Question: We want to race with a Roots blower. There are standard Roots blower bottom openings, and there are smaller ones. Some with a small pie shape towards the front. What is the influence from the size of blower output opening
Answer: A smaller bottom opening reduces reversion into the blower from the manifold boost and makes it more efficient. That is discussed further in Fuel Injection Racing Secrets. Regarding the opening size in comparison to the port size that is being fed by the manifold boost in the blower manifold, a major contributor to engine efficiency is reduction of intake pumping losses. Pumping losses occur from any change in direction and change in speed of the air & fuel; fuel going to the engine; or a change in cross sectional area of the intake pathway to the engine. A Formula one engine has the intake port biggest at the inlet and gradually getting smaller to the valve seat and as straight as possible. In contrast, the Roots blown combinations that we race are a real mess from that standpoint. Add to that the fuel flinging from the rotors and it becomes a massive trial and error task. A discussion of the pumping issue and intake design is in 5000 Horsepower on Methanol. Pumping loss discussions and info are one of the biggest shortcomings in all of the information resources we have seen and, I believe, one of the areas of improvement for the greatest gain. That is why we provide some of that info in our books. It is more often the key to why one engine combo makes more power than another.