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Old 31st March 2011, 12:15   #46
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Default Re: All you enthusiastic drivers - DONT OVER-REVV

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Originally Posted by drpullockaran View Post
For good and safe power in normally aspirated Diesels, Petrols and turbo charged petrols reduce the percentage values by half by which I mean instead of 50% use the 25% values. Remember that peak torque in all Petrols and normally aspirated diesels happen at a higher rpm.
For example: The GTX has peak torque at 4200 rpm so up shift at 25% above that rpm which works out to 5250 rpm. Though the GTX sings to 7000 rpm it is bound to damage the engine if revved to this level, though I have not heard of any GTX with a seized engine as yet. Down shift at peak torque values.
I haven't yet redlined any car in my life - i prefer driving slow. but i try to follow upshifting at around 5,000 RPM whenever there is an open stretch. upshifting at around 5,000 RPM usually gives me goose bumps and i always slow down after looking at the speedo.

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For fuel efficiency in all cars including the GTX up shift at 20% below peak torque rpm which for the GTX works out to 3360 rpm. Driving the GTX below 2000 rpm is counter productive since auto fuel cutoff in the GTX while decelerating only happens above 2000 rpm. Below 2000 rpm in the GTX fuel is continuously flowing even with your foot off the accelerator.
so lets say we take our foot off the accelerator at 3,000 RPM - the fuel is cut-off and again starts flowing at 2,000 RPM? but should it always cut off fuel once foot is taken off the pedal?

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Read the workshop service manual not the owners manual if you have doubts.
Do you have a soft-copy of the workshop manual?
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Old 31st March 2011, 16:39   #47
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Default Re: All you enthusiastic drivers - DONT OVER-REVV

Please note that REDLINING and OVER-REVVING are two entirely different things:

Redlining : Taking the engine to the redline. Some guys like me will insist that it's actually good for your petrol engine, especially if its done occasionally, on a well-lubricated, sufficiently-warmed up engine

Over-revving : This is mechanical, and does not require accelerator input. For example, say you are cruising in 5th gear at 120 kph, and then mistakenly downshift to 2nd (instead of 4th)....your (low) 2nd gear ratio will make the engine revv to well OVER the redline (thus, the term over-revv). Production engines aren't built for such high revvs and hence, your engine will inevitably self-destruct.

While the 1st situation is entirely optional, and there are some sedate drivers who will never redline their engines, the latter is completely accidental & can happen to the best of them.
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Old 31st March 2011, 17:32   #48
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Default Re: All you enthusiastic drivers - DONT OVER-REVV

Then how can engine braking be achieved without over revving.

Over revving and red-lining are 2 different aspects, but the final consequence would be the same right i.e engine is revving above its level for the gear ratio? Though till now I am not able to master engine braking(), I have seen my friends do that. When cruising in 5th gear at 120-140, they directly shift to 4th/3rd, and the engine automatically over-revs. This also might caues harm to the engine right?
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Old 31st March 2011, 17:49   #49
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Default Re: All you enthusiastic drivers - DONT OVER-REVV

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Originally Posted by _abhishek View Post
Then how can engine braking be achieved without over revving.

Over revving and red-lining are 2 different aspects, but the final consequence would be the same right i.e engine is revving above its level for the gear ratio? Though till now I am not able to master engine braking(), I have seen my friends do that. When cruising in 5th gear at 120-140, they directly shift to 4th/3rd, and the engine automatically over-revs. This also might caues harm to the engine right?
If at all you happen to hit the revv limited on downshifting ,that means you are already near the redline in the higher gear.

Over revving is the engine hitting the rev limited at much higher than the cut off revs.

I use engine braking most of the times ,no matter what speeds I am in ,but i let go the accelerator for a while and then downshift.
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Old 31st March 2011, 18:14   #50
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Default Re: All you enthusiastic drivers - DONT OVER-REVV

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Originally Posted by GTO View Post
Please note that REDLINING and OVER-REVVING are two entirely different things:

Redlining : Taking the engine to the redline. Some guys like me will insist that it's actually good for your petrol engine, especially if its done occasionally, on a well-lubricated, sufficiently-warmed up engine

Over-revving : This is mechanical, and does not require accelerator input. For example, say you are cruising in 5th gear at 120 kph, and then mistakenly downshift to 2nd (instead of 4th)....your (low) 2nd gear ratio will make the engine revv to well OVER the redline (thus, the term over-revv). Production engines aren't built for such high revvs and hence, your engine will inevitably self-destruct.

While the 1st situation is entirely optional, and there are some sedate drivers who will never redline their engines, the latter is completely accidental & can happen to the best of them.

I completely agree with GTO, At ford also, all cars that are released in the market are tested thoroughly and most of these engines have also been driven at the redline continuously for more than 24 hrs at race tracks around the world (just stopping for fuel in between). We make sure that this does not have any immediate or short term effect on the engines, However the life of the engine does decrease marginally in the long run but not significantly.

However, Nothing can be said of Over-Revving. Cars are simply not tested for that and will never be tested for that. Defects can range from No Change to a burnt head gasket to the engine seizing to operate completely, Basically anything may or may not go wrong with them.

So it is important that when you are driving spiritedly, make sure you put the correct gear or else...
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Old 31st March 2011, 18:22   #51
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Default Re: All you enthusiastic drivers - DONT OVER-REVV

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Then how can engine braking be achieved without over revving.
Very good question, Abhishek!

Engine-braking is HIGHLY recommended. However, use it cautiously. Do NOT drop into too low a gear at too high a speed. The best way to engine-brake (if you aren't familiar with your engine characteristics) is to go one gear lower at a time. Thus, in my previous example of cruising at 120 kph in 5th gear, and if I want to slow down, I'd drop to 4th....watch the revvs, then 3rd (and so on). Again, use engine braking but don't drop into too low a gear.

NOTE : Don't get too aggressive with diesels. Stay conservative. The limited revv range, among other reasons, is why. Engine breaking of diesels (vis a vis petrols) is one of the biggest disadvantages to an enthusiast.

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Cars are simply not tested for that and will never be tested for that.
Leaving aside testing, everyday car engines just aren't built to withstand 10,000 rpm (a possibility if you drop into 2nd at 120 kph).

Last edited by GTO : 31st March 2011 at 19:48.
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Old 31st March 2011, 19:34   #52
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Default Re: All you enthusiastic drivers - DONT OVER-REVV

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At ford also, all cars that are released in the market are tested thoroughly and most of these engines have also been driven at the redline continuously for more than 24 hrs at race tracks around the world
Thats great to know. Somehow due to poor NVH characteristics could never go beyond 5000 RPM in the Ikon Flair. However Fiesta 1.4 was different, much smoother all the way.

Lets say we are pottering at 4th gear at 45-50kmph when RPM is around 1.5K. If we shift quickly to first gear at that point and RPM increases to 5-6k, will this be an example of over revving?
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Old 1st April 2011, 01:00   #53
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Default Re: All you enthusiastic drivers - DONT OVER-REVV

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Originally Posted by planet_rocker View Post
so lets say we take our foot off the accelerator at 3,000 RPM - the fuel is cut-off and again starts flowing at 2,000 RPM? but should it always cut off fuel once foot is taken off the pedal?

Thats the one part of the blue motion technology that the new passat is harping about which was there in the GTX 11 years ago. I do not know the reason why they do not implement it below 2000rpm since it is bound to save fuel. They must have a very good reason to continue fuel flow below 2000rpm.


Do you have a soft-copy of the workshop manual?
The soft copy is 260mb,
file for download from Palio Users Group
.
My answers are below your questions in Italics and underlined.
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Old 1st April 2011, 07:37   #54
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Default Re: All you enthusiastic drivers - DONT OVER-REVV

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Originally Posted by dot View Post
Thats great to know. Somehow due to poor NVH characteristics could never go beyond 5000 RPM in the Ikon Flair. However Fiesta 1.4 was different, much smoother all the way.

Lets say we are pottering at 4th gear at 45-50kmph when RPM is around 1.5K. If we shift quickly to first gear at that point and RPM increases to 5-6k, will this be an example of over revving?
Yes the RPM will go above 6K in that case and will cause over revving.
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Old 1st April 2011, 10:18   #55
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Default Re: All you enthusiastic drivers - DONT OVER-REVV

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Though till now I am not able to master engine braking
Its very easy. Just imagine that you are zooming at 120 speed. If you need to brake just start pressing the brakes. As the speed reduces you have to know what the load taking capacity of the engine is. As speed lowers start shifting gears to lower value. Simple.

Yesterday saw "Superfactories: Audi".
Do you guys know that "each" Audi R8 engine is redlined for a long time at its max value of 9k rpm. Infact it goes so hot that the entire exhaust tubing around the engine gets red. Yes guys. RED HOT. I saw it. Wonder why it did not catch fire.They keep it at that level for a fixed amount of time. Then the engine is taken off and then let to cool. Then its fitted.

OT: The roof of Audi R8 is made using a hydo something. In simple terms pressurised water is put on the metal sheet so that it bulges out in the correct shape. Now how cool is that?

OT OT: Audi 4 rings symbolise the intial 4 companies which came together to form it.

Last edited by download2live : 1st April 2011 at 10:24.
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Old 1st April 2011, 11:04   #56
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Default Re: All you enthusiastic drivers - DONT OVER-REVV

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Originally Posted by download2live View Post
...
Yesterday saw "Superfactories: Audi".
Do you guys know that "each" Audi R8 engine is redlined for a long time at its max value of 9k rpm. Infact it goes so hot that the entire exhaust tubing around the engine gets red. Yes guys. RED HOT. I saw it. Wonder why it did not catch fire.They keep it at that level for a fixed amount of time. Then the engine is taken off and then let to cool. Then its fitted.
...
I was about to mention this when I saw your post. Seeing that thing red hot (like you see at a blacksmith's place) was scary to say the least.

I do redline my car occasionally on open roads.
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Old 1st April 2011, 13:00   #57
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Default Re: All you enthusiastic drivers - DONT OVER-REVV

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Originally Posted by GTO View Post
Redlining : Taking the engine to the redline. Some guys like me will insist that it's actually good for your petrol engine, especially if its done occasionally, on a well-lubricated, sufficiently-warmed up engine
And why is that. I have heard several people saying its true. But what is the logic?

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Originally Posted by GTO View Post
Over-revving : This is mechanical, and does not require accelerator input. For example, say you are cruising in 5th gear at 120 kph, and then mistakenly downshift to 2nd (instead of 4th)....your (low) 2nd gear ratio will make the engine revv to well OVER the redline (thus, the term over-revv). Production engines aren't built for such high revvs and hence, your engine will inevitably self-destruct.
The solution is simple. Design a ECU that will put the transmission in neutral or disengage the clutch when the RPM goes over 7000. Not impossible I guess.
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Old 1st April 2011, 13:33   #58
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Default Re: All you enthusiastic drivers - DONT OVER-REVV

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And why is that. I have heard several people saying its true. But what is the logic?
The Italian method of blowing out cobwebs.

Works. By validating the engine. If you don't push your engine from time to time, you don't know how off tune it is. Beyond that, guess no logic, except that might blow/ burn soot out of the exhaust system.

Redline my cars, including Diesels regularly.

Regards
Sutripta

Last edited by Sutripta : 1st April 2011 at 13:35.
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Old 1st April 2011, 13:47   #59
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Default Re: All you enthusiastic drivers - DONT OVER-REVV

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The solution is simple. Design a ECU that will put the transmission in neutral or disengage the clutch when the RPM goes over 7000. Not impossible I guess.
That would be dangerous, may result in accidents or losing control.
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Old 1st April 2011, 15:42   #60
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Default Re: All you enthusiastic drivers - DONT OVER-REVV

What happens when you down shift at high speeds on an auto box(automatic)..?
My 1st Prado which had 90k on the clock when I got a new one. i used to frequently downshift on the auto box because I hated the brakes(I still do). Nothing happened to the engine then and the new owner has clocked another 80k on it and the engine still sings well.

The second Prado is at 85k now with even harsher treatment and no problems yet.

Can anyone post comments with regards to an automatic gearbox.
What are the consequences of downshifting at high speeds on the gearbox and ancilliary components apart from the engine ?

OT > If anyone can please answer this.
What is the effect(on the engine) of idling the engine with ac on for over 48 hours in the middle eastern desert summer above 50'c ?

Thanks,

Jay
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