Engineers, Mechanics, Techies, I have a question..

"K-Roll-PorscheTamer" (k-roll390) 03/15/2015 at 18:05 • Filed to: Question

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We already know the performance difference between Turbos and N/A, but is it true that Turbocharged engines, while presumably more complex than naturally aspirated engines, are actually more efficient? What exactly defines efficiency in this case, the factors? from internal and structural standpoint, which engines are more long-lasting, durable and reliable?

Let me pose some examples. BMW's S65 V8 in the E9X M3 and the newer S55 twin turbo I6 in F8X M3 and M4. Which of the two would be the more durable, reliable engine, the more efficient regardless of what EPA says?

Or howabout this. Ford's awesome Coyote 5.0L against the 3.5L Ecoboost in the F-150. Same questions apply.

Or even Merc's AMG turbo engines against their natural counterparts?

Twingo Tamer - About to descend into project car hell. > K-Roll-PorscheTamer 03/15/2015 at 18:10

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It really depends on a lot of factors that are way too detailed to put in a reply. Turbos can need more care in regards of sticking rigidly to oil and air filter changes and some cars go through them quicker than others. Some N/A engine can be fragile too though as we know.

Turbo cars arent always more efficient than a larger N/A engine especially depending on driving style. If you keep off boost they can be very efficient, however I notice on my car (turbo'd) that if you drive too hard it'll drink fuel at a much higher rate.

Tareim - V8 powered > K-Roll-PorscheTamer 03/15/2015 at 18:12

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to keep it simple, the efficiency comes from making use of the exhaust gasses, on an N/A car they are completely discarded 100% waste, on a turbo car they are used to spin a turbo to create more power (amongst other things)

Jordan and the Slowrunner, Boomer Intensifies > K-Roll-PorscheTamer 03/15/2015 at 18:12

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Kind of depends on fuel, manufacturer, purpose, etc. For instance, one of the most reliable engines, if not the most reliable engine ever built, isn't naturally aspirated(Cummins 6BT).

Zipppy, Mazdurp builder, Probeski owner and former ricerboy > K-Roll-PorscheTamer 03/15/2015 at 18:13

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forced induction engines are often built to higher standards due to the extra stress introduced by the turbo or supercharger, so forged components are used to dissipate the heat better. often times on an N/A engine, they go by with cast and 'hyperteutetic' pistons, which cannot take much heat compared to forged pistons.

Turbo engines are often more efficient because the manufacturer can detune the engine so it puts out less power off boost. Often times more power = more fuel usage, which is why they run leaner off boost. That being said, N/A is more consistent with their fuel consumption, and doesn't rely on boost.

garagemonkee > K-Roll-PorscheTamer 03/15/2015 at 18:15

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When you talk about efficiency in the sense that you're talking about, you're talking about volumetric efficiency. In the case of internal combustion engines, this refers to an engine's ability of an engine to move air into and out of the cylinders, which is why a turbo can increase an engine's volumetric efficiency.

This is not to be confused with fuel efficiency. They can be linked, for example, the power output of a small turbo engine can meet, when demand requires, the power output of a large non-turbo engine, while being small and fuel efficient when a large power output is not required.

K-Roll-PorscheTamer > Jordan and the Slowrunner, Boomer Intensifies 03/15/2015 at 18:18

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If you were to compare the examples above?

K-Roll-PorscheTamer > Tareim - V8 powered 03/15/2015 at 18:18

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What about from a structural point?

K-Roll-PorscheTamer > garagemonkee 03/15/2015 at 18:20

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Sounds reasonable enough! What more can you tell me.

Jordan and the Slowrunner, Boomer Intensifies > K-Roll-PorscheTamer 03/15/2015 at 18:21

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I would say they are probably pretty similar. Time will tell. While the S55 has more to go wrong, the S65 is a more high strung engine, as in you have to work it more to make it's power. The S55 also probably has stouter internals on top of that.

Jedidiah > K-Roll-PorscheTamer 03/15/2015 at 18:27

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Very high compression or forced induction motors will used forged pistons for a durability standpoint.

The level of aluminum in cast pistons is referred to by the its composition relative to the eutectic point on the phase diagram.

Hypereutectic aluminum is probably the best material to use for regular motors with a good factor of safety due to the differences in the rates of thermal expansion between forged and cast hypereutectic aluminum.

There is a reason why motors tend to run between 180 to 210 F, because thats when cast aluminum expands somewhat optimally for the operating temperature of motor. When you have good rings, this makes the motor ideal for preventing blowby and keeping things working properly.

Combine that with lower compression (hence low stress), you are more likely going to get more life out of a naturally aspirated motor because you won't have to rering it as often. In a forced induction motor, you have to deal with higher stresses that have to mitigated with material selection and poorer ring life.

An overbuilt, simple motor with low compression (not insanely low because then it will run poorly), will be the longest lived choice I imagine.

Kevin Barrett > K-Roll-PorscheTamer 03/15/2015 at 18:30

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"Efficiency" in this question needs more definition. From the fundamental elements of internal combustion, we know that engines are limited in their output by the amount of oxygen they can combine with fuel inside the cylinder. NA engine tuning is all about getting better volumetric efficiency, making sure that the engine, with unrestricted air flow, can get atmospheric pressure inside the cylinder when the piston is at BDC between intake and compression strokes. It never will, but if it could, it would have 100% volumetric efficiency. Supercharging gets an engine over that threshold by mechanically stuffing air into the manifold faster than atmospheric pressure would supply it.

Voila, more efficiency! But this does not automatically mean more fuel efficiency, or a longer living engine, or anything else. It's just an extra tool in the engineer's tool box to make a powerplant for a vehicle. In aviation, supercharging isn't used for power or efficiency at all, but rather enabling an engine to function at higher altitudes where the density of air is decreased.

JDMatt > K-Roll-PorscheTamer 03/15/2015 at 18:31

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I'm not adequately qualified to answer this question, however:

Turbo engines need higher quality gasoline and motor oil to run under ideal conditions. Assuming there's a trickle down effect to car maintenance, a turbo car will be in operating condition in the long run.

Manuél Ferrari > K-Roll-PorscheTamer 03/15/2015 at 18:31

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This is my layman's understanding: while lots of factors play into it the engine's displacement makes a huge difference.

If we use your example of the two M3 engines the new one is a lot more efficient when cruising down the highway because it's smaller. They both are DOHC engines so you can compare the displacement apples to apples (whereas you can't compare a BMW engine to a pushrod engine because the pushrod can be more efficient even when the displacement is higher).

When you're cruising and therefore not getting into the boost the turbo I6 will always beat the S65's fuel efficiency. It's smaller and also has direct fuel injection.

Now when you're in the boost then who knows how they will compare. I dunno if the new M3 will be more efficient when track.

lonestranger > K-Roll-PorscheTamer 03/15/2015 at 18:32

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I think your engine examples are apples and oranges, and perhaps you're only considering "efficiency" to mean " fuel efficiency". Compare two engines of identical manufacturer, layout and displacement, and of similar design other than the requirements for turbocharging. The turbocharged engine can be tuned to either

A: have a higher power and/or torque output than the N/A engine, with similar fuel consumption

B: have similar output to that of the N/A engine, with superior fuel consumption

or

C: somewhere in between.

Any way it's tuned, the turbocharged engine will likely be considered more "efficient". It may not necessarily be more efficient in its consumption of fuel, but it makes more effective use of its displacement and other fundamental design features than its N/A version would.

Back to your apples and oranges Coyote vs. EcoBoost, the EcoBoost could* be said to make more effective use of its 3.5 litres than the Coyote does of it's 5.0 litres does.

* I don't know their power or fuel consumption figures off hand. I don't know if it does or not, I'm just speculating.

DoYouEvenShift > K-Roll-PorscheTamer 03/15/2015 at 18:34

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Im not familiar with these motors youre talking about. But as far as reliability goes, and most other things being equal.

I would say the engine with less complexity, less moving parts, less specific output will be more reliable.

K-Roll-PorscheTamer > Kevin Barrett 03/15/2015 at 18:37

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Ah! That's very fascinating! So would it be fair to say that a turbo works the exact same as a supercharger then?

Tareim - V8 powered > K-Roll-PorscheTamer 03/15/2015 at 18:38

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as others have eluded to, a turbocharged motor will need to be stronger to withstand the pressure so in theory should last longer

K-Roll-PorscheTamer > JDMatt 03/15/2015 at 18:38

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That's interesting to know, thanks.

K-Roll-PorscheTamer > lonestranger 03/15/2015 at 18:42

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On the apples to oranges comparo, take the 435hp 5.0 V8(16 city/25 highway) and the 365hp Ecoboost V6 (18 city/25 highway). or howabout more directly, the 2.3L Ecoboost that's replacing the 3.7L V6 in the Mustang?

PheeNoIVI > K-Roll-PorscheTamer 03/15/2015 at 18:45

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Off boost sure, efficient. I don't see how a turbo is more efficient though. Since its basically forcing more air into the engine and thus more fuel. I guess because the engines are smaller.

Kevin Barrett > K-Roll-PorscheTamer 03/15/2015 at 18:47

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Technically, a turbo is a supercharger, and I've used it here in that sense—it's full name is a "turbo supercharger." They don't work the same way, because a "turbo" scavenges wasted energy from exhaust gasses and uses it to increase manifold pressure, and the "supercharger" you're thinking of use mechanical energy from the crankshaft to increase manifold pressure—but did you know that there are "turbo" systems that don't increase manifold pressure, but instead scavenge waste energy from the exhaust to deliver it as mechanical energy to the crankshaft? That system is called a "power recovery turbine."

K-Roll-PorscheTamer > Kevin Barrett 03/15/2015 at 18:54

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This whole perspective of the subject is all new to me. The system you last mentioned with the "power recovery turbine", it almost sounds like a combination of a turbocharger and a supercharger. Or a supercharger with a turbine to recover exhaust gasses and bring them back to the intake? Am I close?

MrDakka > K-Roll-PorscheTamer 03/15/2015 at 18:57

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http://en.m.wikipedia.org/wiki/Thermal_e…

TLDR: higher compression ratio=higher thermal efficiency

Specific heat ratio remains more or less fixed, so increasing compression ratio is the usual recourse

MasterMario - Keeper of the V8s > K-Roll-PorscheTamer 03/15/2015 at 18:58

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They provide the same function, forcing more air into the engine, but they work differently. Turbos use the exhaust gases as their energy source whereas a supercharger steals some power from the engine itself as its power source

lonestranger > K-Roll-PorscheTamer 03/15/2015 at 19:02

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365 ÷ 3.5 = 104.3 HP/litre.

435 ÷ 5.0 = 87 HP/ litre.

In this example, the turbocharged engine has a significantly higher specific output than the N/A one does, while consuming a similar amount of fuel. That's basically my "A" scenario above. Apples-to-apples, a 5.0L V8 version of the F150's EcoBoost could theoretically produce 521 HP, albeit with poorer fuel efficiency than either of the other examples.

MasterMario - Keeper of the V8s > K-Roll-PorscheTamer 03/15/2015 at 19:05

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Reliability and durability are generally more about how over engineered an engine is. There are examples of both turbo and NA engines that are unbelievably reliable (cummins 5.9 and fords 4.9 come to mind) as well as examples of both that are notoriously unreliable. Most engines that are really reliable tend to be over engineered, as in they could easily make more power without major modifications.

crowmolly > K-Roll-PorscheTamer 03/15/2015 at 19:11

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No. They both pressurize the charge but a turbo re-uses exhaust gas while a supercharger uses a belt driven off of the crankshaft.

K-Roll-PorscheTamer > lonestranger 03/15/2015 at 19:19

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I see, thanks so much. :)

Kevin Barrett > K-Roll-PorscheTamer 03/15/2015 at 19:35

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Let's cover individual components:

A turbine is a device which is introduced into the path of moving fluid (it could be air, exhaust gas, or even water) to scavenge mechanical energy from it. The fluid passes through the turbine blades (or an impeller) and moves them around the axis, and then the fluid continues on, now a little slower (out the tailpipe of your car). The turbine has one input (fast moving fluid) and two outputs (slower fluid and rotational mechanical energy).

A compressor is a device for mechanically moving a fluid. When it is doing its job, there is a higher pressure of that fluid on the outlet than there was on the inlet. It is basically a pump, and your car has several of them in it already; oil pump, water pump, fuel pump, etc. When the pump is moving air for an engine that uses a "charge" of air for combustion, it is a "supercharger." It has two inputs (low pressure fluid and rotational mechanical energy) and one output (high pressure fluid)

The "supercharger" as we know it today is a compressor that gets its rotational mechanical energy from the crankshaft, and the turbocharger that we use today is a compressor that gets its rotational mechanical energy from a turbine.

samssun > Tareim - V8 powered 03/15/2015 at 20:00

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The making use of "wasted" energy thing is not true. Any pressure against the turbine blades is also directed against the piston face, so you're literally pushing the turbo with your crankshaft. The only exception is exhaust expansion happening when the exhaust valve is closed.

Power costs fuel. A turbo isn't more efficient at making power, it's just able to make less power most of the time. So a big turbo will get better mileage than its peak power would indicate because 90% of the time it has no boost or power. And the small turbos manufacturers are using are designed to get in the boost early, which makes them both usable and not particularly great on mileage.

TANSTAAFL.

Vicente Esteve > K-Roll-PorscheTamer 03/15/2015 at 20:04

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<3

samssun > lonestranger 03/15/2015 at 20:05

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"In this example, the turbocharged engine has a significantly higher specific output than the N/A one does, while consuming a similar amount of fuel." Which is just another way of saying that power costs fuel regardless of how you make it, and hp/L is an arbitrary measurement outside of artificially imposed limitations (racing specs, or laws written by control freaks).

In other words, F1 should toss all engine requirements, give each team 100 hectares of fuel or whatever to play with, and let them pick whether they want 1.5L turbo V6s, 6L NA V12s, quad rotors, etc.

Tareim - V8 powered > samssun 03/15/2015 at 20:07

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Turbo car's can get better mileage than N/A due to the turbos, the EcoBoost is a good example of that, the 1.0 125bhp has a claimed mpg of 65 whereas the 1.6 which is only 118bhp has claimed mpg of 48, obviously real world figures will be lower but the turbo car is still higher than the non turbo

samssun > K-Roll-PorscheTamer 03/15/2015 at 20:13

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Forget the "waste heat" stuff. A turbo is spun by exhaust gases, which have to be pushed out of the engine by the piston face. So when your exhaust valve opens, you have a tube with the piston at one end and the turbine at the other, and your piston is literally pushing the turbine up to speed. Once the exhaust valve closes, if the exhaust gases are still expanding, you have a tube that's sealed at one end with the turbine on the other, so THAT push is free.

What turbos are actually good at is making non-linear power, which is bad for response but lets you (pretend to) have it both ways. Choose a peak engine power, and the turbo can make a lot less than that most of the time. Or choose a low/mid-range power level, and you can make a ton more up top.

So a small engine with a big turbo can match the peak power of a larger engine, but save fuel because 90% of the time it has no boost and therefore no power. But an engine with a small turbo made to spool quickly and have usable power won't gain much mileage, precisely because of the fact that it isn't gutless in the low/mid-range.

TANSTAAFL.

samssun > Tareim - V8 powered 03/15/2015 at 20:19

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You're only comparing the peak number. What a turbo lets you do is make less power out of boost. It's not making that 125hp more efficiently, it's letting you *not* make 125hp (and therefore not use 125hp worth of fuel) when you're easy on the throttle.

Remember, the whole exhaust stroke consists of the piston pushing gases out and through the turbine. The power to compress your intake is coming directly from your crank, until the exhaust valve closes and you're able to use residual exhaust expansion. Add in frictional losses and intake heating, and you're not gaining much "free" power, you're just letting yourself make less power below peak.

Aaron M - MasoFiST > K-Roll-PorscheTamer 03/15/2015 at 20:27

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Mechanical engineer here to put it all together. Volumetric efficiency has been mentioned before, in essence the amount of power created per volume in engine. Beyond that, turbochargers further improve the power efficiency of and engine by scavenging exhaust heat, thereby increasing the enthalpy of the system (i.e. usable heat, versus unusable exhaust heat).

BUT. Turbochargers do not increase the fuel efficiency of an engine, and that has to do with materials science. More compression equals more heat (Boyle's Law), and thereby a higher chance of knock and premature detonation. The way that this is mitigated is by dumping huge amounts of fuel into the engine, which absorbs heat (the same way meth injection works, by the way) and allows the engine to keep ticking and making more power. This is why a turbo engine is typically tuned to an air-fuel ratio (AFR) of 9:1 to 10:1, despite the fact that perfect stoichiometric ratio (the ratio that is a perfect mix of fuel and air to ensure a complete burn) is 14.7:1. At 14.7:1, under boost, the excess heat would burst most engines apart.

Now, they say turbo engines are more fuel efficient than similar engines of the same output...and this is because a turbo engine doesn't need boost for steady state. When the car isn't boosting, it's using the fuel of a smaller engine, and is tuned for that. Therefore, while you're using more fuel (sometimes a lot more fuel) under boost, you're using less when cruising. That also explains the disparity in, say, the Ecoboost's fuel economy between the EPA testing cycle and real life. An EPA test cycle that uses very little boost (with gentle or no acceleration) will return much higher fuel economy numbers than is possible in actual driving.

lonestranger > samssun 03/16/2015 at 00:07

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Sounds like a good idea. May as well give them bodywork that covers the wheels and call it a day.

samssun > lonestranger 03/16/2015 at 00:48

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The LMP classes still have displacement & cylinder limits, and vary with FI right? Better than nothing but I'm thinking more Can Am, Group B, early F1 laissez-faire, instead of gradually turning everything into a spec series. Flat 12s, active aero, fan cars, and 6 wheelers...bring it all.

lonestranger > samssun 03/16/2015 at 01:11

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There are no limits on cylinder count, nor to any rules vary depending on induction type. It's still pretty wide-open. 5.5L max displacement for non-hybrid engines (unlimited displacement for hybrids), reciprocating engines only (no rotaries), using gasoline or diesel, with conventional valvetrains, and there are limits on fuel flow and boost pressure.

http://www.fia.com/sites/default/…

Engine Specifications

Engine is free except following restrictions:

Only Petrol or Diesel 4 stroke engines with reciprocating pistons are permitted.

Engine cubic capacity is free for "LM" P1-H cars and must not exceed 5500 cm3 for "LM" P1 cars.

Fuel mass flow must not exceed the limit described in the table in Appendix B.

Ratio of supercharging pressure must not exceed 4.0.

Engine must not have more than two inlet and two exhaust valves per cylinder.

Only reciprocating poppet valves are permitted.

The sealing interface between the moving valve component and the stationary engine component must be circular.

Electromagnetic valve actuation systems are forbidden.