Turbo charging off topic

Hello,
I am posting here because this is Somewhat off topic.
I got into a debate of sorts on another site , not mopar related, and i asked if a person were to build two identical cars, same engine, same driving style, etc, Only difference between the cars was one is turbocharged, and the other normally aspirated (fuel injected) would the turbo car be more efficient? Better gas mileage?
I got two replies that were almost hostile stating that "if i could not achieve 50 mpg in a saturn automobile i must be doing something wrong", and "that there has never been any documented proof that turbocharging is more efficient"
They both agreed that more air requires more fuel and therefore = less gas mileage
Am i off base here? I know folks turbocharge for more power, but could one also achieve a thrifty commuter if that was the goal?
Set me straight.
Russ

I have never been absolutely sure, but I don't think the added power offsets the fuel usage.
So I would have to say the turbo engine will use more fuel per mile than the same engine non turbo.

Maybe if it has real mild boost there could be a point where it offsets, but I have NEVER heard anyone say they get better economy when they installed a turbo.
I have heard many say they used more fuel.

I'll toss in a monkey wrench.
If you down-gear the turbo'ed engine to take advantage of the low-speed torque they make, You will almost automatically get better fuel mileage.
And if you downsize the engine, so that the two of them have similar absolute power output, you will again almost automatically get better fuel mileage.
Check out what Ford is doing with their turbo program. Smaller engines with turbos; can make more torque where the vehicle needs it, similar hp,and make better mpgs when off boost.
With this kindof thinking, you can turbo a 273 to equal a hot street 360 in absolute hp, but make more torque in the lower range. If you down-gear it to take advantage of the turbo-torque, you can make plenty of mpgs .
I know this is not what you asked, but it's what popped into my head.
It has been said, that a draw-through system, can help increase fuel mileage by virtue of the fact that the impeller is smashing the gasoline molecules to bits and homogenizing the mixture, so that all of the molecules get burned. Theoretically this would allow you to run a leaner A/F cuz all the cylinders are burning all of the fuel,all of the time. That would get you better MPGs for sure

AJ/FormS said:

I'll toss in a monkey wrench.
If you down-gear the turbo'ed engine to take advantage of the low-speed torque they make, You will almost automatically get better fuel mileage.
And if you downsize the engine, so that the two of them have similar absolute power output, you will again almost automatically get better fuel mileage.
Check out what Ford is doing with their turbo program. Smaller engines with turbos; can make more torque where the vehicle needs it, similar hp,and make better mpgs when off boost.
With this kindof thinking, you can turbo a 273 to equal a hot street 360 in absolute hp, but make more torque in the lower range. If you down-gear it to take advantage of the turbo-torque, you can make plenty of mpgs .
I know this is not what you asked, but it's what popped into my head.
It has been said, that a draw-through system, can help increase fuel mileage by virtue of the fact that the impeller is smashing the gasoline molecules to bits and homogenizing the mixture, so that all of the molecules get burned. Theoretically this would allow you to run a leaner A/F cuz all the cylinders are burning all of the fuel,all of the time. That would get you better MPGs for sure

Click to expand...

I was thinking the same thing when I posted what I did, as there are some hi mpg cars with turbo's out there.
That's what caused me to say there may be a point where efficiency goes away to the pure volume of higher boost. (more fuel/air)

But my reasoning might be suspect.

If you build two IDENTICAL engines...meaning mechanically...the turbo car will get worse mileage if the components related to the turbocharging are the only differences.

Supporting concepts:
Pre-boost, you have less efficient movement of exhaust gasses because of the turbo being, essentially, an obstruction in the exhaust system.
Post-boost, just as stated - when the turbo charger increases the amount of intake air, the fuel must also be increased. You get more power, but it takes more gas to produce it.

Having said all that - what makes turbo cars so efficient is that the engines are NOT identical (mechanically) to their normally aspirated counterparts.

Now, if you had said something like, "two engines that produce the same identical peak horsepower but one is NA and one is turbo'd"...then you could handily argue that the turbo engine would be the more efficient because it would, rationally thinking, not be producing boost all of the time, could be of lower displacement, and would be engineered to mitigate some of the negatives associated with turbocharging. In short, it might take 3 litres of NA engine to match the output of a 2 litre turbo motor and, during most of your low-power cruising or coasting, the 2.0 would be naturally using less petrol.

See, that was easy!

Wow, i never knew, but those explanations seem logical

All this makes me think of smokey's fiero.