TMCnet News

[August 02, 2014]


(National Dragster Via Acquire Media NewsEdge) It was way back in 1988 when I first calculated that Eddie Hill's Top Fuel record-setting 5.066 run at the Gatornationals required just more than 4,000 horsepower. That started a string of National Dragster articles on this topic, last showing 8,000 horsepower for Doug Kalitta's 4.486 at 333.91 mph in Houston in 2003. Antron Brown currently holds the e.t. record with a run of 3.701 seconds at 328.78 mph, set in October 2012 in Reading. Today, we have an engine-dyno sheet for the Matco Tools Top Fuel dragster clearly showing more than 10,000 horsepower and at least 7,400 foot-pounds of torque.

You might say, "Wait a minute. I'm not aware of any engine dyno that can handle 10,000 horsepower. Did someone strap a Top Fuel dragster on a chassis dyno somewhere and measure the rear-wheel horsepower?" To my knowledge, the answer is no. The only dyno we have for the nitro cars is the "dragstrip dyno," and data from that dyno comes with every run, including both the time-slip info and readings from the onboard data recorder.

A little history is required to set the stage for today's Top Fuel horsepower analysis. In 2003, nitro cars raced the full quarter-mile, used a maximum of 90 percent nitro, and the dragsters weighed 2,250 pounds. A short time after Kalitta's record run, the switch was made to 85 percent nitro, and teams struggled for a while to adjust. Then Tony Schumacher fired a "shot heard 'round the world" when the Alan Johnsontuned U.S. Army dragster ran 4.428 seconds at 327.98 mph to not only set the record but win the season-ending event in Pomona and the NHRA Mello Yello Top Fuel championship all at the same time. It was a spectacular achievement that stood for a long time. A short time later, NHRA decided to limit fuel cars to racing to 1,000 feet, added 70 pounds to the dragster minimum weight (2,320 pounds), and let the nitro percentage go back up to 90 percent. The rules transition makes absolute time-slip comparisons a little more difficult.

The strategy for today's horsepower analysis is to use all of the time-slip data from both the 1,320- and 1,000-foot eras, combine that with some actual RacePak data supplied by Lee Beard from Steve Torrence's Top Fuel dragster, and fill in the gaps with motorsports engineering and computer simulation. The chart above-right has the time-slip information for four different Top Fuel runs, including Brown's current e.t. record run of 3.701 seconds at 328.78 mph. I have included estimates of what the dragsters would run today if turned loose for the full quarter-mile for Brown's record run and Torrence's run in the first round of the 2013 Chevrolet Performance U.S. Nationals that was low e.t. of the event.

Rev limiters For the last several years, all of the fuel cars have employed a so-called "rev limiter" to reduce the engine rpm and resulting speed at the end of the track. It's really a "timing retard" set to start pulling out ignition timing at 7,900 rpm, active after 2.5 seconds into the run for the Top Fuel cars. The dragsters hit this limiter at around 850 feet. Reducing timing reduces horsepower dramatically and limits the top speed, and it would also limit the top speed if the cars ran to 1,320 feet, so the predicted quarter-mile speeds for today's era are not that much faster than Kalitta's nearly 334-mph run from way back in 2003.

NHRA Nitro Technical Consultant and former crew chief Beard recently asked me to come up with a horsepower estimate for Brown's record run based on my previous experience and motorsports engineering tools and methods. I sent him a list of data I would need, including the weather, time slip, aerodynamics, front/rear weights, etc. I also requested engine rpm, driveshaftrpm, and G-meter graphs from the RacePak data recorder. Beard could not supply the data from Brown's dragster, but he did supply a complete set of data I could use from a slightly slower run by Torrence. The two graphs below show the actual measured race car data (engine rpm, driveshaftrpm, G-meter) along with the calculated speed (mph) from this analysis vs. elapsed time.

My first pass at a calculation for Brown used my old trusted QUARTERjr computer software and resulted in 9,900 horsepower; however, I've learned a lot in the last 10 years consulting with a number of drag racing teams and decided to take another, more-detailed approach to look at the data. Thanks to Beard, I finally had some real-world data for a Top Fuel dragster - nobody had ever shared that level of detail with me before.

I decided to set up a spreadsheet and calculate the engine horsepower and torque at the flywheel for every data point on the RacePak graphs using a bottom-up approach - that is, backing into what the engine-dyno data must look like by adding up all the horsepower components along the way.

You can see that when Torrence mashes the loud pedal, the engine revs up to almost 8,700 rpm at about .5-second into the run, pulling just over 4 Gs of acceleration. At this point, the clutch starts dragging the engine rpm down, and the timing-management system is used to take horsepower away to set the rear tires for rebound and keep the dragster from spinning or shaking early in the run. At about 2.5 seconds, the engine is down to 7,075 rpm and a maximum of 4.8 Gs are recorded. Once the clutch-management system gets hold of the engine (and the rev limiter kicks in), the G-meter falls steadily to 2 Gs at the end of the run.

The analysis requires that the engine horsepower be broken down into a number of components as it travels from the flywheel down to the contact patch between the rear tires and the racetrack surface. In this bottom-up analysis, we are going to start at the tire and work our way back toward the horsepower at the engine flywheel.

Acceleration horsepower As drivers, fans, and racers, we can all appreciate the power required to simply accelerate the race car. Since we have the G-meter data and the weight of the dragster, this is a very straightforward calculation using Sir Isaac Newton's Second Law of Motion (F = MA, or force = mass X acceleration). We have the mass (weight) and the acceleration (Gmeter); we just need to calculate the force and turn that into horsepower.

Beard reported that Torrence's dragster weighed 2,330 pounds at the scales following the run. It would have been about 50 pounds heavier when leaving the starting line due the large amount (more than five gallons) of fuel burned during the run. The RacePak data showed that at 2.5 seconds it hit 4.8 Gs. Newton's law says this requires 5,939 horsepower, but that's not all the horsepower that is required of the engine at this point.

Total aero drag horsepower The aerodynamic drag on a Top Fuel dragster is huge. The dragster is big, and it's aero dirty - all kinds of things are hanging out in the wind. Drag comes from the chassis, body, engine, tires, and wings.

Beard had wind-tunnel data for both the front and rear wings at 300 mph. I estimated what the drag of the chassis, body, exposed rear tires, and wing struts would be and came up with a total race car drag of 2,880 pounds-feet at 300 mph (at sea level). That works out to 2,304 horsepower at 300 mph! The engine has to provide 2,304 horsepower to simply move the air out of the way at this speed.

Aerodynamic drag rises exponentially with speed. Actually, the aero drag horsepower varies with speed to the third power. You can see that at the end of Torrence's run at Indy, the total aero drag was nearing 3,000 horsepower.

Friction horsepower Several sources of friction need to be accounted for as well. First is the rolling-tire friction. The big, sticky Goodyears take some effort to simply roll down the racetrack with all the static weight (2,380 pounds at the start and 2,330 pounds at the finish line) of the dragster and the dynamic downforce provided by the front and rear wings. Beard reported that at 300 mph (at sea level) the wings provide an additional 5,661 pounds of downforce, making the tires feel like they are supporting more than 8,000 pounds of weight. At the finish line at 329 mph, the total downforce on the tires is 9,885 pounds, and it takes 387 horsepower just to roll the dragster down the racetrack.

In order to get maximum traction between the tire and the racetrack surface, the tires must also slip just a bit going down the track. Clear evidence of this tire slippage are the black streaks that run down the track following a run and the resultant rubber that builds up on the track. The amount of tire slippage is not great, but at 2.5 seconds into the run, 235 horsepower is lost due to the slipping tire. This energy shows up as heat in the tire and racetrack surface.

Another source of mechanical friction is the meshing of the ring-and-pinion gears inside the third member. Every gear mesh loses a little power; not all the horsepower coming down the driveshaftmakes its way to the rear axle. Typical hypoid spiral bevel gear systems have an efficiency of around 97 percent. That means that 3 percent of the engine's horsepower is lost and turned into heat in the third member and accounts for 242 horsepower at the critical 2.5-second point of the run.

Horsepower balance chart The horsepower balance chart is where we add up all of these calculated horsepower components to get to the flywheel horsepower. At the bottom of the chart, we start with the aero drag horsepower and see how that increases as the dragster goes faster. On top of the aero drag horsepower, all the other horsepower components are added in, one by one, to work our way up to the top line for the engine horsepower. This chart gives a very good visual presentation for where all the engine horsepower is going at every point in the run. Clearly, not all the engine horsepower gets used for acceleration.

Clutch slippage horsepower The horsepower balance chart shows that Torrence's engine made maximum horsepower just after 2.5 seconds into the run when the dragster achieved 4.8 Gs of acceleration. The engine rpm at this point was 7,075, and the driveshaftrpm was 6,275, so there was 13 percent clutch slippage - the engine running 13 percent faster than the six clutch discs - and a 13 percent loss in power. This is another horsepower waster that gets turned into heat. But look at .5-second: The slipping clutch is eating up more than 5,700 horsepower! This is why all the clutch parts are so hot after a run and must be handled very carefully by the crewmembers.

Inertia horsepower Finally, accelerating all of the rotating parts of the dragster and engine takes horsepower, just like accelerating the mass in a straight line down the dragstrip takes horsepower. There are two major groups of parts that must be rotated in the Top Fuel dragster. The first group can be associated with the engine rpm and includes the basic engine-rotating assembly, supercharger and blower-drive accessories, flywheel, clutch floaters, stands, and clutch cover (hat). The second group is associated with the driveshaftrpm and includes the wheels and tires (front and rear), brakes, axles, spool, ring-and-pinion gears, coupler, reverser, input shaft, and clutch discs.

Any time you have to increase the rpm of these two rotating assemblies, it requires horsepower. The heavier the rotating mass is or the faster you increase the rpm, the more horsepower it will require. As you can see from the RacePak graph, the driveshaftrpm is increasing quickly at 2.5 seconds, whereas the engine rpm is nearly constant at this point. The horsepower required to accelerate the rotating mass of the big Goodyears (each rear wheel and tire weighs 85 pounds) and third member at this point of the run is 577 horsepower. The engine is actually slowing slightly at 2.5 seconds and provides an additional 10 horsepower to help push the dragster down the track.

Torrence dragstrip dyno data This horsepower balance chart combines all of these detailed calculations for every data point recorded on the racetrack. This data can then be used to construct a dyno sheet for the engine. The data points on the dragstrip dyno chart come from the bottom-up flywheel horsepower analysis. Torrence's engine was operated at over a range of rpms and had different calculated horsepower and torque values at every point, each point being every .25-second into the run. There are two outlier data points that result from timing being taken out around the 1.0-second point. The red line on the dragstrip dyno chart represents the horsepower curve of the engine, just like you would get if you ran the engine on an engine dyno. The blue line is the torque curve, measured in foot-pounds.

So what does the Torrence dragstrip dyno tell us? We really don't have any data below 7,000 rpm. It looks like both torque and horsepower decrease as the engine rpm increases past 7,100 rpm. The peak horsepower for the 500-cid Top Fuel engine is almost 9,400 at 7,200 rpm. The observed peak torque is right at 7,000 foot-pounds at 7,075 rpm. Based on my experience and the shape of the dyno curves, the engine might make more torque at an rpm lower than 7,000. Perhaps it's more than the tires and racetrack can handle.

So how much more horsepower does Brown's record 3.701 e.t. need than Torrence's 3.775? They both ran about the same speed. Beard, Torrence's tuner at the time, provided the actual RacePak data for that run. With nearly all the data about the Top Fuel dragster known, I was able to put together a complex spreadsheet to determine the horsepower required at every point on the track. I have the time slip and the weather conditions for the record run but no RacePak data, so the next thing to do was computer simulation. The two graphs below are from a computer simulation of what the RacePak data from Brown's record run might look like.

Using this simulated RacePak data in the spreadsheet I developed for Torrence, it results in the following calculated data and horsepower balance chart for Antron Brown.

The Top Fuel horsepower balance chart shows that Brown's engine peaked at a max of just over 10,100 horsepower when the dragster hit an estimated 5.1 Gs 2.5 seconds into the record run! The engine was pulled down by the clutch to 7,180 rpm at this point. The same technique developed for the Torrence analysis was used to construct the dragstrip dyno data for Brown showing both the estimated horsepower and torque curves of the engine.

Matco Tools Top Fuel crew chiefs Brian Corradi, right, and Mark Oswald have tuned an engine to more than 10,000 horsepower to set the national e.t. record at 3.70 seconds.

Some of the horsepower made is applied toward rotating the mass of the five- or six-disc clutch assemblies. At times during the run, more than half of the horsepower is essentially wasted on clutch slippage and turned into heat energy.

NHRA Nitro Technical Consultant Lee Beard provided much of the data used to calculate horsepower from his stint as crew chief on Steve Torrence's Top Fuel team last season.

Top Fuel Fun Facts Some interesting numbers for both fans and racers also come from this analysis: * 0-60 mph takes .54-second * 0-100 mph takes 1.04 seconds * 0-200 mph takes 1.96 seconds * 0-300 mph takes 3.05 seconds * You get about 115 horsepower for each gpm (gallons per minute) of 90 percent nitro you burn Isaac Newton's laws of motion tell us that with everything else about two Top Fuel dragsters being equal, on the same racetrack with the same weather conditions: * It would take about 82 horsepower to pick up one-hundredth in elapsed time * It would take 93 horsepower to gain 1 mph Antron Brown set the national e.t. record in Top Fuel at Maple Grove Raceway in 2012.

(c) 2014 National Hot Rod Association

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