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Delay Boxes 101

Written by Kym Oberauer.

Biondo Little Wizard Delay Box

Love’em or hate’em, delay boxes are a part of Drag Racing in Australia and are legal in Super Sedan, Modified and Super Gas. Racing without one is like turning up to a gun fight with a knife. Sure you could go a few rounds without one, but more often than not you are going to get shot down at the tree.

So what is a delay box?

In its purest form it's an electronic control device that delays the release of your trans-brake by a pre-determined amount of time. Your trans-brake button is wired to the delay box and a wire then runs from the delay box to your trans-brake solenoid.

When you release your trans-brake button, the delay box counts down the required time and then releases the trans-brake.

The purpose; cut better lights, out-react your opponent and win more rounds.

The importance of a good reaction time

You need to react before you see the green light on the Christmas tree because of two things:

  1. It takes time for you to let go of your trans-brake button – let’s call that your personal reaction time (PRT).
  2. Your car has to move forward or rollout about 6.5 inches (if it drives out from the line) for the stage beam to reconnect and start the timer in your lane – let’s call that your vehicle reaction time (VRT).

The average human reaction time is approximately 0.18 seconds and as a rule of thumb let’s say that each 1000lbs of weight in your car equals 0.1 seconds of vehicle reaction time. So if you car weighs 2800lbs, your vehicle reaction time would be 0.28 seconds.

So now we have VRT of 0.28 and a PRT of 0.18 giving a total reaction time of 0.46. In this instance, if we were aiming for a perfect reaction time (0.000 seconds) we would need to let go of the trans-brake button 0.46 seconds before the green light comes on. Hmmmm…easier said than done.

Drag Racing Christmas TreeThe lights on an ANDRA Christmas tree are timed at 0.4 second intervals and there are 3 amber lights. This gives us a total time of 1.2 (3 x 0.4) seconds from the flash of the first amber until the green light comes on. Now, in the example above, in order to cut a perfect light we would need to release the trans-brake button 0.06 BEFORE the last amber light comes on. Even if you were playing it safe and wanted to cut a 0.03 light, you are still going to have to leave 0.03 before the last amber light comes on in this example.

If we waited until the last amber light comes on, the best light we could cut would be a 0.06. This may win you a few races but that leaves a pretty big gap for our opponent to out react us. And the racer with the better reaction time is in control of the race and it is theirs to lose. If they don’t break out or are over their dial-in by the less than the difference in reaction times then they will win the race, simple as that.

Here’s an example; racer A dials in with a 10.00 and racer B dials in with a 9.00. Racer A’s reaction time is a 0.04 and racer B’s reaction time is a 0.08 – that’s a start line advantage of 0.04 seconds to racer A. Racer A can now run anywhere between 10.00 and 10.04 and win the race and there is nothing racer B can do about it. In fact, as long as racer A crosses the finish line 0.04 or less in front of racer B they will always win, no matter what the situation (barring a rules infraction).

Hopefully, that illustrates why it is so important to win the battle at the tree.

Why use a delay box?

As discussed above, we want to win the reaction time battle, but leaving on or around the last amber is not very consistent and does not allow for changes in racing conditions. This is where a delay box can help you win more races.

Fundamentally a delay box, when used correctly, will provide the following:

  • Consistency - improved consistency and therefore better reaction times
  • Tunability - the ability to maintain consistent reaction times irrespective of changing conditions
  • Flexibility - many of today’s delay boxes include features that allow you to have multiple shots at the tree or modify the delay time after you have let the trans-brake button go
Modified Winternationals 2012Times are very tough in Modified if you don't run a delay box  (Photo courtesy www.dragphotos.com.au)


With a delay box you will no longer pick a spot on the tree to leave on and anticipate the light – say the last amber. From now on you will let go of your trans-brake button when you see the first amber light. The delay box will then count down the allotted time and release the trans-brake.

The amount of delay that you put into the box will depend upon a number of factors including your personal reaction time and your vehicle's reaction time as described previously. In that example we had a combined reaction time of 0.46 and we know it takes 1.2 seconds from the first flash of amber for the green light to come on. If we subtract the reaction time from the time it takes for the tree to count down to green we get 0.74 seconds (1.2 – 0.46). 0.74 is the time we would enter into the delay box if our aim was to cut a perfect light (0.000).

Now, this is a theoretical example. In most cases our aim is not to cut a perfect light and it would be virtually impossible to do so consistently anyway, there are just too many variables at play. But what we can aim to do is cut a consistently good light (say between 0.01 and 0.025) to minimise our chances of red lighting and leaving only a small window for our opponent to out react us.

If you are not sure what you personal or vehicle reaction times are, an easy way to find the right delay range is to start with what I call the neutral setting by entering 0.8 into the delay box. If you are red lighting, add some time to the delay. If your reactions are over 0.01 then take some time out of the delay until you find the time that works for you and the car. It’s a process of trial and error but it won’t take long to find the appropriate range.

TIP: If you have a Portatree Super 2000 practice tree, you can work out your personal reaction time by setting it to pro tree mode, switch off the perfect tree mode and enter 0 for the rollout. This will then give you an accurate representation of how quickly you react to the flash of the amber light.


A delay box allows you to tune your reaction times to the changing conditions, which is much more difficult to do when you don’t use a delay box.

For example, your reaction times can be influenced by the following:

  • Time of day – you react quicker at night as the lights appear brighter. The opposite can be said when the sun is shining on the lights.
  • Rollout – all tracks are not created equally. Rollout may differ between tracks therefore affecting your reaction times.
  • Available traction – traction can vary from lane to lane, hour to hour. Theoretically, the more traction the quicker the reaction, less traction the slower the reaction.
  • Obstructions – do you have to look around your scoop or roll cage to see the tree? This can affect your reaction time.
  • Staging – the deeper you stage the quicker the reaction time. While a delay box can’t help you here it highlights the importance of staging the same way each time, preferably shallow.

And with a delay box you can counter these changing conditions by adjusting the amount of delay. A common problem for racers is that most qualifying occurs during the day and then the later rounds of racing are at night. At night, you can actually react approximately 0.015 seconds quicker because of the contrast between the darkness and the amber light. Knowing this, you can add extra time to your delay to make sure you don’t red light and continue to cut consistent reaction times.

Frank Bogaart - Super SedanThe dreaded cherry - can the little black box help fix this problem? (Photo courtesy www.dragphotos.com.au)


Like all technology, delay boxes have developed over time to include many more features that will help you become a more consistent racer. Common features now include:

  • Tap-up / Tap-down – this feature allows you to add or subtract an amount of time from the delay if you feel you were early or late.
  • Cross-over – this feature allows you to react off your opponent’s side of the tree if you are the quicker car. You enter your dial in and your opponents dial in into the delay box and it automatically calculates the difference. It then adds this time to your delay setting when you leave off your opponents light. Therefore, you are reacting to the very first flash of amber which happens to be on your opponent’s side of the tree. This feature is only applicable on trees where you can see your opponent’s lights.
  • Multiple hits – with multiple hits you can react off of your opponent’s first amber light and your own amber light, using one or two buttons. The delay box will then choose which ever was the quicker of the reaction times. This is an extension of the cross-over feature.

These are just some of the features a modern delay box includes.


Delay boxes are invaluable if you want to improve your reaction times and give yourself every chance of going rounds. However, like everything in drag racing, it will not make you a champion over night. It is simply a tool, which when used correctly and with the necessary skill and knowledge can help you become a better and more consistent racer.

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