[clevermax]

Originally Posted by firstguri

Well I'm the engineer so I'll clear this out. The basics first- T/C's are basically two fans connected by a shaft. One fan is driven by the exhaust gases (called turbine) and this rotates the other fan (called blower). The blower forces in more scavenge (fresh) air into the engine. More air -> more oxygen -> more complete combustion -> more power and better efficiency. So the exhaust gases that anyway go out are made to do some work. And no other power is being used for this extra scavenge air that is being forced inside. So T/C's only add to the engine's efficiency and are not some fancy over-hyped equipment. Yes you do need to fit in other things along with it and it needs maintenance but after all it's increasing the efficiency of the engine.

Thanks for the simple explanation, but I wanted to know one more thing, most of the turbos kick in at a particular rpm, like 2000. Why is so? What prevents them from operating from idle rpms? Or it is useless in lower rpms? Sorry to be off-topic.

[theEnd]

Originally Posted by firstguri

"in one way" you're missing the whole point. First of all ANHC's engine and Linea's engine are not in their maximum state of tune. They'll be capable of making a lot more so we can never know whose engine can make more absolute power. Secondly the three things that manufacturers primarily design their engines around are- power, FE & emissions. Now its upto the maker what configuration and setup they choose to reach their targets. Some might go with a large naturally aspirated engines while others may choose smaller turbocharged engines and someone else may go with any other hi-fi tech'. So as long as the product is competent with others in its segment, who gives a heck about engine size? The thing that matters (if at all) is engineering finesse and depth. VW has 1.2 TSI that makes 103 bhp! They do it by using a supercharger, a turbocharger and direct injection. So what would you say- that it's a shame that VW has to use such a lot of tech' for its engine to be competent!

I guess a lot of people have woken from their slumber to come defend Fiat and their engines. Fair enough, after all Fiat is also the company that owns Ferrari and nobody's going to find fault with those power-plants.

Just to clarify though, the 1.2 TSI only utilizes a turbocharger. The twin charger (supercharger + turbocharger) combination can be found on some (but not all) of the 1.4 TSI engines that VW makes.

Originally Posted by clevermax

Thanks for the simple explanation, but I wanted to know one more thing, most of the turbos kick in at a particular rpm, like 2000. Why is so? What prevents them from operating from idle rpms? Or it is useless in lower rpms? Sorry to be off-topic.

Unless the exhaust gasses are moving fast enough, the turbine wont be able to spin quick enough to get the blower to suck in enough air. At low rpms, the turbine will be using up more power (by restricting the exhaust gasses) than the blower can add.

[EssYouWe]

The pressure of the exhaust gases is just not enough to drive the rotor to overcome its rotational inertia. The time taken by the pressure to build up enough to drive the turbo is the time during which a 'lag' is perceived.

At such times, the engine is behaving much like any normally aspirated diesel engine.

Hope this helps.

[firstguri]

Originally Posted by clevermax

Thanks for the simple explanation, but I wanted to know one more thing, most of the turbos kick in at a particular rpm, like 2000. Why is so? What prevents them from operating from idle rpms? Or it is useless in lower rpms? Sorry to be off-topic.

As others have mentioned- T/C's need a certain amount of exh' gases to be able to spool up sufficiently. Higher rpms are achieved by injecting more quantity of fuel and thus the quantity of exh' gases also increases. So a particular rpm is needed to get the T/C to work. And at what rpm the T/C kicks in actually depends on design. It is possible to design a T/C which starts boosting from low rpms only but then at higher rpms will result in too high scavenge pressures, which again is detrimental for efficiency. In general T/C's are designed to kick in around 1500-2000K and even then there's excess pressure at higher rpms. This is where the wastegate comes in. Basically a valve which lets off the extra boost.

Originally Posted by EssYouWe

At such times, the engine is behaving much like any normally aspirated diesel engine.

Actually the performance at such times is less than naturally aspirated engines.

@ TheEnd
Sorry for the goof up. Confused the 1.4 with the 1.2. Thanks for bringing it to my notice.

[clevermax]

Thanks folks for the neat explanation. Now, what's different in VGT? Is it also like a NA engine till the turbo kicks in? From the name I guess it's effect slowly appears compared to the very evident turbo kick in normal turbos.

I guess we are going off-topic, we need to stop this after this is also answered.

[ImmortalZ]

Originally Posted by clevermax

Thanks folks for the neat explanation. Now, what's different in VGT? Is it also like a NA engine till the turbo kicks in? From the name I guess it's effect slowly appears compared to the very evident turbo kick in normal turbos.

I guess we are going off-topic, we need to stop this after this is also answered.

You can make turbos spool at low RPMs by varying the turbine geometry. But turbos configured this way will end up "redlining" at the mid range band and choke the engine in the high end. The same turbo configured for mid end and high end power won't spool at low RPMs, causing turbo lag.

Old solution? Twin turbos. New solution? VGT. Change the turbo's geometry with the RPM and keep it working at a much wider RPM band than a single or fixed geometry turbo.

[firstguri]

Originally Posted by clevermax

Thanks folks for the neat explanation. Now, what's different in VGT? Is it also like a NA engine till the turbo kicks in? From the name I guess it's effect slowly appears compared to the very evident turbo kick in normal turbos.

I guess we are going off-topic, we need to stop this after this is also answered.

OK I'll try to be as simple as possible. Take a water hose and assume water's coming out of it. Now what happens when you place your thumb on the end of the hose and cover about 2/3'rd of the dia? The water comes out at a greater velocity. It's called Venturi effect. So basically in VGT's there are movable vanes which open and close to maintain a certain velocity of the exh' gases. At low rpms the flow of gases to the turbine is less. In VGT then the vanes close so the velocity of the gases increases and the turbine rotates at a higher speed. So sufficient boost is still maintained even at low rpms. In practicality this means less turbo lag.

Here are a few links to make you understand the concept better.
How does Variable Turbine Geometry work?
AutoZine Technical School - Engine
www.cummins.com/turbos - VGT

[gomzi]

@firstguri: Excellent posts and really easy to understand explanation on turbo-chargers and VGT.

I was always curious about this, but never ended up finding out about them. Thanks, I learnt something new today

[firstguri]

Originally Posted by gomzi

@firstguri: Excellent posts and really easy to understand explanation on turbo-chargers and VGT.

I was always curious about this, but never ended up finding out about them. Thanks, I learnt something new today

Thanks a ton dude. At your service anytime, anywhere.

[clevermax]

Thanks ImmortalZ and firstguri for the explanation again. It is well understood.

[firstguri]

Originally Posted by clevermax

Thanks ImmortalZ and firstguri for the explanation again. It is well understood.

Glad that I could be of help.

[shreeps]

The waiting is getting difficult. One more month to go. I've postponed my car buying decision and am waiting for the T-Jet to come.

[firstguri]

Originally Posted by shreeps

The waiting is getting difficult. One more month to go. I've postponed my car buying decision and am waiting for the T-Jet to come.

I asked the salesman at our dealership yesterday about T-Jet. He said its gonna take some time. What idiots these people are- we have more info than them!!

[SkyWalker]

Shreeps - be patient. FIAT has pushed the original launch of Linea so much, i will be surprised if they lunch this one in time.

if it helps any, I guess it will be a stonker of a car and worth the wait.

[grules]

Originally Posted by firstguri

I asked the salesman at our dealership yesterday about T-Jet. He said its gonna take some time. What idiots these people are- we have more info than them!!

@firstguri: You atleast got a sensible reply from the salesman. When i asked about it, he corrected me saying "Saar, you got the engine name wrong. It's not T-Jet, it's Multi T-jet and is already available". I realized there is no point in arguing further.