The NHRA’s Top Alcohol Dragster division is an interesting one, because you get to see both supercharged and injected nitromethane combinations square off on the same playground. The two combinations share only minor similarities, and the nitro-burning machines are a whole different beast from their blown counterparts. Will Smith and Dave Hirata know this as well as anyone, and they shared with us what goes into campaigning an A/Fuel dragster.
The A/Fuel dragster runs on nitromethane, but that doesn’t mean it’s an exact copy of a Top Fuel dragster. These cars don’t have a supercharger to help stuff oxygen into the engine and they’re not quite as long. Now, they do have a similar driveline, meaning there’s no transmission, and a multi-disc clutch system is used to apply horsepower to the racing surface.
Smith provides some more details about the wild engines that power A/Fuel dragsters.
“The injected nitro engines are finicky…any time you deal with nitro it’s a controlled bomb. With an A/Fuel nitro car, we of course can’t have a blower and we’re crossing the finish line at 6,400-6,500 rpm. The manifolds have direct-port nozzles in them for fueling and there are fuel rails in the cylinder heads that spray fuel directly into the cylinder. I come from big-block nitrous racing and the way these engines behave is very close to one of those. ”
Smith is more than just a wheelman for Hirata Motorsports, he’s elbows deep in between rounds assisting with the car. That has given Smith a vast understanding of how the nitro-powered machine works — it also allows him to make better decisions as a driver.
Everyone on the team has a job to do and they know what needs to be done prior to each run to ensure things go as planned. Smith will be the first one to tell you how involved it is to make a pass in one of these cars. Before a run, Smith puts on his safety gear with the help of his crewmember and friend, Brian. This is a two-person job and that includes strapping Smith into the car.
“When we’re at the ready line there will be someone checking tire pressure, another crew member is adjusting the wheelie bar height, and there are other final adjustments being made. Dave is making a final check of the track and showing me where I’ll need to do the burnout and line up. While all of that is going on, someone is getting the methanol bottle we start the car with attached and the starter is being put on the front of the engine,” Smith says.
As Smith mentioned, the A/Fuel car is started up using methanol; as the engine heats up the team makes a few final checks before it’s switched over to nitro. Once the nitromethane is flowing through the cylinders, Hirata will have Will bring a fuel pump online so the fuel pressure can be set — this is a critical step, and the fuel pressure must be consistent for each run. After that, the idle is set and Smith will roll forward to do his burnout. The burnout is another process that must remain consistent so it doesn’t change anything with the clutch — just like a Top Fuel dragster.
Smith backs the dragster up after the burnout and follows Hirata’s directions to make sure it’s in the groove. When Smith has returned the car to the starting line the team makes some final checks, Hirata will motion for the car to be pulled forward into the pre-stage beam.
“My favorite part of the run is when I get to turn the fuel pump all the way on, let the clutch out, hear it tug the engine down, and inch into the staging beams with the handbrake. To me, that’s just the coolest feeling ever. You stomp on the loud pedal and then I do my job as a driver. Hopefully, everything goes as planned, but as a driver you have to be ready for everything, from tire shake to a wheelstand,” Smith says.
At the top end, Smith has a few tasks to complete, like rolling up the chutes, turning the air bottles off, and resetting the timing on the engine. The crew will make their way down to pick up Smith and the dragster so it can be scaled, go through fuel check, and return to the pits for service.
“After every run, we bring the car back, run a leak down to see where we’re at on the tune-up, and determine if we hurt anything. We check the plugs to see what they have to say about the tune. We put rod bearings in the engine after every pass; nitro is very hard on parts and it’s basically trying to push the crank out of the bottom of the engine. Because of that force, we have to check the lower main bearings to make sure everything is okay — generally, the upper main bearings don’t wear that much. The engine puts a lot of force on the upper rod bearings so we replace those every run,” Smith states.
An A/Fuel dragster uses a centrifugal-style clutch, much like the one you would see in a snowmobile. The clutch spins and begins to apply what’s known as plate load that pushes the discs together, allowing the dragster to move. Hirata is the clutch man for the dragster and he spends hours grinding disks to get the right thickness and performing Rockwell tests to determine disc hardness. The floaters are also ground down as needed and receive a thickness check. When all of this is done, Hirata assembles the clutch packs so they have the same thickness, that way he doesn’t have to adjust the stands the clutch rests on.
“When the car is going down the track the clutch is spinning. We have levers that get weight added to them and as the clutch spins, the levers pivot due to centrifugal force, and as they pivot it squeezes the clutch tighter. It’s totally a mechanical process…we don’t have anything to activate when things happen inside the clutch. Now, a Top Fuel car has ways to adjust clutch plate load, but we don’t have any control or means to manipulate it. This setup is very primitive, Hirata says.
Clutch maintenance never ends on an A/Fuel dragster. Hirata will have hours invested in grinding on discs and floaters at home. The clutch is the most important part of making sure the dragster gets down the track. Each clutch pack must be precisely set up and adjusted based on track and atmospheric conditions to make sure power is applied correctly.
“In between rounds I take the bellhousing off, pull everything out, and take the pressure plate to the grinder to just touch it to make sure it’s not damaged. The pack will get hung out to cool and we torque the flywheel. After the bottom end guys are done and the clutch is cool I’ll start my service again. I’ll install the new pack, put the pressure plate on, set the air gap, and finish assembly,” Hirata explains.
A/Fuel dragsters are one of the more unique machines in drag racing…nevermind they are the quickest and fastest naturally-aspirated vehicles on the planet. Now you know what goes into making these cars run in the low 5-second range at over 270 mph at tracks across the country.