does it use gas to slow down by downshifting
08-04-2005 | 07:05 AM
#31
Joined: Mar 2001
Posts: 37,305
Likes: 16
Originally Posted by sars,Aug 4 2005, 06:01 AM
why are you heel-toeing for downshifts at such low RPM's (and on the street no less?).
This is just one of those concepts I spoke of that certain drivers have no understanding of. They do it because it's "neat" ("I heel/toe all the time") or because they see race car driver's do it or they've been told by someone else with the same misconception to do it. The whole time they do it, they never found out WHY they are supposed to do it."Waiting till 2000 rpm" before downshifting (and heel/toe yet)? I can't imagine. Maybe he's not really "heel/toeing" at all. A few have "thought" they were "heel/toeing" and when it was described, it turned out they weren't really doing it in the first place.
08-04-2005 | 08:05 AM
#33
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From: Scatterbrainia
Originally Posted by xviper,Aug 4 2005, 06:59 AM
Meth, thank you for finding my earlier quote and posting it here. That'll save me some time now.
There certainly is a lot of misconception going on here. Using engine braking to CONTROL the car has been around since the manual transmission has been around. You rev-match to reduce the wear and tear on the driveline components. This is absolutely NO DIFFERENT from rev-matching when you are accelerating. YES, you should be REV MATCHING when you change gears UP. Most of you do this instinctively by letting the rpm drop to an appropriate level. Those who are jerking like crazy when you upshift are ................ you guessed it ............... NOT rev matching.
Yes, brakes are for slowing down the car and stopping the car, BUT this whole thing about "brakes are cheaper than driveline components to replace" really have no concept of what's going on in the real world. In the "real" world of daily street driving (and even track driving, depending upon the exact circumstances involved), you use engine braking in conjunction with the "service" brakes. You use each one according to need. In the normal state of things, you downshift into each successive gear as the road speed decreases. You use your brakes if engine braking under those particular conditions is not enough. Downshfiting as your road speed decreases is good driving habit. It places the gearbox into the proper gear for that road speed so that you can be ready to move off if you need to or HAVE to. It also keeps the drive wheels connected to the driveline. This is CONTROL. We should all go down the road with as much CONTROL as possible.
Oh and this "extra wear on the engine" philosophy? Motivating the car using the engine's power takes much more power and torque. "Decelerating" when no combustion is taking place is nowhere near as much wear and tear on the driveline parts. So, you're using up, what? Maybe shortening the life of the driveline by ............................. a few thousand miles over a lifespan of 100,000 miles? I think the car can take it. Usually, those who don't downshift/rev match are those who could never master it well and go through life without till they develop driving skills to somewhat compensate for it and then call themselves good drivers because they've never "needed" it.
Those of you who go down the road with clutch to the floor while you are coming to a stop or slowing down, I truly hope you drive as far away from me as poosible. The fact that you don't understand this basic and simple concept means that you most likely don't have an understanding for other driving concepts either.
And to address the "how do we know that there is no gas useage during engine breaking?" What's the proof that the injectors shut down? Not only has Honda techs on this board told you so, but those of you who have air/fuel gauges can confirm this easily. When you engine brake, the a/f number instantly sky-rockets (rise) till they are off the range of the gauge. It reads "-----", meaning the exhaust is pretty all air and no fuel. You cannot display a number when the fuel is ZERO (ie, you divide by ZERO).
I'm sure there will still be those who can't understand what's been discussed here or don't want to believe it. That's your choice. Just stay away from the rest of the motoring public, mostly for their safety. Your safety? Well, I'm sure Darwin' law will prevail.
There certainly is a lot of misconception going on here. Using engine braking to CONTROL the car has been around since the manual transmission has been around. You rev-match to reduce the wear and tear on the driveline components. This is absolutely NO DIFFERENT from rev-matching when you are accelerating. YES, you should be REV MATCHING when you change gears UP. Most of you do this instinctively by letting the rpm drop to an appropriate level. Those who are jerking like crazy when you upshift are ................ you guessed it ............... NOT rev matching.
Yes, brakes are for slowing down the car and stopping the car, BUT this whole thing about "brakes are cheaper than driveline components to replace" really have no concept of what's going on in the real world. In the "real" world of daily street driving (and even track driving, depending upon the exact circumstances involved), you use engine braking in conjunction with the "service" brakes. You use each one according to need. In the normal state of things, you downshift into each successive gear as the road speed decreases. You use your brakes if engine braking under those particular conditions is not enough. Downshfiting as your road speed decreases is good driving habit. It places the gearbox into the proper gear for that road speed so that you can be ready to move off if you need to or HAVE to. It also keeps the drive wheels connected to the driveline. This is CONTROL. We should all go down the road with as much CONTROL as possible.
Oh and this "extra wear on the engine" philosophy? Motivating the car using the engine's power takes much more power and torque. "Decelerating" when no combustion is taking place is nowhere near as much wear and tear on the driveline parts. So, you're using up, what? Maybe shortening the life of the driveline by ............................. a few thousand miles over a lifespan of 100,000 miles? I think the car can take it. Usually, those who don't downshift/rev match are those who could never master it well and go through life without till they develop driving skills to somewhat compensate for it and then call themselves good drivers because they've never "needed" it.
Those of you who go down the road with clutch to the floor while you are coming to a stop or slowing down, I truly hope you drive as far away from me as poosible. The fact that you don't understand this basic and simple concept means that you most likely don't have an understanding for other driving concepts either.
And to address the "how do we know that there is no gas useage during engine breaking?" What's the proof that the injectors shut down? Not only has Honda techs on this board told you so, but those of you who have air/fuel gauges can confirm this easily. When you engine brake, the a/f number instantly sky-rockets (rise) till they are off the range of the gauge. It reads "-----", meaning the exhaust is pretty all air and no fuel. You cannot display a number when the fuel is ZERO (ie, you divide by ZERO).
I'm sure there will still be those who can't understand what's been discussed here or don't want to believe it. That's your choice. Just stay away from the rest of the motoring public, mostly for their safety. Your safety? Well, I'm sure Darwin' law will prevail.
I'm still curious though, if there's no combustion going on during engine braking, why is the car still loud when coasting down through a gear?
08-04-2005 | 08:08 AM
#34
Joined: Mar 2005
Posts: 641
Likes: 3
From: Jacksonville, FL
Man this really worries me that so many people think that engine braking is bad. It just blows my mind. After reading a few of these discussions, yes there have been many, I drive around and find myself wondering how not to use the engine to slow down especially under even slightly spirited conditions. Like xviper said you have to have control of the car...when the clutch is disengaged you have very diminished control of the car.
08-04-2005 | 08:15 AM
#35
Joined: Mar 2001
Posts: 37,305
Likes: 16
Originally Posted by i_heart_my_DB8,Aug 4 2005, 09:05 AM
I'm still curious though, if there's no combustion going on during engine braking, why is the car still loud when coasting down through a gear?
Have ever quickly pulled the plunger out of a syringe? It makes a "popping" noise, yet there is no combustion. This is kinda what's happening in a turning engine with no combustion. You are still compressing air on the compression stroke and because of the timing and overlap of the valves beginning to open on the exhaust stroke, it is "popping" some compressed air out the exhaust.
Of course, there may still be some "combustion" downstream in the exhaust system. Remember, we have a somewhat rich running engine. Not all of the fuel is 100% burnt up. There can still be combustion aft of the header, cat, etc. You know how the emissions air pump shoves air into the exhaust after a cold start? This is to help further the combustion process to reduce emissions. Shoving more air into the exhaust system by way of engine braking will still do this momentarily.
08-04-2005 | 08:19 AM
#36
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Joined: Apr 2005
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From: Scatterbrainia
Originally Posted by xviper,Aug 4 2005, 08:15 AM
Perhaps not the perfect analogy here but it's sorta the same principle:
Have ever quickly pulled the plunger out of a syringe? It makes a "popping" noise, yet there is no combustion. This is kinda what's happening in a turning engine with no combustion. You are still compressing air on the compression stroke and because of the timing and overlap of the valves beginning to open on the exhaust stroke, it is "popping" some compressed air out the exhaust.
Of course, there may still be some "combustion" downstream in the exhaust system. Remember, we have a somewhat rich running engine. Not all of the fuel is 100% burnt up. There can still be combustion aft of the header, cat, etc. You know how the emissions air pump shoves air into the exhaust after a cold start? This is to help further the combustion process to reduce emissions. Shoving more air into the exhaust system by way of engine braking will still do this momentarily.
Have ever quickly pulled the plunger out of a syringe? It makes a "popping" noise, yet there is no combustion. This is kinda what's happening in a turning engine with no combustion. You are still compressing air on the compression stroke and because of the timing and overlap of the valves beginning to open on the exhaust stroke, it is "popping" some compressed air out the exhaust.
Of course, there may still be some "combustion" downstream in the exhaust system. Remember, we have a somewhat rich running engine. Not all of the fuel is 100% burnt up. There can still be combustion aft of the header, cat, etc. You know how the emissions air pump shoves air into the exhaust after a cold start? This is to help further the combustion process to reduce emissions. Shoving more air into the exhaust system by way of engine braking will still do this momentarily.
08-04-2005 | 08:30 AM
#37
Joined: Nov 2002
Posts: 723
Likes: 0
From: Laredo
Xviper's description and explanation is one-hundred-percent accurate. It is more than adequate in quality and quantity and covers essentially all the salient aspects related to this maneuver.
If you have any remaining doubts or questions regarding this issue of engine braking, you really need to read his post again, and again. It is all there, just pay close attention to what he is saying and use some common sense and judgement.
Xviper: Awesome writing!
Cheers,
Daniel
If you have any remaining doubts or questions regarding this issue of engine braking, you really need to read his post again, and again. It is all there, just pay close attention to what he is saying and use some common sense and judgement.
Xviper: Awesome writing!
Cheers,
Daniel
08-04-2005 | 09:18 AM
#38
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Joined: Nov 2004
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From: Racine, WI
Originally Posted by i_heart_my_DB8,Aug 4 2005, 10:19 AM
Ok, that makes some sense, thanks. How long have Hondas been shutting off the fuel injectors upon engine braking? Is it something that would've been featured on my '95 Integra?
08-04-2005 | 09:56 AM
#39
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From: Calgary, Alberta, Canada
Originally Posted by xviper,Aug 4 2005, 08:59 AM
Those of you who go down the road with clutch to the floor while you are coming to a stop or slowing down, I truly hope you drive as far away from me as poosible. The fact that you don't understand this basic and simple concept means that you most likely don't have an understanding for other driving concepts either.
It is incredibly prevelant here. I can just imagine what it's like on the civic boards.I crack up every time I read "I'm an above-average driver" and in the same post they ask what rev-matching is.
08-04-2005 | 10:51 AM
#40
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Joined: Jun 2005
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While everyone has brought up very good points for both rev-matching as well as coasting while on the brakes, I thought I would bring up a couple more issues that are closely related to this topic:
1) Downshifting, we all agree, tends to bring about extra revolutions on our motors, but my understanding is that it is not good to coast for extended distances. The owner's manual recommends not "coasting" for long periods of time out of gear. Correct me if I'm wrong, but when coasting, the brake system is not being charged by the engine's revolutions and when called upon, can run short of vacuum, thereby running into a bad situation, i.e. no power assist for the brakes. While this would likely be exceedingly rare, it could possibly happen, say coasting for many miles down a long mountain road out of gear while using the brakes intermittently - ? Perhaps under certain circumstances, the braking system would run short of power? I had an old Porsche that had non-power disks all around and it took an iron leg to stop that car. Power brakes rule! heh heh...
2) The advantage to downshifting saves time when approaching a slower corner/stoplight and then being in the correct gear and out of the clutch well before, enabling us to accelerate away without needing to clutch the car and get in gear before moving out.
Just my 2c. Anyone with more mechanical knowledge out there don't hesitate to correct me.
1) Downshifting, we all agree, tends to bring about extra revolutions on our motors, but my understanding is that it is not good to coast for extended distances. The owner's manual recommends not "coasting" for long periods of time out of gear. Correct me if I'm wrong, but when coasting, the brake system is not being charged by the engine's revolutions and when called upon, can run short of vacuum, thereby running into a bad situation, i.e. no power assist for the brakes. While this would likely be exceedingly rare, it could possibly happen, say coasting for many miles down a long mountain road out of gear while using the brakes intermittently - ? Perhaps under certain circumstances, the braking system would run short of power? I had an old Porsche that had non-power disks all around and it took an iron leg to stop that car. Power brakes rule! heh heh...
2) The advantage to downshifting saves time when approaching a slower corner/stoplight and then being in the correct gear and out of the clutch well before, enabling us to accelerate away without needing to clutch the car and get in gear before moving out.
Just my 2c. Anyone with more mechanical knowledge out there don't hesitate to correct me.