converters/ fluid couplings

["John G. Napoli" <john@xxxxxxxxx>]

> Quoting "John G. Napoli" <john@xxxxxxxxx>:
>
> > Exactly.  That's why lockup clutches on trannys with torque converters
> > are
> > very important.  Depending on the stall speed of the converter and the
> > weight of the car, you can see a 10% drop in engine rpm once the lockup
> > clutch is engaged, at highway speeds.  That's a measurable improvement
> > in
> > mpg.  Fluid couplings would show a much smaller improvement.  Hard to
>
> John, its a lot less than that for cars like our 60's and early 70's
> Imperials.  For normal crusing it can get as low as 1% or even less (see
my
> prior post).  Even at WOT, as long as the engine speed is around 4000 rpm
or
> more, it will be of the same order (1-2%).  Modern cars with small engines
have
> high stall converters, and these will slip a lot more.  Also, these
engines
> have a lot less torque, so the lock-up clutch can be a ot weaker, and it
often
> locks on all gears.
>
> D^2

I don't have any experience with any Imperial as 'new-fangled' as a 60s or
70s model.  :)

Most highway cruising, though, is at way less than 4000 rpm, so presumably
slippage becomes a factor for them, too.

On 80s-vintage Jaguars with the B-W 66 automatic, slippage IS an issue.
These cars have 2.88 rear end ratios and as such cruise at low rpms.  10%
slippage is normal (I have measured it).  Perhaps this is why an aftermarket
industry has emerged to retrofit more modern automatics and manuals into
these cars.

Best,

John