Whilst it is true that it will increase volume, there is also more area to fill so it'smost likely effect is to shift the torque curve around, lower down.
The reason why the engine runs leaner on some pots is not down to the plenum design so much as the WATER PUMP POSITION!!, the front pot(1) is getting cooler water than the back, hecnce why the gasket normally lets go of the water jacket at the back, bad design cooling system, done with "parts bin" stuff , perfect for the power it had as N/A pinto but a bit weedy for ton up terry!!
It is always advisable to put any injectors that are slightly lower flow than the others at the front pot.

tabetha