Balancing performance and safety in Top Fuel racing is getting a helping hand with the use of electronics – a high-tech approach previously frowned upon in this highly traditional community. By the start of the 2016 season, all teams will be required to have the same MSD Power Grid Pro Mag Digital Timing Control (PN 8771) on their cars – although most will likely have it in place this year. The system is designed to pull timing out of the engine at a precisely controlled rate with a goal of keeping trap speeds below 330 mph.
The Power Grid takes the place of the MSD Pro Mag Digital Timing Control and Graphic Editor, which was a bit cumbersome with an outdated hand-held touchscreen display. Those timing controls were implemented midway through the previous decade in response to escalating speeds and a couple of high-profile fatalities on the track. All of the timing controls familiar to the crew chiefs will carry over to the Power Grid along with more precision and flexibility. Now the ignition timing can be set with a wireless tablet or hooked up to a PC.
The continued favorable acceptance of this solution may even open up more opportunities for electronics in the nitro classes. While at the PRI show last December, EngineLabs talked to NHRA national technical director Danny Gracia about the MSD timing system. He said his team had visited MSD two weeks prior for briefings and feedback on the system.
“It’s the way to go,” said Gracia. “Obviously we have to keep control of [excessive speeds] before they run away from us again.”
Gracia was then asked about expanding the use of electronic controls to other functions of the vehicle, including the clutch.
“Definitely, probably in a couple years,” he said. “First, we have to run with what we have now. If we feel comfortable, then the teams need to come to us and say maybe it’s time to do this.”
Medieval rules in Top Fuel
The NHRA has long enforced tight restrictions on Top Fuel powertrain development not only to help keep the top speeds in check but also preserve the historic character of the class. The rules were often considered medieval, allowing only one engine architecture with a certain type and size of supercharger and mandating a 3.20:1 rear axle ratio. The sanctioning body also banned turbochargers in addition to any type of sophisticated electronic controls for engine or clutch management. The central nervous system of the cars could only evolve into a mish-mash of pneumatic timers and switches along with the accompanying spaghetti bowl of air lines.
At launch, you need 60 to 65 degrees of timing to get power up. – Joe Pando, MSD
“Everybody was coming up with scenarios on how to slow down the cars, and they were usually too expensive,” remembers MSD’s Joe Pando. “We stepped in and said we can help by doing it with electronics to control the timing.”
Even with those constraints, speeds were climbing fast, culminating in 2005 with Tony Schumacher’s 336.15 mph in competition and an amazing 337.58 mph in a qualifying pass.
Timing retarder, not rev limiter
Working with NHRA, MSD adapted a speed limiter into the timing controls already utilized by the teams. While there are records of Top Fuel teams using a conventional rev limiter that cuts power to the coil in the ‘90s, those deliberate misfires can be disastrous in a nitro engine that pours so much explosive fuel into the cylinders. If there’s no spark, the unburned fuel would normally go out the exhaust. But nitro engines are so violent that a busted valve spring or other malfunction could keep that exhaust valve closed, and since fuel cannot be compressed like air, all that pressure on the piston and crank usually results in a spectacular explosion.
Top Fuel vs. Funny Car
Top Fuel and Funny Car engines are quite similar with only a few differences. Dean “Guido” Antonelli has tuned both types of racecars for John Force Racing, including Brittany Force’s dragster. In a conversation with EngineLabs almost two years ago, he noted the following differences:
- Funny Car has dry-sump oiling with about 3.5 gallons of oil while Top Fuel is wet sump with about 5.0 gallons on board.
- Shorter headers on dragsters changes the back pressure, so cam changes are necessary to get the engine happy.
- You can hit the clutch harder on the dragster since the engine is sitting back on the tires.
- You can burn more fuel in a Funny Car from half track to the lights than in a dragster.
Early versions of the MSD system drew considerable ire from teams who claimed the timing reductions were too abrupt or there were crossfires that caused numerous costly engine explosions and oil downs, which can draw fines and deduct championship points away from the driver. The rev limits and rate of retard have been adjusted over the years in response to speeds or concerns voiced by the teams. The current redline target is 8,250 rpm for Funny Car engines and 7,900 rpm for Top Fuel.
“[Crew chiefs] were leaning so hard on the rev limiter to the point they were destroying parts and then blaming us,” says Pando, noting that crossfire scenarios are mechanically related stemming from incorrect rotor phasing. “We said it’s designed to do that. Let’s refocus ourselves on keeping the drivers alive. After those discussions we saw teams try to run on the rev limiter and not get past it.”
Following the death of Funny Car driver Scott Kalitta in 2008, NHRA reduced the race distance from the traditional 1,320 feet to 1,000 feet for the nitro classes – a move that not only brought trap speeds down about five percent but also provided 320 feet more track for the cars to stop. Maximum Top Fuel speeds were held in check around 325 to 327 mph over the following years, then shot up and surpassed 330 mph frequently in 2012 – including a 334.15 run by Shawn Langdon at Maple Grove that couldn’t be backed up to establish a NHRA record. Spencer Massey then laid down a 332.18 at Charlotte and backed it up to establish the current official mark.
What is the forbidden zone?
No teams surpassed 330 mph in 2013, but last year saw three teams run over 330 on five occasions. Why is 330 mph the forbidden zone? Tires and liability. Even with improvements to tire construction and tire-pressure mandates, officials don’t want teams testing the limits beyond 330 mph. And that’s also the mark that is reportedly the red flag for any insurance company with ties to drag racing.
The return of 330 mph speeds is attributed to a number of reasons, including better track preparation and much improved supercharger design and manufacturing.
“It’s also more fine tuning,” says Gracia. “At the end of the day, everyone has the same package. Some people just understand it better than others.”
With higher speeds the emphasis again returned to the timing retard. A nitro engine needs a considerable amount of ignition advance due to the slow-burning characteristics of nitromethane, that glorious rocket fuel from the ‘40s that carries its own oxygen atoms. In fact, the air-fuel ratio for a Top Fuel car need be only in the neighborhood of 1:1.
“At launch, you need 60 to 65 degrees of timing to get power up,” explains Pando. “As you’re leaving, the clutches are starting to come in and then they start to pull timing out.”
At the start, the tires are throwing big slabs of rubber at the track but a few feet into the run they start to stand up, reducing the contact patch and traction with the surface.
“You start bringing timing back as the clutches are applied,” adds Pando. “If you get the marriage right, the car will run fast.”
When to pull timing
At about 2.75 seconds into the run, if the MSD system senses the engine speed is too fast, then it starts pulling timing back.
“It’s an active system,” says Pando. “If you push hard against it, it’s going to keep pulling more timing. It could be pulled back as much as 30 degrees.”
“The rate is the most important thing,” adds Gracia. “In the early days it came on too fast for the RPM. Everything is pretty stable now.”
“We (MSD and NHRA) have strategies implemented,” continues Pando. “There’s a period between two lines a tuner could come down from the timing curve and try to shove it all in. Between those two lines the timing is limited to 15 degrees per second of timing advance. That doesn’t allow timing to come back in too fast, as most teams would want.”
In the old days before an electronic solution, Top Fuel teams used two or three MSD Six Shooter Module Selectors in series. The Six Shooter could adjust the timing six different times with the use of plug-in modules. By stacking the Six Shooters, crew chiefs could control timing up to 18 times during the run.
Countering a pedal fest
The Power Grid gives the crew chief considerable flexibility in controlling the timing curve – even when traction is lost and there’s a “pedal fest.”
“There’s a secondary timing map,” explains Pando. “We look at wide-open-throttle. If at anytime WOT comes open, that is, backing off the throttle, we’ve got the ability to yank all the timing and see if the engine can recover. Then we can gradually put timing back in or keep it out through the run.”
Whenever electronic controls are allowed, the industry is forever concerned over unauthorized invasion or tampering in addition to mid-run failure.
“The system has so much redundancy built in,” says Pando. “It’s a two-channel system. We look at each crank trigger’s signal. If you lost a crank trigger, no one would know – the driver, the crew chief, the Racepak. It’ll keep the engine lit with both mags going.”
“There’s also a lot of encryption,” continues Pando. “We invite people to try to break it. It’s not just in the unit, there’s also encryption in the interface.”
Unique to the new MSD system is a wireless tablet or laptop for the crew chiefs to input timing curves. The previous system employed a hand-held screen that had to be plugged in before the crew chief could tune the ignition. With the new system crew chiefs can adjust the timing from the race trailer.
Strengthening the top of the engine
“We had problems with manifolds coming apart,” says Gracia. “A lot of the old castings were real porous. These suppliers have taken steps to make them better.”
“You get these [supercharger] rotors going 12,000 rpm, you’ve got a Category 12 tornado going in that manifold,” says former Top Fuel driver Dave Grubnic, who will serve as crew chief for Clay Millican’s new team in 2015. “The supercharger can bleed a lot, meaning that if the rotor flexes and moves around it can bleed internally. Once we got the new billet rotors and cases, we cut down the leaks.”
Since he is starting with a new design, Grubnic is relying on previous tuning models and personal data to establish a baseline for the engine. But he admits he has concerns with the timing retard strategy.
“The challenge is going to be on the actual restriction itself and implementing that into the current setup,” says Grubnic. “We’ve got to be careful. There is a potential of retarding these engines harder at the finish line and could potentially cause it to drop a cylinder.”
Even with ignition retard, Grubnic says the engines can run on their own.
“They’re actually running on the plugs,” he notes. “The engine’s retarding but I don’t see see the engine dropping down. It’s still making power. The only logical answer is that it’s running on the plugs.”
A Top Fuel engine will burn through 16 spark plugs on every run. The required MSD Pro Mag 44 magneto produces 44 amps of primary current, which about equal to a small arc welder. But there’s so much cylinder pressure that the plugs are basically destroyed before the run is over. In fact, one study showed that a Top Fuel engine can generate over 13,000 psi peak pressure inside the cylinder. That compares to about 1,500 psi in a naturally aspirated Formula 1 engine, according to the paper.
That much pressure generates a tremendous beating on the internal components, significantly reducing their usefulness. One leading crew chief told EngineLabs that crankshafts are good for eight-to-12 runs, rods can last eight runs and pistons vary from five to ten runs. Oil rings get changed every run while the other rings are changed as needed.
For bearings, the upper rod get and lower main get changed every run while the other halves could last a few more. Camshafts last 25 laps but lifters and pushrods can see 30 or 40 runs. Valve springs have a useful life of ten runs and clutch discs sometimes last up to three runs but are always reground after every run. Finally, a cylinder block is good for 30 to 50 runs but often is outfitted with new liners after every race.
For this season, parts life expectancy may increase a little bit. The NHRA has implemented tougher oil-down rules that increase fines and points penalties, even for the first infraction. So, we’ll see how hard crew chiefs lean on the rev limiter in 2015.