Algebra and Restrictor Plates

S

stridsberry

Guest
What with all the talk about restrictor plates, I got to wondering how much they literally affect throttle response. I know what the laymen's response is - a lot. But since I plan on majoring in mechanical engineering, I like to know things like this. So I put the area-of-a-circle formula that I learned so long ago to a good use - finally. ;) The formula for a circles area is:

A = r^2 X pi

Where A is the area, and r is the radius of the circle. So you can use this to know how many square inches are open for fuel to flow through the carburetor. A regular, unresctricted WC carburetor is 2 inches in diameter, so the formula would be A = 1^2 X pi. So each hole would be an opening of about 3.14 square inches. Any restrictor plate opening is then measured as a % of pi, which translates roughly into throttle response.

The current plate size is 7/8". So the radius is 7/16". When plugged into the formula, it comes out to .601 square inches per hole - in other words, not much. When taken as a % of pi, it comes out to .1914. This means that the holes are about 19% as big as on an unrestricted carburetor. That's also about as much throttle response that they have. This really shows how much the plates affect the cars. Here's an example to drive my point home. Say that with an unresricted WC engine, you could go from 0-150 mph in 12 seconds (I don't really know how fast they can do that, but that's not important right now). But putting a 7/8" plate on that carburetor, it takes more than 5 time as long to get to 150 mph - roughly 63 seconds in this example. Even if you went up to 1-inch plates, the holes would still be 4 times smaller than on an unrestricted carburetor, and it would still take 48 seconds to go from 0-150 mph.

I hope you understood all of that. But it's still pretty amazing to think about, isn't it? :blink: :blink: :wacko: :wacko:
 
Interesting stuff.

How would changing the plate to 1" affect the racing at restrictor plates. It would speed up the cars. How much I do not know. Would this allow the pack to seperate more? Would Nascar ever research or test this?
 
Originally posted by Dinoforthe3@Apr 4 2003, 04:55 PM
Interesting stuff.

How would changing the plate to 1" affect the racing at restrictor plates. It would speed up the cars. How much I do not know. Would this allow the pack to seperate more? Would Nascar ever research or test this?
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Under the rules package that was in place in 2001, they were originally going to have 1" restrictor plates. On the eve of the first race with those rules - Talladega, fall 2000 - they reduced the size to 15/16", because cars were running just under 200mph in the draft.

Since the cars are more aerodynamic now than they were under that rules package, they would undoubtedly be over 200 mph in the draft. I don't think it would separate the field out too much, but I also think that cars could pass without needing 3-4 drafting partners, since they'd have more throttle response.
 
So throttle response--or lack thereof--is more of a contributing factor to the anemic racing at these tracks than the draft or aeropackage could ever be?Just a question,I wont even pretend to know the answer.
 
Originally posted by 97forever@Apr 4 2003, 05:09 PM
So throttle response--or lack thereof--is more of a contributing factor to the anemic racing at these tracks than the draft or aeropackage could ever be?Just a question,I wont even pretend to know the answer.
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I think it is. Since the cars have so little throttle response, they have to run wide open all the way around in order to keep up. In order to make a pass by yourself, you need to be able to back off and then make a run. But with no throttle response, you can't afford to back off; if you do you go straight to the back, and need forever to catch back up. If you opened the plate up some, you can afford to back off and then make a run, because you have more power to the wheels. Just my opinion.
 
Originally posted by majestyx@Apr 4 2003, 03:54 PM
strids, I'll take your word for it! ;)
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I also will take your word for it!!!
 
Originally posted by stridsberry@Apr 4 2003, 05:23 PM

I think it is.  Since the cars have so little throttle response, they have to run wide open all the way around in order to keep up.  In order to make a pass by yourself, you need to be able to back off and then make a run.  But with no throttle response, you can't afford to back off; if you do you go straight to the back, and need forever to catch back up.  If you opened the plate up some, you can afford to back off and then make a run, because you have more power to the wheels.  Just my opinion.
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Herein lies the heart of solving the problem, if it is granted that there is a problem.

Given the tires, suspensions, and aero downforce of todays Winston Cup cars they can circulate this speedway at speeds in excess of 200 MPH fairly easily. Any engine combination, be it restrictor plate, reduced displacement, or whatever that creates speeds at or below that figure will result in the same problem. If you can hold the hammer down all the way around there is no such thing as throttle response. Wide open is wide open, no matter what size the plate is. You just have no throttle response at a higher speed.

The reason the plates are used is to keep the speeds below that 200 MPH mark due to safety concerns. Whether those concerns are justified is a different discussion and does not include only NASCAR and the race teams. It is pretty much at this point dictated by the insurance folks.

There are obvious ways to create a situation where the cars cannot circulate at more than 200 MPH without lifting. Aero changes, track changes and such. The fly is those ointments is what happens to the competition if they are used. If the cars won't handle well enough to run those speeds, do ya end up with a race where there is only one way around the track, at the very bottom? The second groove is not effective and passing remains difficult. It has been argued both ways many times and no one has a concrete answer that I know of.

There is another consideration to these solutions as well. If you have the set=up designed to where the car cannot hold the turn at a high enough rate of speed, but in so doing allow the amounts of H{ currently available, how fast do ya reckon these teams can go on the straight? Maybe 220 or 230 or even faster? Realize at some of the tracks with much shorter straights they hit 200 now. And at those places, Atlanta, Texas, and a couple of the flat tracks the danger of racing into those turns from those speeds is already being discussed.

And did you elimate the first reason for the plates? Nope, if a car blasting down the straight at 220 is not acceptable now, it will not be acceptable under those circumstances either.
 
Originally posted by stridsberry@Apr 4 2003, 03:51 PM


The current plate size is 7/8". So the radius is 7/16". When plugged into the formula, it comes out to .601 square inches per hole - in other words, not much. When taken as a % of pi, it comes out to .1914. This means that the holes are about 19% as big as on an unrestricted carburetor. That's also about as much throttle response that they have. This really shows how much the plates affect the cars. Here's an example to drive my point home. Say that with an unresricted WC engine, you could go from 0-150 mph in 12 seconds (I don't really know how fast they can do that, but that's not important right now). But putting a 7/8" plate on that carburetor, it takes more than 5 time as long to get to 150 mph - roughly 63 seconds in this example. Even if you went up to 1-inch plates, the holes would still be 4 times smaller than on an unrestricted carburetor, and it would still take 48 seconds to go from 0-150 mph.

I hope you understood all of that. But it's still pretty amazing to think about, isn't it? :blink: :blink: :wacko: :wacko:
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oh if it were only that simple. Yeah true they are 19% the size of of a normal carb, but the engines are still making over 400 horses making it about half the hp of a normal engine. 63 sec to 150, probally not, thats a long time even given the circumstances. They have the engines tuned for power right where they need it, a sweet zone, whereever that is because I don't remember where they run, say 7800. Thats where the power is and the torque curve is long gone by then. Say even a little let off will know you down to 6000 real quick and thats well out of the sweet zone and plus you got negitive momentum going for you at those speeds. I would imagine they run pretty low 1 and 2nd gears to get going. When its about speed its about the drag to power ratio. Power needed to overcome drag goes up with drag Cubed, so a drag-to-power ratio isn't very useful. You'd want a drag^3-to-power ratio to get top speed if you would want to compare plate and non plate engines. I will get into this a more in the morning. Tired. Hope this helps.
 
Ok.... i wasn't going to go there on this subject again, but i have to get my 2 cents in again....lol. On the plate tracks it is all about throttle response, if you have it you can pass....no matter what the aero package is. Simply put if you have extra throttle to use , as in pushing down the accelerator pedal while you are in the process of passing another car, you will in fact pass them. There is no other way around it. If there is no extra throttle to use, as in pedal all the way to the floor , flat out all the time, you have to rely on how well your car goes through the air! There is no way to get around another car other than to slip through the air better than he does. I pose this why is it that on other tracks: Michigan, Texas, Atlanta,even Kansas where the speeds exceed 200, the cars are not restricted? Think about that and tell me the "true reason".
 
Two big things you're not considering mopardh;

1) No track averages 200 mph, the closest was likely Atlanta when it hit 197 in qualifying and there was talk right away of the possibility of using restrictor plates. But the speeds there fell off anyway. The tracks you mention will on occasions toy with a very very brief blip into the 200 mph, but that is about it. The you have to consider..

2) You are talking qualifying speed in your references, not race speed which is notably slower. However at both Talledega and Daytona the cars are faster in the race than they are in qualifying. That is not true at any other track on the circuit.
 
Stridsberry,

Pretty good, but you are assuming constant fuel atomization. Crack the throttle on a plate more and all the fuel falls out of the air stream for a good long while....but hang in there, your giving good thought!
 
You still didn't answer the question....why do we have plates? Answer : to keep the cars equal so they run in packs, so the newbie fans go gaga over the so called "racing". And of course so there is a huge accident that makes everything really exciting. On the subject of speeds at the other tracks....going into turn 1 at Michigan at 205-208 isn't a little on the edge i don't know what is, whether it be qualifying or not that is too fast!
 
They also draft at these tracks and do go faster than daytona or dega when they do, how could they not? More horses going down the straight equals more speed.
 
First, why do they use plates. I hear the competition thing here and there. But it if that were the case, would it not follow that the plates would be on at places like Atlanta and Texas which have nearly enough speed to justify it? If the logic holds for Dega and Daytona that the plates are there to increase the closeness of competition it would hold for any track on the circuit wouldn't it?

If you understand gearing and acceleration, which I am sure you do, you would realize that much longer straights at Daytona and Talledega would allow much greater speed if the HP were not restricted than any other circuit on the schedule. More HP equals more speed but ya gotta have the space and time factored into the equation. I mean would that mean the cars are just as fast on the straights at say Bristol as they are at Texas? Speed is not quite that simple.

Yes the draft can figure into the game a bit at Atlanta and Texas or any other track, but it is not the same as it is at Dega and Daytona by a long stretch. Either restricted or unrestricted. The draft was born and raised at these tracks is considerably more of a factor than anywhere else.

Do not know if ya have the ability to watch the telemetry consistently at during the races. I suggest you might give it a try on Trackpass sometime. The top speeds on the straights at Daytona and Talledega might surprise ya. Give you something else to look at. Check the Happy Hour speeds when the cars are in race trim at Talledega and compare them to Atlanta and Texas. Let me know what ya find.
 
Why do we have plates? I hope I don't offend anyone, but it's because NASCAR is retarded. There are too many other solutions out there.
 
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