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Old 29th November 2010, 16:55   #16
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Originally Posted by aargee View Post
This is a pure coincidence that I was talking to a friend of mine regarding the turbo kicking & few people shifting their gears before the turbo kicking in to get best mileage & my friend was saying its wrong.

Why is it not possible to kick in the turbo using some other methods such as source from the battery to kick in turbo electrically rather than mechanically at certain RPMs using ECU? Wouldn't that bring the best of both worlds in terms of mileage as well as power? So if an engine kicks it turbo at 2.5K RPM & gives best mileage at 1.8K RPM, why not kick in the turbo at 1.8K instead of doing it mechanically?

Next, why is it that the gear shifts should be done only when the turbo kicks in? For instance why not shift the gear at 2.4K RPM & the engine should not necessarily lug right?

Pls help me understand as I've never owned a Diesel car before.
If you want to know exactly what the most fuel efficient way to run a turbo Diesel is when the power comes from the gas pressure and not from the piston speed. But hardly anyone can work out what this means in practical terms. Manufacturers can tell you this according to their experiences on the different models and it depends on the specific engine design.

The turbos aren't just blowers that are linked to the exhaust. You can have turbines being designed for the specific engines that they come on boost already at tickover. Problem is to keep this boost all through the rpm range, which means the turbo would soon run out of puff. If the turbo is very big for the engine capacity then you have the low end boost problem and a lot of lag. This can be partly compensated with the use of varable geometry turbines. But they have their limitations too and are very costly. A even better solution is a sequential turbo set up, giving boost early without lag and boost all the way through to the rpm limit. But they are even more expensive.

Unfortunately there is a number of problems with turbo applications the manufacturer have to solve in order to have a trouble free long term running, which does affect in practical terms the efficiency of the turbines.
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Old 29th November 2010, 17:53   #17
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Originally Posted by vasanthn21 View Post
A few questions:
  1. People suggest up-shifting as early as possible - Isn't this good only from the perspective of fuel efficiency? If
    one up-shifts early, can it harm the engine as this (shifting as early as possible) would strain the engine? ( I believe this is preached by the manufacturers in India as we are obsessed with "kithna deti hai?" km/l)\
If you look at the optimal RPM range given in the user manual "as early as possible " means when you enter power band. So this should not strain engine. However if you interpret as early as possible to be below this range it wil surly strain engine and is called lugging.
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Old 29th November 2010, 18:00   #18
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Originally Posted by bhp_maniac View Post
Turbo is a forced induction system. There are forced induction system which relies on power from engine rather than the exhaust and they are called super chargers. There are conventional super chargers which are run from the engine crank shaft and also electric chargers which use the electric power generated by the engine. There are engines which use a combination of both turbo and super chargers to get the best out of both worlds. Turbos are used more since the efficiency is on the higher side than super chargers. Hope this clarifies.

Also, as somebody said the turbo is always spinning. It is not that the turbo starts spinning at the kick in rpm. The kick in rpm is the threshold at which the boost generated by the turbo overtakes the power needed to spin it at that rpm.
yes there are electric chargers but this forum itself has confirmed them to be a whole lot of BS.! !
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Old 3rd December 2010, 09:47   #19
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Brilliant topic ! This always has been a doubt of mine and never posted in t-bhp ! And owning a turbo-charged Swift D, this could not have come any time better.

I see here that everybody is stuck on to RPMs for shifting gears. I for one, dont bother about the RPM at which I shift, its rather based on the speed at which I drive.

So as soon as I move from a stand still, at around 10kmph, I shift to second ! 99% of the times, the car moves without any fuss at all.

So like wise 2-3 shift and 3rd to 4th comes in pretty soon and sometimes i shift to 5th gear in as low as 40 kmph. For me, this is the best as I travel inside city and there is no point for me to wait till 80kmph to shift to 5th [which I think is recommended, or is it 60kmph at which manufacturer "recommends"] .

Mostly I am the only guy in the car and 5th gear at 40 kmph is quite cool to drive without any knocking or strain on engine.

At the same time, on highways I mostly up-shift @ 2000 RPMs [don't let the turbo interfere] as I see good straight roads and lesser traffic.

Note: I remember shifting up the gears at low speeds dont give the turbo lag feel at all and the car feels faster as well [or its just a notion?] . Its when we rev hard at low RPMs where the turbo lag is more prominently felt.
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Old 3rd December 2010, 10:02   #20
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Originally Posted by swiftnfurious View Post

Note: I remember shifting up the gears at low speeds dont give the turbo lag feel at all and the car feels faster as well [or its just a notion?] . Its when we rev hard at low RPMs where the turbo lag is more prominently felt.
That's just because, being up shifting below 2000 RPM, you're simply not using the turbo and the engine will work in its NA range of RPMs. No turbo means, no lag. I've seen a lot of people complaining about the city drive ability because of turbo lag. But for me, the diesel torque is the perfect counterpart for the bumper to bumper traffic in city conditions. Also, why somebody want to be in the boost range in normal city conditions?
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Old 3rd December 2010, 10:21   #21
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Originally Posted by greenhorn View Post
I have two modes of driving. When I'm crusising ( relaxed) , i shift at 2000ish rpm, and try to prevent the turbo from kicking in. On the other hand, When I feel like flooring it, upshift at 3000ish and downshift at 1700 to keep the turbo on the boil
this is for the tata 1.4 tdi engine
I do exactly this on my Optra magnum 2.0.
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Old 3rd December 2010, 21:08   #22
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Originally Posted by greenhorn View Post
I have two modes of driving. When I'm crusising ( relaxed)
Since when Greeine?

Sorry for the OT, couldn't resist!

Quote:
Originally Posted by aargee View Post

Why is it not possible to kick in the turbo using some other methods such as source from the battery to kick in turbo electrically rather than mechanically at certain RPMs using ECU? Wouldn't that bring the best of both worlds in terms of mileage as well as power? So if an engine kicks it turbo at 2.5K RPM & gives best mileage at 1.8K RPM, why not kick in the turbo at 1.8K instead of doing it mechanically?
I have heard they use superchargers for marine (diesel) engines. I suppose they are not used (?) in cars because the engines don't usually Rev High?
Maybe someone could through more light!

Last edited by mobike008 : 6th December 2010 at 15:33. Reason: back to back posts within 20 mins. Next time use the EDIT button!
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Old 3rd December 2010, 23:04   #23
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Originally Posted by bhp_maniac View Post
That's just because, being up shifting below 2000 RPM, you're simply not using the turbo and the engine will work in its NA range of RPMs. No turbo means, no lag. I've seen a lot of people complaining about the city drive ability because of turbo lag. But for me, the diesel torque is the perfect counterpart for the bumper to bumper traffic in city conditions. Also, why somebody want to be in the boost range in normal city conditions?
Doesn't no turbo boost translate into turbo lag? In other words are you not driving in a permanent state of lag if you always up-shift before the turbo can spin up and produce meaningful boost? Please correct me there is more to turbo lag than that.
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Old 4th December 2010, 01:32   #24
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Originally Posted by YaeJay View Post
Since when Greenie?

Sorry for the OT, couldn't resist!
when on chaffeur duty (dad/mom/guests etc)
Quote:
Doesn't no turbo boost translate into turbo lag? In other words are you not driving in a permanent state of lag if you always up-shift before the turbo can spin up and produce meaningful boost? Please correct me there is more to turbo lag than that.
a turbo engine has essentially two modes of operation, with and without the turbo on. the delay taken for the turbo to spin up is called the lag time. If you are driving around with the turbo not juiced up, its just like driving a non turbo car, thats all
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Old 4th December 2010, 10:02   #25
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Originally Posted by mile201 View Post
Doesn't no turbo boost translate into turbo lag? In other words are you not driving in a permanent state of lag if you always up-shift before the turbo can spin up and produce meaningful boost? Please correct me there is more to turbo lag than that.
What you said is correct. When you up shift before the turbo boost range, you are in the lag range. But since you never come out of the lag range, you will not feel that a lag is there. Just human psychology. I know a friend of mine who test drove a Dzire VDi and told me, "What I liked in Dzire is that there is no turbo lag in this car" And afterwards when I enquired the dealer, he told that the turbo in the demo car was having bearing issues and hence not producing any boost
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Old 4th December 2010, 13:05   #26
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Originally Posted by bhp_maniac View Post
when I enquired the dealer, he told that the turbo in the demo car was having bearing issues and hence not producing any boost
When I test drove the Manza too, there was no Turbo, forget the lag. Also, the vehicle was yet to under go PDI.

This makes me doubt; can the turbo be deactivated/detuned for minimal turbolag(by dealers)?. Does the ECU have a role in switching on/off the turbo, with regard to engine RPM, rather than exhaust pressure only? (As the speedo on test vehicle was deactivated) .

That way, can the dealers convince the ignorant buyers about the infamous turbolag?.

Quote:
Originally Posted by bhp_maniac View Post
I know a friend of mine who test drove a Dzire VDi and told me, "What I liked in Dzire is that there is no turbo lag in this car"
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Old 4th December 2010, 14:05   #27
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Originally Posted by bhp_maniac View Post
Also, as somebody said the turbo is always spinning. It is not that the turbo starts spinning at the kick in rpm. The kick in rpm is the threshold at which the boost generated by the turbo overtakes the power needed to spin it at that rpm.
True. Turbo is connected to engine exhaust, as soon as the engine runs the exhaust gas will start running the turbo. As the engine gains rpm the quantity,pressure velocity etc of the exhaust gas increases which in turn speeds up the turbine rotation. And it'll take time to build up speed and the boost that time is the turbo lag.

But in case of supercharger, as it is connected to the engine, will gain speed faster than a turbo. Turbo doesn't use engine power to work, that is the main advantage.
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Old 4th December 2010, 14:44   #28
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Its the same philosophy in all vehicles- shift gears at the manufacturer recommended RPM/speeds.
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Old 5th December 2010, 03:04   #29
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Originally Posted by bhp_maniac View Post
What you said is correct. When you up shift before the turbo boost range, you are in the lag range. But since you never come out of the lag range, you will not feel that a lag is there. Just human psychology. I know a friend of mine who test drove a Dzire VDi and told me, "What I liked in Dzire is that there is no turbo lag in this car" And afterwards when I enquired the dealer, he told that the turbo in the demo car was having bearing issues and hence not producing any boost
Hey thanks I can see how that would happen. Mind is a powerful thing . This may be a little off-topic but is there a difference between the amount power produced by a turbocharged engine before the turbo kicks in and the same engine in non turbo form at the same RPM. I heard somewhere that turbo engines are tuned in such a way that they produce less power than an identical NA engine before the turbo starts producing boost...does this make sense?
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Old 5th December 2010, 17:50   #30
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Originally Posted by IndigoXLGrandDi View Post
Thanks all of you.

I will try to upshift
1) at 2500rpms for Indigo LS (IDI) since Max Torque is generated at 2500rpms.
2) at 1800-2000rpms for Indigo XL Grand DiCOR since Max Torque is generated at 1800-3000rpms.

My pick with the Manza and other tata diesels today would be 2000-2100 rpm for the upshift, gives you a good fuel efficiency(Avg. efficiency now 19.2 for my Manza diesel) and still gives you spirited driving. Too High rpmīs can be dangerous for your engine and AC compressor, but do not ever resist from downshifting when the engine is not pulling. Again too low rpms at load can also damage your moving parts.
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