Drag racing/traction control...?

Why don't Dragsters use traction control?  Is it banned by the rules or is there a technical reason why?

Lots of drag racers use traction control or boost by gear where it isnt outlawed.

I know its pretty common in the no prep crowd.

In reply to stroker :

Technical reason on the huge HP cars. They actually need a little slip and wheelspeed to get traction. Often there's a weighted clutch or boost by time involved as well. So there is a traction control, just not in the traditional way you are thinking.

A street traction control system is probably not appropriate for the tires/grip/surface/power/etc in dedicated drag racing, but that's just a question of software and tuning.  F1 used to have traction control for their standing starts before it was banned.  A computer can do everything to maximize traction that a person can, only better and faster. 

In short, it's all rules.

Real traction control would cost too much time and be too inconsistent.  The way they tune traction is with timing.  Put more in or take more out to control when your power comes in.

We have also set up a simple front to rear wheel speed table with a variable timing table based on slip %.  This is pretty common but it was a grudge/street race car.

Pretty sure that aftermarket ECUs with decently functional TC systems are fairly rare, or at least fairly recent developments. Pretty sure that for a while the only really affordably priced option was to find a used racelogic standalone system. Then there's the matter of actually tuning them to work well and consistently.

But people certainly do use it. Some also have anti-wheelie systems, with a ride height sensor on the front end and the ECU pulls power if it lifts too much or too quickly.

dps214 said:

Pretty sure that aftermarket ECUs with decently functional TC systems are fairly rare, or at least fairly recent developments. Pretty sure that for a while the only really affordably priced option was to find a used racelogic standalone system. Then there's the matter of actually tuning them to work well and consistently.

It doesn't take much tuning to get the RL system to work -- I have one in my (turbo) Miata and it was pretty much just wire it in and it works.  They don't make them any more, though.

Traction control is slow to react and often over done.  You stab the throttle, waste your R/T on a little tire spin, then the nanny kicks in and wastes a half second doing it for you, then lets it go again.... Some cars can add over 1 second to your E/T with traction control.

You're better off just doing it yourself.

Now LAUNCH control on some of the exotics with high-res wheel speed sensors and high-frequency PWM brake or throttle control... that's a different story, but a Chrysler with an optional gimmick to make mom feel safer in the snow doesn't really help on a drag strip.

Depends on the class. We use it all the time for fwd drag cars. Have front and rear wheel speed, calc slip % and can adjust fuel timing and boost to react if needed. 
 

The big classes have it too, built into the slipper clutch. 

Dragsters (Top Fuel) have a hilariously small number of revolutions per run, something like 540, so any control which would cut power would be way too slow (at best, 1/540th of the run) and way too detrimental to the engine. Any braking system would have to be huge to overcome the power. I suspect it would slow them down a lot.

Plus rules.

tuna55 said:

Dragsters (Top Fuel) have a hilariously small number of revolutions per run, something like 540, so any control which would cut power would be way too slow (at best, 1/540th of the run) and way too detrimental to the engine. Any braking system would have to be huge to overcome the power. I suspect it would slow them down a lot.

 

Plus rules.

It's all rules.  Any working, legal launch control system would completely change the sport, the team that built it would clean up.  Race car engineers get REALLY inventive when things like that are on the line.  Top Fuel isn't any different from F1 in this regard, stuff like the specialized clutches are very much the same kinds of off-the-wall solutions to work around rules limits than F1 uses (F-duct, anyone?).

Consider that a modern supercar's 0-60 time is massively influenced by the traction/launch control, and yet it does that in fewer revs than the 540 you mention above.  (also you get 4 combustion events per revolution in a 4-stroke V8, so 2160 would be a more useful number).

Traction control is generally about reducing power... who really wants less power? In stick shift drag racing it's usually not excess power that breaks the tires loose, more often than not it's poorly controlled inertia release.

An engine's entire rotating assy (crankshaft/flywheel/pressure plate/balancer/etc) is one big flywheel style energy storage device. You must put energy into it to speed it up, you must take energy out of it to slow it down. While engine rpm is climbing, engine torque alone is accelerating the car. When the engine is getting pulled down by the clutch, inertia energy is being added to the torque being produced by the engine.

It helps to think about a stick shift car itself, and it's engine's rotating assy, as separate energy storage devices similar to batteries that get charged by the engine. On the starting line, the car itself is not moving and contains zero charge. On the starting line the engine is running, so it's rotating assy contains at least a partial charge. When the car crosses the finish line, wheels/tires, driveshaft, etc are all going to be charged to capacity (spinning at max rpm/mph). If the car is geared correctly, the engine's rotating assembly will also be charged to capacity as you cross the finish line. Since the engine is making the power to charge both, and the car itself starts out with zero charge (zero mph) prior to launch, there's an advantage to starting a drag strip pass with the rotating assy as charged as possible prior to triggering the clock.

Here's a graph showing evidence of additional torque due to stored inertia energy being pulled out of an engine's rotating assy by the clutch.
...Red is engine rpm
...Blue is accel G
...Green is driveshaft rpm
Notice that all the highest points of the Accel "G" trace on the graph occur while the engine's rotating assy is losing rpm (discharging energy) against WOT. But then as soon as the clutch stops pulling engine the down and engine rpm begins to climb, the G trace drops like a rock as engine torque alone is now accelerating the car with no help from discharged inertia...

On the graph above you see zero wheelspin during launch, but note the sudden loss of 2000+ rpm against WOT after the shifts. When the clutch pulls an engine down too quick, a big portion of that released energy can end up wasted in intense wheelspeed spikes. The clutch is what determines the rate that the engine is pulled down against WOT, in other words how fast the clutch pulls the engine down is what determines the rate that released inertia energy hits the input shaft.

Quick bit of hillbilly physics- the inertia energy contained in an engine's rotating assy increases exponentially with rpm.
...Lets say a rotating assy spinning at 1000rpm contains 1 unit of inertia.
...Double the rpm to 2000, now it contains 4 units of inertia.
...Spin it up to 7174rpm like the launch on the graph, now it contains 51.46 units. The clutch then pulled the engine down to 4630rpm from 7174, that's 30.03 units of inertia energy dumped into the input shaft in 0.589sec.
...After the shift, the engine got pulled down from 7820rpm to 5132rpm. That's 34.82 units of energy dumped into the input shaft in only 0.163sec. More inertia energy dumped after the shifts than during launch, in a far tighter time frame. A spike like that can put a lot of hurt on a car's drivetrain. If you are trying to stick radials at the track, a spike like that can send you back to bias slicks.

Might help to think of it like accelerating a glass by pulling on a tablecloth. Jerk the tablecloth too quick, the glass doesn't move. Pull slow and the glass moves, but not very quick. Happy medium for accelerating the glass as efficiently as possible lies somewhere in between.

Here's a few different ways you can adjust your car's inertia release rate...
...1- modulate clutch engagement with your foot. Impossible to do with optimum efficiency, also puts a lot of wear/tear on the clutch/drivetrain when you miss the sweet spot.
...2- select a clutch with just enough clamp pressure to optimize inertia release rate. Mixing/matching clutch components in the search for optimum release rate can get expensive and labor intensive, things also change as the clutch wears. Adding nitrous to your car will force you to compromise your car's NA potential.
...3- use an external controller like my Hitmaster system to temporarily reduce clutch clamp pressure. Makes it possible to adjust your car's inertia release rate by simply turning a knob. Turn the system off for street driving if you want, also makes it easy to switch between NA or nitrous launch settings. Tires last a lot longer, you may find that you no longer need to do burnouts.

It's pretty much impossible to produce this shape of TOB pressure release curve using your foot, the system's use of a timer also limits excessive wear/tear on the clutch...

My Hitmaster system is in-line hydraulic, and generally limited to cars with hydraulic clutch release systems. For cars with mechanical release linkage, my ClutchTamer is easier to install. For power adder cars, the Hitmaster is generally preferred over the ClutchTamer as it gets to full clutch clamp pressure much quicker.

After you discover that you can consistently control the rate that inertia energy is fed into the chassis, you will then soon realize that there's not much keeping you from raising launch rpm to make more inertia energy available during launch. Raising launch rpm allows you to take advantage of a much longer lasting inertia surge without drawing the engine down below it's torque peak. So why launch the car from 4500rpm with 20.25 units of inertia, if you can dial in a dead hook 7500 hit with 56.25 units on board without breaking anything? Being able to put that extra rpm/inertia energy to work is like adding a shot of nitrous during launch.

Grant

In reply to weedburner :

Thank you for that post!

also, it is not lost on me that Weedburner makes something called the Hitmaster.

Isn't that essentially what a two-step does?

In reply to Woody (Forum Supportum) :

A 2 step is just a rev limiter

In reply to Patientzero :

Yes, but doesn't it accomplish the same thing?

Top fuel classes have a very serious, complex and mechanical traction control.  The release bearing is controlled by a series of air solenoids and mechanical timers working against weights on the pressure plate that progressively apply the clutch over time.

NHRA banned electronic controls 25 or 30 years ago, so they came up with the mechanical timer system.

Big difference between a 2-step rev limiter and a clutch hit controller.

...2-step is a way of limiting the amount of inertia stored in the rotating assy prior to the start. So in that regard 2-step is a form of traction control (power reduction) as it reduces potential energy available for launch.

...Clutch hit controller allows you to store as much energy as possible prior to the start, as you can adjust the inertia draw rate to a level that the chassis/tires can efficiently handle.

What would happen if the engine in that graph I posted were capable of raising the launch rpm from 7174 to 9000, with shift points/etc remaining the same?  The answer is the amount of energy available for the G surge would almost double  from 30.03 to 59.57 units of inertia. Draw that 59.57 units in the same 0.589sec time frame that the 30.03 units were drawn out, the hit on the input shaft almost doubles in intensity which would likely either break something or knock the tires completely loose. But if you use a clutch hit controller to draw that 59.57 units at same draw rate as the 30.03 unit hit, now intensity of the hit does not increase but the surge can last almost twice as long. The engine's power curve does not need to extend to 9k to exploit this, just capable of spinning 9k on the starting line without flying apart. Just an example of what the ability to control inertia draw rate can allow you to do.

Grant

There are a ton of things that can be done but legality depends on the class. Heck, even in our 4.90 1/8 car we adjust timing to improve off the line hookup basically by the foot. Traction control is reactive and things happen so fast in a drag race that it must be anticipated. 
hilariously I find drag racing to be very similar to golf- and hear me out. 
Say I hit my stock 7 iron 200 at sea level in 50% humidity, with no wind. That would change if any of those variables change at all. 
drag racing is similar. You should know that your car will run 4.90 at certain conditions. However: altitude, humidity, track temp, ambient temp, wind, how much vht is down- can all affect that. Much of racing is using current conditions and trying to predict with accuracy what the car will do. That includes your 60ft- which is really where the race is won. 

There's also the very simple launch control that can be accomplished with aftermarket ECUs (holley, Haltech, etc)

As I understand it: Single trigger switch to engage 2step and an ignition timing vs time map. Hold the button down and bring the engine up against the 2 step for launch rpm. Upon release of the button as you let the clutch out (or have the trans brake release off that button too) the timing map comes into play. For example you could have 10 degrees pulled out upon release of the button with it ramping back in over 1.5 seconds before the map becomes null/void. Basically tune the launch rpm and amount of timing retard required to maintain traction. May not be the "best" but simple enough for the average person to figure out.

Asphalt_Gundam said:

There's also the very simple launch control that can be accomplished with aftermarket ECUs (holley, Haltech, etc)

As I understand it: Single trigger switch to engage 2step and an ignition timing vs time map. Hold the button down and bring the engine up against the 2 step for launch rpm. Upon release of the button as you let the clutch out (or have the trans brake release off that button too) the timing map comes into play. For example you could have 10 degrees pulled out upon release of the button with it ramping back in over 1.5 seconds before the map becomes null/void. Basically tune the launch rpm and amount of timing retard required to maintain traction. May not be the "best" but simple enough for the average person to figure out.

This is similar to the approach with the pro Bosch ECUs except, instead of a timing table, it used target rpm vs ground speed. Essentially, this is slip vs. ground speed but slip gets into divide-by-zero problems at a standing start. After some threshold, it changes over to traction control which targets slip instead of rpm since now the speed is high enough to more stably calculate slip, and targeting slip is gearing-agnostic whereas targeting rpm has to be changed every time the gear ratio changes. The whole ECU relied on torque as the common currency between all the different algorithms, so a PID+pre controller would operate on the launch control conditions and kick out a max torque. It's simple, but extremely effective when dialed in right.

As weedburner noted though, there is a LOT of inertia in the system, and every component is a torsion spring. This is why electric cars are getting such blistering 0-60 times. Your fast gas-powered cars have the power to spin their tires all the way through 60, so power isn't the issue. It's control. You just can't get the tires to operate on the perfect slip from the other end of the car. Good systems can trim spark timing, fuel, boost, and throttle, but it is all still going to have a delay between the pistons and the tires. Systems that operate on the brakes or driveline are going to allow much better fine-tuning. 

When I took in Midlana to have its ECU tuned, I noticed two different prices for tuning: "locked" and "unlocked." I asked what that was about, whether it was to hide the fuel map and timing tables from competitors, or to keep people from doing dumb things.

Nope, the tuner said that these days, it's easy to get 1000 hp out of a four cylinder (longevity aside); the problem is getting it to the ground. Their lower "locked" price is to hide their traction control settings from whoever, and presumably their higher unlocked price compensates them for any potential lost sales.