The pre-heater (heating grid as you call it) are only for starting. When the coolant is below a certain temp. (varies by engine) the turn on, kind of like glow plugs in older diesel engines. And I have never seen anything that by-passes a intercooler. The whole point of an intercooler is to reduce the intake temps. A cooler charge is a denser charge, and a denser charge makes more power. Why would you want to reduce horsepower, I don't know. Plus, a hot air temperature can lead to detonation, which will destroy an engine in short order. Furthermore, the heat developed by the pre-heater does not have enough of an effect to physically light the fuel. As the air compresses in the cyl, it creates enormous amounts of friction which raises the temperature. But it still isn't just the temperature that does it, it's only the by-product. It's not uncommon to see injector pressures in diesel engines in the 20,000 to 30,000 pound range in order to just get the fuel into the cylinder.
My point was that at certain power settings, the turbo is along for the ride, and not producing boost. If you get into a situation where your at altitude, and have to bring the power back to idle, or even a setting that there is no load on the engine you could loose the engine until a lower altitude. Diesels are run at WOT all the time, and power is simply controlled by varying the amount of fuel, and when it is injected into the cyl. There is no carb./throttle body on a diesel.
As for the weight, most diesels are now aluminum, save for the Cummins, which is still the same block(different accessories) for the last 30 years at least, and are still much heavier than a standard gas engine. The block is only half of the equation. The internals are much much heavier in order to withstand the pressures of a diesel engine. The crankshaft, rods and pistons have to be. You are going from a typical compression of around 8.5/10 to 1 with a typical gas engine up to 18+to 1 on a diesel engine. Higher compression levels equate to more pressure developed by the engine. More pressure require stronger parts. Take for example the rod bearings of a dodge 5.9 gas engine. They are .872 inches wide and 2.5 inches around. A 5.9 diesel (same displacement) are 1.57 inches wide. Diameter on the gas motor is 2.5 inches, and 2.7 on the diesel. Connecting rods are 12 inches on the diesel and 6.123 on the gas engine. The parts simply have to be bigger to keep up with the loads. Put more boost to it, and expect to have even stronger parts.
I just don't think it's the solution. It reminds me of the the Wankel engine. It's a good idea, and works well in some applications, but just isn't the fix to the problem, only a solution for some of the special applications.
BTW, the only reason Cummins had the pre-heater was to aid in cold starting to reduce the amount of smoke that came out of the engine. When I left, they had revised the programing to shut it off after a vehicle speed of 10mph was reached. It did nothing for the helping of burning of the fuel. As for where this knowledge comes from, I have the plaque somewhere(I hate looking at it), but I was Diesel/Sprinter/Viper/Prowler/Silver Certified before I left the auto industry. The only tests/classes I had left to attend were four automatic transmission classes. I'd have to say I have a good working knowledge of most things mechanical.
