8. Current trends

8.1 Effect of a displacement change

If you increase the stroke of a car engine without modifying its intake or timing, you'll generally see a gain in torque at low and medium engine speeds, without maximum power increasing in the same ratio as displacement. The reason for this is that permeability has not increased in line with displacement, whereas air flow should be greater, thus increasing pressure losses and limiting refuelling at high revs.

At intermediate engine speeds, filling variations will be small as relative permeability varies: the mass of fresh air will increase in proportion to engine displacement.

At low revs, the fuel tank will be fuller, so torque will increase faster than displacement.

This will...