On Sat, 2 Mar 1996, Paul Caskey wrote:
> I thought I knew something about street racing, but you're throwing out
> some vocabulary I don't understand. So I'm going to confess my
>ignorance and ask you about a couple of terms.
> Mel> That's why I loveto race people with 4 speeds. The automatic is
> Mel> faster off theline, especially if you flash the converter and then
> ^^^^^^^^^^^^^^^^^^^
Flashing the converter, at least in the way I use the term, means quickly
taking it up to it's stall speed while holding the brakes in third after I
have done my burnout and before I make my final approach to the staging
beams. If the converter stalls (RPM stop climbing) at a known RPM, I know
the transmission is OK. IF the RPM is dropping, I know to stage deeper as
the vehicle's reaction time is going to drop off. After I stage, I either
apply the transbrake (in my Shelby Dakota) or use a line-lock and/or foot
brake (RAM Club Cab) in low gear and bring the RPMs up to as close to the
maximum torque output of the engine (but, obviously at or below the stall
speed of the convertor) at the starting line to have the benefit of the
highest starting ratio (see next section).
> Mel> footbrake against the throttle for maximum torque multiplication.
> ^^^^^^^^^^^^^^^^^^^^^
The following is taken from the Mopar Performance Chassis Manual, 8th
edition. This discussion of starting ratio was taken from chaper 4.
--------------------- begin quote -------------------------------------
"The starting ratio of a drag car is rarely discussed, but is very
important. It can easily be overdone. Yet changing the starting ratio
can certainly help the car's response time against the staging lights.
With all this in mind, what is the starting ratio?"
"In an overly simple definition, starting ratio is the transmission's
first gear... ratio multiplied by the rear axle ratio. The tire diameter
can be considered but, for simplicity, will be assumed to remain
unchanged. So, the simple equation is SR = TR x AR. For a standard
manual transmission, this equation works fine. A typical drag car first
gear transmission ratio is 3.0. A typical [racing] axle ratio might be
4.8. The starting ratio for this manual transmission example is 3 x 4.8
= 14.4."
"This simple equation doesn't work for automatic transmission cars. A
factor has to ge added for the torque converter. For reference, it has
nothing directly to do with stall speed. The primary function of the
converter, based on its original design, was to convert engine torque to
drivetrain torque. This conversion is measured by a ratio called ...
[the] converter's torque ratio curve, which is not a constant. In drag
racing, the starting line, where the torque converter is in stall, is of
primary interest. Under these conditions, the torque converter has a
[positive] stall-torque ratio. Unlike stall speed, the stall-torque ratio
cannot be measured or approximated in the car. It must be measured on a
torque converter dyno by the manufacturer. Typically, the stall-torque
ratio [or torque multiplication] varies from 1.5 to 2.0. For most current
race converters 1.8 is a convenient number."
"The equation for use with automatic transmission cars is SR = STR x TR x
AR. In a typical race car this might give the following numbers: 1.8 x
2.45 x 4.8 = 21.2. Note that the automatic starting ratio is much higher
than the manual version."
--------------------- end quote -----------------------------------------
What this means to me, Paul (and by the way, I am sorry to be so long in
replying, but I wanted to research my facts before shooting off my
mouth), is that even with a taller first gear (2.45 vs 3.0),
an automatic has a terrific advantage at the starting line because of
the torque multiplication characteristics of the converter. Ideally, you
would want your engine to produce peak torque at the converter's stall
speed and have a combination that could hook up when you left the line.
That is why my RAM leaves so hard comparable to it's weight and
horspower, my 60 foot times (2.3 seconds) are comparable to much faster
(top end) and lighter cars, and my .520 reaction times are competitive
with most delay box racers even though I don't use electronics to race.
In an automatic, you can leave harder and break fewer parts than the
manual transmission racer; although I will admit that an expertly driven
4 speed car (Sox and McCandless come to mind here) is sight to behold and
one you will never forget.
> That's some very interersting info, by the way. Care to enlighten me on
> those underlined terms?
I hope this was of some interest.
-mel
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