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How to Read a Timeslip

Take a moment to figure out what all those numbers mean and what you can learn from them before you stuff it in your glovebox.

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The slip of paper you get after an exhilarating quarter-mile dragstripride is much more than a license to brag (assuming it's a stellar run).All those numbers on that little piece of paper are important tuningtools that can help identify improvements or problems in your car'sperformance. But if you're like most of us, maybe you take a quickglance at the 60-foot time, e.t., and top-end mph then simply stash theslip away between the seats. If so, then it's time to find out whatyou've been missing.

Of course, having a pack of timeslips doesn't do you much good if youdon't have any detailed information about the conditions, tune-up, ordriving technique used on each of those runs. Make it a point to writedown all the details immediately after a run. Include any changes ormodifications to the vehicle, launch rpm, shift points, tire pressure,and weather and track conditions. Keep all your timeslipstogether--ideally in the logbook that you record these details in.

Knowing how to read a timeslip and keeping detailed notes on each runwill result in a valuable performance portfolio that can help determinewhat changes worked and what didn't, and keep you moving in the rightdirection. Above all, it's free. Let's take a closer look at what allthose numbers mean and how you can use them to your advantage.

Breaking Down the Digits

A timeslip is nothing more than a printout that records in detail how quickly you traversed the 1,320 feet from start to finish. These distances are measured in several individual increments.

Reaction: The time it takes you to get the car to move forward after the tree turns green.

60-foot (I1): The time it takes a vehicle to cover the first 60 feet of the track. The greatest indicator of traction.

330-Interval (I2): Secondary timers record the time it takes a vehicle to cover 330 feet; a good indicator of chassis setup.

1/8 e.t. (I3): Secondary timers record the time it takes to cover 660 feet.

1/8 mph (I3): Secondary timers record a vehicle's miles per hour.

1,000-Interval (I4, when given): Secondary timers record the time it takes a vehicle to cover 1,000 feet.

1/4 e.t.: Secondary timers record the time it takes a vehicle to cover the quarter-mile

1/4 mph: Secondary timers record a vehicle's miles per hour; also known as the speed trap, these timers are located 66 feet before the finish line. Between 1,254 feet and 1,320 feet, the average speed between the two lights produces the mph on your timeslip.

Driver's Round Table

Going fast doesn't happen overnight. To get an insider's perspective, weconvened a panel of seasoned heads-up veterans featuring NMCA Pro StreetChampion and former NHRA Pro Stock racer Pat Musi, NMCA Drag RadialEliminator racer Troy Pirez, and NMCA Real Street racer PatrickTopolinski from The School of Automotive Machinists, to find out howreading timeslips helps them stay at the top of their game.

Car Craft: How important is it to understand the numbers on a timeslip?

Pat Musi: Very important. When read properly, the timeslip can tell youexactly what the car is doing at any given moment of a pass.

Troy Pirez: Numbers are everything. Without them, you'll never knowwhat's going on, which is crucial considering we're trying to get to theend of the track as fast as we can.

Patrick Topolinski: Without the numbers, we would never know if ourtuning changes were working. More importantly, you need to know what thecar runs on a regular basis to effectively use the information.

CC: What numbers do you concentrate on most?

PM: We concentrate on all the numbers equally. There are so manyvariables in a car that runs over 200 mph in the quarter-mile andknowing every interval is vital for peak performance.

TP: My car usually runs the same after the 330 [foot] interval. Being ondrag radials, if I can optimize my 330 e.t.'s, then I know I'm on a goodrun.

PT: Mostly the 330 interval. If we run decent 330 times, then we knowthe chassis is right where we need it and we're just along for the rideat that point.

CC: Would you say the 60-foot times are any less valuable than the 330interval?

PM: All the numbers are important, but some people really get freakedout if the car won't 60-foot. Here's a tip--always compare your hometrack's starting-line rollout to every track you race at. You may besurprised at how well your car can 60-foot again once you know where tostage the car on the starting line.

TP: Not at all, but to me the 60-foot is more of a sign of torque andpower. A car can hook like crazy, but if he doesn't have power, he's notgoing to go anywhere anytime soon.

PT: It really depends on the car. If your car runs its fastest at acertain 60-foot, then being off by one hundredth can mean the differencebetween winning or losing by a full tenth.

CC: At the end of a pass, what are you looking for?

PM: Consistency. Since all tracks vary, we'll take the numbers from theintervals and plug them into our Auto Meter Data Logger to see how acurrent pass compares to another. If we abort a run, it'll then help uspredict what the pass would have been. Without all of the numbers, itwould make it much more difficult to be consistent and evaluate what thechassis and drivetrain are doing.

TP: As long as my 330 times are up to par, I know my chassis is dialedin and that numbers on the big end will produce some good times. If the330 intervals are great and I'm slowing down, then I'll check the airconditions or try to pinpoint a problem with the drivetrain.

PT: If the 60-foot and the 330 intervals look good, we'll look at thegains from the eighth-mile to the quarter-mile. Let's say if wetypically gain 28 to 30 mph and for some reason only managed to go 24mph faster, then we know there's a problem. It could have been the airquality, maybe we lost a cylinder, or it could even be a sign that ourtranny or converter is going south. By keeping records, we can diagnosethe situation quicker and try to get ready for the next round.

Rollout and Its Effects On Reaction Time

Rollout is the distance thefront tire must travel from the point the frontmost portion of the treadtriggers the stage beam until the rear portion clears it, which turnsoff the reaction timer and starts the e.t. timer. Deep staging--rollingforward enough to turn out the pre-stage bulb after staging--produces aslower e.t. because the car doesn't get as much of a running start atthe beam, but it can cut reaction time because there's less distance totravel before tripping the timing beam. If you generally tend to be slowoff the line, deep-staging may help produce consistently fasterlaunches. Heads-up racers who want the absolute maximum e.t. on everyrun will stage as shallow as possible. By barely tripping the secondbeam (stage light), you give yourself more of a rolling start before thee.t. clock begins. If you find yourself consistently slower or faster oncertain tracks (assuming air quality doesn't come into play), be sure tomeasure the rollout, since many tracks tend to vary slightly, in orderto help find where you and your car prefer to be staged. It's theattention to detail that makes championship-winning racers consistent.

Shallow Staging
Increased reaction time
Quicker elapsed time
Higher trap speed

Deep Staging
Decreased reaction time
Slower elapsed time
Slower trap speed

Absolute Air Pressure, Barometric Pressure, Humidity...Oh My!

There's more to racing than dumping the clutch or releasing the transbrake and holding on for dear life. A good drag racer also has to be an amateur weatherman. Since dragstrips are located at various elevations and regions all across the country, it's pretty rare for any two tracks to experience identical weather conditions, and it's not uncommon for the weather to change throughout a race day.

To better understand what constitutes good-air and bad-air conditions, we need to first get familiar with a few basic terms: absolute air pressure, barometric pressure, and humidity. Absolute air pressure (14.7 psi) is a constant indicating the weight of air at sea level. Barometric pressure measures the current atmospheric pressure (again rated in psi), and humidity tells us how much moisture is in the air.

Under ideal conditions, you'll have high barometric readings, low air temperatures, and low humidity. The higher barometric pressure helps force the air into the engine, while the low air temperature along with low humidity creates a much denser charge with a high oxygen content for greater combustion.

Poor conditions would be barometric readings lower than the atmosphere absolute air pressure of 14.7 psi, higher air temperatures, and higher humidity. In essence, the motor is starving for air. Top that off with a high-elevation track and you can forget about obtaining optimum performance from your combination.

So the next time you're at the track, don't be afraid to ask someone in the pits if they know the current weather could explain why you're going faster or slower than you expected.

NHRA Correction Factors

We get a lot of letters and e-mails asking why some of our project vehicles are slower than readers think they should be. The straightforward answer is that killer e.t.'s and big mph on the top end require an abundant amount of air traction that our hometown track just doesn't offer. Los Angeles County Raceway (LACR) is located 2,700 feet above sea level, and most cars typically slow down by four tenths and three mph even on a good day. The NHRA conversion factor for this track is to multiply the observed e.t. by 0.9679 and mph by 1.0339 to "correct" to sea-level conditions. That means a 12.00 at 112 mph pass at LACR's high elevation would equate to an 11.62 (12.00 x 0.9679) at 115.80 (112 x 1.0339) pass at sea level.

We don't believe in fluff, and we tell it like it is. Our theory is to run what we brung. If we can post decent numbers at our track, rest assured you'll be flying anywhere else. On those rare occasions when we do use the correction factor, we don't neglect to print both the corrected and uncorrected numbers. We're proud of that. For a list of correction factors for other tracks and elevations, log on to

Diagnosing the Numbers

The data below was generated by a small-block 408ci we dropped into an '85 Mustang for last year's street car shootout ("Chevy vs. Ford: Street Car Shootout," July '02). The timeslip on the left is from a Friday evening grudge night at LACR; the one on the right is from the following day at Carlsbad Raceway in Carlsbad, California. The air was decent for both days of testing, and the only difference was in the track elevation. Going from the LACR's 2,700-foot elevation to Carlsbad's much lower 300-foot elevation made the difference of 3.14 mph and almost two tenths!

We were surprised to find we had better traction at LACR, however, the lower elevation did allow us to run slightly quicker by the 330 marker. By the eighth-mile marker, the speed at the lower-elevation track had already jumped by almost 3 mph and finally propelled us across the finish line nearly two tenths faster. No tuning changes were made during individual testing days.

LACR Carlsbad
60-foot 1.555 1.758
330-foot 4.723 4.775
1/8-mile e.t. 7.290 7.247
1/8-mile mph 96.224 98.97
1,000-foot 9.522 N/A
1/4-mile e.t. 11.353 11.167
1/4-mile mph 120.35 123.49

Power for the Masses

Trying to determine your quarter-mile potential based solely on horsepower readings can be tricky. You'll also need to address several other variables, namely, how efficient your chassis and drivetrain are. Is the chassis dialed in for optimum weight transfer with drag-style suspension? Will you be running on street tires or drag slicks? And what type of transmission will you be using? A manual transmission may have a distinct advantage over a conventional factory automatic, but a transmission specifically built to handle the rigors of drag racing with a custom-built converter matched to the engine may be much more consistent. This chart from Mopar Performance predicts theoretical "optimum" performance from a car with a topnotch suspension setup.

Manual Automatic
15.0 87 15.2 85.5
14.5 90.5 14.7 88.5
14.0 93.5 14.2 92.0
13.5 97.5 13.7 96.0
13.0 100.0 13.2 99.5
12.5 105.5 12.7 104.0
12.0 109.5 12.2 108.0
11.5 115.0 11.7 113.5
11.0 121.0 11.2 119.0
10.5 126.0 10.7 125.0
10.0 134.5 10.2 132.5
9.7 139.0 9.8 137.6
9.4 144.3 9.5 141.6
9.1 149.3 9.2 147.0
8.8 154.9 8.8 154.1
8.4 162.3 8.4 162.6

*Source: Mopar Performance's Direct Connection Performance book.

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