They are not reducing crankcase space as more reed area space. Think of it this way, you have a very fast moving column of air coming down the intake tract. This is great and what we want, the manifold is smaller and it spills into the reed area happily with no restriction. Shaping the flow by going larger is not really helping as it’s coming out a small hose into a larger. Let’s put it this way if you put a funnel up the end of a hose and turn it on does it now cone out or does it come out in a solid stream. Either way the reed stuffers would have no effect on power at this stage but what about when the reeds shut, the colum of air is heading to a trapped space, this means it has no choice but to back up in there and increase pressure slightly. When the column stops completely it’s going to now look for the next place to go which is back up the intake manifold. Why in this great gods name would we think that’s its good idea to make it easier for that to happen. We have already paid for the air to go in one direction and now we are going to reverse it, and when the reeds open we now have to change direction again. So what does a reed stuffer do, well you can see from it’s design it simply funnels the air back so it can flow nicely up the intake manifold. If it’s not there then it has a much harder job to reverse the flow. Stuffers are a great way to reduce the torque of your engine and also throttle response as it’s waiting for the column of air to go in the right direction
