Originally Posted by
Garage19
The plenum is tappered to create equal air flow into each cylinder. The problem with a straight shape is that air has a momentum as it enters the plenum and this will tend to mean it bypasses the first cylinder and favours the later cylinders.
Seeing as the original Swedish plenum is tapered then the cheaper copies should be too if the product is to be sold as a Swedish copy plenum. I buy my Swedish plenums from Sweden as I don't like copies. My original comment was based on a tapered version.