NONO
Do not modify the standard system. It works perfectly fine as Volvo intended.
Do however service the 47 year old components of the engine.
They are old, and so is pretty much everything else to do with the car.
For starters, change all of the fluids and filters. Change the spark plugs. Replace anything which you feel is more than 10 years old.
After doing the above, you would be suprised how much more powerful the engine will feel