Family Software Newsletter #13 - April 30, 2001



1. 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 your TSF.

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 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 Server. We have established a privacy policy and it is posted on the web site.

Bob Kodadek
SC 1596
Family Software - Drag Racing Computers and Software - 610.497.5561(Voice/Fax)

[ Back To Top ]

[ Home ][ Products ][ Contact Us ][ Articles ][ Links ][ Photos ][ Downloads ]

Copyright 2000, Family Software. All rights reserved.