The Pipes: The EFRA 3004 tuned pipe is based on the race winning 9901 tuned pipe but now accommodated to the new regulations.
With the new regulations the 4 bypass holes in the 2nd camber are now not legal anymore, and combined with thicker walls will give a reduction in the noise level.

Manifold choice:
The short manifold (41019) gives you engine a lot of top speed or more power in higher RPM regions, but reducing bottom-end power.
This manifold is the best choice when you race at a fast track with long sweeping corners.

While the long manifold (41005) gives your engine more power at lower RPM, and reducing power in higher RPM, which makes this manifold good for use on tracks with tight technical "stop and go" corners.
The 41020&41021 manifolds are even longer, when the 41005 manifold is still to short, you can also try these 2.

The medium long manifold (41001) is a good compromise between the short&long manifold, and is the most used.

These manifolds and pipes can also be used on 4,66cc NOVA engines.