Let me just clear up one misconception about centrifugal superchargers before this thread goes any further. You don’t get “lag” with a centrifugal supercharger. Lag is something you get with a turbo because in order for it to move air, it requires a sufficient amount of exhaust flow to accumulate pressure. The turbo actually acts as a restriction until building sufficient pressure, therefore you get the momentary “lag” as a result.
Centrifugal chargers are always moving air and there is no “lag” to speak of as it builds pressure. The results of a centrifugal blower are only less dramatic at low rpm because the smaller impeller must be spinning much faster than that of say a set of lobes or rotors in a positive displacement blower in order to move any large volume of air. Positive displacement blower are so much more noticeable down low because of the vast amounts of air they move in comparison to each revolution. This is why the rule the roost from the get go. But, this same principal also works against them as RPM increases. These lobes/rotors have a much larger surface area and overall mass than the smaller, more efficient impeller and as such create loads of unwanted heat as blower and engine rpm increase. Yes, the KB design is more efficient than your typical “roots” set up beyond 6-7psi, or so, but they’re not immune to heat as many have been lead to believe. The 1.7KB reaches peek efficiency at 14psi….which is not to say that it’s more efficient that a centrifugal, just the most efficient for it’s own design. Truth be told, the 1.7 is far less efficient than say a comparable M90 roots design below 6psi. Their differences are only really apparent beyond the 6psi level and because the 1.7KB is slightly larger, moving a larger volume of air from the get go.
A centrifugal is not as efficient from the sense that at low blower rpm, it will not move the same volume of air that a positive displacement blower will, but from a heat perspective it kills them all, hands down. Centrifugals were designed to spin hard and as are not often comparable to the KB at low boost levels. A KB will murder nearly any Centrifugal at or below 6-7psi, but you’ll notice that after that, the gap starts to close and by 10psi the centi has pulled even with the KB and by 14psi the completely turned and the KB has run out of it’s efficiency ranger (and out of breath) in the process.
This is why KB’s make excellent street blowers, but are not as hard hitting at the track. But that’s not to say that a centrifugal can’t be a great street blower as well. Because if it’s higher efficiency (the ability to move more air, while making less heat) a centrifugal can be fitted with a smaller pulley and spun harder (assuming engine internals and other supporting components permit) and as such reach peek boost levels much quicker than they would if they were fitted to spin at say a max of 7-8psi. This would put them nearly even ground with the KB down low, but remain far superior in the mid range at top end. The big boys of the sport know this and as such is why 95% of them stick with the Centrifugal design.
