I found the 2.4l manifold seems to shift the power band higher in the rev range, to the point where it still feels like its getting stronger as you hit the rev limit, However, I have a set of piper cams and the profile of them is designed to give that effect so how much was directly atributable to the manifold alone I cant say. I also considered the 2.4l manifold to reduce the typical 2.2 flatspot around 3,500 rpm that all the 2.2's experiance. However, the 2.4 manifold did suffer from a lack of low end torque, again, perhaps partly because of the cams, but it was very noticable after changing the manifold alone. Having said this, Its hard to say weather the 2.4l manifold ever really did provide a good power gain. It could well have been that the loss of low down torqe was to such an extent that when the engine finaly did come on cam, its percived as a lot stronger than before, when really it isnt.
I had my 2.4l manifold fitted for about 6 months and did a long 2000 mile trip across germany and the nurbugring, as well as the mountinous black forest region. I removed it because I had fueling issues. I was melting the center exhaust silencers and thats usually an indication of to much heat, caused by either running lean or on the other side of the scale, too rich and throwing fuel into the exhaust. In the end I think it was more an issue of the exhaust design and since I removed the manifold and had the system completely rebuilt in 2.5" the next day, so i'll never really knowwhich was the problem. What i can tell you is that having re-fitted the 2.2 manifold, the car was an absolute pleasure to drive again. The low end torque had returned and I didnt feel it was any slower when I spanked her a little. It sounded better, the fuel economy improved slightly and driving round town was no longer hard work.
I have no doubt that the 2.4l maifold has the capacity to flow more air than the 2.2. but It wasnt principly designed for the 2.2 capacity and so the runner lenghts and diameter cost you some low end power, but if your building a screamer, with cams and a ported head then the extra flow will probably see you a gain over the standard manifold. I guess it depends how you want to go.
There was some good comparisons at courntneys last year when we had our RR event. There was two of us with almost identical mods, except I had a 2.4 manifold over and above the other chap. I think I beat him by 2 or 3 bhp......its not an exact science, and he had a remap where I didnt at the time, but you can see its close.
