Why turbo's often don't yield the anticipated MPG improvements |  |  |
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The apostrophe is there to denote a contraction.
[www.sussex.ac.uk]
' Turbo's ' is a contraction of 'turbochargers'.
Edited 1 time(s). Last edit at 04/24/2016 05:47PM by Roger987. (view changes)
[www.sussex.ac.uk]
' Turbo's ' is a contraction of 'turbochargers'.
Edited 1 time(s). Last edit at 04/24/2016 05:47PM by Roger987. (view changes)
Laz - 7 years ago |
Laz - 7 years ago |
| One factor that people do not know is MarknearChicago - 7 years ago |
that those of us with high-boost engines like the modified I5 engine in my 95.5 Audi S6 have extra fuel injected to help keep cylinder head temperatures in check. When my turbo-ed I5 engine went from220hp to 370hp gas mileage went down by 10% (when driven the same). Fun factor went up so I'm ok with that.
| Re: One factor that people do not know is Roger987 - 7 years ago |
You're right - the linked article includes that as one of the factors leading to higher consumption:
"A turbocharger changes the picture. Because it compresses the incoming air, the fuel injection system automatically adds more fuel to keep the mixture at the correct ratio. And this is where the problems begin. As the pressure in the combustion chambers rises, you run the risk of pre-ignition (commonly known as “knock”) – this is caused when raw ignites before the spark plug fires.
Knock is destructive (imagine millions of tiny grenades exploding inside your engine), but is easily prevented by computerized engine control systems that monitor fuel flow and cylinder in real time. If your engine is on the verge of knocking, the computers have an instant fix: they shoot extra fuel into the cylinders to cool things down. As you can imagine, this hurts fuel economy. But it does help your engine last."
"A turbocharger changes the picture. Because it compresses the incoming air, the fuel injection system automatically adds more fuel to keep the mixture at the correct ratio. And this is where the problems begin. As the pressure in the combustion chambers rises, you run the risk of pre-ignition (commonly known as “knock”) – this is caused when raw ignites before the spark plug fires.
Knock is destructive (imagine millions of tiny grenades exploding inside your engine), but is easily prevented by computerized engine control systems that monitor fuel flow and cylinder in real time. If your engine is on the verge of knocking, the computers have an instant fix: they shoot extra fuel into the cylinders to cool things down. As you can imagine, this hurts fuel economy. But it does help your engine last."
| Doesn't surprise me Guenter in Ontario - 7 years ago |
| I wrote this article last year ... Pedro (Odessa, FL) - 7 years ago |
.. . [pedrosgarage.com]
Happy turbo'ing
Pedro
Pedro Bonilla
1998 Boxster 986 - 311,000+ miles: [www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)
Racecar spelled backwards is Racecar
"Racing is life. Anything before or after is just waiting" ... Steve McQueen as Michael Delaney in "LeMans"
"If you wait, all that happens is that you get older"... Mario Andretti
"Being second is to be the first of the ones who lose" ... Ayrton Senna
Happy turbo'ing
Pedro
Pedro Bonilla
1998 Boxster 986 - 311,000+ miles: [www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)
Racecar spelled backwards is Racecar
"Racing is life. Anything before or after is just waiting" ... Steve McQueen as Michael Delaney in "LeMans"
"If you wait, all that happens is that you get older"... Mario Andretti
"Being second is to be the first of the ones who lose" ... Ayrton Senna
| Re: I wrote this article last year ... Roger987 - 7 years ago |
| not entirely.... grant - 7 years ago |
Yes, there are two issues that you all have noted, and they are true:
1. gaming the system, as noted
2. the fact that given any fuel--> work function, people may spend it on fuel economy or performance
But there are also 3 reasons why a turbo of similar performance numbers, and used in a similar way will in fact yield better fuel economy:
1. it weighs less
2. it has less friction (smaller, fewer cylinders, etc)
3. It operates at less vacuum ( which is parasitic) more of the time
That's it.
documented by an MIT study and another from one of the national labs on the west coast.
The magic combination seems to be turbocharging + direct injection so as to keep the static compression ratio hgih.
yea, sure you can just mash the loud pedal, but you could do that n the old, larger, NA motor too.
Grant
Grant
gee-lenahan-at-gee-mail-dot-com
1. gaming the system, as noted
2. the fact that given any fuel--> work function, people may spend it on fuel economy or performance
But there are also 3 reasons why a turbo of similar performance numbers, and used in a similar way will in fact yield better fuel economy:
1. it weighs less
2. it has less friction (smaller, fewer cylinders, etc)
3. It operates at less vacuum ( which is parasitic) more of the time
That's it.
documented by an MIT study and another from one of the national labs on the west coast.
The magic combination seems to be turbocharging + direct injection so as to keep the static compression ratio hgih.
yea, sure you can just mash the loud pedal, but you could do that n the old, larger, NA motor too.
Grant
Grant
gee-lenahan-at-gee-mail-dot-com
| Re: not entirely.... Guenter in Ontario - 7 years ago |
Quote
grant
But there are also 3 reasons why a turbo of similar performance numbers, and used in a similar way will in fact yield better fuel economy:
1. it weighs less
2. it has less friction (smaller, fewer cylinders, etc)
3. It operates at less vacuum ( which is parasitic) more of the time
That's it.
documented by an MIT study and another from one of the national labs on the west coast.
The magic combination seems to be turbocharging + direct injection so as to keep the static compression ratio hgih.
yea, sure you can just mash the loud pedal, but you could do that n the old, larger, NA motor too.
Grant
| Re: not entirely.... Guenter in Ontario - 7 years ago |
As far as the weight. Fact is the 718 weighs more than the 981, not less. Maybe just a more sophisticated / heavier turbo?
As noted in my earlier post, the 718 S is rated at 26 mpg highway. My 981 regularly get 28 mpg or better on the highway. Where is the advantage?
It will be interesting to see what happens in real world tests.
As noted in my earlier post, the 718 S is rated at 26 mpg highway. My 981 regularly get 28 mpg or better on the highway. Where is the advantage?
It will be interesting to see what happens in real world tests.
MikenOH - 7 years ago |
Quote
Guenter in Ontario
As far as the weight. Fact is the 718 weighs more than the 981, not less. Maybe just a more sophisticated / heavier turbo?
As noted in my earlier post, the 718 S is rated at 26 mpg highway. My 981 regularly get 28 mpg or better on the highway. Where is the advantage?
It will be interesting to see what happens in real world tests.
With less displacement--and similar gearing---you would expect better mileage.
With the mustang product line--3.7L V6 vs, 2.3L turbo 4 (same tranny and similar gearing) the epa highway test numbers have the 4 cyl at +3mpg vs the V6.
The 981S vs. the 718S has the 2.5L motor -2mpg using the same gearbox; that sounds odd.
IIRC, the move away from NA engines was driven by both hitting new mileage numbers, reduced emissions requirements--and more power.
Maybe the emissions reducing issue was the driving force on this change?
BTW, I can't find any info on the 3.0L motor mileage figures used in the 991.2 at this point--I guess Porsche hasn't released them yet.
Fuel Consumption
Manual PDK
City (estimate) 20 mpg 21 mpg
Highway (estimate) 26 mpg 28 mpg
Which is a bit less (28mpg?) than on the 981S.
Interesting....dropping the displacement by nearly a liter you'd expect a drop in consumption in a steady state highway mode but not on this model.
BTW, comparing the prices on the 718S--equipped the same way we have it on our 981S--the price goes from a MSRP of $66K to $75K in 4 model years.
Looking at the standard equipment and options, is it still correct that there is no bluetooth connectivity in the basic radio setup to stream music (Spotify/Pandora)? With the price on this model in the $70K without many options I'd hope that would be included given cars in the $20-25k range have it standard.
Edited 1 time(s). Last edit at 04/25/2016 09:30AM by MikenOH. (view changes)
Manual PDK
City (estimate) 20 mpg 21 mpg
Highway (estimate) 26 mpg 28 mpg
Which is a bit less (28mpg?) than on the 981S.
Interesting....dropping the displacement by nearly a liter you'd expect a drop in consumption in a steady state highway mode but not on this model.
BTW, comparing the prices on the 718S--equipped the same way we have it on our 981S--the price goes from a MSRP of $66K to $75K in 4 model years.
Looking at the standard equipment and options, is it still correct that there is no bluetooth connectivity in the basic radio setup to stream music (Spotify/Pandora)? With the price on this model in the $70K without many options I'd hope that would be included given cars in the $20-25k range have it standard.
Edited 1 time(s). Last edit at 04/25/2016 09:30AM by MikenOH. (view changes)
Quote
MikenOH
Fuel Consumption
Manual PDK
City (estimate) 20 mpg 21 mpg
Highway (estimate) 26 mpg 28 mpg
Which is a bit less (28mpg?) than on the 981S.
Interesting....dropping the displacement by nearly a liter you'd expect a drop in consumption in a steady state highway mode but not on this model.
BTW, comparing the prices on the 718S--equipped the same way we have it on our 981S--the price goes from a MSRP of $66K to $75K in 4 model years.
Looking at the standard equipment and options, is it still correct that there is no bluetooth connectivity in the basic radio setup to stream music (Spotify/Pandora)? With the price on this model in the $70K without many options I'd hope that would be included given cars in the $20-25k range have it standard.
Interesting. I agree that you'd think the 4 cylinder turbo would get much better gas mileage on the highway, where the turbo wouldn't likely come into play in steady state cruising. Cruising on the Interstate at a steady 70 - 85 (where permitted of course) cruising, my 981S will get around 28 mpg. The 718 S gets 26 (manual) mpg. in the test cycle. What's it going to get in real world driving?
I seldomly do city only driving on a tank, but with a mix of city and highway driving, mine averages 22 - 24 mpg, compared to the 718S's 20 mpg.
The only time I get less than 22 mpg is in the Blue Ridge Mountain roads. Must have something to do with the mountain air.
As for price. The Canadian Porsche website still lists the 2016 Boxster, as well as the 718 specs and prices. The current Boxster S starts at $72,900 CDN and 718 S starts at $78,000 CDN.
Laz - 7 years ago |
And aside from some direct injection carbon on the tailpipes, there're pretty much petunias blowing out the exhaust. The new turbos are also DI, so if they also throw carbon particulates, apparently it doesn't concern the EU. For whatever likely minuscule emissions reductions are realized, it seems like a huge expenditure for design, retooling, and revised production. One would think mpg (kpl) would be at least as great a concern, yet the "official" highway figure is lower.
I hope Porsche keeps all the NA 6 cylinder production machinery around for variants, if not a return at some future point.
Edited 1 time(s). Last edit at 04/28/2016 01:04PM by Laz. (view changes)
I hope Porsche keeps all the NA 6 cylinder production machinery around for variants, if not a return at some future point.
Edited 1 time(s). Last edit at 04/28/2016 01:04PM by Laz. (view changes)
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