Chevy GM LS3 Dual Plane 4150 MID-AIR™ MidRise Aluminum Intake Manifold [Satin] it has a square bore

it has a square bore carb flange instead of a spread bore

but with several important modifications

along with optimized winding

The quality of these throttle bodies are better than others available today

The OEM replacements get harder to find as time goes on

Chevy GM LS3 Dual Plane 4150 MID-AIR™ MidRise Aluminum Intake Manifold [Satin] it has a square boreThe Speedmaster MidRise Air design features the identical plenum and runner design as the normal MidRise. The main difference is that there is an open area under the plenum chamber. This feature is sometimes called an air gap design. The air flowing under the plenum provides a cooler charge for the incoming air with less heat transfer from the engine. This cooler air charge provides additional power and torque.