<VV>PG

[Brent Covey]

Hi Padgett!

> I disagree. PG amounts to a three speed minus *second* gear. Just about
> every three speed automatic  I know (OK not a slim jim) will do 40-50 in
L,
> just the same as L in a Covair PG.

I was thinking in broad terms, any Powerglide car, not specifically Corvair-
the old Impala with 2.73-3.31 axle and Powerglide upshifts from first about
70-80 MPH. Vegas get way up there too. Most of the difference is axle ratio,
a Corvair with an FWD X car's 2.94 ratio would run 2450 rpm at 60 it top and
57 mph in first on WOT upshift at the regular ~4400 rpm upshift speed. If
tomorrow morning everyone with the THM 350 woke up to find Powerglide in
thier cars very few would notice.

A Corvair with an imaginary 110HP/TurboHydramatic/3.55 axle (2.48/1.48/1.00
ratios)would shift out of first at 34 mph, and second at about 57 mph at the
same WOT max RPM it shifts at 48 mph currently with Powerglide. This wouldnt
make a huge difference probably in most driving. Powerglide usually has a
1.82 low ration, some of the big cars had a 1.76 such as my Impala example.

Turbo Hydramatic 400  has a habit of 'forgetting' to downshift into first
gear when they get old occasionally and this is usually not even noticed by
the driver if they arent paying attention, they still drive away on the
converter without anything catching your attention usually, even in a heavy
vehicle like a Cadillac or pickup.

Axles got a lot taller starting with 1965 Pontiac, Cadillacs/Toronados etc
used 3.21's most of the sixties. Pontiac offered a 2.41 for '65 and by '75
these sorts of ratios became much more common, Monza 2+2 V8, Cadillac and
some of the intermediates had standard ratios as tall as 2.29 by 1976-'79.

> Starting in second (we had a '61 T-bird
> in normal flatland operation, started in second) is entirely different.
> Don't think I have ever had a three-speed auto that did less than 70 in
> second which made it a nice passing gear.

My 454 pickup with 3.73 axle runs 2550 rpm at 60 MPH, and seconds only good
for ~70MPH on WOT upshift. With 4.11/4.56 it would be operating in the realm
of the Corvair's RPM doing most stuff.
>
> One thing I am curious about is how much multiplication are you getting
> when floored in Drive at 2500 rpm (50 mph with 3.55) ? Doesn't seem to be
> much change in engine speed but I have no tach. Could someone with a PG
let
> me know what the floored but no downshift RPM is at 50 or 55 and what the
> axle ratio is please?

You wouldnt be getting any torque multiplication at that rpm, the stall on
the stock Corvair converter is around 1700 rpm (same as most 1975 up cars)
and its not effective at highway speeds. For multiplication to happen that
stator has to lock which only can happen with a large difference in the pump
and turbine rpm that permits the sloshing oil returning from the turbine to
lock it on its clutch.

On a wet road, you can really feel the points the converter is effective, it
adds a lot of WOT jam up to 18-20 MPH in first then almost feels like a
clutch letting out as it couples up, theres a sort of oozing surge forward
and then flat performance. As you've pointed out, the converter has a very
modest amount of slip in the realm of 100-300 rpm depending on load at
speeds above 'stall' which is why upshifts happen at 4200 rpm in most
standard production GM cars of the era with automatics- the transmission
upshifts at 4200 but the engines going a little faster with the slip,
perhaps 4400. The big car switch pitch trans in 'performance angle' can
provide some multiplication to about 2800 rpm or so depending on what
configuration is used (intermediates got higher stall smaller diameter
converters than the Electra 225's). Generally converter slip in a Corvair is
so minor as to not really effect engine rpm calculations, rounding rpm data
'up' is adequate to account for it.

Experimenting with a 140 manual trans style engine and Powerglide with 3.55
axle, its possible to hit an indicated 65 mph locked into low range (5700
rpm+ slip, prolly approaching 5900 engine rpm) and then upshift to direct
for quite a dramatic improvement in acceleration. The shift when it occurs
is imperceptible as the engine is now at 3200 RPM in second and you're back
on top of the output again and the actual transmission output power is
pretty similar.

I still think Larry Formans experience of a tach in a Turboglide car is the
best thing I've heard all week, about as informative as a vacuum guage on a
diesel, thats really funny;-)

Brent Covey
Vancouver BC