Getting air into your engine seems simple enough, but there’s a delicate balance between airflow and filtration. You could just let unfiltered air into your engine like a top fuel dragster—if you don’t mind tearing down your engine after every mile like a top fuel dragster. At the other end of the spectrum you could design some complex, Rube Goldberg contraption that would filter out all particulates but choke your engine in the process. We had been running a simple oiled cotton filter on the top of the 460 engine in our 1977 Ford F-150, but when we saw dust and silt in the throttle body after a recent trip to the desert we knew that we needed better filtration.
Chris Sparks at Rock Hound Off Road suggested we look into the cannister-style filters used on tractors and other heavy equipment. A look through the Donaldson catalog revealed that we had an overwhelming number of options, with prices ranging from a few hundred dollars to several thousand. We were discouraged, but Sparks wasn’t. He simply sourced a common Donaldson filter (PN B085011) and built a custom housing for it.
The cavernous engine bay of our old truck made it easy to plumb the cannister to the MSD throttle body fuel injection on top of the engine using off-the-shelf parts from Summit Racing Equipment that cost us under $250. With all the parts we needed in hand, it took Sparks and Alex Anderson less than a day to fabricate the cannister and plumb the intake, providing us with plenty of clean air no matter what conditions our do-it-all truck finds itself in.
We sourced a bunch of 4-inch pieces of aluminum tubing and silicone couplers from Summit Racing Equipment to build the intake. Rock Hound Off Road then supplemented these parts with some custom fabrication for our specific application.
We previously just had a circular K&N filter on top of the engine. This would be a fine choice for a hot rod and worked well on the streets and when rockcrawling, but in the mud and silt we needed better filtration.
Spectre makes this affordable polished aluminum intake plenum to fit on the top of most standard carburetors, or in our case our MSD Atomic EFI. After test-fitting the plenum we trimmed the threaded rod that was previously used for our 6-inch-tall air filter.
Chris Sparks TIG-welded a custom aluminum cannister for our engine that accepts a common Donaldson filter. The only tricky part is changing the filter, since the entire cannister needs to be removed and the top unbolted, but fortunately this is not something we have to do very often.
Sparks cut and welded blades inside the cannister to provide a spin effect that allows larger, heavier dirt and sand to fall to the bottom of the intake rather than enter the engine. These blades are the reason the diameter of the cannister needs to be so large.
The Donaldson filter we used is 8 1/2 inches across and 11 long. It’s popular with Cummins owners, who affectionately refer to it as the Big Honkin Air Filter (BHAF). Replacement filters are easy to source and only cost about $40.
The intake cannister takes up a lot of real estate under the hood, but since Rock Hound relocated our batteries to the bed of the truck (“Charged Up,” Apr. 2019; bit.ly/2C57rjw) we have plenty of room to work with. This is one advantage of working on an older truck with minimal electronics and accessories.
The old lead acid battery gave us a head start on drilling a hole through the inner fender to route in the intake to the canister. Fortunately the aluminum intake is much lighter than a battery, because there isn’t much metal left in the inner fender.
The 4-inch silicone elbow takes up a lot of space, but it’s far enough forward in the wheelwell that the tire doesn’t contact it at full stuff. And since the intake is not pressurized like it would be with forced induction, we just used normal hose clamps.
Air is fed through the grille next to the headlight into the intake canister. This location should be plenty high for most mud pits and water crossings—and even if water does enter the tubing it still needs to make its way to the canister and past the filter before it finds its way into the engine.
The canister made slight contact with the brace inside the hood of our truck, requiring slight trimming to maintain clearance and keep the hood from vibrating and buzzing.
We perceived no loss in power, suggesting that the intake is plenty big to feed our 460 engine. Now the only thing left to do is customize the giant canister. R2-D2? Beer can? Let us know how you would paint it if this were your truck!