Quote Originally Posted by SFBullnose View Post
I wonder why the hose adapter was used?
Your guess is prolly as good as anyone's. The only sound reason might be if the one-way reed valve failed somehow, allowing exhaust gases to pass the valve and enter the intake via the hose. To check this with the engine running (might also need to be fully warmed up?) there should only be a pulsing vacuum sucking air into the valve via that big hose, no "blow back" pushing any gases out of the valve.

That aside, we can only speculate what the PO might have been thinking. Maybe they heard something about "smog pumps" robbing HP, but that only applies to actual belt-driven pumps injecting air into the exhaust under pressure, rather than passive air induction setups like these, and those pumps only rob like 1/2 HP or so anyway. Or maybe they mistook that secondary-air induction setup for EGR and thought they might improve performance, mileage, or reliability by disabling it.

BTW speaking of EGR, its purpose is not to "reburn residual hydrocarbons in the exhaust" as many think. Rather, EGR reduces combustion temperatures by diluting the intake charge with already-combusted inert gases from the exhaust that don't significantly affect the fuel:oxygen ratio, thereby reducing NOx emissions that are formed at higher combustion temps.