I can assure you that naturally aspirated car engines making 100 bhp per litre are rare and use variable cam timing strategies and/or variable volume intakes to make them tractable at lower RPM due to the very high state of tune, most of them make peak power at close to 8000 rpm, they use ITB's and are VERY expensive to build due to needing completely forged internals.
I've personally seen a 1.6 litre Peugeot TU5JP4 making over 200bhp on an engine Dyno at 8800 rpm, however such an engine would be unusable in a road car since it would stall at every red traffic light.
We're talking about engines from Porsche, Honda, Ferrari, BMW etc.
I repeat, there is no way to get a lowly AUB lump to such a state of tune without going all in on head mods, cams, ITB's and a custom exhaust manifold and system, you'd also need forged Conrods and pistons since the stock items would not last long at 7500 rpm, which is what you'll need to be spinning to make 150 bhp.
Put crudely, a 50% increase in power requires the engine to pump 50% more air, so that 1.4 will need to pump like a 2.1.
This isn't rocket science but it is expensive and tuning companies tend to exaggerate to make sales.