Re: Diff Swapping (Very different than wife swapping!)

[SMILLER@xxxxxxxxxxxxxx]

GGray, has anyone pointed out to you yet...

>Date: Tue, 10 Nov 1998 16:31:48 EST
>From: GGray657@domain.elided
>Subject: Diff swapping and percived performance
[big snip]
>Take the corvette  six speed that goes from second to fourth, last
>time I checked that didn't make for real good performance...
>
>  Been there done it a few times.
[more snipped]
>Ggray 

... that the Corvette 6 speed goes from 1st to 4th, not 2nd to 4th?

(For those of you who don't know about this, the way Chebby got
decent fuel economy out of the 'Vette 6 speed is to have a
solenoid-actuated mechanism in the shift gate.  Under normal
acceleration, it locks out 2nd gear.  As you pull the shift lever back from
first gear, the mechanism directs the shifter over into the 4th gear gate. 
Under full throttle acceleration, the mechanism moves out of the way,
making 2nd gear available.  I'm not sure whether 3rd gets locked out, too,
or whether it remains available.  Seems to me that you should still be able
to downshift into 3rd, if you want, right?  Anyway, since the V8 has
such GOBS of TORQUE, it doesn't mind being lugged around in 4th gear
at relatively low speeds.)

Anyway, more to the point, and way overgeneralizing, changing to a
lower (higher numbered) gear ratio results in:

Faster acceleration (not accounting for affects of shift time)
Lower top speed *
Worse gas mileage
More engine noise at a given road speed, assuming same gear
More engine wear at a given road speed, assuming same gear
Inaccurate speedometer/odometer readings, if not properly corrected

(I think BMW diff's with the internal speed sensors are immune from this
last problem, but what do I know?)

* True, most cars with overdrive transmissions won't pull redline in top
gear, and some won't pull top speed in top gear, and they might do those
things with different diff gears, but remember, I'm way overgeneralizing
here.

So basically agreeing with you, GGray, changing to a lower (higher
numerically) set of diff gears is great if you want faster acceleration and
don't care about fuel economy, noise, engine wear or  top speed.  Or
whether you can convince officer John F that you really didn't know
how fast you were going because the new gears threw off your
speedometer.   :^)

Scott Miller 
Golden Gate Chapter
BMW CCA #44977

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