HOW POWER PULSE REDUCES TURBO LAG

Lag is an issue in all turbocharged engines, because it takes time for exhaust gases to spin up the turbo before it can really start pushing air at force into the inlet manifold. There are a few ways to try to get around it: fitting a small and big turbo, where the smaller one has less inertia so spins more quickly; or give a turbo two scrolls to try and achieve the same thing; or electrically boost it (as in the Audi SQ7); or do some clever things with valves to try and bypass the turbo or keep it spinning.

Volvo’s Power Pulse system on the D5 diesel engine (which already has two turbos, one small, one large), is another system again. Under marginal loads, the engine compresses a 2.0-litre chamber with fresh air. And should you be at low revs and need to get the turbo spinning, that chamber exhales the air quickly into the turbo, getting it spinning more quickly than if you just waited for the exhaust gases to do it. It’s a cheap, practical and reasonably effective system.