Originally Posted by Nick62095
This is very helpful, thank you, and not only do I have to fix it but all the better it gives me an excuse to go aftermarket ;) I will have to give this a try this weekend.
Eh, I wouldn't purchase a Cosworth manifold for $600 or the Chinese knockoff for $400 off Ebay without purchasing some other things also. If you just put the aftermarket manifold on the car- you'll lose power. It's the same thing if you remove the tumble flaps which is another method of fixing the sound. If you'll search for tumble flaps in the Duratec Performance forum
, you'll find a thread where someone removed the flaps, and then was unimpressed with the resulting performance. That's what I was referring to about managing air flow volume vs velocity. High velocity air flow at low rpm produces more torque in an engine, but high velocity typically means small plenums. When the engine starts turning higher rpms, it needs more air or power will suffer. That's when higher volume of air flow is needed. The velocity will be there because the engine is requiring so much air. The tumble flaps help keep velocity at as even of a level as possible.
That aftermarket manifold has much bigger plenums than the factory manifold to begin with- and no tumble flaps. It is also designed specifically for the 2.3L engine- not the 2.0. To make it work as right as possible, you'll need high lift camshafts, different valve springs, a flash programmer, and a tune for your car. Other things that would help would be a free flowing exhaust system and a header. If you simply put a Cosworth manifold on your engine, then you'll end up losing power because your air velocity will be low, and you won't benefit from higher flow at high rpm because your camshaft won't have the lift to produce a need for higher flow.