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
4. FREE Software Download
5. REAL World Technical Support
6. Most Accurate Digital Altimeter
-- 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 factor.
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 your factor.
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.
When throttle 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
Once 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 to this.
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.
-- FREE 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
-- 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!
-- Most Accurate Digital Altimeter --
We have in stock, the best digital electronic altimeter that we have
ever seen. It has a resolution of just one (1) foot. This unit is just
$149.95. You just can't beat that! Using this gauge and one of our CMM880
Digital Temperature/Humidity gauges, you'll get better air readings
than ANY other weather station/trailer station on the market, guaranteed.
To read the specs on this unit, just go to the Products page on our
web site and click on Digital Altimeter.
-- Toll Free Ordering --
We also have a new Toll Free Order line to save you even more money!
If you're placing an order by phone, call 877-497-0992. If you need
information or technical help, call 610-497-5561.
-- Secure Ordering --
You can safely order directly from our web site. All of your information
and it is posted on the web site. Our company is registered with the
Public Eye for safe, secure ordering. If you have questions or topics
that you would like to see covered in this newsletter, please E-mail
them to me.
Family Software - Drag Racing Computers and Software
http://www.iFamilySoftware.com - 610.497.5561(Voice/Fax)
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