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Overdrive 22% to 28% - RPM and Speed

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Swiss Toni

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I've installed a 28% fast road OD (standard is 22%) and I was expecting a decent drop in RPM at a 130 kph / 80 mph cruise over the standard OD previously installed, but I've not see much if any. It now turns about 3300 rpm at that speed.

The speedo is under reading now by about 15 kph / ~10mph.

Any thoughts?
 
Swiss Toni said:
I've installed a 28% fast road OD (standard is 22%) and I was expecting a decent drop in RPM at a 130 kph / 80 mph cruise over the standard OD previously installed, but I've not see much if any. It now turns about 3300 rpm at that speed.

The speedo is under reading now by about 15 kph / ~10mph.

Any thoughts?
Click to expand...

There are too many variables/not enough detail here. Please explain the before and after rpms at 80mph and the before and after speedometer reading. 3300 rpm at 80 sounds in line with the 3.9 rear axle ratio.

Have you looked at the little brass plate on the outside of the overdrive to verify your new one is indeed 28%?
 
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