Guideline for C43 coolers:
Coolant flowrates > 80 l/min:No restrictor is normally needed.
Coolant flowrates < 80 l/min: A plug or a restrictor can be used. As standard, these coolers have a fully internal by-pass in the centrehole. To increase or tune the heat performance, all coolers can be equipped with a centre hole plug to force more coolant through the coolant channels.