Software Newsletter #13 - April 30, 2001
How To: Compute your Throttle Stop Factor Properly
2. Hints and Tips: Carburetor
Bowl Vent Baffles
3. New! High Temp Gun-Style Infrared Thermometer
FREE Software Download
5. REAL World Technical Support
6. Most Accurate
-- How To: Compute your Throttle Stop Factor Properly
There are many different ways to incorporate a throttle stop. Depending
on how your throttle stop has been implemented and how other devices, such as
shift timers, function, your Throttle Stop Factor (TSF) must be calculated in
a particular fashion. For example, if you are using needle valves to slow the
closing and opening rate of your throttle linkage, then you cannot use a wide
open run and a throttle stopped run to calculate your factor. The amount that
the needle valves slow the ET is not a variable that is part of the throttle stop
timer. If you use a full pass and a throttle stop pass, your calculated TSF will
be much larger than it is in reality and you will always be 'chasing' the number.
In this case you must always compare only throttle stopped runs to calculate your
A second example would be if you are using a shift timer rather
than an RPM activated switch and it is actuated prior to, or while the car is
on the stop. Let's say that when bracket racing you set your shift timer to 1.600
seconds, but when throttle stop racing you set it to .5 (five tenths of a second.)
Shifting the car this early will knock at least .2 to .3 off the ET all by itself.
Again, this slows the car, but it is not part of the throttle stop ratio. So,
you cannot use any bracket runs to compare to throttle stop runs in calculating
If you can use a wide open pass and a throttle stop run
to calculate your factor, then you can take all your throttle stop runs and convert
them to Standard Pressure (STP), Wide Open Throttle (W.O.T.) runs, giving you
a method to accurately monitor your throttle stop function. All of your STP W.O.T.
ET's should be the same. Any variance in how the throttle stop functioned can
be seen immediately. In the example of the shift timer above, just make a full
pass with the shift timer set at .5 and use this run as a basis to compare throttle
stop runs, but only if you are not using needle valves. Our RaceLog Pro software
has this function built in. It will correct all your runs to STP and remove the
effect that the throttle stop had on the run. This gives you an STP W.O.T. ET
for each run. Then using our exclusive Run Segment Analysis feature, you can easily
determine how your throttle stop effects your car and where.
stops are incorporated early in the run, the car gets back up to MPH sooner, and
the throttle stop does not have an effect on the car in every segment of the track.
Therefore, if you are using the 1320 foot ET to calculate your TSF, you are shooting
yourself in the foot. By doing this, you are adding the effect of head wind and
tail wind into your TSF. Using our Run Segment Analysis, you can see where your
throttle stop doesn't effect the car. Then, you can use just the ET segments in
where the stop is 'working' to analyze and calculate your TSF.
you have chosen the method that you need to use, the calculation is simple. Using
STP ET or STP segment times only, divide the difference in ET by the difference
in timer duration. For example, if the STP corrected difference in ET between
the runs is .520 and the difference in the actual timer duration was 1.000 seconds,
then your stop TSF is .5200.
You must be extremely careful to only use
the actual timer duration to calculate your TS factor. Most timers start counting
when the trans brake releases. If you activate your timer at .200 into the run
and you have the second number set to 1.000 seconds, your actual timer duration
is not 1.000, it is only .800. You must subtract the first number from the second
number in your timer to get the actual timer duration. If you don't do this right,
than your factor will not be right. In this example, your actual TSF would be
.6500, rather than .5200. That's a big enough difference to make you want to quit
throttle stop racing after a short time!
-- Hints and Tips: Carburetor
Bowl Vent Baffles --
Most of us know that jet extensions are mandatory
in a Holley carburetor when it is mounted in the customary position (not sideways)
on the manifold. But, Bowl Vent Baffles are just as important and for a similar
reason. When the car accelerates the fuel in the front bowl climbs the face of
the metering block and exits out the vent tube into the primary venturi. It is
usually only a problem in low gear. The G-forces fall off dramatically in high
gear and the fuel level is less effected. Our DataMaster Sportsman computer can
easily show how the performance is effected by the bowl vent tube. The engine
RPM will begin to vary about the time the converter begins to lock up until the
car shifts into high gear. You can't see it with a play back tach or any other
data recorder on the market today. Their sampling rates are far too low. Yet,
it is a major variable in your car's performance.
Hint: If your car's
throttle stop doesn't seem to repeat, you might want to pay particular attention
You must use a bowl vent baffle in the primary bowl and it must
be long enough that it can't pick up fuel. Some of the HP carbs have the baffle
trimmed off to clear the float, but they are trimmed too much. It's better to
use the full length and change the angle of the baffle so that it clears the float.
I personally don't like to use the old trick of connecting the vent tubes with
a piece of hose. I once witnessed what can happen if the hose comes off and gets
stuck in the throttle plates. It wasn't pretty. A properly installed vent baffle
and possibly a longer vent tube can do wonders for your performance and your safety.
-- New High Temp 'Gun-Style' Digital Infrared Thermometer --
We now offer another Digital Infrared Thermometer with Laser Sighting, Part #
IRT4. The new Gun Style unit has a temperature range of 0 to 788 degrees F, has
a backlight, an 8:1 Optical Resolution, and an Auto-Off feature. The introductory
price is just $99.95! That is about what you would pay for a unit WITHOUT laser
sighting and with a lower temperature range. Comparable prices for a unit with
these specifications is about fifty or sixty dollars more.
Software Download -- The DOS version of our DataMaster Analyzer software,
Version 2.0, is available to you as a FREE download on our web site. (The Windows
version is too big to download because of all the associated Windows Dll's and
other MicroSoft files that have to be installed.) You don't need a data recorder
to test the software and see exactly what a DataMaster Sportsman Computer does
better than any other data logger system in the world! Yes, better than the most
expensive data logger in the world. Only, ours is not expensive. If you have any
older version of this software, download this as a FREE update.
REAL World Technical Support --
With Family Software, you'll get better
technical support than anywhere on the planet. Why? Because, we design and/or
use all of the products that we sell. All of my 30+ years of racing experience
and knowledge is available to you and our other customers. Try to find that kind
of information at any one of our competitors. You won't be able to, I guarantee
it! Family Software cares about the racer and his/her success as a racer. The
other companies just want your money!
-- Secure Ordering --
You can safely
order directly from our web site. All of your information is handled on our Secure
Family Software - Drag Racing Computers and Software
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