AQM 981 Shorter Final Drive Ratio


The Issue
 
One of the most common complaints about the GT4 has been the long gearing. This is especially prevalent on the track where it takes a good bit of time to rev through the powercurve, and you’d be hard pressed to find a track anywhere in the world where you’d ever use 6th gear. The factory final drive ratio has a top speed equivalent of 201mph, which sacrifices the intensity of the acceleration curve and leaves us with a GT4 that is not nearly as quick or responsive as it could be on track and not as exciting as we’d like on the street.
 
Our Solution

 
We have spent over 18 months researching and developing a new crown ring and pinion to shorten the final drive ratio. Our new ratio is 19% shorter, reducing the final drive from 3.89 to 4.62. The new gear ratios are now perfectly suited for track use, and much more exciting for street driving. The new shorter final drive ratio is much more responsive, feeling similar to having an additional 50hp at your disposal.

Comparison Charts



When Porsche released the last GT3 manual transmission car (997.2) they shortened the ratio in the RS 13% (from 3.44 to 3.89). Why? Simply to improve the acceleration and on track performance, which helped contribute to the RS’s 7 second improvement over the GT3 on the Nürburgring. The 19% reduction in the GT4 final drive ratio (from 3.89 to 4.62) will have a similar effect on the GT4’s performance, improving 0-60 time by approximately 4/10ths of a second and improving lap times on most longer/fast US tracks by at least a second. As an example, the GT4’s top speed with the 4.62 ratio on the back straight at Sebring will be 2-3 mph faster and only 2-3mph off the top speed of the more powerful 997.2 GT3 RS. Virtually all of that 2-3mph gain will have occurred at the point of initial acceleration i.e. coming out of turn 16 onto the back straight. This gain (advantage) is maintained for the majority of the back straight until the GT4 with the 4.62 ratio shifts into 6th where an additional slight gain occurs over the GT4 with the standard ratio.
 
The 1st chart compares thrust vs speed of a 997.2 GT3 RS and a GT4 with our 4.62 ratio and bolt-ons (est. 40hp increase). The 2nd series of charts compares the thrust vs speed of a GT4 with the 4.62 ratio and a GT4 with the 3.89 standard ratio. In this example, both cars have equal power upgrades.
 
From studying these charts what can we learn? Firstly, let’s compare the GT4 with the 4.62 ratio to the GT3 RS. The GT4 will now be slightly faster 0-60 than the RS, even though the RS has a horsepower advantage (450hp), and the GT4 will still be fractionally ahead at 90mph. After that, the RS’s extra horsepower allows it to pull slightly ahead and by the time it gets to 150mph it’s 2-3mph faster than the GT4 with the 4.62 gearing, as opposed to being 4-5mph faster than a GT4 with standard gearing. How is this achieved? The GT3 RS is doing the acceleration run from 90-150mph using three gears, the GT4 is now doing it using four gears. The additional gear and the shorter ratios allow the GT4 to nearly maintain the same terminal velocity and forward thrust as the more powerful GT3 RS up to 150mph. As the speed increases beyond that, the RS’s additional horsepower will allow it to pull a bigger advantage.
 
The second series of charts compares the thrust vs speed of the GT4 4.62 ratio versus the standard 3.89 ratio, both with equal bolt-on upgrades. As you can see with these charts, the GT4 with the 4.62 ratio will have a noticeably faster 0-60 time. It will also have an additional gain in the 75-110mph acceleration range, which is the critical acceleration range coming out of most of the slower corners on track. This allows the car with the shorter ratio to pull out 1-2 car lengths, which it will maintain down the length of the straight. These incremental improvements exiting the corners is how the car with the shorter ratio is able to improve its overall lap time. From 110mph to 145mph the forward thrust is virtually equal. Above 145mph, the car with the shorter final drive ratio has a slight edge.
This equates to not only a faster GT4 but one that is more engaging and fun to drive : )






Installation

 
Replacing and setting up a crown ring and pinion correctly can be a challenging task and requires specialized experience. To maintain our 12 month product warranty, we have made arrangements with one of the leading Porsche Transmission Specialists in the US, BMC & G in Ohio, to perform the installation and assist in the shipping of your transmission.

Fitment
 
  • 981 Cayman S/GTS/GT4
  • 981 Boxster S/GTS Spyder
Price

$2598 (new crown ring and pinion only)

Longer 6th gear available per request

***We are now taking $1000 deposits for January 2018 delivery***


Placing an Order

 
While we are not yet set up for E-Commerce we will efficiently take your order via our contact information below. We would also love to take the time to learn a bit more about you, the goals you have, and offer our recommendations to meet them and maximize your driving experience. With few exceptions, as long as we aren't on track or taking a nap we are available : ) Shoot us a call, text or email 24/7!

Contact Information
John Gaydos
Cell: 484 883 6197 (text available)
Work: 239 432 1700
Email: john@autoquestms.com

Let's Chat : )

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