Bracket Racing 101: It's All In The Timing, Pt. 2
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In "It's All In The Timing, Pt. 1", Al Smyth from Portatree Systems (www.PortaTree.com) helped us dissect the beginning portion of the dragstrip, specifically the timing system at the starting line. Now that we’ve hit the gas and are off and running, let’s take a look at the various increments we’ll encounter along the way.

The typical 1/4 mile dragstrip is wired with timing sensors at 60 ft., 330 ft., 660 ft., 1,000 ft., and 1,320 ft. In addition to these timing sensors, there are speed clocks at 660 ft. and 1,320 ft. Each of these increments are useful to us bracket racers when trying to tune a vehicle or figure out what the vehicle would have actually run if we hadn’t lifted before the stripe.

I asked Al to discuss the various increments. “60 foot times are a great indicator of track conditions and starting line performance of the race vehicle. Suspension adjustments as well as clutch refinement are all part of the 60 ft. number interpretation.” This is the first increment to look at when you’re doing a mental run-completion after a pass in which you lifted before the stripe. “330 ft. times are a good reference for acceleration and shift point adjusting. You can make all sorts of changes to enhance the 330 ft. time in order to improve the acceleration of the race vehicle.” I’ve experienced fluctuating 330 ft. times when I had a rear-suspension issue that caused the Dodge to unload the rear tires after the 60 ft. clocks.

The first increment that includes both time and speed is the 660 ft. “The 660 ft. time is the first you receive after you are in your final gear. Some vehicles shift into a final gear after the 660, but you will find that they are few and far between. The 660 ft. MPH is important as well because it can be used as a horsepower indicator.” I use the 660 ft. number to figure out what kind of pass the Dodge was on during windy conditions because wind is less of an issue at mid-track vs. at the finish line.

The 1000 ft. increment is the big one we use to complete a run. In reality, the 1,000 ft. data is probably more important than the ET at the stripe. If we’re doing our jobs correctly, the final ET will be all over the place throughout the raceday (thanks to lifting, killing, whomping, etc.), and we’ll be using the 1,000 ft. number to figure out what to dial. In a future column I’ll be dissecting a time slip, so this will be discussed in more depth at that time.

Now we’re finally at the stripe; I asked Al about the distance between the MPH clock and the finish line, and about the finish-line beams: “The MPH trap has been set to a 66 ft. standard for over 20 years. You are actually getting an average speed across the 66 ft. distance prior to completing the race. All non-starting-line sensors are 6 inches off the track surface. The only exception is the 60 ft. clocks which are 10 inches off the surface to capture most wheelstands. Therefore all race vehicles start with sensors that are about 2 inches off the ground and tripped by the front tires and finish the race with sensors that are 6 inches off the ground and usually tripped by the body. Keep in mind that most race cars at rest have bodies that are lower than 6 inches ahead of the front tires. Under full acceleration the body will be higher than the finish line beam but any sudden stop in acceleration at the finish line could cause a premature trip of the finish beam with the nose of the race car. Example: race car has an 18 inch overhang. Top speed of the race car is 120 MPH which is 176 feet per second. Converting to inches and thousandths of a second makes the race car going about 2 inches every .001 seconds. If the nose trips early, then the 18 inch overhang will lower the ET by .009 seconds. MPH is affected as well. The MPH formula is 45 divided by the time the race vehicle is in the trap. At 120 MPH the race vehicle goes through the trap in .375 seconds. If we lower the trap time from .375 to .366 then the MPH will go from 120 MPH to 122.95 MPH!!” So in this example, if you dialed 11.00 and were on a dead-on pass but hit the brakes at the wrong time, you could actually break out with a 10.991, and have a higher MPH to boot!

Thanks for reading and good luck at the track.


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