amazing drag racing engine statistics...

Not quite. If you're talking only about overcoming drag, doubling speed actually requires 8 times the power. Drag force scales with speed squared. The power lost to this effect scales as speed cubed.

Anyway, that can't be directly applied to a drag car. Air resistance is certainly an important consideration in its performance, but a 1/4 mile run does not get anywhere near the car's top speed.

Another consideration to worry about is that the peak power of a top fuel dragster is not as relevant as it is on other types of cars. Most (street or race) cars have many gears that can be used to keep the engine near its power peak at all but the slowest speeds. Full throttle can also be applied without slipping most of the time. That's why power to weight ratios are usually such good indicators of straight-line performance. Those generalizations don't work well for top fuel cars.

 

As far as I know a top fuel car runs right at the power peak for the whole run. Mash the throttle all the way to the floor, the multi-plate clutch pack engages the different gears after a time pre-set by the crew chief (not the driver). After the run the clutch assembly is one solidly fused mass, all melted togeher. Only drivers who chicken out or break something let up before the trap. Also don't forget that the diameter of the rear tires increases significantly as the speed increases, for additional gearing advantage.

Aerodynamics is critical for a vehicle traveling at 330+ mph. (top fuel record is 4.428 seconds @ 336.15 mph)

I believe the 8000 hp claim. A typical top fuel dragster weighs about 2200 pounds.

Other fun "facts"

At full throttle the exhaust gasses exiting the pipes exert about 800-1000 pounds of downforce.

The exhaust noise exceeds 150 dB at WOT.

At 325 mph, downforce from the rear-mounted wing can be as high as 12,000 pounds.

A top fuel dragster uses over 20 gallons of fuel warming up, doing the burnout, staging, and then making the run.

The superchargers are typically set to provide 55-65 pounds of boost but up to 75 pounds has been used.

Oil pressure is typically in the 165 psi range.

 

Bob Norwood's 4,000-hp Turbo-Fuel Max-4 powerplant can lift 2.2 million lbs--1,100 tons--a foot in one second. This is about the weight of a 50-car freight train, but then again, the Max-4 has as much power as a railway locomotive. Another way to look at 4,000 hp is that the Max-4 is capable of lifting one ton straight upward 1,100 feet in a single second. Try to comprehend an engine in which every power pulse--each putt--can lift 4.4 tons upward one foot in one second. This is the type of mayhem a 4.8-liter inline four is capable of when you force-feed it air at a rate of 200 lbs per minute and pump it full of nitromethane at a rate faster than you could dump it out of a bucket. No matter how you quantify it, this is the extreme edge of high-tech performance.



With the Max-4 Turbo-Fuel Type R Funnycar, Dallas supercar builder Bob Norwood once again exhibits his well-known penchant for bringing a sledgehammer to a fly-swatting contest. The Type R drag car and Max-4 powerplant are designed to deliver 250 mph and 5.50-second quarter-mile performance on alcohol and nitromethane. The vehicle is designed around a narrowed Mark Williams tube-frame chassis with a narrowed one-piece composite "Integra Type R" body. At 286 cubic inches, the engine is clearly the largest non-aviation four-banger ever constructed in modern times.
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Actually it is quite the opposite. Today's T/F cars have far more drag than the old ones ever did. The rear wing adds a bunch of drag even at the 2 degrees maximum on the main plane. Funny cars are more aerodynamic and under the right wind conditions will actually achieve higher top speeds. Having worked NHRA nationals for 15 years I am still amazed at some of the things these cars can do.

 

There is absolutely NO WAY these cars require almost 4 times the HP to only go 25% faster.

8 times the force? You need to go into NASA's K-12 education site and do some studying. Aerodynamic wind loading, lift to drag ratios, and static and incipient drag forces have been known since the Wright brothers built the first powered aircraft. Its in text books, they teach this stuff in class rooms, its basic ground school flight training. The wing on a current dragster only generates 6500 pounds of downforce. That kind of downforce could be calculated through lift to drag formulas quite easily, and converted to HP. But thats not a lot of lift, and certainly wouldnt require much HP. An F1 car reportedly generates close to 5000 pounds of downforce, and it certainly does not have anywhere near 8000 HP.

But here is the real reason I believe 8000 HP is total BS. Back when these engines "only" made 2500 HP they were taking them down after every run the same as today and finding mashed pistons, bent valves, and twisted rods each time. They blew heads off the block, grenaded blowers, tore up engine blocks and twisted up crankshafts just as readily as they do today, yet the displacement is identical at 500 cubic inches, the connecting rods are still aluminum, nothings really changed. The fuel is EXACTLY the same, methanol alcohol with as much as 10% nitromethane. So while the basic motor is the same, and its burning the same fuel, they somehow have managed to pull almost 300% more energy out of something that was already at its structural and metalurgical limits? I dont think there is any one single reciprocating component that could achieve, or withstand that kind of increase.

And being that HP is directly linked to the BTU energy in fuel, why arent the modern cars carrying 60 gallon fuel tanks? They have the same 15 gallon tanks they were using over 35 years ago. Or are they somehow making almost 4 times the power on the same amount of fuel? These guys should go to work in aerospace, because nothing man has made over the last 30 years has experienced those kinds of gains in power output without burning more fuel. They could empty a 15 gallon tank over 30 years ago, and they do the same thing today.

There are some smart guys on here, I am sure someone could do some back to back study and calculate the pressures per square inch on one those pistons, and the fuel quantity required that would generate 1000 HP per cyclinder, and find that its impossible.

Tim (2NA) was talking recently about starting a thread on rocket cars. He has a hydrogen peroxide rocket powered go cart hanging on his wall out in the shop, that did some 179 mph in the 1/4 in under 8 seconds with 700 some pounds of thrust IIRC. The sad truth is that Top Fuel is so hyped up that virtually no one realises that a simple jet powered or rocket propelled car could so blow one away in the 1/4 mile thier game would fall apart like a house of cards.

 

"The fuel is EXACTLY the same, methanol alcohol with as much as 10% nitromethane."

You need to get up to date on the fuel specs. NHRA allows a limit of 85% nitro in the alcohol. This is down the last few years from 90% and before that the percentage was unlimited. You need to go to one of the races, they will be in Minnesota in a few weeks, and have a look around. They will be glad to talk to you.

By the way, the Pro Stock cars with 500 CI motors and two 4-barrels put out about 1300 hp. No blowers, no nitro.

 

You're just throwing out buzzwords here. There are a lot of misunderstandings in what you said. I claimed that it takes 8 times the power to double a car's top speed with optimal gearing (which is not the same as the amount of power required to double a car's 1/4 mile trap speed). Force and power are not the same thing, and what I said is not at all controversial. It's in most introductory physics books. Look it up.

Another interesting point is that in the absence of any drag whatsoever, a car putting out constant power will accelerate over a fixed distance to a speed depending on the cube root of the power (again). So even in the best of conditions, a little more trap speed requires much more power. This is obviously even more true when drag and other effects are put in.

From my understanding, these cars are effectively slipping their clutch down almost the entire track. They only lock and put full power to the ground towards the end. This negates much of the benefit of extra power. There just isn't enough traction to use it for very long.

As for fuel requirements, a perfectly efficient engine requires approximately 0.1 gal/s of nitromethane to produce 8000 hp. Say that these engines are 10% efficient, so increase that by a factor of 10. You get 1 gal/s at full throttle. So a 1/4 mile run requires maybe 5 gallons of fuel. Add in idling, burnout, and a 15 gallon tank is perfectly reasonable.

Anyway, I don't know how much power these engines actually make. It wouldn't surprise me at all if some of the stuff on these lists is made up. I'm just correcting your arguments against it.

 

This is a good post, I haven't calculated but I'll take your word on the nitro flow rates.

About the hp numbers: I don't see why something approaching 8,000 hp should seem so impossible to some people. The Formula One turbo engines of a quarter century ago were only 1.5 Liters and they put out around 1500 hp in qualifying. That's 16 hp/ci from an engine that had to do some laps, not just a 4.5 sec run. Top fuel engines are 500 ci. At 8,000 hp that would be guess how much?............16 hp/ci.

 

Okay

http://www.grc.nasa.gov/WWW/K-12/airplane/short.html

 

Or here, read down in the power section:

http://en.wikipedia.org/wiki/Drag_(physics)

 

This is rather deep and complex, but read down into 7.6.3, and 7.6.4.. It gives some pretty detailed descriptions of power vs drag as a factor of speed.

http://www.av8n.com/how/htm/power.html#sec-power-vs-speed

 

1. I think some here are too hung up on aerodynamic drag as it relates to dragsters. That is not the biggest factor in determining hp requirements to do a specific trap speed, the biggest factor is accelerating the mass of the car at a higher rate regardless of aero drag. (And HP VS SPEED is not a linear function)

2. Just because someone says there is "no way they are making that kind of power" doesn't make them right. Do the actual calculations and you will conclude that it does take in the neighborhood of 8,000 hp to do the 1/4 at 336 mph in a dragster. (A dragster spins and heats tires and clutches, etc. so there is no simple exact formula).
Less opinion, more fact.

 

NHRA claims 7000 hp. http://www.nhra.com/streetlegal/funfacts.html

Motor Trend via Schumacher Racing who campaigns the "US Army" dragster claims 7500 hp. http://www.motortrend.com/features/consumer/112_0502_top_fuel_numbers/

 

I've corrected your link in this quote. It agrees with what I said, by the way. Power lost to drag scales as speed cubed (assuming that the drag coefficient remains constant, which is a good approximation for the systems we're discussing). 2^3 = 8, so double the speed requires 8 times the power.

You didn't give a direct link to the relevant portion of NASA's page, but I assume you wanted me to look at this: http://www.grc.nasa.gov/WWW/K-12/airplane/drageq.html. It states that the drag force scales as speed squared. Using high school physics, that implies that the power lost agrees with the equation in Wikipedia.

You're misinterpreting the aircraft link. There, you purposely change the drag (and lift) coefficients by moving control surfaces/changing your AOA. Increasing speed with no change in trim leads to an altitude gain. If you don't want that, you decrease your lift coefficient, which in turn decreases your drag coefficient. So changing speed in an airplane can't be compared to changing speed in a car.

Regardless, teak360 is right. This discussion is not particularly relevant.

 

I'll admit I didn't have time to read all the above posts, but we supply engine components to teams who claim they are 'somewhere over 7k HP'. Sorry I don't have data to support this, just comments from their engineers...

 

I am not misrepresenting anything, your misreading things. Open up a POH on any aircraft and plot the speed at different power settings. 55% power through 100%. If your 8 times power figure to double velocity were correct, and it is not, a little Cessna 150 would need a 400HP engine to go from about 65 MPH with 55% power, to 125 MPH with 100% power. But it only has a 100 HP engine. Now go see what the same aircraft can do with 50% more power from a 150 HP engine. This is a common repowering of that aircraft, and fits the cubed formula of the square of velocity almost perfectly. It cruises at just about the same 120 mph with 75% power, or roughly 112 HP. Where did your 8 times more power go?

 

Did you read what I wrote? The factor of 8 applies for an object with a constant drag coefficient. That's something which stays the same shape and keeps the same orientation with respect to the airflow. An airplane which changes speed at constant alititude does not satisfy this criterion. The factor of 8 therefore does not apply there.

 

Power is torque/sec. and since a second is a constant, power is directly proportional to torque.

The confusion on both sides of the argument are because there are several factors at play here.

Top speed in STEADY STATE conditions is a function of power (or torque at the wheel or prop) and velocity squared.

Dragsters are never at steady state though; they are under constant force (the limit of traction) acceleration for the first part of the run where Velocity = acceleration x time squared. Then it gets related to the engine torque curve and hard to solve.

Anyway, the point that there is undoubtedly a point where it would take 8 times the power to double the top speed through the speed traps, and there is also a point where the power needs to be squared, but they’re both the exceptions, not the rule. The actual rule I think is a second order differential equation….that I neither have the ability to derive nor solve

 

Just a thought,

The Starfighter weighs over 10 tons with fuel. Neither airframe or engine optimized for operation near sea level.

The GE J79 jet engine has powered a number of Land Speed Record cars over the years and at least one drag strip jet car (a bit of overkill on a short track).

 

The F1 cars were making 16 hp/ci with 0% nitromethane (100% methanol). The top fuel cars are making 16 hp/ci with 85% nitromethane and 150% final supercharger drive ratios. So the real question is, why are they making only 8000 HP?

 

"A second is a constant" is not a meaningful statement here. Power is defined to be the rate of change of work. The work done by some force is (in this case) the force multiplied by the distance it acts over. The power is therefore [force] x [velocity]. Equivalently, you can write it as [torque] x [angular velocity] for an engine. Since the drag force goes as the velocity squared, the drag power scales with the cube of the velocity.

Anyway, I certainly agree with the rest of what you've said. The correct description of this problem does require solving a differential equation. That's very hard to set up when so much of a dragster's behavior depends on slipping clutches and tires. The equations for a regular car are much simpler to write down, though they're still difficult to solve. There are a couple of approximations which work remarkably well, however. It's actually been shown empirically that to a surprisingly good approximation, almost all street cars have trap speeds very close to what you'd expect if they applied a certain fixed fraction of their peak power throughout their entire run (with no drag or slip). Showing this mathematically is a little tricky, but possible.