Scott, Roughly the first 11,000 SV's were equipped ( rather
ill-equipped ) with the 4.22 rear end , overdrive or not. I changed
mine to a 3.89 this past winter and it helped. It's easier to swap the
whole differential than to change the ring and pinion. Once you pull the
axles you can simply unbolt , remove the old and insert the new. No need
for shims and guages. You can find a used one for $65. I did some
testing last week with stop watch,mile markers,and hand held tach and
determined that I needed 4100 rpms to get 60mph. According to the shop
manual I should be getting 17.6mph per 1000 rpm. That would have me
traveling 71 mph , not 60. I don't get it. Could my tire size make
that much difference?
Okay, the rest of you get out your calculators. Tell me if this
makes sense. 1rpm on the engine = 1 turn of the drive shaft in 4th gear
( no OD ) . So 3.89 turns of the drive shaft = 1 turn of the tire. If my
tire is 70" around and there are 63360 inches in a mile then it takes my
tire 905 revolutions to travel 1 mile. Multiply by 3.89 and get 3521
drive shaft and engine rpms per mile. Travel this distance in 1 minute
and you get 60 mph at 3521 rpms. Are these correct assumptions? Then
why does it take me 4100 rpms to get 60mph unless both my tachs,my watch
or the mile markers are reading incorrectly?
Rob Nanzig
67SV
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