How to Run Downdraft Carburetors on a 4.6 Engine - Old-School Modular

If the phrase old-school modular seems like an oxymoron (much the same way the phrase jumbo shrimp doesnt really make any sense), then let us explain.

When put to the test, just about anyone can recall what the engine of a mid-60s Ford Cobra used for racing looked like. Typically topped with a pair of four-barrel carbs or, even better, a set of four Weber 48 IDA downdraft carbs, the look of the engine was only surpassed by its legendary performance.

The factory 60s-era engines for the street were simple and looked great but, as government regulation and emission controls began to infiltrate the automakers design centers, manufacturers began to cover up their engines and, in doing so, effectively removed the soul of the car. By the 90s it was almost to the point where a guy couldnt modify any of the newer engines for performance or lookswell, almost.

Jamie Johnson, a 38-year-old second-generation hot rodder, recently showed us a different way to think about one of Fords modular motors. If his name is familiar, then you might remember the copper-colored modified he built a few years back at Hot Rod Haven, his shop based in Albuquerque, New Mexico. Or maybe the maroon 32 three-window with the reverse Halibrands on the cover of our July 09 issue. Or maybe the blue Model A highboy on the June 10 cover. You get the ideaJamies got a good eye.

But hes also recently turned his attention to some of newer powerplants Ford has produced and, in particular, modular motors. Since the early 90s, Ford made several versions of their modular motor (from 281-inch V-8s up to 413-inch V-10s), which also include the popular 302-inch, 5.0L Coyote engines youve recently seen popping up in rodders engine bays.

But, before the 5.0L Coyote, there was the 4.6L 281. It first came in the 91 Lincoln Town Cars in a two-valve per cylinder, single-overhead cam (SOHC) layout but, through the years, a 24-valve variant was also available as was a 32/four-valve design. The 24-valve SOHC was found in some Fords between 2005 and 2010, but its the four-valve engines Jamie was interested in.

The four-valve 4.6-liter is a four-cam, dual-overhead cam (DOHC) design first used in the 93 Lincoln Mark VIII, and most of the motors used an aluminum block with six-bolt mains. Late-90s Lincolns (both the Mark VIII and Continental), the 03-04 Mustang Mach 1, the 03-04 Mercury Marauder, and even the 03-05 Lincoln Aviator all sported this engine.

The early versions of the 4.6 4 V (from 1993 to 1998) utilized two intake ports per cylinder but that design was revised in 1999 so there would be one intake feeding two valves. The change helped boost performance and, in the 99 to 01 Ford Mustang SVT Cobra, the engine produced 320 hp and 317 lb-ft of torquenot bad for 281 inches. But the supercharged, iron-block version found in the 03-04 SVT Cobra maxed out at 390 hp!

Though installing one of these slicked-up engines in a hot rod has been done before, most folks have left the factory injection and wiring system alone (possibly for fear of cutting one wrong wire and making it a paperweight!). But thats where Jamie comes back into the picture. He recently showed us how he converts the 99-and-newer 4.6L 32-valve injected motor into a powerplant topped with your choice of old-school carbureted induction. Thats right, we said carbureted, as in a single or dual four-barrel setup or, if you really want to dress to impress, a four 48 IDA Inglese carb system that looks like it was taken out of one of those old Cobras.

The simple fix was creating an adapter that allows you to run the old Ford 289/302 intake manifolds (and thereby allowing any type of old-school induction) on the modular block, and following it up with an Edelbrock timing control box (made by MSD) that picks up MAP, crank, and cam positions. The stock alternator gets moved to a new location and a replacement idler arm goes in its old location. And, with a one-piece remote oil filter adaptor and water outlet housing change, you have everything you need to run downdraft carburetors on a 4.6.

But sliding one of these 4.6 motors into your early Ford (i.e. 32 or 34) might be a chore: theyre 29.25 inches wide at the outside edge of the valve covers. Compare that to roughly 19 inches for a 302 Ford, 20.5 inches for a 351W Ford, and 22 inches for a Chevy 350. By comparison, the new Ford Coyote measures 28.5 inches while a vintage Chrysler 354 Hemi comes in a fraction larger than a 4.6 at 30 inches (and nowhere near as heavy by about 200 pounds!).

But, as we said before, Jamie has figured out how to do it, and has done six of these installs already: everything from a 40 Ford coupe to a 65 Mustang, with some having a five-speed trans bolted up and some with Fords AOD transmission behind it. He indicates the powerband generated with these engines is fantastic (some street 4.6L engines with ported heads, different cams, and twin turbos can produce over 1,000 hp!) and, what might be the ultimate deal maker: no problems with the engines since their installation.

STREET RODDER wanted to get more familiar with the 4.6 and how Jamie got an old-school modular motor to work; we thank Hot Rod Haven for letting us stop by to check it out.

Though hot rodders like performance, there are other constraints to consider when installing an engine. Both weight and physical size are two other points to consider, so STREET RODDER decided to illustrate the physical size difference between three engines: the 4.6 Ford, the 351W Ford, and the 350 Chevrolet. For this comparison, the height is measured from the bottom of the oil pan to the air filters mounting surface. The width is measured from the outside edge of each valve cover, and the length is from the face of the bellhousing to the water pump pulley. All measurements are approximate.

The stock 4.6 injection system, from the airbox to the injector manifold, is removed before the new manifold adaptor plate is attached.

The 32-valve 4.6 looks impressive with a full set of Inglese 48 IDAs up top, but equally as menacing with a pair of Edelbrock four-barrel carbs. A single carb setup just looks like something is missing (like another carb!).

Back in 2005, Del Packwoods 41 pickup was the first 4.6 conversion Hot Rod Haven did.

Jim Johnson (Jamies dad) has owned this 40 Ford DeLuxe since 1983. In 2011 he and Jamie installed a 4.6 and a five-speed out of an 03 Mach 1 Mustang, and reports no trouble driving it wherever he wants to go (including a recent trip to Bonneville).