i know on carb engines, spacers allow more room for the fuel and air to mix, its also said to keep the engine running at higher rpms. not sure what they're expected to do on fuel injected engines.

 

This is because BOTH AIR & FUEL pass through the spacer... This additional Plenum space helps atomize the AFR by giving it more time to mix... On a MULTI PORT FUEL INJECTED ENGINE...the only thing that passes through the spacer is AIR... NOTHING else passes through the spacer. The Fuel is not introduced until the end of each intake runner... That means the fuel is introduced over 20" AFTER the spacer... So the spacer literally has ZERO effect on a MULTI PORT FUEL INJECTED ENGINE!

SPEED SAFE, AIR RAM