Thread: drag racing facts

Tweet

Thanks... sorry to be an irritant, egg-head or not I love the sport and agree it doesn't matter.... but your math is all wrong

7200rpm/60spm = 120rps, 120rps*4.5s = 540revs

spm = seconds/minute

Ok... I'm done

Nitro

You don't divide it by 4.5---you divide it by 60 (seconds in a minute) and multiply by 4.5

7200 revolutions per minute divided by 60 eguals 120 revolutions per second

120 rev/sec multiplied by 4.5 seconds equals 540 revolutions per run

My wife says I got to go mow the back yard

Jerry

I was supposed to mow the yard today but it's SNOWING... first snow so far.

Sorry I was getting yelled at and was slow to enter

Jerry

okay I see where you're headed. ANd it's alright to be an egg head. Look at Austin Coil. And I love that man. I was giving a standing point of launch if you could use 7200 RPM, carry it through a great 4.5 second run to complete the quarter, 1600 for 4.5 seconds of grunt. Siplified to see that yet a motor that doesn't need all 7200 RPM's to run but it is more than 540 like the prof pointed out. I've seen Dtat sheets from competitors that went as low as 1120 and ad high as 1700plus. Physics makes a strange bedfellow because what the math says rarely happens even in the best of runs

Originally Posted by DennyW

Hey, is that on a 4 stroke motor ?? Or a one stroke ??

doesn't matter... I'm not talking about how often the plugs fire... rpm is rpm, no?

Originally Posted by nitrowarrior

okay I see where you're headed. ANd it's alright to be an egg head. Look at Austin Coil. And I love that man. I was giving a standing point of launch if you could use 7200 RPM, carry it through a great 4.5 second run to complete the quarter, 1600 for 4.5 seconds of grunt. Siplified to see that yet a motor that doesn't need all 7200 RPM's to run but it is more than 540 like the prof pointed out.

I think we'll need to agree to disagree

That's cool Skids......it won't be the first......Remember it happens differently during application than on paper. Wouldn't it be great if what was put down on paper were to really come true? Oh wait, the crew chiefs would work for a lot less It's still a lot of fun to ponder and I'm glad to have worthy members step up and quiz qwhat it's really all about.

I read somewhere that if the facts don't support your theory, get a new theory---guess I'll go take off the mower and mount the snow blower

Jerry

Skids, next time you're watching an NHRA event on the tube, especially the final round in the evening, watch the top fuel cars. Everytime there is a flame out of a header tube that's a cylinder firing. When the car launches you can't see the pulses, just one solid flame out each cylinder that is still burning.... There is far more slippage due to clutching and tire spin then you would ever think. If you ever get near a top fuel team computer and can look at the run data you will clearly see that drive shaft rpm and engine rpm aren't even close to the same as your calculations would assume they are. Even in top alcohol, the clutch at launch on the first set of arms was in excess of 40% slippage, on a bad track, even lighter clutch loads then that. I've never driven a top fuel car, but even in our much lower horsepowered alcohol cars and then only on a perfect track with perfect conditions you were at full lockup on the clutch for MAYBE the last hundred feet of the quarter.....

I doubt today's top fuel cars are ever at full lockup on the clutch.....

I'm far from being a mathematics whiz, but your equation would be closer to accurate if the top fuel car were at a constant speed, and not at a stand still. In a bracket car, with four or five forward gears, the velocity and rate of acceleration, gear ratio, clutch and converter slippage, tire spin and a bunch of other variables would have to come into the formula. As I said, with the car locked up at a 1:1 final drive ratio meaning the crankshaft and driveshaft rpm were equal and the gear ratio in the rear was 1:1 then it would be accurate. Just because the engine only runs for X seconds at X rpm is not an accurate portrayal of how many times each cylinder must fire.....The crankshaft and the rear axle are never at the same rpm, which your formula would seem to assume......

Look everybody----by Nitro's own data-- average 7200 REVOLUTIONS PER MINUTE----And 4.5 seconds--- his math is wrong--the run takes 4.5 seconds, not 4.5 runs per minute--there always has been 60 seconds in a minute--time is a constant-- it doesn't matter if the car goes 50 feet or all the way to the moon, it takes 4.5 seconds, thats 540 cranshaft revolutions, the drive shaft revolutions don't matter, this is a time related deal, gears, tire size, clutch/tire slippage is not a part of the equation

Originally Posted by nitrowarrior

That's cool Skids......it won't be the first......Remember it happens differently during application than on paper. Wouldn't it be great if what was put down on paper were to really come true? Oh wait, the crew chiefs would work for a lot less It's still a lot of fun to ponder and I'm glad to have worthy members step up and quiz what it's really all about.

Scientists in the 60's also proudly procalimed that the fastest quarter mile speed possible would be 6 seconds.... They based it on a lot of physics and matematics formulas and theories....

Originally Posted by jerry clayton

Look everybody----by Nitro's own data-- average 7200 REVOLUTIONS PER MINUTE----And 4.5 seconds--- his math is wrong--the run takes 4.5 seconds, not 4.5 runs per minute--there always has been 60 seconds in a minute--time is a constant-- it doesn't matter if the car goes 50 feet or all the way to the moon, it takes 4.5 seconds, thats 540 cranshaft revolutions, the drive shaft revolutions don't matter, this is a time related deal, gears, tire size, clutch/tire slippage is not a part of the equation

If this is true, then if the tires are spinning or the clutch is set to slip then each cylinder still only hits 540 times in a quarter mile if it's done in 5.4 secs????

Jerry: are you the same Jerry Clayton that campaigned the Keeling-Clayton cars back in the early '70s? I was in diapers at the time so didn't have an appreciation for the sport in those days....

Anyhow, I wanted to let this one die but I'll venture one last illustration (my own personal character flaw of trying to get the last word):

Take a motor, any motor, put it on a stand in a shop and run it 4.5 seconds at 7200rpm, how many times did it turn over? Answer: 540... how many times did your timing light flash? Answer: 270

Take the same motor put it on a rocket ship to the moon... same deal run it at 7200rpm for 4.5 seconds. How many times did the motor turn over?

Take the same motor put in a top fuel dragster...

etc, etc, etc....

I know there is inherent slippage and I don't think lockup ever occurs in a TFD. The point I'm trying to make is that it doesn't matter... how many times does the motor turn over in 4.5 seconds?

I don't know how big TFD tires are but lets figure 35" for the sake of argument (I know even at that they grow considerably as they spin so let's not go there)...

Simplified model: circumference = 35"*pi = 110" = 9'2"
Quarter mile = 1320'
Revolutions of this hypothetical tire (with 100% traction) in a 1/4 mile = 144

All this is beside the point of how many times the motor turns over...

Sorry to beat a dead horse one more time...

-Chris

Originally Posted by Dave Severson

If this is true, then if the tires are spinning or the clutch is set to slip then each cylinder still only hits 540 times in a quarter mile if it's done in 5.4 secs????

No... if the average engine speed is still 7200rpm, then it would turn over 648 times in 5.4 seconds... nothing up my sleeve, this is just basic math