Does more power = more efficiency?

[Oddmodman]

When you put more fuel and more air into your engine, are you creating power at the cost of mpgs or are you making it more efficient, or is there a line at which it changes? I ask because I know someone who put a 3.3BT (I realize these engines are entirely different besides fuel) into a Jeep Comanche, and he got into the low 40s in mpg by putting more and more air and fuel into it. Really what I'm asking is: by modding up my D24T, am I going to make it into more of a fuel guzzler or will it actually get better mileage?

[v8volvo]

All depends on what kind of mods you do and how you drive it. In general one of the most compelling things about diesels is that modifying for increased power does not necessarily decrease efficiency, and actually may increase it. With a diesel, since it's an air-rich cycle where as long as oxygen supply is sufficient, output is controlled directly by injected fuel quantity, changing the *maximum* fuel and air conditions has no impact on the amount of fuel required to produce a given amt of power under routine conditions. If you modify the motor to run more max fuel and boost and then change your driving habits (perhaps involuntarily :D) to use that additional fuel margin frequently, then there will be a drop in mileage, but if you drive it the same way, there should be no change at all. In fact, frequently ECM tunes on computer-controlled motors, e.g. TDI, will result in an increase in mileage during normal driving, if they call for additional boost under light-load conditions.

Many modifications usable on a D24T in principle can improve MPG, from free-flowing exhaust to intercooling, increased turbo pressures, etc. Any mod that you do that aims to raise output by increasing the engine's thermal performance and reducing pumping losses rather than just dumping in more fuel, e.g. harnessing more waste heat from the exhaust, and/or creating a denser intake air charge, and/or freeing up exhaust and intake airflow, has the potential to increase efficiency as well as power.

I suppose there is a line that can be crossed where the rules change, and that line probably lies where your modifications begin to be of the extreme type that detrimentally affect the engine's operation during light-load situations. (Examples might be lowering compression ratio, using huge injectors, etc). But by and large one of the most appealing things about turning up a diesel is not having to pay any MPG penalty for your fun, as long as you can keep it within the bounds of reason. :)

[Oddmodman]

Cool cool. I've heard that diesel is throttled by fuel whereas gassers are throttled by air so: do you gain any effect by increasing boost without increasing fuel? What about WMI? (Particularly curious about this since I live in Alaska and would need a correct ratio so the mixture doesn't freeze)

What do you think of propane injection?(http://www.ferrellautogas.com/Resource_/PageResource/Vehicles/Bi-Fuel/Learn_About_Propane-Diesel-Injection.pdf)

[745 TurboGreasel]

Cool cool. I've heard that diesel is throttled by fuel whereas gassers are throttled by air so: do you gain any effect by increasing boost without increasing fuel?Either smoke clears, or EGTs go up, depending if you were overfueling to start with.