Quote:
Originally Posted by Ragnorak  I think the gearing plays a big part in the fuel economy here. I'm planning on picking up a 318ti for a winter beater/commuter car and want to play with the ratios a bit. Consider this: Automatic 318ti Gear Ratios: - 1st: 2.86
- 2nd: 1.62
- 3rd: 1.00
- 4th: 0.72
- Diff: 4.44
- 70 MPH RPM: 3318
Manual 318ti Gear Ratios: - 1st: 4.23
- 2nd: 2.52
- 3rd: 1.66
- 4th: 1.22
- 5th: 1.00
- Diff: 3.45
- 70 MPH RPM: 3074
When comparing ratios between a manual and an auto here, you basically "skip" 1st gear in the automatic trans but you have overdrive in 4th gear. It makes up for the gearing differences with the very tall 4.44 diff. So what if we have an automatic 318ti and swap out the stock 4.44 diff for the manual 3.45 diff? 70 MPH RPM drops to 2389 RPM. That could make some serious differences in gas mileage as long as the car can handle the lower effective torque output. If not, I can try a 3.73 or 3.91 ratio to not drop the gearing as much. Performance would obviously suffer, but that's what I have the other build for. Has anyone experimented with this? |
I had a 2.93 LSD diff in my ti for a while (5spd) and it was liveable but it was plainfully slow. I got 31mpg from mostly freeway driving with 89oct but I was being carefull. I couldn't stand it though so now I'm using 3.46, Ill see what I get mpg wise, I now also have the midnight tune so I wonder if that will make a difference.