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Old 28th November 2010, 14:15   #1
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Question When do you shift gears?

What is the Correct Way to Upshift the Gears in Turbocharged Engines in case of Petrol and Diesel Engines?

Should the Engine be revolved more than the Rpm at which the Turbocharger comes in action (Typically 2000-2500rpms) or is it OK to upshift at lower rpms?


Also, in Indigo Diesel's Manual it is given that "Shift to higher gears as soon as it is possible. Use each gear upto 2/3rd of itís maximum engine speed."

Should I revolve the Engine of Indigo LS (IDI) and Indigo XL (DiCOR), upto 3000-3500 rpm before upshifting or is it OK to upshift at 2000-2200 Rpms?

Last edited by aah78 : 8th June 2011 at 22:36.
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Old 28th November 2010, 14:47   #2
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Quote:
Originally Posted by IndigoXLGrandDi View Post
What is the Correct Way to Upshift the Gears in Turbocharged Engines in case of Petrol and Diesel Engines?

Should the Engine be revolved more than the Rpm at which the Turbocharger comes in action (Typically 2000-2500rpms) or is it OK to upshift at lower rpms?


Also, in Indigo Diesel's Manual it is given that "Shift to higher gears as soon as it is possible. Use each gear upto 2/3rd of itís maximum engine speed."

Should I revolve the Engine of Indigo LS (IDI) and Indigo XL (DiCOR), upto 3000-3500 rpm before upshifting or is it OK to upshift at 2000-2200 Rpms?
I don't have any personal experience with turbo-diesels but i did find this bit of info dangling on the web:
Because of the low RPM torque of a turbo-diesel engine, one can upshift earlier to save fuel. However, don't upshift so early that the engine lugs. In vehicles with exhaust gas recirculation (EGR), particulate soot combines with oil from the turbo and can build up on the walls of the intake. This buildup reduces power and economy and is exacerbated by lugging the engine (demanding more torque than is available, below the RPM that the turbo spools up). This is because reduced air velocity in the intake allows for more buildup. The solution is to make sure not to shift too low and to let the engine spool up to higher RPMs under load every so often. This issue has been documented by many VW TDI drivers. For these engines keeping the RPMs above 1800 when accelerating is a good rule of thumb.

When driving, gear up as soon as you can. Get into the habit of spending the least amount of time possible in the lower gears. Conversely, gear down (or speed up) whenever you hear your car struggling in a high gear. You should not feel a strain on your transmission, but most people tend to wrongly delay their shifting to higher gears by several hundred RPM. You will feel a slight decline in your acceleration when you shift sooner, but once again, try hard to shed any addiction to power, speed, and acceleration. Those things are incompatible with optimizing fuel mileage. Try hard to retrain yourself to the new shift-times.
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Old 28th November 2010, 14:51   #3
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Shifting gears depends on various conditions.

If you want to accelerarte as quickly as possible you shift when the torque is starting to drop significantly.

If you want to shift fuel efficiently you shift in smaller turbo engines to drop in the next gear to about 1500rpm. As different cars have different gear ratios it is very difficult to be specific.

Very large turbo Diesel tick over at 200rpm and peak at 1200 to 1500 rpm these would be shifted much earler.

Du to the kind of engine the Diesels are it is not advisable to run them prolonged near the rev limit.

Petrol turbos especially when they are of small capacity should be operated in the rpm range where the turbo kicks in unless it is in first and second gear.
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Old 28th November 2010, 16:19   #4
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Well in case of Diesel turbo charged engines, the best/ efficient method to shift up is at the top of torque curve. So if your car's max torque band is 200-2500 rpm, then shift up at in that range but preferably closer to higher side so that even with the drop in revvs, the engine is still in the torque band.

My 2 paisa.
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Old 28th November 2010, 18:28   #5
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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.
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Old 28th November 2010, 18:42   #6
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I dont think there is any specific way to upshift for a turbocharged engine.
Point being - if you shift at too low an rpm, you risk lugging the engine and stalling.
if you rev in gear till you are in the zone where the turbo spools then thats OK too.
Case in point - the Safari engine turbo comes in at 2200-2500rpm(correct me if im wrong). If you upshift below 2000rpm, the vehicle will still pull, but some vibration is felt inside the cabin while the engine lugs. Above 2000/2200 rpm, the vehicle pulls normally.
So if your trying to increase economy without affecting your ride comfort, its best to upshift at the point where your engine is not gasping/starved of revs.
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Old 28th November 2010, 19:40   #7
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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
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Old 28th November 2010, 20:30   #8
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Quote:
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
+1 to what he said. It clearly depends upon your driving style. Shift early for mileage and shift late for more power. Anyway shifting in between 1800-2200rpm will give you both power and decent mileage, coz there is no point in having a turobo'd engine unless and until you use it!
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Old 29th November 2010, 09:31   #9
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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.
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Old 29th November 2010, 10:29   #10
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Quote:
Originally Posted by IndigoXLGrandDi View Post
What is the Correct Way to Upshift the Gears in Turbocharged Engines in case of Petrol and Diesel Engines?
There can be no universal correct way it depends on engine and gearbox in question.
Quote:
Originally Posted by IndigoXLGrandDi View Post
Should the Engine be revolved more than the Rpm at which the Turbocharger comes in action (Typically 2000-2500rpms) or is it OK to upshift at lower rpms?
The key is to keep the vehicle in the power-band. If the turbo kicks in at 2000 RPM then shift above this
Quote:
Originally Posted by IndigoXLGrandDi View Post
Also, in Indigo Diesel's Manual it is given that "Shift to higher gears as soon as it is possible. Use each gear upto 2/3rd of itís maximum engine speed."

Should I revolve the Engine of Indigo LS (IDI) and Indigo XL (DiCOR), upto 3000-3500 rpm before upshifting or is it OK to upshift at 2000-2200 Rpms?
As soon as possible here means when the engine enters the correct power-band and speed. Pushing RPM too high will increase fuel consumpetion and does not make any sense untill you are racing against someone
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Old 29th November 2010, 10:35   #11
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Quote:
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?
the turbo is always spinning, its only at 1.8k rpm or 2k in certain cars that the car gets the boost into the engine i.e pressurized intake manifold air after the sufficient boost is reached .So we set it at a lower rpm, the intake would get a lower boost (lesser pressure)and performance would not be the same what you would get at higher rpm boost. If your question is about running the turbo with a motor and battery ? the reason why its not possible at the moment is because a turbo spins at very high rpm , 50,000rpm + and there are very few electric motors which run at that speed .
This my understanding, someone correct me if i am wrong!

Last edited by amulu10 : 29th November 2010 at 10:38.
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Old 29th November 2010, 11:07   #12
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Quote:
Originally Posted by amulu10 View Post
the turbo is always spinning, its only at 1.8k rpm or 2k in certain cars that the car gets the boost into the engine i.e pressurized intake manifold air after the sufficient boost is reached .So we set it at a lower rpm, the intake would get a lower boost (lesser pressure)and performance would not be the same what you would get at higher rpm boost. If your question is about running the turbo with a motor and battery ? the reason why its not possible at the moment is because a turbo spins at very high rpm , 50,000rpm + and there are very few electric motors which run at that speed .
This my understanding, someone correct me if i am wrong!
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.
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Old 29th November 2010, 15:04   #13
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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?

A turbo charger is something that works with the help of exhaust gases. And in most engines, the required exhaust pressure to for the turbine to spin is at around 2k. Now, if your goal is just forced induction and need boost earlier, you can use a supercharger instead of a turbo charger, but the whole point of power with efficiency (which is used in small hatchbacks) will be lost. Also, I think installing a supercharger is expensive.
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Old 29th November 2010, 16:35   #14
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I always follow the simple Rule,
Upshift after you have moved slightly above the max torque rpm.
Downshift when the rpm drops close to 1300 rpm mark .
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Old 29th November 2010, 16:53   #15
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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)
  2. Will up-shifting at high rpms heat the engine to above the idea engine temperatures?
I assumed that there could be different ways of up-shifting/down-shifting depending on what one wants (3 scenarios below):
  • Fuel efficiency
  • Spirited driving (rev-happy drivers)
  • Driving in a way that is optimal for engine life, thereby working well until very high mileages.
Can the gurus throw some light on this?

Last edited by vasanthn21 : 29th November 2010 at 16:55.
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