make a mistake and loose corner speed it takes you longer to make it back up and you will be slower.

Gearing will always be a compromise unless you are willing to change it for every track you go to, other than Road America and Road Atlanta the 3.31 will not make much since for the tracks I go to, and for a track like Barber or Putnam or other short tracks the 3.73 is going to be the better choice but the 3.55 may not hurt you if you have done some engine bolt ons and have the TQ to pull form 4500rpm as well as you can pull from 5000rpm. In the beginning you will be faster on a 3.73 gear because you can make more mistakes and drive off the corner faster, as you learn to carry more corner speed you will need more shifts, more RPMs, or both to get faster. After a certain point you will need to look for other ways to be faster and one of them is to reduce shifts and that is when the gear change will be needed.

The other option is to drive the 3.31 and put your money into seat time and develop the corner speed needed to make the 3.31 a positive.

Dave

 

[Grintch]

Great info. Top speed on the back straight was my big concern with 3.73's at Road Atlanta.

At Barber and TGPR, I am right at the redline in 4th at the ends of the longest straights. So a taller gear would save me from bouncing off the limiter occasionally or lifting a bit early, which is faster than shifting to 5th and then almost immediately shifting back down.

 

[3star2nr]

I have a Base 2016 Mustang GT. I am considering doing some road racing on weekends. What would the optimum gear ratio if I kept it NA?

Depends on the track and how u like to drive. I have 3.73 and I'm mostly bouncing between in 4th and 5th... I'll get close to 6th on the straights going into turn one.

I'd say your stock gears are probably fine. If you get 3.73 id really recommend raising the rev limit... Holding and pedaling it because there's no time to upshot can be annoying. And in the tight section, being able to stay in the gear a little longer before hitting red line is really beneficial.

 

[3star2nr]

The one massive advantage to the 3.73 is the instant torque in everygear so if u mess up, just floor the gas... Get in a slide, floor it, running wide, lift a bit, turn in more then point and floor it. About to hit a wall, not today, point, floor it...

The Car will make it happen every time. I was really nervous about driving this car until I got it on track and realized that its actually really really hard to crash, or lose control over these cars.

When in doubt stay calm, let it slide then point and floor it...

As long as youre on the gas you cant crash...

 

[bnightstar]

The Mustang GT4 car is with 3.31 gear ratio.

 

[Norm Peterson]

The Mustang GT4 car is with 3.31 gear ratio.

Doesn't it also use a Hollinger gearbox?

Meaning that the ratios are probably a bit different from either the MT-82 or the MT82-D4 (I couldn't find any information on this), which would affect final drive ratio selection.


Norm

 

[bnightstar]

Doesn't it also use a Hollinger gearbox?

Meaning that the ratios are probably a bit different from either the MT-82 or the MT82-D4 (I couldn't find any information on this), which would affect final drive ratio selection.


Norm

Holinger Sequential Gearbox w/ Electronic Paddle Shift

I totally forgot about this small difference. Thanks for pointing it out.

 

[JohnD]

Holinger Sequential Gearbox w/ Electronic Paddle Shift

I totally forgot about this small difference. Thanks for pointing it out.

LOL! $25K difference just for the gearbox alone, not counting who knows how much to actually install one. But who's counting?

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