Top Fuel "Facts"

"pedal-force" (pedal-force) 08/09/2014 at 22:36 • Filed to: antiviral

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Alright, so these "facts" (I use quotes because I'm not so sure on some of them) have been going around the internet for at least 10 years. The first source is possibly !!!error: Indecipherable SUB-paragraph formatting!!! , but it is just a paste of an e-mail chain the author got. It lists some stuff from the 2003 season though, so it can't be much earlier than that.

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Someone copy-pasted them into the comments section of the !!!error: Indecipherable SUB-paragraph formatting!!! about Top Fuel Funny Car engines exploding and how cool it looked (it does indeed), complete with terrible formatting (thanks Kinja!) but I've seen them long before that.

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Here they are for you, numbered for convenience.

1. One Top Fuel dragster's 500-cubic-inch Hemi engine makes more horsepower than the first four rows at the Daytona 500.

—- This one is pretty easy to fact check. Estimates are Top Fuel cars make between 8000-9000 HP. Unrestricted NASCAR makes around 800 HP, but restrictor plate tracks (like Daytona, aha, tricky list maker) they only make about 450 HP (source: !!!error: Indecipherable SUB-paragraph formatting!!! ). So, 2 wide, times 8, is 16 cars, at 450 HP, 16*450 is 7200. They could probably tack on another row if they wanted and say 5 rows. Whatever. This one checks out, but only because Daytona is a restrictor plate track. This means it's true, but misleading.

edit: I'm an idiot and doubled the cars twice. There's only 8 cars in four rows, not 16. I doubled in my head, then doubled on paper. So it should be 8 cars * 450 HP is 3600 HP in the first four rows. So they actually way underestimated, I don't think they realized Daytona is a restrictor plate track. Thanks to Dusty Ventures for noting my mistake.

2. A stock Dodge Hemi V-8 engine cannot produce enough power to drive the dragster's supercharger.

—- This one is again in the "true but misleading" camp. Yes, the supercharger when in use on a Top Fuel engine takes about 800 HP to run. But if you put that same supercharger on the aforementioned stock Hemi V-8 it would run it just fine, at the amount of air and pressures that a stock Hemi V-8 would require. It only requires a lot of HP because they're running ridiculous amounts of air at 60 PSI.

3. With 3000 CFM of air being rammed in by the supercharger on overdrive, the fuel mixture is compressed into a near-solid form before ig-nition. Cylinders run on the verge of hydraulic lock at full throttle.

—- This is the first one that stood out to me. I find it hard to believe they're compressing the mixture into "near-solid form". I know the compression ratio is 7:1, and they're flowing 80gpm of fuel at peak torque according to !!!error: Indecipherable SUB-paragraph formatting!!! . Peak torque is probably around 4k RPM maybe? 4000 revolutions, 80 gallons, 80/4000 is 0.02 gallons/revolution. But times four for each cycle is 0.08 (only get fuel once every four revolutions). Then divide by 8 for each cylinder, 0.01 gallons per cylinder per cycle. That's 2.31 cubic inches of fuel per stroke. Each cylinder is (500 cubic inches/8) 62.5 cubic inches. With compression ratio of 7:1 that leaves (62.5/7) 9 cubic inches compressed. So 2.31 cubic inches of fuel in a 9 cubic inch combustion chamber. That's hardly hydro lock. Did I do something wrong (I probably did something wrong).

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edit: Yeah, I did something wrong. A couple things actually. Shocking, I know. !!!error: Indecipherable SUB-paragraph formatting!!! pointed out that you get fuel every 4 strokes but every 2 revolutions. !!!error: Indecipherable SUB-paragraph formatting!!! pointed out that I forgot the 60 psi of boost, which significantly changes the compression ratio (duh, I've tuned turbocharged cars, I should know this). That being said, I have no way of figuring out the dynamic compression ratio of a Top Fuel engine. We can assume it's much, much higher than 7:1 though. A rough estimate is to use the amount of atmospheres and multiply compression by that. So absolute manifold of 60, 60/15 is 4, so 4*7 = 28:1 compression. I find it hard to believe that wouldn't pre-ignite, so it must be lower, maybe 20:1 or something. 62.5/20=3.1 cubic inches. But you're now only getting 1.15 cubic inches of fuel (because of my math error earlier), so my statement stands. It's a hell of a lot of fuel in a cylinder, but I don't think it's close to hydro lock.

4. At the stoichiometric 1.7:1 air-fuel mixture for nitromethane, the flame front temperature measures about 7000 degrees Fahrenheit.

—- This is so easy to fact check it's ridiculous. The flame temperature of nitromethane is only about !!!error: Indecipherable SUB-paragraph formatting!!! . So, not correct then. Unless you consider 4400 to be "about" 7000. !!!error: Indecipherable SUB-paragraph formatting!!! pointed out that the flame front may be a different temperature than the simple flame temperature in open air. And they're right. It looks like at high pressure and stoichiometric ratios, the flame temperature in constant volume is around 6700*F. So I think this one may actually be true. Damn that's hot. This is actually because of the main important property of Nitro, which is that it contains its own oxygen already.

5. Nitromethane burns yellow. The spectacular white flame seen above the stacks at night is raw burning hydrogen, separated from atmospheric water vapor by the searing heat of the exhaust gases.

—- This seems to be wrong. Water dissociates at 2500* C. That's about 4500* F. Exhaust temperatures at the end of a run are under 2000* F. So this isn't really possible.

6. Dual magnetos supply 44 amps to each spark plug. This is the output of an arc welder in each cylinder.

—- This one is true. The cheapest arc welder at Harbor Fright is 70 A, so yeah, it just barely beats the cheapest POS arc welder.

7. Spark plug electrodes can be totally consumed during a single pass. After half-distance, the engine is dieseling from compression plus the glow of exhaust valves at 1400 degrees Fahrenheit. The engine is shut down by cutting the fuel flow.

—- This is a myth that was maybe true 30 years ago, according to the CarCraft article linked above. "Top Fuel is also a place where myths abound, especially in regard to ignition systems. Just 30 years ago, Armstrong says fuel engines ran on far less fuel, making them leaner, which turned spark plugs into glow plugs, which continued combustion even after the ignition system failed completely. But with today's fire hose-like delivery of fuel, Armstrong says, "You couldn't do any of this without a strong ignition system."

8. If a spark plug fails early in the run, un-burned nitro can build up in the affected cylinder and explode with sufficient force to blow the cylinder head off in pieces or split the cylinder block in half.

—- Well, yeah, duh. Nitro blows up.

9. In order to exceed 300 mph in 4.5 seconds, dragsters must accelerate at an average of more than 4 g's. In order to reach 200 mph before half-distance, the launch acceleration approaches 8 g's. A Top Fuel dragster reaches more than 300 mph before you have completed reading this sentence.

—- 200 mph is 293 feet per second. 8 g's is 258 feet/s^2, not 80, that's meters, because I'm an idiot. Thanks to !!!error: Indecipherable SUB-paragraph formatting!!! ith for pointing out my mistake. It would take 1.12 seconds to get to 293 feet per second, or 200 mph. That makes me think 8g is probably too high, since if they got to 200 mph after only 1.12 seconds. Here, I'll let someone !!!error: Indecipherable SUB-paragraph formatting!!! do the math, since I clearly can't handle it. They show it's actually more like 5g, so false here. Yet again.

10. With a redline that can be as high as 9500 rpm, Top Fuel engines turn approximately 540 revolutions from light to light. Including the burnout, the engine needs to survive only 900 revolutions under load.

—- Redline is actually more like 8250-8500. And they only run 1000 feet now. But whatever, it's basically true.

11. Assuming that all of the equipment is paid off, the crew works gratis, and nothing breaks, each run costs an estimated $1000 per second.

—- I have no way of checking this exactly, but it doesn't seem unreasonable. Tires are $1000, last about 3-4 runs, fuel is $20/gallon, they use 20 gallons or so, which is $400 per run right there.

12. The current Top Fuel dragster elapsed time record is 4.441 seconds for the quarter-mile (October 5, 2003, Tony Schumacher). The top-speed record is 333.25 mph as measured over the last 66 feet of the quarter-mile (November 9, 2003, Doug Kalitta).

—- This was true at the time. It's 3.701 now, but that's at 1000'.

13. Putting all of this into perspective: You are driving the average $140,000 Lingenfelter twin-turbo Corvette Z06. More than a mile up the road, a Top Fuel dragster is staged and ready to launch down a measured quarter-mile as you pass. You have the advantage of a flying start. You run the Vette up through the gears and blast across the starting line and past the dragster at an honest 200 mph. The "tree" goes green for both of you at that moment. The dragster launches and starts after you. You keep your foot down, but you hear a brutal whine that sears your eardrums, and within three seconds, the dragster catches you and beats you to the finish line, a quarter-mile from where you just passed him. From a standing start, the dragster spotted you 200 mph and not only caught you but nearly blasted you off the road when he passed you within a mere 1320 feet.

—- This is pretty easy to do the math. They ran 4.5" for 1/4 mile, which is right at 200 mph average. So they couldn't even get this one right. You would actually exactly tie if you were averaging 200 mph. He would pass you at the line doing 320 mph, but you'd still tie. So, false, I guess.

Arch Duke Maxyenko, Shit Talk Extraordinaire > pedal-force 08/09/2014 at 22:51

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8 g's is 78 feet/s^2

8 x 32.2 ft/s^2 is 257.6 ft/s^2

Dusty Ventures > pedal-force 08/09/2014 at 22:53

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1. One Top Fuel dragster's 500-cubic-inch Hemi engine makes more horsepower than the first four rows at the Daytona 500.

—- This one is pretty easy to fact check. Estimates are Top Fuel cars make between 8000-9000 HP. Unrestricted NASCAR makes around 800 HP, but restrictor plate tracks (like Daytona, aha, tricky list maker) they only make about 450 HP (source: http://en.wikipedia.org/wiki/Restricto… ). So, 2 wide, times 8, is 16 cars, at 450 HP, 16*450 is 7200. They could probably tack on another row if they wanted and say 5 rows. Whatever. This one checks out, but only because Daytona is a restrictor plate track. This means it's true, but misleading.

Looks like this one's not misleading at all. In fact they underestimated, and that's using the non-Daytona horsepower. They said four rows, which is eight cars. At the full 800 horsepower (non-restrictor plate) that's 6,400 hp, 1,600 short of the minimum of the 8,000-9,000 top fuel horsepower estimate. It's more accurate to say one top fuel dragster makes at least as much horsepower as the first five rows at a non-plate NASCAR track (or the first NINE rows at the Daytona 500).

pedal-force > Arch Duke Maxyenko, Shit Talk Extraordinaire 08/09/2014 at 22:53

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Thanks, damn units got me. I did it in meters (obviously) because I actually know gravity in meters but can never remember it in feet. I'll update. Obviously that changes the math significantly.

pedal-force > Dusty Ventures 08/09/2014 at 22:58

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Damn, I did the rows twice, oops. I'll edit it. There's only 8 cars in 4 rows, not 16.

Arch Duke Maxyenko, Shit Talk Extraordinaire > Dusty Ventures 08/09/2014 at 22:58

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Top fuel is up to 10,000 HP now a days.

webmonkees > pedal-force 08/09/2014 at 22:59

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Dialing it in, Adam busts the racing myth that the IZOD uniforms have little alligators on them.

pedal-force > Arch Duke Maxyenko, Shit Talk Extraordinaire 08/09/2014 at 23:03

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Really? I've seen more like 8500-9000. They actually don't really need any more HP, they're traction limited basically all the way down the track. Do you have a source? Not that it can actually be measured anyway, they blow up before you can measure them.

Arch Duke Maxyenko, Shit Talk Extraordinaire > pedal-force 08/09/2014 at 23:25

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I watch a lot of NHRA. They still go for as much power as they possibly can and they are getting about 10,000 now. The teams tune the centrifugal clutch to engage at different points down the track based on traction.

pedal-force > Arch Duke Maxyenko, Shit Talk Extraordinaire 08/09/2014 at 23:27

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Yeah, the clutch tech is amazing. I love NHRA. I don't follow it super closely, but I'll watch if it's on TV. Honestly though, after being there in person (4-Wide at Charlotte) TV just doesn't do it justice. The feeling of them making a pass four at a time is insane.

Arch Duke Maxyenko, Shit Talk Extraordinaire > pedal-force 08/09/2014 at 23:35

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I bet that's fucking sweet. I'll go one day.

pedal-force > Arch Duke Maxyenko, Shit Talk Extraordinaire 08/09/2014 at 23:38

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It is. I wrote it up way back. http://oppositelock.jalopnik.com/nitro-and-alco…

The pounding in your chest when they're making a run, it blurs your vision, you can barely see as they pass you. Just insane.

justregisteralready > pedal-force 08/09/2014 at 23:43

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Party pooper.

pedal-force > justregisteralready 08/09/2014 at 23:46

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Believe me, I wish they were all true, because I love NHRA and they make great stories. Luckily, Top Fuel is so insane that you don't have to make shit up. When they run 4-wide at Charlotte your eyes shake and everything gets blurry as they go by, and that's from halfway up the stands. It's just madness.

Garrett Davis > pedal-force 08/10/2014 at 00:05

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Awesome, thanks for writing this up. I read that earlier and knew it was a bunch of chain email BS. Glad someone did the research.

Dumahim > pedal-force 08/10/2014 at 00:53

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only get fuel once every four revolutions

You get fuel once every four strokes, but every two revolutions.

tc_corty > pedal-force 08/10/2014 at 02:03

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In reference to your compression ratio calcs, that 7 would be the motors static ratio. If you take the 60 pound of boost you stated earlier, the compression ratio will be a hell of a lot more than 7. Its called dynamic compression ratio. It takes into consideration the boost, overlap etc. Have fun learning and working that out haha. Interesting article though, good work :)

Zoom > Arch Duke Maxyenko, Shit Talk Extraordinaire 08/10/2014 at 08:58

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Bucket list it.

It's amazing. During launch, the overpressure from 20,000 horsepower vibrates the fluid in your eyeballs so you can't focus on the car for the first 300 feet . Everyother engine you have ever seen, every one, is tame in comparison.

No joke.

Zoom > pedal-force 08/10/2014 at 09:04

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While the facts stated are at the best possible scenario, you seem to be going out of your way rebutting most of them at the other end of the spectrum.

The one that interests me of all, are you sure the flame front is not a higher temp than what nitro actually burns? I'm not schooled enough in thermodynamics. I would inmagine the average flame temp might be what you've stated, but the leading edge (the 'white part') might be considerably higher.

pedal-force > Dumahim 08/10/2014 at 10:25

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Ah, yeah, thanks.

pedal-force > Zoom 08/10/2014 at 10:51

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I was trying to be fair, but it's possible I had a little ax to grind last night after people jumped down my throat for calling these BS. Which ones do you have a problem with?

Actually, you may be right about that part, but I'm not sure. I found a chart that shows that at high pressure and stoicometric ratios, it can burn as high at 6700F in a constant volume area (like a cylinder). I think the temperature I found before was in constant pressure (like open flame).

Tentacle, Dutchman, drives French > pedal-force 08/10/2014 at 15:06

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If, for #2, the supercharger means blower and gears in their Top Fuel dragster ratio, then it's a valid claim.

As for #5, dissociation of water at combustion engine temperature may be questionable. But at those temperatures and pressures that 2500°C may be lower.

pedal-force > Tentacle, Dutchman, drives French 08/10/2014 at 15:09

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Yeah, that's why I called it true but somewhat misleading. Still an interesting factoid.

The pressure at the exhaust exit has to be essentially 1 atm, because it's open to the air, so I think that ones still false.

Tentacle, Dutchman, drives French > pedal-force 08/10/2014 at 15:29

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But the pressure further up the exhaust will not be 1 atmosphere. Even straight pipes have some back pressure at that kind of huge flow. Plus shockwaves. Don't forget those.

pedal-force > Tentacle, Dutchman, drives French 08/10/2014 at 15:40

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That's true, there is some water vapor in the exhaust gases, so it could happen then. And I'm also not a chemist, but I can't find any evidence that the pressure actually affects the temperature of dissociation for water.

Zoom > pedal-force 08/10/2014 at 16:22

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I could believe any and every one of them.
There's more

pedal-force > Zoom 08/10/2014 at 16:28

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9 and 13 are just plain wrong, clearly, because math, so why would you believe them? The second half of that post, the "did you know" seems to have come from NHRA, and all looks correct. Even that lists the acceleration as about 5G, which is what the other site I had shows.

Tentacle, Dutchman, drives French > pedal-force 08/10/2014 at 16:31

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I've got an MSc degree in Materials Science & Engineering, so I've got some chemistry, but not enough to call this one with confidence.

What I do know is that the exhaust of a top fuel engine is a true cauldron of hot pulsed-pressure gasses. A mix of burnt fuel, unburnt fuel and partially burnt fuel. Pretty nasty and agressive because burning nitromethane produces nitric acid too. Mid-burn there are ionized gasses abound. There is no telling what the dissociation constant will do.

By the way, dissociation is a balance thing, and lower pressure will drive the balance towards the gas-part of the equation. So with increasing pressure, less hydrogen and oxigen will form. A bit of vapor will dissociate at flame temperature of nitromethane, which is 2400°C. But is that enough??

The whiteness of the exhaust flames are from hydrogen burning. That part is probably true. Does the hydrogen come from dissociation or from an engine running rich? Because nitromethane can burn as a monopropellant. In other words, it can burn without added oxigen.

2 CH 3 NO 2  2 CO + 2 H 2 O + H 2 + N 2

The jury is still out, I think.