Currently using OpenCV 2.4.0's C apis, will C apis of OpenCV 2.1 and below be faster?

[Shishir]

I'm using OpenCV 2.4.0's C apis for real-time face detection in a video stream in Android 2.3.3, and I find that the cvHaarDetectObjects call is not fast enough for my application. Because of this the video output is very laggy. I need to process around 7 frames per second, which is at max 20 milliseconds for face detection. Will the C apis of older version of OpenCV be faster than the current version? If the C apis of the older version are not faster, is there any other way to make the face detection work faster? Also, the video resolution i plan to use is 176*144 pixels.

[Andrey Pavlenko]

I wouldn't say that the legacy C API in OpenCV is faster than the modern C++ one: 

both C and C++ functions usually call the same internal implementation that is sometimes in C and sometimes in C++ (yes, some C functions are wrappers to C++ ones!).

And I also wouldn't expect older OpenCV versions to be faster than later ones, it's more chances that newer version is faster due to more effective implementation or newer algo behind...