Question on blower cams

[Fox466]

I was looking at a set of heads in the classifieds and saw that in the description the cams are best for screw type blowers, not so much for centrifugal or turbos.

Why? Isn't boost boost? This makes no sense to me!

[Captain Crawfish]

roots vs centri are actually pretty different. each blower has its own characteristics and the specs on the cams are matched for that. Roots type blower cams will typically have wide LSA's, little overlap, and big duration numbers to allow more time to pack charge into the cylinder on intake and to blow down and pump out exhaust. Centrifugal blower cams seem to lean towards the specs seen on a NA cam because these blowers are not positive displacement so they dont move much air until they are spun to a higher rpm. If you cam it like a roots blower cam you may loose so much cylinder pressure at low rpm's due to reversion that the engine would be a total dog.