[McLaren Rulez]

Originally Posted by NannuBhai

I am not an Auto Technical Expert. But the way I understand it, a car charged with Turbo is best used when the Turbo is in use. The car has been designed in the first place so that the Turbo is used. That's when the efficiency of the car is at it's best and is considered to be "optimally" used. By efficiency, I am not particularly talking about Fuel Efficiency. A car like TSI, like I said earlier, is a powerhouse. So, it's best used like one. You use the Turbo and that's when the car is running optimally.

I'm not an expert either but I'm quite interested in knowing where in the rev range one can get maximum FE. You may be right in your conclusion that the car is more efficient in boost rpm range, but your reasoning is not. Just telling me that a car has a turbo and therefore, it must be most efficient when the turbo works doesn't add up.

My reasoning was that, in general, a car cruising at lower rpm is more efficient. I assumed that a turbo's presence does not change that. At lower rpm, you are always running more efficiently. Hence, driving below boost rpm should be more efficient.

Feel free to correct the errors but do provide more logical reasoning. Plus, I'm not sure what you mean by optimal.

[wildsdi5530]

Originally Posted by Shan2nu

The Variable Cylinder Mangement on the Accord V6 works something like this. When crusing at a constant speed, it switches off 3 cylinders making the engine breathe like a 1.75L 3pot engine (taking in less air which translates to less fuel being consumed) but as soon as you increase throttle pressure, it goes back to 3.5L V6 mode.

Shan2nu

Precisely. So Wouldn't you say that driving a 3 pot engine at it's max level is less efficient than driving a 6 pot engine at low revs?
At a speed of 140 kph, will an M800 give a better mileage or a Honda Accord?
I've noticed that my Honda city Gxi gives an excellent mileage at 80 - 100 Kph. But if I drive at 140 - 160 kph, the mileage drops to half. I routinely get a much better mileage in the city than on the highway.

[Caramelo]

the same engine is in superb! and its more fuel efficent than the honda accord! so if you put that engine in the lighter laura. you got a pretty decent engine!!

[ganesh_evo75]

Originally Posted by iraghava

IMP - I had the 1.8TSI on test for 5 days and all through the test she never averaged above 6kmpl in my hands. Mind you, I drive fairly hard and almost all of the driving was fast in-city driving.

Dear IMP,
Laura TSI, if its giving you @6 kmpl FE, as you said with your driving style better avoid the buy, ofcourse unless until you are diehard lover of Power.
But If you can balance the best of both world, of the car then my dear IMP there is nothing a great car then this.

[imp!]

Sorry folks, ever since I've been off work on Saturday, I've been pushing some mean engines, driving TSI's, TDI's, 6 speeds, 5 speeds, DSG's all in the name of trying to arrive at a decision. Confused as I am, I managed to clear a few things up. Laura it certainly is. FE for the petrol is good enough for me, especially considering what the car is capable off. I can expect an average of 10 between highway and city driving, that is okay, even if I put 20K kilometers a year, I don't mind the expense since I absolutely love the petrol engine. My dad loves the feel of the diesel engine, but he is almost sure this is because for the past decade, he has driven only diesel cars. Once he is sure that he can get used to driving an insane petrol car, that is what we are buying ( I think he is pretty darn sure already though :-) );
Skoda is offering 40 grand of the TSI engine, we are trying to get them to throw in a an upgrade to 16" rubber as well (what are the chances of this? )
The colour is now the main bone of contention in our family. Skoda is currently offering (according to the sales rep, although I get the feeling he may not be entirely upto speed on this) Black, White, Lime Green, Capuccino Beige and Silver. We all love Black, but it is too hard to maintain. Lime Green is out, no one really likes it too much. That leaves Capuccino Beige and Silver. Does Skoda also offer Anthracite Grey on the Laura? I think I've seen one or two in Bombay but I may have been mistaken.
Looks like we will be booking the car sometime in the next coupel of days since there is a 2-3 week delivery and we need to take delivery of the car before the end of the month!
Thanks for all your help its been one incredible experience made all the more special due to your interest!

Cheers!
imp!

[Shan2nu]

Precisely. So Wouldn't you say that driving a 3 pot engine at it's max level is less efficient than driving a 6 pot engine at low revs?
At a speed of 140 kph, will an M800 give a better mileage or a Honda Accord?
I've noticed that my Honda city Gxi gives an excellent mileage at 80 - 100 Kph. But if I drive at 140 - 160 kph, the mileage drops to half. I routinely get a much better mileage in the city than on the highway.

Who is asking you to cruise at 140-160kmph man? U guys just make up things out of nowhere.

You cannot be doing 160kmph in a Laura when driving below boost rpm (irrespective of what gear you're in). So theres no question of high crusing speeds.

And even in the case of the Accord, it will automatically switch back to V6 mode when you apply a certain amount of throttle pressure. So cruising in 3 cyl mode at 160kmph is unlikely.

And even if it was possible to do 160 in 3pot mode, i'd still say the Accord would give much better FE than in V6 mode since the gearing of the car remains identical for both modes. So you have the engine running at identical rpms at a given cruising speed in both modes.

So if an Accord does say 4000rpm in 5th@160kmph, it would be more efficient when running in 3 pot mode.

Shan2nu

[pb10gagan]

Originally Posted by Shan2nu

The thing is that Turbo cars can give good FE if you drive at a constant speed below boost rpm.

The engine starts consuming more fuel as the boost kicks in.

Shan2nu

I don't think the engine starts consuming more fuel as boost kicks in.

Why TFSi more economical?

Same reason as a diesel is.

What is that reason?

More torque down the RPM range and also reaching to peak torque at a lower rev range.

coupled with a taller gearbox.

The principle of fuel consumption is the more the RPM the more the fuel consumed. so the fuel consumption is directly proportional to RPM.

Now lets say the NA petrol engine reaches its peak torque at 3800 RPM, hence you need gear ratio which is less tall that the turbo engine which reaches peak torque at 1800 RPM.

so if in a NA engine and smaller ration gearbox you are cruising at 90kmph at 3000 RPM you can do 90 kmph at 2000 RPM in a turbo FSi engine.

Now the direct injection allows you to burn fuel in a way that you can reach peak torque at lower rev range and have a flatter torque curve, because of more compression inside the cylinder hence a bigger blast.

[Shan2nu]

I don't think the engine starts consuming more fuel as boost kicks in.

Why TFSi more economical?

Same reason as a diesel is.

What is that reason?

More torque down the RPM range and also reaching to peak torque at a lower rev range.

And how does a Turbo help an engine produce more torque at such low revs?

Why would you want your engine to produce this high amount of torque when you're cruising at a constant speed?

Shan2nu

[pb10gagan]

Originally Posted by Shan2nu

And how does a Turbo help an engine produce more torque at such low revs?

Why would you want your engine to produce this high amount of torque when you're cruising at a constant speed?

Shan2nu

not the turbo but the FSi (direct injection at higher compression)

because in FSi engine you can cruise at 90kmph at 2000 RPM where as in normal air+fuel mixture you can not.

because the normal air+fuel mixture engine will belt equivalent or less torque at 3000 to 3500 RPM

hence more efficiency in the FSi one.

[d_himan]

Originally Posted by imp!

Skoda is offering 40 grand of the TSI engine, we are trying to get them to throw in a an upgrade to 16" rubber as well (what are the chances of this? )
imp!

Imp, saw a Autobahn ad on today's TOI Mumbai on Laura discounts. (11.99 lacs - it reads)

[Shan2nu]

because in FSi engine you can cruise at 90kmph at 2000 RPM where as in normal air+fuel mixture you can not.

because the normal air+fuel mixture engine will belt equivalent or less torque at 3000 to 3500 RPM

Firstly, why are you comparing FSI vs regular engine? The discussion is only between the crusing rpm in the same engine (which is TSI "Turbocharged").

2ndly, what kind of fuel efficiency are you talking about? Is it efficiency related to cylinder cumbustion or efficiency related to distance travelled per ltr (fuel economy to be precise, which the thread starter wanted information about).

Shan2nu

[pb10gagan]

Originally Posted by Shan2nu

Firstly, why are you comparing FSI vs regular engine? The discussion is only between the crusing rpm in the same engine (which is TSI "Turbocharged").

2ndly, what kind of fuel efficiency are you talking about? Is it efficiency related to cylinder cumbustion or efficiency related to distance travelled per ltr (fuel economy to be precise, which the thread starter wanted information about).

Shan2nu

i mentioned FSi because the 1.8 engine in laura is TFSi, i mean a trubo charged direct injection petrol engine (though they call it TSi), if the discussion was only about the turbo petrol (non-FSi) then i guess my points are invalid.

i was talking about distance travelled per liter. (because if you are doing 90kmph at 2000 then you are buring 1/3 less fuel than doing 90kmph at 3000).

[imp!]

Originally Posted by d_himan

Imp, saw a Autobahn ad on today's TOI Mumbai on Laura discounts. (11.99 lacs - it reads)

There is no ways that is the on road price ! I think that the ex showroom price on the Laura is 12.98 lacs? if this is true, that is one fat discount indeed ! I wonder how I can get that discount out of Tafe/Vinayak in Bangalore.

[Shan2nu]

i mentioned FSi because the 1.8 engine in laura is TFSi, i mean a trubo charged direct injection petrol engine (though they call it TSi), if the discussion was only about the turbo petrol (non-FSi) then i guess my points are invalid.

Yup, the discussion is only about TSI/TFSI engine.

i was talking about distance travelled per liter. (because if you are doing 90kmph at 2000 then you are buring 1/3 less fuel than doing 90kmph at 3000).

This is again invalid bcoz we are not talking about what rpm other engines do at 90kmph.

All im saying is, if a TFSI engine does a certain rpm at a given vehicle speed in the boost zone, producing high torque figures and consuming more fuel to do so.

Driving this same car slightly below boost rpm (at a lower cruising speed) where large amounts of air and fuel is not being forced into the engine to produce high torque, it should still be able to maintain a constant speed comfortably, while consuming lesser fuel.

You dont need the extra torque to maintain a constant speed. And if you do feel the need to acc, just bring the rpm into the boost zone. Its as simple as that.

Shan2nu

[pb10gagan]

Originally Posted by Shan2nu

All im saying is, if a TFSI engine does a certain rpm at a given vehicle speed in the boost zone, producing high torque figures and consuming more fuel to do so.
.......

Well the FSi engines produce more torque because of their working in the direct injection mode and high compression ratio.

not because they are burning up more fuel at turbo boost.

and for the TFSi the turbo boost is at 1500 RPM, so driving it at below turbo boost may not be all that pleasant, i guess.

the peak torque range for TFSi 1.8 is 1500-4200 RPM.