The Melling Hellcat was just a project made by numpties who cant quite work out that big cars dont go fast. It has the aerodynamics of a bloody brick and would be very lucky if it reached 200mph to be perfectly honest. Plus, with its "quad turbo, 1175bhp engine", it'll never do that because there wont be near enough any traction. I've just spent my morning reading about a car being built in NZ - around 900bhp pulling about 1500ft/lb torque - that thing spins its wheels in fourth, so unless Melling have some absolute mega gear ratios or some bloody good traction system, there will never be enough space to get to 300.
ETA : Here's Melling's predictions of vmax -
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Now, lets take the Veyron for instance. On an engine dyno that will pull about 1300bhp, but road factors limit that to 1001. Now if VW/Bugatti put absolutely billions into that project (if you work it out - development costs / number of cars, they lose about £4-5million on each) , how can some company that hardly anyone has heard of do it. I'm not trying to knock them, but it's an impossible task.