Go Back   Team-BHP > Under the Hood > Technical Stuff


Reply
 
Thread Tools Search this Thread
Old 4th February 2007, 10:52   #91
Newbie
 
Join Date: Jan 2007
Location: Boston
Posts: 21
Thanked: 4 Times
Default

Do you guys mean to say that there is never a time that you're coming to a stop because someone in front of you is braking, or that you're never coming to a stop without someone behind you?

Maybe it *is* a true driving-culture difference here, but every single day I find at least a dozen circumstances where I'm not putting myself in an adverse situation by coasting in neutral.


Funny story about a red light though -- I was driving behind a friend of mine in my brother's POS Ford Explorer ("exploder") and it was raining terribly. I called him to tell him to slow down because it was scary to drive in the rain (he was driving a well-tired sportscar and could go much faster). As we come up to a light it turns yellow with WAY more than enough time for both of us to go through, but he accelerates, hesitates, then decides at the last second he's going to stop for the light. I ended up in a panic stop knowing that I couldn't avoid hitting him (huge discrepancy in stopping ability), he noticed and floored it at the last second to lessen the impact. That acceleration didn't make much of a difference either way, but the car was fine.
Multiades is offline   Reply With Quote
Old 4th February 2007, 15:21   #92
Senior - BHPian
 
Shan2nu's Avatar
 
Join Date: Feb 2004
Location: Hubli - Karnata
Posts: 5,525
Thanked: 87 Times
Default

Quote:
Do you guys mean to say that there is never a time that you're coming to a stop because someone in front of you is braking, or that you're never coming to a stop without someone behind you?
We do come to a stop, but we're never in neutral at that point. The only time i use neutral is when the car needs to be stopped for a certain peroid of time (EG : At a red signal).

If it's a stop-go situation, i use the clutch.

As far as i know, i never coast in neutral.

Shan2nu
Shan2nu is offline   Reply With Quote
Old 9th April 2007, 22:57   #93
BHPian
 
rdkarthik's Avatar
 
Join Date: Sep 2005
Location: bangalore
Posts: 206
Thanked: 11 Times
Lightbulb

Quote:
Originally Posted by RX135 View Post
Thanks Rehaan! I had understood about that wheel running the engine part and also the logic behind cutting off the fuel supply as you mentioned. I was just curious to know, what happens when NO fuel is supplied to the cylinders. Do the cylinders fire (since there is nothing to fire without fuel)? Does it change or should it change the exhaust note?
Quote:
Originally Posted by Gordon View Post
Is this possible?!
If there is absolutely no fuel supplied => engine is stalled/off.
When an engine is driven by the wheels, i.e. when engine RPM is more than about 1500 - 1800RPM with throttle at idle position, the ECU enters what is called as "decceleration mode", where fuel to the engine is cut off completely as Rehaan said...

On most cars its just a fuel-only cut. Plugs will still fire, but it does not matter as there is no fuel to combust. As regards exhaust sound, even if you turn off your engine when decelerating in-gear it still sounds the same....

Its different on a carb engine, in this condition of high vacuum in manifold, small amounts of fuel does get into cylinder, and if its slightly on the richer side ( with appropriate ignition timing ), you hear a 'pop' in the exhaust, thats the mixture burning through the exhaust stroke...
rdkarthik is offline   Reply With Quote
Old 10th April 2007, 00:16   #94
BHPian
 
sreenivass's Avatar
 
Join Date: Oct 2006
Location: Bangalore India
Posts: 872
Thanked: 6 Times
Default I think it is genrally more complicated

Quote:
Originally Posted by vid6639 View Post
Thats the best example Shan2nu. Happened to me once too. saw amber light approaching a signal at which no one was there. braked hard. cause it would have been red if i tried to shoot past and what happens instead, A girl driving a Santro rear ends my car and end up having Rs.50K of repairs.

If I had looked back and was in gear I would have jumped the signal. I generally glance at the mirrors before braking hard but missed it that time. I'm always in gear for that very reason If I see that the guy behind cant brake I accelerate.

My friends Esteem got converted to a 800 after he braked for a speed breaker but the truck behind didn't see it. The car was a total write off as the trucker was doing probably 60+kmph.

Highly unpredictable here and you never know when you have to brake dodge or even accelerate. You need to be ready to do any of the 3.
On rare occasions what you said might be true vid, but in general I have seen the situation is more complicated. It is like we are stuck between a rock and a hard place. Cross traffic eager to move 10 seconds before the loght goes green and guys behind pressurizing to go because it is the last few seconds before the light turns red. One can not avoid sudden brakes because our pedestrians/bikes/ autos could fall from sky and appear right infront of us.
sreenivass is offline   Reply With Quote
Old 10th July 2007, 01:44   #95
Distinguished - BHPian
 
Thad E Ginathom's Avatar
 
Join Date: Jun 2007
Location: Chennai
Posts: 7,839
Thanked: 7,211 Times
Default

Three months later, and got redirected to this thread from this one (Which is the right Sequence Clutch-Brake Or Brake-Clutch).

I'd like to add a point... If you changed in to neutral and coasted, even on a clear road, whilst taking a British driving test, you'd fail. Similarly you'd fail for depressing the clutch too soon before a stop.

Actually, the British test is a pretty fair assessment of one's ability to control a car and perform all the basic manoeuvre's required of every-day driving. For a start (no pun intended) it includes an emergency stop. Many candidates fail it one or more times (second time pass, myself <Blush>)

As a previous poster put it in this thread, it is not about brakes, or engine wear, it is about control and stability.
Thad E Ginathom is offline   Reply With Quote
Old 31st January 2008, 10:04   #96
BHPian
 
Sagittarian's Avatar
 
Join Date: Aug 2007
Location: Chennai
Posts: 61
Thanked: Once
Default

If i see a toll gate 1000 mts ahead while travelling at a speed of 80 kmph. Just i will remove my foot from the acceleration pedal & slowly apply the break, till it goes to the stage of knocking before which I press the clutch and turn it to neutral.
Good practice. In modern ECU-driven cars, shifting to neutral would mean sending more fuel to the engine than lifting the foot from the gas-pedal.
Sagittarian is offline   (1) Thanks Reply With Quote
Old 31st January 2008, 18:39   #97
Team-BHP Support
 
Rehaan's Avatar
 
Join Date: Feb 2004
Location: Bombay
Posts: 22,367
Thanked: 22,586 Times
Default

Quote:
Originally Posted by Sagittarian View Post
If i see a toll gate 1000 mts ahead while travelling at a speed of 80 kmph. Just i will remove my foot from the acceleration pedal & slowly apply the break, till it goes to the stage of knocking before which I press the clutch and turn it to neutral.
Good practice. In modern ECU-driven cars, shifting to neutral would mean sending more fuel to the engine than lifting the foot from the gas-pedal.
Correct, but also downshifting while braking will give you better engine braking, allow you to go slower before the knocking begins and also reduce load on your brakes.

cya
R

Last edited by Rehaan : 14th January 2009 at 01:38.
Rehaan is offline   Reply With Quote
Old 31st January 2008, 19:54   #98
Senior - BHPian
 
ram_hyundai's Avatar
 
Join Date: Jun 2006
Location: Calicut ,trisur
Posts: 2,019
Thanked: 48 Times
Default

you can put to neutral at any point of time.but not on a down hill drive.the only disadvantage i feel in putting neutral a few meters away from the stop light is excessive usage of brake pads.the amount you save on fuel by doing this would match the amount you spend on changing the pads earlier.
ram
ram_hyundai is offline   Reply With Quote
Old 31st January 2008, 20:04   #99
Senior - BHPian
 
Join Date: Jun 2007
Location: Kochi
Posts: 2,147
Thanked: 143 Times
Default

There was a talk about people can coast in neutral with engines off. (The post discourages the practise - and I agree). Here is some more info you should consider before deciding that you do not want to take the risk.

Most cars nowadays come with power assisted brakes - and almost all of us are used to it. And then, we are also used to power steering too. With engines off, both power assist brakes and power steering will not work. Braking will take longer, and more effort. And steering is going to be a lot more stiffer. Do not coast in neuteral. Do not even think of moving a car with engines switched off.
BaCkSeAtDrIVeR is offline   Reply With Quote
Old 1st February 2008, 00:06   #100
Distinguished - BHPian
 
Thad E Ginathom's Avatar
 
Join Date: Jun 2007
Location: Chennai
Posts: 7,839
Thanked: 7,211 Times
Default

No, you should not shift to neutral, or drive with your foot on the clutch, at any time* except when the car is about to stop.

Why? Because engine braking gives more control over the car.

Haven't we covered this pretty extensively?

*stop-start crawling traffic has to be an exception: if the car would be going too fast in 1st or second at idling engine speed, then we must depress the clutch and use the brake to slow down. This is the time when I most want to be driving an auto!
Thad E Ginathom is offline   Reply With Quote
Old 10th November 2008, 10:57   #101
BHPian
 
Join Date: May 2007
Location: CHENNAI
Posts: 168
Thanked: Once
Default

I think you are applying the break bit early and brake stress would be more when you press BRAKES when the car moves @ say 80 kmph.Instead what i do is ..when the car moves at 70-80 before a toll or a signal and when the road ahead is sort of safe manoeuvre then i remove my foot from the accelerator....it slows down and at the time of car "just" before getting into engine knocking i shift gear to neutral . one needs to press the brake just before the toll/signal when car moves at about 15 to 25 kmph . this -to me- is better for brakes and car FE would be more effective as it does not move too much on NEUTRAL which is not FE friendly when you compare to today's car which actually cut off fuel when there is no LOAD on the accelerator . ( correct me if iam wrong--CMIIW . The idea is to use the combination of engine braking, light braking and reduce clutch/gear shift more than it REALLY needs.

Quote:
Originally Posted by Surprise View Post
If i see a toll gate 1000 mts ahead while travelling at a speed of 80 kmph. Just i will remove my foot from the acceleration pedal & slowly apply the break, till it goes to the stage of knocking before which I press the clutch and turn it to neutral.
shapath is offline   Reply With Quote
Old 10th November 2008, 14:20   #102
Team-BHP Support
 
Rehaan's Avatar
 
Join Date: Feb 2004
Location: Bombay
Posts: 22,367
Thanked: 22,586 Times
Default

Shapath,

Your procedure and logic sounds correct. Though...

Quote:
Originally Posted by shapath View Post
..it slows down and at the time of car "just" before getting into engine knocking i shift gear to neutral . one needs to press the brake just before the toll/signal when car moves at about 15 to 25 kmph ....
...if you downshift to 2nd you shouldnt have to press the clutch or shift to neutral until about 5-10km/h (which is when the knocking will begin).

(Also, I prefer 5>4>3>2>N or even 5>2>N than 5>N)

cya
R

Last edited by Rehaan : 10th November 2008 at 14:21.
Rehaan is offline   Reply With Quote
Old 27th December 2008, 15:42   #103
GTO
Team-BHP Support
 
GTO's Avatar
 
Join Date: Feb 2004
Location: Bombay
Posts: 47,729
Thanked: 89,228 Times
Default

According to Toyota, shifting to neutral doesn't save any fuel. Most modern cars come with a fuel-cutoff system. Thus, stay in gear so you save fuel & get free engine braking.

Quote:
"We went in search of an expert opinion on this one. According to Paul Williamsen, the product education manager at Toyota, “All contemporary Toyota and Lexus vehicles (and every other car built since the 1990s that I’ve looked at) can detect the condition when engine revs are higher than idle with a fully closed throttle: Under these conditions, all current to the fuel injectors is stopped, and no fuel is injected.” That means if your foot is off the gas while the car’s in gear, you’re not using any fuel.
C&D linky
GTO is offline   Reply With Quote
Old 29th December 2008, 12:33   #104
BHPian
 
the_maassk's Avatar
 
Join Date: Sep 2008
Location: Vadodara/ NG7 2QP
Posts: 205
Thanked: 4 Times
Default

Quote:
Originally Posted by GTO View Post
According to Toyota, shifting to neutral doesn't save any fuel. Most modern cars come with a fuel-cutoff system. Thus, stay in gear so you save fuel & get free engine braking.



C&D linky
I can confirm this is true. I have an Aveo U-VA with a ScanGauge II installed. If I take my foot off the A pedal, the fuel to the engine is cut-off (ScanGauge shows 0.0 LHK (liters per hundred kilometers) and the Fuel Loop is open.
the_maassk is offline   (1) Thanks Reply With Quote
Old 29th December 2008, 20:23   #105
BHPian
 
GTO - Touring's Avatar
 
Join Date: Aug 2004
Location: Mumbai
Posts: 713
Thanked: 13 Times
Default

Quote:
Originally Posted by the_maassk View Post
I can confirm this is true. I have an Aveo U-VA with a ScanGauge II installed. If I take my foot off the A pedal, the fuel to the engine is cut-off (ScanGauge shows 0.0 LHK (liters per hundred kilometers) and the Fuel Loop is open.
Sweet! Thank you for sharing your scangauge results. Now, you don't have any reason to shift to neutral while coasting. Plus, the engine braking makes it safer to stay in the gear.
GTO - Touring is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Palio 1.2 nv - Pressing the clutch pedal while starting the car kapilsharma80 Technical Stuff 24 18th February 2013 22:12
Xing: High rev when pressing the clutch during gear change raghu Technical Stuff 11 11th October 2009 07:06
cheen-cheen-cheen noise when pressing accelerator vebmetal Technical Stuff 15 27th August 2008 13:33
Which is the right Sequence Clutch-Brake Or Brake-Clutch ankura12 Technical Stuff 2 9th July 2007 10:02


All times are GMT +5.5. The time now is 04:39.

Copyright 2000 - 2017, Team-BHP.com
Proudly powered by E2E Networks