i mean sequentially turbo charging. you get parallel twin turbos which is where 2 identical turbochargers function simultaneously, equally splitting the turbocharging duties for example on a straight 6 having 2 T104E's being few by 3 cylinders each running 14psi and you get sequential turbos which are set-up with one turbocharger for lower engine speeds, and a second or both turbochargers in some cases at higher engine speeds. typically the larger turbos are not as efficient at low RPMs so you lower intake pressures making them laggy as foook. while almost opposite smaller turbos spool up quickly at low RPMs with almost no lag but cant supply enough air at higher RPMs. so instead of having one ... or the other. why not have both is what im saying, like a mazda rx7 or possible (dont quote me on this as i need to look into what cars have this set up) some of the modern derv BMW's