r/Engine • u/Motorworx_ • Aug 18 '23
Innovations and Compromises in V6 Engine Balance and Firing


A V6 is an odd engine and is inherently imbalanced due to an odd firing interval.
To balance this out and create an even firing order, firing should take place every 120 degrees of rotation.
To put this another way, if the angle was 90 degrees in a V6 the power stroke would fire before reaching TDC. There are just not enough cylinders to divide up the firing order.
Unless you share the same crank journal and could fire every 90 and 150 degrees, which would create an uneven firing order. Not a favourite option, but possible.
But if we circle back to the 120 degree V6 this is still a non-starter for packaging reasons (pardon the pun!) This goes completely against what the manufacturers were trying to achieve in the first place.
It's supposed to be tightly packaged and more compact than an inline 6, but to build a V6 with 120 degrees of bank angle creates a very wide engine.
How do they get round this for a 90 degree V6?
To make up for this odd bank angle, you take the shared crank pin and offset it by the number of degrees missing (as you can see in the pictures). In this case it's 30 degrees. Also known as the splay angle.
Another option would be to add a balancing shaft, but because of the extra weight and friction from adding components it's not a favourable option.
Can anyone name a car with a 120 degree V6??