Thread: drag racing facts

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All right---things have changed, only a few items remain the same and a couple of them are constants, time, distance, gravity

A long time ago to put some things into a perseptive that a person could understand---1320 ft---time 6 seconds---rpm average of 10,000

Engine in 6 seconds 1/10 of minute would turn over only 1000 revolution , each spark plug would fire only 500 times---- a fuel burn of 6 gallons equalled 60 gallon per minute or 3600 gallons per hour or about the same as one/half of a tanker truck at a rate about egual to how fast the tanker could unload at a gas station!!!The time was early 70s and 6 seconds was a medium et and was more easily understood as you could just move decimal points for calculations.

Jerry

I'm not sure where you were headed with the post. But yes, times have changed. A constant in count for count does not exist. To overcome the distance with the factors of traction (friction), to advance the time (negitively) and to use gravity (don't forget co-efficient drag factors), things do not or turn according to the calculator Something has to give to allow the process of consuming a mass of fuel and overtake the forces fighting against the machine. Engines no longer turn 10,000 RPMs and driveshafts speeds are up above what the prof tried to tell you they were.

Where I'm headed---

My post was something about some facts of drag racing in the days that a pocket calculator cost $400, and the so called pc computor didn't exist---
an era when to work with numbers, you actually had to have a feel for a concept whereas you have 10 toes and fingers for something besides picking your nose or scratching---the decimal system is still about zeroes, ones, tens, etc

There is still 1320 feet in 1/4 mile, gravity and time are constants---

Our engines didn't turn 10,000 rpm, we didn't run exactly 6 seconds and our single fuel pumps were the biggest that anyone built at the time---Crower, Hilborn and Enderle kept records and we had the highest flow rates

I used some simple numbers that were close enough to the real numbers to come up with a few thoughful insights that almost anyone come fathom---

Today---some of the top people in dragracing were youngsters around my operation

And the results that we see race after race still show that with all the computers, clutch, timing, fuel controls that they still have tire shake, smoke the tires, etc

So tell me ---what has changed---20 people for a 75 minute turn around--we did it with 3-5 and 45 minutes

And they were 32 car fields


Jerry

Originally Posted by nitrowarrior

AH ha....Tire and clutch slippage. You forgot to factor that part. I'ts a major part of why a crew chief gets his salary. Management of the clutches to slip enough to roll out and start to get a bite creates a revolution count higher than the theory indicates. Tires never do get a perfect bite throughout the run. Too much slippage, it takes the skins right off quickly. tires only good for a few passes. Too much bite, you either suffer "shake" or internally break the casing down to a point that no more than two runs per pair. The Engines turn on average of 7200 RPM. Fluctuating slighty(if it's a good run) a few hundred RPM. So let's say the geometry that the calculator was count for count. The car could have gears for wheels, the track would have a rack gear laid out to accomodate the wheel gears. Then according to the circumference of the Gear/Wheel it would only take so many revolutions to complete the run according to the gear ratio of the axle. Not everything is on the track as it is on paper. Fun stuff to ponder to figure how to get your car down the track.

I understand there are drivetrain losses but the simple math of how engine rpm and the length of time from start to finish (not counting burnout and staging) add up really gives you very few revolutions down the quarter mile... for instance:

Lets say you average 7200 revolutions per minute 7200 / 60 (seconds per minute) makes 120 revolutions per second...

Now if it takes 5 seconds for 1/4 mile ET (a slow TFD), you end up with 120 *5 = 600 revolutions of the engine from starting line to finish line...

Same illustration with a 12 second bracket car:

Maybe 5000rpm average = 83.33 rps * 12seconds = 1000 revolutions from start to finish.

In the 12 second car, if there were no drivetrain losses, it would only take something around 850 revolutions to cover the distance (30" tire, 4.56:1 gear, discounting gear reduction in the transmission) but the math above only covers the engine rpm and the amount of time the run takes... no other drivetrain characteristics matter.

It is fun to figure this stuff out even if the particulars aren't particularly important


Edit: sorry... posted this without reading the rest of the thread... anyhow, I think Jerry and I are trying to say the same thing.

Skids, remeber at the hit of the throtle, it goes from 2250 to 7200. If things were locked up as you imagine, it would blow the tires off. It uses clutch management by slipping. Therefore the engine is cover it's feet per second at the crank but the rest of the car has to catch up. Even the drive shaft is rotating faster than the paper work says because it's finding a balance of the right traction and not overkill to blow the tires off. More RPM is obtained than the calculator states to cover the quarter mile. And like I stated before the tires never really stop spinning. Even at the top end, there is some traction give so more RPM is made than the theory of the count for count the numbers will bring up.

About the only significant change from then to now is that the gas running out of the tanker is $3 instead of $.3 per gallon---simple as moving a decimal point.

And may I ask NitroWarrior , who are you?

Jerry Clayton

An old racer who spent more time on the circuit instead of at home...bummer part is, I have no offspring that has the bug like I did.......I guess it's time to find something else to play with.

Originally Posted by nitrowarrior

Skids, remeber at the hit of the throtle, it goes from 2250 to 7200. If things were locked up as you imagine, it would blow the tires off. It uses clutch management by slipping. Therefore the engine is cover it's feet per second at the crank but the rest of the car has to catch up. Even the drive shaft is rotating faster than the paper work says because it's finding a balance of the right traction and not overkill to blow the tires off. More RPM is obtained than the calculator states to cover the quarter mile. And like I stated before the tires never really stop spinning. Even at the top end, there is some traction give so more RPM is made than the theory of the count for count the numbers will bring up.

I guess I'm not explaining myself clearly. I really don't want to argue this one to death and I know you know what you're talking about and I understand that driveline losses are a requisite part in the vehicle for this sport...

yes engine rpm will vary from launch to finish but it is what it is on average(?) Average rpm takes it into account... Say max rpm is 9200?, average is 7200?, min is 2500?... engine rate and time tell you how many times the engine turns over in a certain period of time... there's nothing else in that equation: revolutions per minute, revolutions per second, whatever. So pick a number or many numbers to describe the engine speed over the course of the run... from the factors you've provided, I still contend a top fuel dragster motor will turn over somewhere between 500-600 times from the starting line to the finish line... granted this is a pursuit of trivia and doesn't really matter so much in itself to maintaining a top fuel car.

How many revs do you think it takes to cover the quarter mile?

I mean no disrespect and I value all the contributions you've made...

Originally Posted by jerry clayton

About the only significant change from then to now is that the gas running out of the tanker is $3 instead of $.3 per gallon---simple as moving a decimal point.

And may I ask NitroWarrior , who are you?

Jerry Clayton

He is Jungle Jim and he is being very modest.

I wish...Pam was pretty hot!

I was going to ask what you did with Jungle Pam

Originally Posted by nitrowarrior

I wish...Pam was pretty hot!

Darn,it.
We just about had him going!!

There sure used to be some hot babes around the pits

I wish I could post some of our pictures here but its my wifes computer and see might see them

Jerry


PS I got enough trouble back then over the trophy girls

Put 'em on floppy Jerry, then we can all see but she can't...

Skids to put your question to bed (this is not literal but an easy reply to how many RPM's) 1600. On paper, 7200 divided by 4.5 second run is 1600. I't not factual but it shows how the egg heads start over analyzing the run. Just had to throw a bone there.