turbo charged or naturally aspirated most fuel efficient??
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It does not matter if it is forced induction or not. THe efficency does not really change. THe efficency is keyed to the combustion cycle and fuel type used.
Two cycles are much more effiecent then 4 stroke engines but they are also much dirtier wich is why they are dying off in so many applications.
Two cycles are much more effiecent then 4 stroke engines but they are also much dirtier wich is why they are dying off in so many applications.
If you want a pure practical answer a non-turbo car will tend to get better MPG, because turbo cars usually have some type of fuel richening scheme to prevent high pressure detonation and besides it's too much fun with the turbo......
The whole idea of a turbo is to get more power from a given displacement. More air is forced into the engine, so in order to keep the mixture correct, more fuel has to be added. That's where the power comes from. Given that, if you had two cars with the same engine, one turbo, one NA, you'd probably get more mpg from the NA engine, especially if the cars were driven hard where the turbo really had a chance to work, but better power from the turbo.
If two cycles are much more efficient then 4stroke engines, why do the various cycle and power equipment makers state otherwise?
They aren't, except for hp per cubic inch.
Given a single cylinder, a 2 stroke engine delivers 1 combustion event per crankshaft rotation, while a 4 stroke delivers 1 combustion event per every other crankshaft rotation. That's why 2 strokes are more powerful. The way a 2 stroke gets fuel to the cylinder is a little messy, though. Basically it goes into the cylinder in the back side of the piston (where it lubes the bearings and cylinder walls), then gets pushed to the front side through a tube as the piston gets pushed down from the combustion event. I don't know all the details, but the result is a less efficient burn than a 4 stroke, resulting in much dirtier exhaust. I believe a big part of the reason is that you have fresh fuel and air mixing with the combustion gasses, which results in less oxygen available for the combustion. You're also burning oil with the fuel, which can lead to smoky exhaust.
I think a lot of it is charge density. I enjoyed both good mileage and power in my Grand Am with the HO Quad 4 and 10:1 compression. Do not confuse that engine with the more common 16 valve versions and 8.5 or something. It would lay rubber in third gear and still get 35 mpg running 75 on 2 lane roads.
Turbo mode starts with a denser charge. Likely the harder you run it, the more efficient, but the efficiency is going to power, not mileage. Run hard, the Grand Am didn't get very good mileage either.
Turbo mode starts with a denser charge. Likely the harder you run it, the more efficient, but the efficiency is going to power, not mileage. Run hard, the Grand Am didn't get very good mileage either.
In terms of straight thermal efficiency, a non-turbo Spark Ignition engine is more efficient than a turbo.
Reason for this is that the Compression ratio has to be lowered for a given peak chamber pressure (and therefore temp), that gives a lower expansion ratio also. Lower efficiency.
There was a guy experimenting with small turbos in J-Cars a few year ago (1.3 turbo vs 1.8 na), and found that for equivalent power, the smaller turbo won overall.
Turbocharged diesels are a different kettle of fish. No drop in Compression Ratio, and an increase in excess air means greater fuel combustion, and lower chamber temps (less heat loss).
Reason for this is that the Compression ratio has to be lowered for a given peak chamber pressure (and therefore temp), that gives a lower expansion ratio also. Lower efficiency.
There was a guy experimenting with small turbos in J-Cars a few year ago (1.3 turbo vs 1.8 na), and found that for equivalent power, the smaller turbo won overall.
Turbocharged diesels are a different kettle of fish. No drop in Compression Ratio, and an increase in excess air means greater fuel combustion, and lower chamber temps (less heat loss).
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"Turbocharged diesels are a different kettle of fish"
So I gather from what you said (Shannow) that in a car the NA will generally be more efficient .
And a marine engine in a off shore supply vessel will have better efficiency if it is turbocharged?
Am I correct on that Shannow?
"Turbocharged diesels are a different kettle of fish"
So I gather from what you said (Shannow) that in a car the NA will generally be more efficient .
And a marine engine in a off shore supply vessel will have better efficiency if it is turbocharged?
Am I correct on that Shannow?
Back in the 50's cummins was using the 855 cu in diesel engines in trucks.
They were 220hp non turbo.
250hp non turbo.
And a 262 hp turbo'd engine that was basically the 220 with a turbo.
The 262 got much better MPG than the non-turbo engines.
Adding the turbo from the 262 to the 250 made a 290. Man if you had 290hp in the 50's you were the cats meow!
They were 220hp non turbo.
250hp non turbo.
And a 262 hp turbo'd engine that was basically the 220 with a turbo.
The 262 got much better MPG than the non-turbo engines.
Adding the turbo from the 262 to the 250 made a 290. Man if you had 290hp in the 50's you were the cats meow!
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The basic difference that I see is ..little engine..lots of power. It allows more design flexiblity with a lighter, and perhaps smaller, power plant. If you need 190 hp to propell a vehicle in an acceptable manner. You can use 4.2 liters ..or 2.5 liters. One may weight 350-400 lbs. the other 240 lb (or less). One will have perhaps 6 cylinders ..the other 4.
There is replacement for displacement ..it's just not cheap.
There is replacement for displacement ..it's just not cheap.
frankiee,
yep. A NA spark ignition engine with th highest compression that it can run safely for it's fuel will be more thermally efficient than a turbo, with its lower compression.
The turbodiesel will be more thermally efficient that the N.A. version. (The big marine diesels are knocking on 50% thermal efficiency)
yep. A NA spark ignition engine with th highest compression that it can run safely for it's fuel will be more thermally efficient than a turbo, with its lower compression.
The turbodiesel will be more thermally efficient that the N.A. version. (The big marine diesels are knocking on 50% thermal efficiency)
Another good comparison would be the two Impreza models with the same displacement engines:
Subaru Impreza 2.5RS: 2.5L NA engine
165 hp @ 5600 rpm
166 lb-ft @ 4000
5-spd manual mpg: 23/30
curb weight: 2972 lbs
Subaru Impreza WRX STI: 2.5L turbocharged engine
300 hp @ 6000 rpm
300 lb-ft @ 4000
6 spd manual mpg: 18/24
curb weight: 3298
When you make the statement, which "is the most fuel efficient", there's no question it's the turbos.
Automotive gasoline turbo engines in the US are made for extra power, fun and sporting driving almost exclusively. Not to get the very best mpg. If it were to get the best mpg, they'd take the smallest engines they sell now, say the 1.5 to 1.9 liter engines, make them smaller then turbo them. The displacements would probably be 1 liter or less.
If you look at all semi diesel engines and all locomotive engines, they all have turbochargers. I don't think they spend the extra money turbocharging them so the people that drive them can have more fun. It's so they can get the job done reliably at the lowest operating cost.
Automotive gasoline turbo engines in the US are made for extra power, fun and sporting driving almost exclusively. Not to get the very best mpg. If it were to get the best mpg, they'd take the smallest engines they sell now, say the 1.5 to 1.9 liter engines, make them smaller then turbo them. The displacements would probably be 1 liter or less.
If you look at all semi diesel engines and all locomotive engines, they all have turbochargers. I don't think they spend the extra money turbocharging them so the people that drive them can have more fun. It's so they can get the job done reliably at the lowest operating cost.
Good points Kernel Potter. The power to weight ratio is also favourable for a turbocharger, and turbochargers are less maintenance intensive, in theory, than reciprocating engines.
In applications where the 'weight' of the engine is a lot of mass to carry around, turbochargers can increase the power with minimal additional mass compared to the use of a larger displacement block and all the extra stuff that entails.
In applications where the 'weight' of the engine is a lot of mass to carry around, turbochargers can increase the power with minimal additional mass compared to the use of a larger displacement block and all the extra stuff that entails.
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