Yeah but...
Is that really a benefit?
Most missions carried out by commerical helicopters require a flight time of less than 3hrs (@ cruise power). If we go to jet fuel then the cost of fuel becomes a relatively unimportant part of the operating cost, so we are back to considering the weight issue as the design driver.
Considering the total weight of the engine system as the weight of engine+fuel then for an example helicopter requiring 200hp.
SMA SR305-230 Diesel
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Engine=225kg
3hrs Fuel = (200hp*0.36lb/hp-hr*3hrs)/2.2lb/kg = 98kg
Total = 323kg
SavioPower Turbine
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Engine=17kg
3hrs Fuel = (200hp*0.5lb/hp-hr*3hrs)/2.2lb/kg = 136kg
Total = 153kg
Therefore the turbine unit, despite using more fuel offers a 170kg payload advantage for a realistic mission which is the difference between 2-seats or 4-seats plus bags in your helicopter for the same power and MTOW. (Or 2-seats with high performance and a crash worthy fuselage depending on how you wish to spend your additional weight budget)
This is why I keep hammering on about diesel engines and helicopters. I love diesel engines, my car has a diesel engine - but I wouldn't dream of putting one in a helicopter because they are not the right engine for the job. Gravy, you correctly point out that automotive diesels are producing BSFC's of 200g/kW-hr. Sadly they wouldn't be able to produce this at peak output and thats how you would have to use them to get a helicopter off the ground.
Hope this helps
CRAN