A 14% hit.... yup, that sounds about right. I like the 3.91 for N/A's I don't think I'd like a 3.73 unless I was a MUCH more mellow driver. My wife would probably like it though. Your speedo and odometer are going to be off quite a bit... hard to correct for as the R154's speedo drive gears don't work in the W58. You may be able to find a drive gear for that end gear out of a pickup with a W series transmission though.
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