EFI retrofits are pretty common nowadays.

But do you know what isn’t?

Swapping out your carburetor for a set of velocity stacks and eight 50mm Weber IDA-style CNC-machined aluminum throttle bodies.

May we introduce you to the Speedmaster Downdraft EFI Stack Intake Manifold.

eight individual velocity stacks on a 383 stroker small block chevy v8 engine within a custom 1971 chevy corvette stingray
We spotted this Speedmaster setup on a 383 SBC Stroker tucked inside a C3 Stingray restomod. Read more about that wicked-cool Corvette here. (Image/OnAllCylinders)

Each throttle body houses a fuel injector to create a multi-point EFI setup that delivers superior idle characteristics and throttle response. The kit comes with fuel rails that feature a built-in fuel pressure regulator, but Speedmaster doesn’t include the injectors with its manifolds—so you can pick the injector size that best fits your performance goals.

(Image/Summit Racing)

You’ll also get a linkage set that incorporates the throttle stops, idle controls, lever arms, and joiner/balancer in one unit. It’s got a single screw adjuster that lets you calibrate front-to-rear throttle shafts. The bell crank has a fully indexable eccentric cable pulley for good low-speed drivability while maintaining full throttle geometry.

testing adjustable intake runner velocity stacks o a generation 3 mopar hemi engine on dyno
Our pal Richard Holdener experimented with a Speedmaster Downdraft EFI Stack Intake Manifold on a 5.7L/6.1L third-gen. Hemi motor. Read about his findings here. (Image/Richard Holdener)

The best news is that Speedmaster makes these systems for a whole bunch of engine applications. Check them all out below:

  • GM LS
  • Gen 1 Small Block Chevy
  • Ford 390-428 FE
  • Ford 289-302
  • Ford 351W
  • Ford 351C/Boss 302
  • Ford 460
  • Mopar 6.1L Gen III Hemi
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