Top Fuelers-how they work
I read this on another forum and thought it was a complete explanation of how Top Fuelers work.
JustinAtAce
Senior Member
Join Date: Jul 2009
Posts: 425
Default Timing and Clutch
Timing control is probably the easiest to explain, short of explaining specifics on electronic signals.. Controlling their horsepower produced, they change the engine timing several times over the course of a 3-4 second pass. What they use is a microprocessor(computer) controller to set their parameters. The basically draw a map of what they want the timing curve to look like and send it to the box on the car. Between timing and fuel control, they adjust the engine's power output. Just like in a street car.. The more advance, the leaner/hotter condition you create in the cylinder. The more retard, the richer/cooler the system runs. There is always a sweet spot for peak power.
I should also add that all the Fuel, Timing and clutch system timers are activated by a switch under the driver's gas pedal that triggers at Wide Open Throttle.
New Products - You can see what they actually use here. And the little box you see the crew chiefs playing with in some of the staging lane shots that programs the controller box.
A typical pass, a fuel car will have 52-60 degrees of peak timing, about 1 second into the pass, they retard it back 20 degrees, open the more aggressive clutch flows, and ramp the timing back in as well as starting to pour more fuel into the engine. How quickly they can bring it back in and how aggressive they can be on the clutch will determine how quick they run.
Clutch control is actually a pretty neat deal. So you've seen how many levers are actually on the Nitro clutch.. Well there are heavier Primary levers and lighter Secondary levers. Primary levers are the big controller levers used to get the car off the line and the Secondary lever functions as the fine tuning as the car goes down the track. The faster the levers spin(more engine RPM) and the more the clutch wears, the more load the levers try to apply to the clutch. So to keep the clutch under control and applying just the right amount of load, they've developed a throwout bearing height control system called a "Cannon". Most use the Automan or JT Stewart cannons which are essentially an Air or air over Hydraulic piston. In the bellhousing, the release bearing for the clutch is mounted to a cross-shaft and fork system connected to the driver's clutch pedal. The "cannon" system is typically installed right on the back side of the bellhousing and when the system is charged with full air(like when they back up after the burnout), the driver can still push the pedal to release the clutch, but the bearing can only travel as far away from the levers as the cannon allows. When the drivers talk about feeling the clutch come in, they are feeling the cannon moving and allowing the levers to gain angle and apply more plate load.
So how do they control this cannon system? It's electronically controlled with a programmable electronic timer activating these adjustable flow control valves. When you see the crew chiefs turning these little knobs, they are either increasing or decreasing the rate that particular valve can release the pressure in the cannon system. Crew chiefs will compound 4-8 of these adjustable valves and use their timer boxes to fire them off and release pressure out of the cannon system, which allows the pressure from the levers on the clutch to push the bearing further away, which allows the levers to apply more clutch. Just some round numbers, with the cannon fully engaged, the clutch will show 7,000 lbs of plate load.. By the time the cannon/bearing is fully retracted, it's around 14,000 lbs.
http://www.electrimotion.com/Clutch%...structions.pdf - Here is a link to the Electrimotion purpose built clutch controller.
What gets really tricky about the clutch flow system is that if the clutch discs wear more than you anticipated at any point in the run, it can create more pressure in the system because the levers are trying to gain attack angle, so what you thought was only supposed to flow "x" amount of air at a given pressure is now at higher pressure, so therefore flowing more and making your clutch application more aggressive than you intended. A good example of seeing this is when a car smokes the tires near the 330. If the discs don't wear enough, the levers never achieve the angles they need to apply the plate load necessary to lock up or keep the cylinders lit.
What people don't always realize about a Top Fuel car is that there is a constant balance between engine, clutch and tires throughout the entire lap. You miss by just a hair on any one of those and you've smoked the tires or worse..
Clutch control is as much a function of keeping the engine happy as it is a traction measure. You don't want to lug the motor too hard to drop RPM severely, but you still want to connect enough power to keep the tires hooked and load on the motor. Drop the power in the motor too much, the clutch will lock up and smoke the tires. Too much power through the same clutch can either smoke the tires right then and there or burn through the clutch and smoke the tires later because of excessive wear.
It really is kind of amazing the cars make it down the track at all when you think about all the has to go right. Hope this helps.. I know it's kind of lengthy.
