NetNews Usenet Archive 1992 #16/NN_1992_16.iso/spool/rec/autos/tech/10325

Text File | 1992-07-29 | 7.2 KB | 123 lines

Newsgroups: rec.autos.tech
Path: sparky!uunet!europa.asd.contel.com!darwin.sura.net!mlb.semi.harris.com!billy.mlb.semi.harris.com!jws
From: [e-mail] (James W. Swonger)
Subject: Re: Increasing power?
References: <[e-mail]> <[e-mail]>
Date: Wed, 29 Jul 1992 13:30:57 GMT
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Organization: Harris Semiconductor, Melbourne FL
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In article <[e-mail]> hinz@bonfire (David Hinz Mfg 4-6987) writes:
>
>If you are looking for performance, you can most likely learn how to
>shift at MUCH better times than an automatic would.  They are usually
>set up for mileage rather than performace, and don't take the engine
>up to optimal power range before shifting.
>

 Automatics excel at some things. The torque converter beats a clutch hands
down for things like towing, pulling a boat up the ramp, or launching off
the line. You get about 2X torque multiplication at stall, and you don't
have to finesse the clutch and gas simultaneously to get the rear wheel
torque you want.

 Using a clutch to transfer torque from a 4000RPM pressure plate to a 0RPM
transmission input shaft is an ugly thing to do. Sure you -can- but all the
excess energy is either heat or wear-off of the clutch material. A clutch
can give you some extra efficiency and absolute control, but then demands
that you control it all the time. In addition a clutch, if it is beat upon,
must be changed out as a wear item. However this necessitates separating
the engine and transmission. Not an especially servicable wear item, though
do-able at home with the right equipment.

 A torque converter uses the transmission fluid viscosity as the coupling
medium/energy dump. The fluid is continuously cooled (people who make
extreme use of the torque converter do/should add extra cooling) and the
converter does not wear out (sure, there are bearings, but they never seem
to go).

 A torque converter can be selected to give a lot of slip up to the point
where the engine gets up onto the torque curve. This matching gives optimal
acceleration because you are not ever down in the low-torque region. With
a clutch you must keep one eye (or ear) on the RPM to ensure you are keeping
the engine at the best speed. The converter should be selected to match the
cam and engine torque/power curve. Of course, a loose converter impacts gas
mileage, and that's a compromise that the automakers bias toward economy
typically. But it wasn't always that way. In fact, in the '60s, many of the
BOP (Buick/Olds/Pontiac) models had a Turbo 400 type transmission with a
variable-pitch torque converter, sort of a missing link between the older
variable-vane 2-speed Powerglide/Dynaflow types and the modern 3-speed,
single-pitch THxxx series. This Sasquatch transmission has two stall speeds,
electrically selectable. One is the same as, or maybe even lower than, the
stall speed of modern cars; these transmissions came behind engines like
the Buick 425 and 430, which had >350HP and idled at 500RPM in gear; newer
cars idle at 600-750 for various V-8s. The other stall speed is much higher
(and aftermarket converters are available which offer different stall speed
pairs; 1400/4000 comes to mind). The stock models controlled stall speed
selection by a switch attached to the throttle; at idle and WOT the stall
speed was high and at part throttle it was low. This gave the best of both
worlds - economy at cruise and optimized WOT acceleration. The neat thing
is the electrical selectability; it's possible to rig one of these up in
any car that presently has a TH400, transparently if you take the stock
switch gizmo, but you can also force one stall speed or the other with a
switch on the dash or steering wheel or shifter.

 If you find this appealing, look for an early to mid-60s ('67 was the last
year) Buick full-size (Electra, Wildcat). If it's got the big block and there
is a funky-looking gizmo on the driver's side of the engine, attached to the
carb with wires running to the transmission, it's probably the Super Turbine
400 which is what you want.

 Getting to the transmission end of things, the shift points of an automatic
and the speed/harshness of the shifts can be tuned in to the driver's
preference as well. By changing the springs on the governor (removable from
outside) or swapping governors, the WOT upshift point may be moved up quite
a bit. 5500RPM governors are readily available. Part throttle shifting is
controlled in some cases by a vacuum modulator (adjustable ones available)
or a throttle position cable/switch (adjustable) or both. Even valve bodies
and orifice plates are commonly sold, with characteristics which generally
give a more positive and rapid engagement/disengagement of the clutch packs
to reduce wear which would occur if they engaged slowly at high differential
shaft speeds. In this area the factory compromises in favor of smoothness
while racers want hard shifts (even/especially if they result in whiplash).

 The higher rotating mass of an automatic does rob some power during rapid
acceleration. Spinning up the torque converter accounts for much of this
transient power demand, and smaller lighter converters are used by the
serious types, who want higher stall anyhow. At cruise though the power loss
is not that bad; a regular converter/automatic vehicle seems to run only a
couple of MPG lower than a standard. Naturally if your converter choice is
still slipping a bit at "normal" crusing speeds then your mileage will suffer
and your car may run hot as the slip energy is dumped into the radiator.
But a proper setup for street, race, or both is a matter of selection and
tuning.

 Engines with narrow power bands may be more driveable with a close-ratio,
more-speeds manual transmission; if required to run over the wider ranges
a 3-speed automatic uses the engine would bog early or fade late. Mileage
compromises favor small engines which make power by RPM, not torque, and
with this sort of engine a manual will give more Fahrvergnugen. The manual
also gives complete control over what the rear end does, which is of some
concern in road racing where lateral forces and acceleration must be
dealt with at once, and unexpected gear changes may mean a sudden change
of itinerary. And of course you have the option of putting the whole power
train in exactly the state you want at any time, which is certainly a
desirable thing if that degree of control saves your life or wins the race for
you.

 For straight-line racing, though, where "Go now" is the basic idea and the
input is a floored gas pedal, an automatic is generally the best choice. The
manuals take over when the power levels get too high and the times get low.
For the slower brackets the consistency, reliability and streetability of
automatics make them more widely preferred. Some folks do use manuals but
it doesn't appear to help them any.
--
##########################################################################
#Irresponsible rantings of the author alone. Any resemblance to persons  #
#living or dead then yer bummin. May cause drowsiness. Alcohol may inten-#
#sify this effect. Pay no attention to the man behind the curtain. Billy!#