If the motor would stay together (1 Viewer)

[ironpony]

Well you obviously understand what is going on. Aircraft R&D here myself, most people throwing out scenarios have no clue as to what it takes to go faster. The do not understand it is not linear, it becomes exponential as you increase speed to drag.

 

[flapjack]

Well you obviously understand what is going on. Aircraft R&D here myself, most people throwing out scenarios have no clue as to what it takes to go faster. The do not understand it is not linear, it becomes exponential as you increase speed to drag.

By chance do you use Fluent for CFD simulations? Just curious, my understanding is that is THE software to have for CFD.

 

[Mike]

Here's a G-meter from a Top Fuel run 3.70. Once the clutch is locked up and the rev-limiter is activated, the acceleration is declining, rapidly.
AlanView attachment 4134

Alan, let me add a little to your analysis. While you are correct in stating the acceleration is declining, you are still accelerating. Although the RATE of change is declining due to timing retard and aero, the overall rate of change is still positive. Even at 3.7ish seconds, you still have a positive acceleration (>0) and thus speed is still increasing. The other factor most don't take into consideration is that because of the speed you are already traveling, the amount of time you have to accelerate and see a change in speed is much less because you are measuring that change across a distance.Speed is the distance covered in a unit of time while acceleration is the rate of change of speed. It can seem as if you are slowing, but you're really still accelerating. Also, the engine is never truly RPM limited. That would be disastrous. The "RPM limiter" is a timing retard that slows the amount of HP you can make thus slowing the engine RPM as aero drag increases. Funny cars have a slightly less aggressive retard (changes to the same as TF next year) and better aero thus they don't get as bogged down as a TF car.

 

[ironpony]

By chance do you use Fluent for CFD simulations? Just curious, my understanding is that is THE software to have for CFD.

I have been out of the aircraft industry since 1990, barely had computers..............hammer, chisel and stone compared to today

 

[Cliff]

Maybe Alan can get some real numbers from one of the teams for Cd and frontal area of a dragster. This is based on just a WAG. Also remember that the wings create drag and down force. It is easy to see even if HP was not decreasing that the amount of HP needed just to press the car through the air at higher MPH starts to become very large.

Stan

Thanks Stan. Would be interesting to me to see how much wind resistance plays a part in the run. You know what? I would put drag racing crew chiefs up against any other form of motor sports, cuz we really have some sharp minds out there. It amazes me that a 500" OHV engine with a 14:71 blower can make so much power. This stuff trickles down to nostalgia AA/FD. 6:71 blower and they can run 5.50 - 275 on a skinny 12" tire.

 

[none]

Alan, let me add a little to your analysis. While you are correct in stating the acceleration is declining, you are still accelerating. Although the RATE of change is declining due to timing retard and aero, the overall rate of change is still positive. Even at 3.7ish seconds, you still have a positive acceleration (>0) and thus speed is still increasing. The other factor most don't take into consideration is that because of the speed you are already traveling, the amount of time you have to accelerate and see a change in speed is much less because you are measuring that change across a distance.Speed is the distance covered in a unit of time while acceleration is the rate of change of speed. It can seem as if you are slowing, but you're really still accelerating. Also, the engine is never truly RPM limited. That would be disastrous. The "RPM limiter" is a timing retard that slows the amount of HP you can make thus slowing the engine RPM as aero drag increases. Funny cars have a slightly less aggressive retard (changes to the same as TF next year) and better aero thus they don't get as bogged down as a TF car.

Oh, what do you know about anything?
(LoL Just kidding)

Mike,
Thanks for weighing in. Considering that the car goes from 0 to 300 in 3 seconds, then from 300 to 330 in the next .7 seconds, yes it is still accelerating but at a much diminished and rapidly continuing to diminish pace.

My contention is, that they are close to being topped out. And I doubt they would not go much faster then 350, given the drag and the reduction in power from the retarder.

Curious as to your thoughts?

And just for the record, I use the term "rev limiter" pretty generically as it has become synonymous with the retarder.

Alan

 

[Stan]

I know this is like comparing a grape and a grapefruit. But lets look at Lagana pass this past week at a non National event (1320 ft). Clearly he is not pulling near the same average G's as Leah's run from 0 to 660 ft but he is pulling more average G's from 660 to 1000 ft.

Average rate of acceleration:
0 to 660 ft - 4.1634 G's
660 to 1000 ft - 2.55 02 G's
1000 to 1320 ft - 1.0507 G's

Stan

 

[ironpony]

I agree Stan but remember they have to tune different to keep the engine together and off the retarder for an additional 320'.
I believe that is the difference, if that was 1000' run they would of wanted to accelerate faster in the first 660' to max out by 1000'

As you said grapes to grapefruit but I do appreciate the current 1320' info, it gives us numbers to compare instead of assuming some things.

 

[Mike]

Oh, what do you know about anything?
(LoL Just kidding)

Mike,
Thanks for weighing in. Considering that the car goes from 0 to 300 in 3 seconds, then from 300 to 330 in the next .7 seconds, yes it is still accelerating but at a much diminished and rapidly continuing to diminish pace.

My contention is, that they are close to being topped out. And I doubt they would not go much faster then 350, given the drag and the reduction in power from the retarder.

Curious as to your thoughts?

And just for the record, I use the term "rev limiter" pretty generically as it has become synonymous with the retarder.

Alan

I agree on them being close to topped out for this rules package, you can't beat physics. It would be different story should we only be shooting for MPH over a longer distance with different rules. That's whole mess of stuff for another day. Fun to think about though. The Dalton/Jackson streamliner is rumored to being switched to nitro. Maybe we'll know sooner than later.

 

[Cliff]

I read that Lagana dropped a cyl during that run. They said it would have gone faster, say 340 for the sake of argument. I agree with Mike Kern that the cars are close to topping out with these rules. Hmmm - same rules with 2.70 rear gears. Or a screw blower. Bigger tires. DOHC engine. More cubes. On and on.... IF you could change the rules, my 2 cents is that they would be going so fast that they'd run out of room to stop. Even if they went to 1/8 mile, think of what a fuel car could do with, say, a screw blower. 350 in the 1/8 mile would not be unreachable. OK, need to stop but I've thought about this for years. The fuel classes really ARE restricted.

 

[.]

What would the cars be running for MPH if there were still clocks 66 ft past the finish line like there were for decades?

 

[Stan]

350 MPH in 2.92 seconds (what Leah's 660 foot time was) is 5.465 average G's acceleration. No guess as to what peak G's would be. Just how much can the human body take?

Stan

 

[none]

Stan,

Using Bobby's 1320 run, it picked up 42.03 MPH over the 340' from 660 to 1000. Then only 15.07 the final 320' 1000 to 1320. That's over 1G? My rental car will accelerate 15.07 MPH in the length of a football field, that can't really be 1G is it?

Not arguing, just asking. I don't believe that it's still pulling over a G at that point.
Alan

 

[ironpony]

Anything x 1 is itself. 1x1=1 1x2=2 1x3=3.................Force of gravity x 1= 1G is what you see standing still.

 

[ironpony]

I read that Lagana dropped a cyl during that run. They said it would have gone faster, say 340 for the sake of argument. I agree with Mike Kern that the cars are close to topping out with these rules. Hmmm - same rules with 2.70 rear gears. Or a screw blower. Bigger tires. DOHC engine. More cubes. On and on.... IF you could change the rules, my 2 cents is that they would be going so fast that they'd run out of room to stop. Even if they went to 1/8 mile, think of what a fuel car could do with, say, a screw blower. 350 in the 1/8 mile would not be unreachable. OK, need to stop but I've thought about this for years. The fuel classes really ARE restricted.

No matter how much power you make the speed is a mathematical calculation, to change it you need to change RPM or gear ratio, bigger tires. Screw blower, DOHC, more cubes, no. More power will get you there quicker.
As Alan would say not arguing, am I missing something???

 

[Cliff]

2 things. Someone told me that if we still had the old MPH "trap', ie: 66' before the finish line & 66' after, it would add about 1-2 MPH to the speed for the fuel cars. One of the T/F cars went 299 last year at the 1/8 mile, so that was really over 300. Use the same formula for 1000' speeds & 340 has already been reached. Also, I posted that if you could change things on a fueler, like more cubes, screw blower, etc, then that would give more power than what the engines have now. Assuming you could get the power to the ground, then the speeds would go way up. I guess I was thinking the current rules have been in place for years & do restrict how much power can be made. Add a screw blower, more air & fuel = more power, etc etc. If you could have a fuel car with, say, a 800 CI engine & screw blower, the whole car might look different than now. Wider tires, chassis would have to be made stronger to take the added power, bigger wings, maybe some streamlining. I dunno. Could think of all kinds of designs that might work. But, I might be missing something. Sorry Alan.

 

[ironpony]

Cliff, not arguing want to understand your point of view.
If engine RPM is x
tire diameter is x
if rear end ratio is x
this is going to determine MPH no matter how much power
am I missing something??

Now more power is going to get it there faster,but then the math says it can only go so fast

 

[Cliff]

Hi Ken. I'm not a driver or a wrench, but just kinda going on what I've seen over the years. I know there is a limit to how fast a fueler can go. Was thinking that if you threw out the rules, then yeah, they could go a lot faster. But like you say, the math says "it can only go so fast". So, what is the limit? I'm thinking the human body might be the limit, cuz the body can only take so many G's before the driver would pass out, or simply not be able to steer cuz of G force. I think that it would be possible to engineer a fueler to go way faster than they go now, but.... where is "the wall"? What would cause the cars to reach the point where they cannot accelerate any more? It's just interesting to think about. The cars are so fast now. Scotty Fenn said around 1951 or so that dragsters would never break 150 MPH barrier, yet in 1955, Lloyd Scott did it in the Bustle Bomb, twin engine car (with one Olds & one Caddy) & went 155. There are so many sharp minds in drag racing that I have no doubt that someone would come up with a way to run, say, 400 MPH, or faster, if rules allowed it. (How do you stop the car???) Anyhoo, just my 2 cents. I really enjoy reading what folks write on this site. Hard core drag racers!

 

[Stan]

Stan,

Using Bobby's 1320 run, it picked up 42.03 MPH over the 340' from 660 to 1000. Then only 15.07 the final 320' 1000 to 1320. That's over 1G? My rental car will accelerate 15.07 MPH in the length of a football field, that can't really be 1G is it?

Not arguing, just asking. I don't believe that it's still pulling over a G at that point.
Alan

Alan,
It is possible that I maybe doing the calculations all wrong. I do not use the length / distance, but use the time and change in MPH. If someone had 3 times slips
12.99 et 110 MPH
12.49 et 110 MPH
11.99 et 110 MPH
Wouldn't each of those have a different average rate of acceleration?

Stan

 

[ironpony]

the acceleration is not linear, look at the graph Alan posted, very fast first 660 then slows down. All of these are variable between passes. Might be slow on the first half and a little quicker on the back half. The cars are tuned to reach their max in XXX' if they went back to 1320 the cars would not be "faster" they would have to slow down the tuneup to not hit the retarder to soon.
At the rate the car is loosing acceleration it maybe zero acceleration in the last 320' possibly slowing the mph.
Think of a TF, hits throttle goes 60' blows up coasts, which is actually decelerating to a 9.90
top sportsman hits throttle accelerates entire track, makes a perfect pass goes 9.90

Acceleration, is the rate of change of velocity of an object with respect to time.
Speed can be thought of as the rate at which an object covers distance.