986 gearbox failure

[911monty]

Originally Posted by edc

Looking at the 2.5 Vs 2.7 box ratios you won't notice any difference as the first 3 ratios are the same.

Not true. The final drive ratio is ultimately the determining factor. This is the ring and pinion gear ratio in the differential section of the transaxle. 3.89 revolutions of the pinion to rotate the ring gear 1 revolution, which rotates the axles, is significantly lower than 3.52 to 1. doesn't sound like much but it is. i.e at 4000 engine rpm 4000/ 3.89= 1028 axle revolutions and 4000/ 3.52 =1136 axle revolutions, (assuming direct drive). So you can see the 3.52 has travelled much further. (additional 108 revolutions) you then multiply that by tire circumference to determine distance travelled. So while the first three gear ratios are the same the 2.5 final output is lower. where the last 2 gears in the 2.7 are much taller.

[The Radium King]

Originally Posted by 911monty

Not true. The final drive ratio is really the determining factor. This is the ring and pinion gear ratio in the differential section of the transaxle. 3.89 revolutions of the pinion to rotate the ring gear 1 revolution, which rotates the axles, is significantly lower than 3.52 to 1. doesn't sound like much but it is. I won't go into the math here but it is easy to look up. So while the first three gear ratios are the same the 2.5 output is lower. where the last 2 gears in the 2.7 are much taller.

which can be modified also by changing the sidewall height of your tires ...

[911monty]

Originally Posted by The Radium King

which can be modified also by changing the sidewall height of your tires ...

Exactly. I modified my original post to reflect tire circumference with some math.