A cheaper alternative to the Schrick manifold is to fit an M50 intake, but you need an adaptor. I think another US firm was marketing it together with adaptor for USD700 odd...you can't extrudehone or polish the M50 intake though...
Instead of playing with manifolds, go the whole hog...About USD2.6k.
The BMP design multi-throttle intake system is designed for maximum intake flow. This system upgrades the flow capacity of the U.S. M3 to that of its European counterpart. Rather than a single 100mm throttle body bolted to a plastic intake manifold, the BMP design multi-throttle body system features six individual 45 mm throttle plates. One for each cylinder. The manifolds and throttle bodies are high quality aluminum castings. The choice of aluminum versus composite permits further porting and polishing for additional performance gains. These pieces are not transplants from another model car. Over two years in development, this system is specifically designed for the M50 or M52 engines. For ordering please specify exact year, model, and E.C.U. number. Not for vehicles with traction control or cruise control. Not smog legal, for racing purposes only. May never be used on a California highway. Kit includes: High quality aluminum manifold, 45mm throttle bodies, cast aluminum intake plenum, custom intake boot, custom linkage assembly, connecting hoses and clamps. We recommend using the Split Second Air Fuel Ratio Calibrator and Mass Air Conversion. Adjustable fuel mixture or custom programming required.
k:
