Weber 48IDA Downdraft Carburetors - Imagine That!

Bob McClurg Mar 1, 2001 0 Comment(s)

Using readily available, cast-aluminum Weber IR intake manifolds as the foundation (ie: Inglese Induction Systems, Moon, Blue Thunder, Ultra for Chevrolet small-block, or Inglese or Moon intakes for big-block Chevrolet applications), the guys from Imagine Fuel Injection designed a billet-aluminum down-draft throttle body, which essentially utilizes all the outer dimensions of the Weber 48IDA. "By doing it this way, we can use the Weber intake manifolds, their induction stacks, and even their air cleaners," said Bob Ream.

And these throttle bodies can be had in two stack sizes. Imagine's low-profile, 4-inch throttle body is absolutely perfect for Bow-Ties with low hood clearance problems. On the other hand, the 5-inch unit is perfect for everything else in between.

Both throttle bodies are manufactured from CNC-machined T-6, 6061 heat-treated billet-aluminum, and feature a 2-inch (50.8mm) standard throttle bore size. On "turnkey" Imagine Fuel Injection systems, these intake manifolds are blended to the IR intake runners to achieve maximum air/fuel flow and performance. Imagine Fuel Injection's billet-bodies can also be had in either a clear bright anodized finish, or an optional polished-aluminum show finish.

Due to the location of the electronic fuel injectors the system's bell crank-type throttle linkage had to be relocated 1-inch higher (than an original 48IDA Weber setup) on the throttle body for clearance. This modification was also necessary to maintain fuel injector-to-intake valve alignment, which is so critical with throttle body-type, multi-point fuel injection systems.

What type of fuel injectors does Imagine use with these systems? "A lot of it has to do with the compression ratio of the engine, the rpm powerband intended for the engine, the cam profile, and horsepower rating. Traditionally, either a constant-pulse Lucas or Bosch-type electronic fuel injector is employed with these applications. For example, we would use a 43-pound-per- hour fuel injector for a 427/454 big-block Chevy, while we would choose perhaps a 30-pound-per-hour electronic fuel injector for a small-block."

Imagine Fuel Injection also manufactures their own CNC-machined, billet-aluminum fuel rails from raw bar stock. At this juncture, it should be noted that on turnkey Imagine IR throttle body systems the base of these injectors is threaded in order for the injector to fit more securely into the injector port opening in the Imagine throttle bodies.

Two types of fuel pumps are recommended with these systems: A standard 200-gph Bosch-type electronic fuel pump is recommended for engines producing 500 hp or less. However, when it comes to engines producing in excess of 500 ponies, Imagine recommends the Aeromotive billet-aluminum high-pressure fuel pump (rated @ 500 gph ) along with the Aeromotive fuel regulator and fuel filter.

So much for the mechanical aspects. Now for the "Star Wars" technology. Imagine suggests using either the DOS-based HalTech F9A or Electro-Motive distributor-less engine management systems, available in either DOS or Windows-based versions. The F9A is a well known unit with a 15-year track record for precision and reliability. This system is primarily used on applications featuring a conventional electronic-type distributor. It's very trouble-free, and in any type of motorsports that is the name of the game.

When it comes to high-tech, or distributorless applications, Imagine recommends the Electro Motive engine management system with the crank trigger feature. This setup utilizes either a DOS or Windows-based program.

How do you setup these
programs? "Electro Motive has a program called Wintech Wizard. You fill one page of information outlining the base perimeters of your engine. What is the Brake Specific Horsepower (BSFC)? What the rating is on the fuel injectors being used? What is the cam profile? What compression ratio, etc.?