Turbo cars.... more efficient than NA on short trips?

[RedMist]

At the same HP levels a turbo engine is more efficient, because it makes it's power lower down in the rev range so therefore has more torque. However when you're not using that torque to good effect (e.g. round town driving), then the NA would likely be more efficient, as it can be run leaner without reliability issues.

I disagree. Turbo engines tend to have considerably higher BSFC's than that of their non compressed counterparts.

[fivebob]

At the same HP levels a turbo engine is more efficient, because it makes it's power lower down in the rev range so therefore has more torque. However when you're not using that torque to good effect (e.g. round town driving), then the NA would likely be more efficient, as it can be run leaner without reliability issues.

I disagree. Turbo engines tend to have considerably higher BSFC's than that of their non compressed counterparts.

Then would you care to explain why they're predominatly used at LeMans for economy reasons.

Somewhere I have an article from Race Engine Technology on the very subject. IIRC the conclusions were the same.

[neon_spork]

I think you have to distinguish between fuel economy and efficiency.

A turbo engine is technically more efficient than a NA one for the same power output. The increased pressure improves the efficiency of the thermodynamic cycle. Or to look at it another way, a turbocharged engine is recovering energy from the exhaust which would otherwise be lost and putting in back into the engine.

Most of us can probably say from experience that turbo cars use a lot of gas. When you put your foot down you make a lot of power and well… it’s pretty hard to resist putting your foot down now and then. Making this power is still going to cost you, not as much as if you didn’t have the turbo but more than if you didn’t make the power in the first place.

A turbo car is probably going to be more efficient, will this give you better fuel economy when driving from A to B? Usually not.

Your best bet is a small displacement turbo engine that doesn’t make a lot of power, but what it does make it does so very efficiently.

[IH8TEC]

i get better fuel economy in my highish hp turbo levin that my mate in his bog std beams altezza, long or short trips. a turbo car should be around the same i think, all depends on tune

[Heylin]

I think the only real comparison could be made using 2 identical model cars one NA and one Turbo, driven around a race track by the same driver and aiming for the same average lap time.

Otherwise theres too many factors to mess things up like gear ratios, weight, driving style, amount of cylinders, aero dynamics.

Pretty sure they would start with even consumption and the turbo would much more as the lap times were reduced and there is more time on boost.

Anyway I graphed my consumption for all of my cars over the years (call me anal)

1987 AW Supercharged - 7L per 100km (highway), 9L per 100km (City)
1990 SW20 Turbo - 10L per 100km (highway), 13L per 100km (City)
1999 Subaru Legacy B4 - 12L per 100km (highway), 15L per 100km (City)
Mazda Cosmo - 18L per 100km (highway), 20L per 100km (City)

[Adoom]

I only live about 5 mins drive* from work...

Get a bicycle. Ride it to work. Save gas/money and get fit at the same time.
I live 15minutes drive from work and there is not 'much' traffic.
I can bike the 18km to work in just under a hour(im not fit) going down the Hutt river trail. Its very fuel economical. Only runs on water from the tap and bananas.

Use the saved gas for the track/weekend/evenings.

SORRY! Thread hijack

[RomanV]

You... do realise that this thread is 2 years old, right?

I dont even have a car at the moment, just quit my job before Christmas, I am on holiday until further notice.

Life is good

[Timmo]

Yeah, but the question is whether or not an NA whale would be just as greedy when it's cold.

Soarer compared to Soarer....no.
FI Soarer uses far more gas than N/A whether it be hot or cold.

Err...im pretty sure the official fuel usage figures for the 30 series Soarer put the turbo Jzz slightly ahead compared to the NA/ Uzz cars.

[Adamal]

*BANG BANG* This thread just WONT DIE!

[RomanV]

Aim for the head, aim for the head!

Or is it a stake through the heart?

Or do I need some silver bullets, or holy water or something perhaps?

[iOnic]

Gotta love how many people confuse "efficiency" for "economy" Turbocharged engines are more efficient than NA engines.

[RomanV]

Efficiency and Economy are one and the same.

Although (As a general rule) turbo motors have a higher peak BSFC, the BSFC when producing say, 20hp required for cruising along, outside of their optimal rpm range, is significantly less flattering.

So, good efficiency for a race car running at full power 95% of the time, not so good for a car that is at full power near optimal RPMs for 2% of the time, aka daily driven cars.

Otherwise they would work out to be more economical/efficient on gas in every situation, compared to NA motors.

[iOnic]

Efficiency and Economy are one and the same.

(example) A 2 stroke engine has 1 Power producing stroke for every 2 strokes in it's cycle. A 4 stroke engine also has 1 power producing stroke but there are 3 "dead strokes" in it's cycle. Therefore the 2 stroke is said to be more "efficient" than the 4 stroke in that there is less wasted energy in it's operation.......Is the 2 stroke engine also therefore more economical? No, it does more work and therefore uses more fuel.

A turbocharged engine "recycles" exhaust gas energy that would otherwise be lost through the exhaust system on an NA engine. It uses this energy to produce MORE power during the next cycle. So therefore it is MORE efficient as there is less energy wasted. Does this mean that the turbocharged engine is also therefore more economical? No, it does more work and therefore uses more fuel.

Efficiency is a measure of how much energy taken in is lost again as waste. Economy is a measure of how much energy is required to carry out a certain amount of work. They're similar but not the same. Efficiency is generally a constant dependent on engine type (most petrol engines today are only about 30% efficient) but economy can vary from car to car even on cars of the same type with the same engine

[RomanV]

The only useful way you'd compare the efficiency/economy of ANY two different motors would be looking at their BSFC maps, not how many combustions they do, or displacement, or what ever else. That's the beauty of BSFC.

There's a difference between peak BSFC and average BSFC through range of RPMs and loads.

It isnt a static number that represents how much power the motor makes for each unit of fuel burnt, in every circumstance.

This is why NA motors use less gas overall compared to an equivilent turbo motor, when driven in a sane fashion.

When at low loads, a turbo doesnt help if the gas flow through the engine is too little to make it do anything useful, and the (generally) low compression ratio (by comparison) means less efficient power generation from each quantity of air/fuel.

[iOnic]

....

[Adamal]

Just a nit pick, but a 2 stroke is WAY less efficient on a single power stroke.

My KT100 easily chewed through a couple of litres in half a day on the track.

[iOnic]

You're confusing EFFICIENCY for ECONOMY. They are NOT the same thing. How much fuel your engine uses does not define how efficient it is. An engine can use shitloads of fuel but if it translates a lot of that into actual power with little waste........it is MORE efficient than an engine that uses bugger all fuel and translates it into bugger all power and lots of waste. Read my post again please.

[Adamal]

No I'm not, due to the way a 2 stroke operates, a lot of unburnt fuel is also wasted. Any engine that leaves fuel unburnt is inefficient. Exactly HOW inefficient it is depends on how much fuel is left unburnt.

[iOnic]

*sigh* All engines produce unburnt fuel (because no engine is completely efficient) A 2stroke engine uses more fuel yes.......but it also produces more power than an equivalent 4stroke which means there is less fuel being translated into waste (heat/unburnt fuel etc) so therefore the 2stroke is still more efficient than the equivalent 4stroke engine. I only used the 2stroke thing as an example because it's common knowledge that 2 stroke engines are more efficient (but less economical) than 4 stroke engines.

Anyway the point I'm trying to make is that Efficiency and Economy while closely related.....are not the same thing. A turbocharged engine is less economical but more efficient than a naturally aspirated engine (everything else being equal)

Consider this

You have two people ( A and B)

A eats 3 meals a day
B eats 1 meal a day
A does more work around the house than B
B spends most of his time on the couch being a lazy $&#$%

Even though A eats more food than B, A translates more of the food energy into work and therefore is more efficient than B even though B eats very little and is therefore more economical to support. It's a percentage thing not an actual amount.

Going into the brake specific fuel consumption just complicates the matter. In the simplest form, turbocharging is more efficient than N/A (even in terms of volumetric efficiency, the turbo is forcing air in and therefore has a higher volumetric efficiency than an N/A engine)

[bbq1988]

My Gen3 3S-GE Curren was more expensive to run around town when cold then my 3S-GTE Caldina.