Porsche 911 1972-86 7/31 Ratio Ring & Pinion. This ring and pinion is for use in cars with mechanical speedometer (note small drive gear on the end of pinion shaft) but can be used in any 915 transmission as the little gear is not utilized in 1976-86 915 transmissions. 7/31 ring and pinion will shorten or lower the overall ratio about 600 revs. A must have for competition use. Notice that this is a matching set with the numbers 8409 etched on both pieces. $900 Questions call 706 865 5200445-911-73-731.jpg