Last week we announced that BangShift.com will deliver a weekly tech series that looks inside an NHRA A/Fuel, nitro-burning, 5-second dragster, and the first installment included some basics of what these cars are all about. This second part is a short installment, taking a look at the intake manifold that sits atop the injected nitro Hemi that powers the Veale and Brown A/Fueler that Scott Darrow and Ethan Brown tune.
Long story short, this is mechanical porn.
This intake manifold was built by Automan technologies of Auburn, California. Bob Ottow builds these babies by hand and they are not exactly budget minded. The team acquired this piece used and sent it back to Bob so it could be updated, but if you are hankering for a brand new one, Scott says that you should expect to pay about $13,000 and expect to wait about six months to see it. Good work takes time.
The one is outfitted with “all the bells and whistles” according to Darrow. Those bells and whistles include all those fuel nozzles, valves, plumbing and nice tig- welded aluminum fabrication.
Look at the actual runners of the intake and you’ll see a fuel nozzle at the base. Make sure to look to the inside of each runner as well. You’ll see yet another nozzle there ready to dump fuel. These are supplemented by the nozzles that are plumbed into the cylinder heads (more on those next time) that finish off the near-fire-hose capability of this system.
The fuel pressure when the car is idling is about 10 psi at the barrel valve and distribution block. At this point, the nozzles in the heads have nothing going through them as they have springs and check balls in them that do not allow any flow until 38 psi. Once the driver puts the fuel pump on the “high side” and full flow is happening, the pressure rockets up to 120 psi at 2,700 rpm, a ballpark normal idle speed. The pumps are put on the high side by the driver moving a lever. This is done after the burnout, normally just before the car is to approach the staging beams.
You’ll notice what appears to be a gaping hole in the front of the intake (see photo below). This actually an air bleed that Scott can use to control the idle speed of the car. In the past this has been done by removing plugs in the manifold to allow more air in, leaning the mix and raising the idle. It was an imprecise science, whereas this valve, Darrow claims, can get him exactly where he wants the car to be idling. As unbelievable as it sounds, a tiny thing like idle speed can make or break a lap in one of these insanely powerful and ultimately temperamental machines.