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Old 12th March 2008, 16:43   #46
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Originally Posted by praveen_v View Post
I have tried coming downhill twice with the car on 2nd gear, but felt that the rpm was getting high. What should I do in such cases??
If RPM gets high then you obviously break and get the RPM to 2500 levels. If it is very steep, in rare instances, you may have to use 1st gear. But this situation is very rare.
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Old 12th March 2008, 17:11   #47
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Originally Posted by rahuldeodhar View Post
Hi Praveen,

#) Engine braking is drain on FE (higher revs meanings more times fuel in cylinder - for reducing distance covered - hits FE- obviously!)
As someone mentioned, ECU can detect this and stop sending fuel to engine. Engine can keep running off the momentum transmitted through clutch.

So, I am not sure about impact on FE.
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Old 12th March 2008, 17:16   #48
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Hi Praveen,

you press the clutch just before engine shows signs of struggling.

While going downhill you should brake while in gear
While going down steep slopes keep yourself in 2nd gear - if the car might seem to rev hard then brake to reduce speed - cruise at slow speed - at speed similar to uphill speed on that same road.

And remember just dont clutch while going down a slope.

Also - I didnt get diesel fans' view on getting to 1st gear - he probably meant something else - and I misunderstood - but I wont go to first gear unless its absolute killer slope I am encountering - have done a few near verticals in Darjeeling Sikkim stretch - 2nd seems to work fine for me.


We need to remember that car with correct-gear engaged is under more control than car in neutral. Anything that keeps you closest to this situation - is best alternative - rest is personal driving style. (I mean method not style as in style statement!)

RD
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Old 12th March 2008, 17:31   #49
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Default ECU and braking FE

Hi Netfreak,

You are right its not so straight forward.

(Thinking aloud)
In most cases ECU does not fully reduce the fuel mix to below idling levels (or does it??)

also even if it does - it does not cut off cylinders
- a brake+clutch pressed engine revs at lower level than - only brake pressed engine - ECU kicks in at some threshold RPM above the idling RPM

I guess its only on recent Toyota Prius where ECU cuts-off cylinders in case of braking. Does any Indian car ECU do that? - please let us know guys.

A test can be - if you brake - and ECU is sending a leaner fuel mix - you will experience drastic loss of power

anycase ECU has to kick in a little higher than idling revs to prevent stalling


- so even with ECU there should be some - however miniscule- FE loss.


RD
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Old 12th March 2008, 17:35   #50
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Originally Posted by DieselFan View Post
If RPM gets high then you obviously break and get the RPM to 2500 levels. If it is very steep, in rare instances, you may have to use 1st gear. But this situation is very rare.
First part is ok. But the thing is the greater the gradient of the slope, higher the RPM in a gear,say 2nd gear. Now if I shift down to first, the rpm will get even higher right??

Quote:
Originally Posted by rahuldeodhar View Post
Hi Praveen,

you press the clutch just before engine shows signs of struggling.

While going downhill you should brake while in gear
While going down steep slopes keep yourself in 2nd gear - if the car might seem to rev hard then brake to reduce speed - cruise at slow speed - at speed similar to uphill speed on that same road.

And remember just dont clutch while going down a slope.

Also - I didnt get diesel fans' view on getting to 1st gear - he probably meant something else - and I misunderstood - but I wont go to first gear unless its absolute killer slope I am encountering - have done a few near verticals in Darjeeling Sikkim stretch - 2nd seems to work fine for me.
Thanks man.. great explanation
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Originally Posted by NetfreakBombay View Post
As someone mentioned, ECU can detect this and stop sending fuel to engine. Engine can keep running off the momentum transmitted through clutch.

So, I am not sure about impact on FE.
How do I know if a car's ECU does this or not??
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Old 12th March 2008, 18:12   #51
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Originally Posted by praveen_v View Post
How do I know if a car's ECU does this or not??
I don't think there could be a way other then testing engine in a lab like situation.

But thats just my opinion and I do not have mechanical/automobile background so take that with a pinch of salt.
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Old 13th March 2008, 11:49   #52
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Originally Posted by hyper123 View Post
In very extreme cases, keep braking as hard as possible without locking up your wheels and simultaneously shift-down one gear at a time but do not blip the throttle (do not rev-match) when you engage the clutch after downshifting, but take care not to over-rev while doing so.
Most important - practice this before hand.

If your are not comfortable doing this, then its best to do what nitrous has suggested.
Can the driver control the locking of wheels while braking hard?
What is blipping the throttle? Could someone explain me in detail (laymans lang)?
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Old 13th March 2008, 18:51   #53
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Can the driver control the locking of wheels while braking hard?
What is blipping the throttle? Could someone explain me in detail (laymans lang)?
No, that is why I said one must practice. If you don't panic during those emergency braking situations, you can the pump the brakes when the wheels start locking up.

When you shift into a lower gear, the engine RPM increases, in order to minimize damage to the synchronisers, etc., you press the accelerator (blip) just before you engage the clutch, so that the engine RPM increases and will already be running at the required RPM for that particular gear.

For example, in my pulsar 150: consider that I'm doing 60 in 5th gear @4700 RPM. Now when I shift to 4th at the same speed, I wring the throttle a little so that tacho reads some 5500+ RPM, and then engage the clutch. It results in a very smooth downshift, no fork-dive whatsoever.
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Old 13th March 2008, 19:26   #54
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Sorry sir, I was not able to understand

Quote:
Originally Posted by hyper123 View Post
For example, in my pulsar 150: consider that I'm doing 60 in 5th gear @4700 RPM. Now when I shift to 4th at the same speed,
Is this down shift to 4th without pressing the clutch?


Quote:
Originally Posted by hyper123 View Post
I wring the throttle a little so that tacho reads some 5500+ RPM, and then engage the clutch. It results in a very smooth downshift, no fork-dive whatsoever.

Already it was down shifted to 4th, then whats the need to engage the clutch (i.e pressing the clutch)
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Old 13th March 2008, 19:31   #55
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Originally Posted by Surprise View Post
Can the driver control the locking of wheels while braking hard?
What is blipping the throttle? Could someone explain me in detail (laymans lang)?
suppose your in 5th gear cruising at 60kmph at 2k rpm. if you shift down to second the rpm will go up to about 5k. now if you do shift from 5th to 2nd just before you release the clutch after slotting it in second you give the accelerator a dab to raise the rpm so that when you do release the clutch the rpm difference is minimised.
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Old 13th March 2008, 19:42   #56
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My guess is that we are taking about engine braking to minimize the stopping distance

Quote:
Originally Posted by akshay1234 View Post
suppose your in 5th gear cruising at 60kmph at 2k rpm. if you shift down to second the rpm will go up to about 5k. now if you do shift from 5th to 2nd just before you release the clutch after slotting it in second you give the accelerator a dab to raise the rpm so that when you do release the clutch the rpm difference is minimised.
Overall intention itself is to stop the car as quickly as possible, if we blip the accelerator while releasing clutch, is not the overall purpose defeated?
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Old 13th March 2008, 20:02   #57
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Originally Posted by Surprise View Post
My guess is that we are taking about engine braking to minimize the stopping distance



Overall intention itself is to stop the car as quickly as possible, if we blip the accelerator while releasing clutch, is not the overall purpose defeated?
i was telling you what blipping the accel is. if you want to stop quickly your obviously not gonna do it.
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Old 13th March 2008, 20:21   #58
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Originally Posted by Surprise View Post
Sorry sir, I was not able to understand
Is this down shift to 4th without pressing the clutch?

Already it was down shifted to 4th, then whats the need to engage the clutch (i.e pressing the clutch)
Step 1: Disengage clutch.
Step2: Shift into lower gear and press accelerator (or wring throttle) and increase the engine RPM.
Step3: Engage the clutch and accelerate.

All these steps combined take just about a second to complete!!

If it is emergency braking, then you do not do this, as I have mentioned here -
Quote:
In very extreme cases, keep braking as hard as possible without locking up your wheels and simultaneously shift-down one gear at a time but do not blip the throttle (do not rev-match) when you engage the clutch after downshifting, but take care not to over-rev while doing so.
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Old 13th March 2008, 21:59   #59
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Thanks Hyper 123 and Akshay 1234.
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Old 10th September 2008, 14:07   #60
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Quote:
Originally Posted by nitrous
This practice of clutching and braking is from Indian bike riding which is carried onto cars.Bad practice in cars!
Just brake,don't clutch.I've done this a million times and although it lugs once the speed goes real low,i cant remember once when its stalled.
That means whether in emergency/non-emergency situations we just need to slam the brakes as heavily as possible with the clutch pressed. No need for downshifting unlike bikes !
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