wuzak wrote:Muniix wrote:They maybe using a crank offset. This effects the piston liner friction from the side thrust reaction force from combustion, it has other effects like a slight increase of the actual stroke length plus other powertrain dynamics that are still being studied and understood.
This piston liner friction effects the apparent inertia of the cranktrain which effects the friction and vibration and hence fuel use. Since the cylinder pressure varies so much throughout the crank/rod angle of the cycle with the boosted engines this would provide some friction reduction and saving of fuel. Their is also a slight change to the piston velocity and acceleration profiles.
Marc
Surely in a vee engine if teh offset benefits one bank it is detrimental on the other?
otoh and fwiw at this moment it seems to me .....
friction benefits are detrimental (ie self-cancel) with banks displaced for spatial reasons eg VR6/Lancia (banks outset) and 1970s Morini (inset)
(ie engines where notionally one cylinder bank is displaced in one direction and the other bank in the opposite direction)
otherwise ie if the both cylinder banks are displaced in the same direction the friction benefit is realised (do any production Vs have this ?)
though remember in a high speed engine the friction related to reciprocational inertia may exceed the friction related to the power stroke
and with our highly boosted ultra lean 'heat dilution' engine the benefits available are relatively less than with conventional engines
because the HD engine piston/rod is working unusually hard on the compression stroke the friction there is unusually high
and conventional offset (ie geometrically favourable on the power stroke) is geometrically unfavourable on the compression stroke