coast or stay in gear when stopping??

I do both, depending on traffic and other conditions. I often knock it out of gear when slowing to a stop, but not usually until I'm traveling under about 40 mph. I would guess that I kick it out of gear about half the time or a little more. My brakes still last a long time. I don't think it makes any significant difference in fuel consumption.

i do whatever the atx makes me do

When I started driving, I never knew people actually did this until I was with someone who did it off the highway. I personally come from the downshifting school of thought.

Several reasons:
1) You're in control of 100% of your car 100% off the time.
2) You're in the appropriate gear if you need to start moving again (rather then having to figure out which gear you need to be in)
3) If you need to make an evasive maneuver in the process, you can (refer to point #1).

Everyone has their own habits. I usually shift into neutral right around 10mph or when the car comes to a complete stop.

I'm with Big Jim when I'm driving a stick. However, my dad is of the sail114 variety (in a different sense). He coasts to a stop, but while doing so runs through all the gears without taking the clutch off. Drives me nuts, but it's probably a better method than just coasting with gear in 5th ... to each his own

Originally posted by 98 SE:
I'm with Big Jim when I'm driving a stick. However, my dad is of the sail114 variety (in a different sense). He coasts to a stop, but while doing so runs through all the gears without taking the clutch off. Drives me nuts, but it's probably a better method than just coasting with gear in 5th ... to each his own

I go down through the gears when I come to a stop also, something my father did and I ended up doing also

Driving must be one of those mimicry exercises: We end up doing things the way we saw them being done or were taught. Dad always rowed through the gears on the way to a stop, Mom downshifts and lets the car do the stopping. I have a mix of the two.

I avoid downshifting because of the stress on the transmission and the wear on the clutch. I'd rather replace my brake pads than have a clutch replaced or the whole transmission. The way I see it, you should know your car well enough to know what gear to put it in if you actually do need to take any sort of manuever. Just my 2 cents worth.

David

I coast coming to a stop. Helps with fuel economy also.

Originally posted by BCSVT:
I avoid downshifting because of the stress on the transmission and the wear on the clutch. I'd rather replace my brake pads than have a clutch replaced or the whole transmission. The way I see it, you should know your car well enough to know what gear to put it in if you actually do need to take any sort of manuever. Just my 2 cents worth.

David

my sentiments exactly......why put added wear on a very expensive part....i'd much rather replace my brake pads than a clutch or tranny....i seriously doubt that either method makes much difference in fuel economy...

How much are you really going to save in gas by doing it one way or the other?

I am one to agree with less wear on the engine/clutch the better.

Here's another question tho...I recently had a European friend visit and he was apalled at how we all drive sticks...apalled that nobody seems to double clutch because it makes the driving experience much smoother. How many of you do/don't double clutch and what are your thoughts on it?

Originally posted by sail114:
Driving must be one of those mimicry exercises: We end up doing things the way we saw them being done or were taught. Dad always rowed through the gears on the way to a stop, Mom downshifts and lets the car do the stopping. I have a mix of the two.

So so true. I recently learned how to match my RPM and shift(I forget what it's called) and for years I was too scared to try to figure it out cause I was only taught the clutch method.
My Dad rowed too but my gears don't slow down enough for my liking to warrant 4-1 shifts. Unless I'm either wanting to hear my engine sound cool or I have 3 miles before I come to a stop...

Originally posted by sail114:
Driving must be one of those mimicry exercises: We end up doing things the way we saw them being done or were taught. Dad always rowed through the gears on the way to a stop, Mom downshifts and lets the car do the stopping. I have a mix of the two.

I mix the two...depends on what kind of stop I'm coming too...

Originally posted by infratl:
my present conclusion is that coasting burns more gas than leaving it in gear when coming to a full stop.

You are wrong.

When you are coasting in gear the PCM shuts off the injectors in series. You are basically getting free mileage for no real fuel spent. The exhaust will be flat out lean. Engine braking (extreme vacuum) is by far the most efficient state an engine can be run in.

When you coast in neutral the PCM tries to idle up the engine and it also runs very rich.

Not only that but coasting out of gear is illegal and can be dangerous. The car is much more likely to stall. (no power steering or brakes)
Especially if you have to use the brakes which are powered by engine vacuum. Panic stops are not good when coasting in neutral because the sudden drop in manifold vacuum will probably stall the engine!

Originally posted by ODC:
When I'm preparing to stop I always go into neutral. It's illegal and unsafe, but I do it anyway.

Originally posted by DemonSVT:
Not only that but coasting out of gear is illegal and can be dangerous. The car is much more likely to stall. (no power steering or brakes)
Especially if you have to use the brakes which are powered by engine vacuum. Panic stops are not good when coasting in neutral because the sudden drop in manifold vacuum will probably stall the engine!

It's illegal?!?

I do it almost on a daily basis. On my way home from work there is a hill that's about a mile long, at the peak when going 50-55 I put it in neutral and coast all the way down. At the end, I have to slow down and turn and I've never had any problem with the brakes trying to stall the engine or anything like that. By the time I get to the bottom of the hill it isn't too uncommon to be going 60+.

DemonSVT:

Originally posted by infratl:

Not only that but coasting out of gear is illegal and can be dangerous. The car is much more likely to stall. (no power steering or brakes)
Especially if you have to use the brakes which are powered by engine vacuum. Panic stops are not good when coasting in neutral because the sudden drop in manifold vacuum will probably stall the engine!

You can't stall the engine while coasting. It can stall if you are in 5th gear and going at 5mph, you can't stall it in neutral, with or w/out the clutch depress.

Nic.

Yea I usually will let the engine help come to a stop for me too. I don't usually press the clutch in until around 1500-2000rpm.

I always coast to a stop, until this car I had driven auto's my entire life, and knowing me, I'd still just want to hit the brakes without the clutch while in gear, and that would stall out my car.

I keep the clutch in and go through the gears in case i have to start accelerating again. Just something i've naturally done.

I forgot to add that I don't coast in Neutral, rather I let it stay in 4th or 3rd and wait till about 1K RPM before I depress the clutch and go into 1st. By then I'm going less than 15 kph and still in a gear, always.

Originally posted by Nic_ContourSE99:
You can't stall the engine while coasting. It can stall if you are in 5th gear and going at 5mph, you can't stall it in neutral, with or w/out the clutch depress.

You are completely wrong eh.

The engine most definitely can and will stall when coasting in neutral.

PLEASE explain that, Greg... I have coasted down 7 and 10%grade hills just for the louge effect, and it drops to idle, then stays there.. EDIT: Also do this on one particularly long, sweeping downhill right hander.. I throw it in neutral and coast through the curve (to lower the rpms and avoid oil issues... never dies../EDIT

I am REALLY asking to be made to look like an idiot, but uhm.. 1. how is coasting any different than idling in neutral (which it won't stall in)?

2. How does that explanation (that you give for number 1) apply to OUR platform, in which I have experienced it zero times in a nearly every day routine.

Thanks.

Ray

Originally posted by Ray:
I am REALLY asking to be made to look like an idiot, but uhm.. 1. how is coasting any different than idling in neutral (which it won't stall in)?

2. How does that explanation (that you give for number 1) apply to OUR platform, in which I have experienced it zero times in a nearly every day routine.

1. The VSS. The PCM knows how fast the car is actually moving and that it is not at rest. It idles up and runs rich when "idling" & moving. A richer mixture is more likely to stall due to a sudden air pressure drop.

2. "Any" car will be more susceptible to stalling when coasting if you hit the brakes or sustain a panic stop. That's a given for any car regardless of computer control or not. Manifold vacuum is vacuum.

Ray:
PLEASE explain that, Greg... I have coasted down 7 and 10%grade hills just for the louge effect, and it drops to idle, then stays there.. EDIT: Also do this on one particularly long, sweeping downhill right hander.. I throw it in neutral and coast through the curve (to lower the rpms and avoid oil issues... never dies../EDIT

I am REALLY asking to be made to look like an idiot, but uhm.. 1. how is coasting any different than idling in neutral (which it won't stall in)?

2. How does that explanation (that you give for number 1) apply to OUR platform, in which I have experienced it zero times in a nearly every day routine.

Thanks.

Ray

I totally agree with you Ray. I never, and you can't stall an engine when it's in neutral. I don't understand why the PCM should get the mixture richter when you are coasting, there is no difference when idling and coasting. The PCM won't send the command to get mixture rich enough to stall the engine.

When the engine revs below a certain RPM, i think it's under 1250 RPMs, the IAC takes control of the idle, so it won't let the engine stall.

Nic.

I'm always afraid when going down a hill OR flat, that when I shift down, to leave the clutch in. Because the RPMs go so high when trying to go down a hill and shifting down....

Should I let the engine just do it with the high rpms, keep the clutch in, or shift to N.

My fuel consumption on the SVT has been poor recently. Not sure if it's my driving habits, or something needs to be cleaned up.

I have an appointment with ford to machine the rotars and put new break pads on, should I have them look at the fuel injector?

Originally posted by DemonSVT:
1. The VSS. The PCM knows how fast the car is actually moving and that it is not at rest. It idles up and runs rich when "idling" & moving. A richer mixture is more likely to stall due to a sudden air pressure drop.

2. "Any" car will be more susceptible to stalling when coasting if you hit the brakes or sustain a panic stop. That's a given for any car regardless of computer control or not. Manifold vacuum is vacuum.

OK, I tested this. Today, going down my favorite hill to coast down, I accelerated up to 70 mph, shifted out of gear (into neutral) and then I stood on the brakes. No stalling, no nothing...

Originally posted by DemonSVT:

Originally posted by Nic_ContourSE99:
You can't stall the engine while coasting. It can stall if you are in 5th gear and going at 5mph, you can't stall it in neutral, with or w/out the clutch depress.

You are completely wrong eh.

The engine most definitely can and will stall when coasting in neutral.

I can vouch for Greg's statement- as I've actually stalled in neutral once.

I was rowing through gears extremely granny style in a parking lot, trying to find a space. Sudeenly a little kid runs out from between some parked cars and I stand on the clutch and brake, screeching to a stop. When the coast was clear, I noticed the engine had stalled. My first thought was that I didn't disengage the clutch fast enough, but then I saw that I wasn't in gear.

For you research/re-creationist guys: I was accelerating slowly from ~10-15 mph, The panic stop occurred mid-shift, I hit the brake & clutch simultaneously. (Yeah, yeah, I know I was probably already pressing the clutch in , since I was in the middle of shifting...) ...And yes, I tore the parent a new one for not paying closer attention to her kid (They were a good 15 feet apart, walking between cars, & the parent was on her cell!)

I usually just push in, out of gear, let the pedal back out then stop, not hold the clutch down, and i don't like to downshift for various reasons, so just coast to a stop is what i do.

I see that there have been a lot of issues raised here will I was gone for a day.

On the legality issue, I'm sure that it varies from state to state. As I remember when I was learning to drive here in California, the vehicle code stated that you could not coast down hill in neutral gears. This was in the days of drum only brakes and very poor ones at that. It was also when overdrive units would go into neutral under 30 mph when slowing down. That is how the units were designed. This is also at a time that every few months you would read of a semi loosing it's brakes and going out of control going down the grapevine grade (between Los Angeles and Bakersfield). Cars, trucks, and brakeing systems have all greatly improved since then. I have not seen this question show up on driving tests when I have renewed my license for many years. It was not a topic of discussion in any of my now grown kids driver education and driver training clases. Although I believe as I'm sure that all of you do that it would take an absolute idiot to try to take a car or a truck down the grapevine grade today in neutral using the brakes only.

On the stalling issue. Stalling an engine at idle isn't any more likely than an engine stalling on deceleration in gear (unless you forget to depress the clutch near the end).I'll make that statement not just on driving experience, but from years of experience as a drivability and tune up technician.

On the fuel economy issue. A difference in overall fuel consumption between closed throttle deceleration coming to a stop in normal driving and allowing the engine to idle by coming to a stop in neutral is insignificant. With a fuel injected car, in theory, the fuel economy would be slightly better with closed throttle and high vacuum, and I believe that indeed it would be, but hardly enough to see a difference when it's time to fill the tank. On a carberated engine, fuel economy is in the toilet on high vacuum closed throttle as the high vacuum sucks a lot of fuel through the idle ports. Again, for nearly all street driving, you are not likely to see the difference when it is time to fill the tank.

What it really boils down to, is that depending on driving situations, it is nice to know more than one way to bring your car to a stop. Just because of smoothness of operation on city streets it makes sense to kick the trans out of gear and coast toward a stop with gentle brake assistance if needed. Other times it makes more sense to select a gear or gears and be prepared for some eventuality.

Some of you may not want to hear this, but when I won an opportunity to take ten laps in a Winston Cup car at Fontana, they instructed us when bringing the car into the pits in the final approach in the pit lane (probably still doing about 50 to 60 mph), to kick the car into neutral and stop with the brakes. So it's done at Nascar (when appropriate) where control of the car is paramount.

I have to agree with DemonSVT's statements about the possibility of stalling. It is, however not very likely, but it can happen.

Personally I have never stalled my old Mystique like that, but I have definitely felt the power drop, and observed lights dimming when brakes are pressed. I sometimes even see this when pulling into my driveway, popping the clutch at between 15-30pmh and making a 90' degree turn whilst braking sharply. I've stalled a couple of other cars doing this, and had to tap the throttle a number of occaisions, but not on the duratec. It would depend on what your engine speed is whilst doing this though. If you're near to the stall line then you could stall it, but if you're up at 1,000rpms or more then you'll likely not notice more than the lights dimming a little and the throttle dropping before lifting up again.

Originally posted by Big Jim:

Some of you may not want to hear this, but when I won an opportunity to take ten laps in a Winston Cup car at Fontana, they instructed us when bringing the car into the pits in the final approach in the pit lane (probably still doing about 50 to 60 mph), to kick the car into neutral and stop with the brakes. So it's done at Nascar (when appropriate) where control of the car is paramount.

I can vouch for this, hell I even had to kill the engine before we even hit the pit lane!

You will have increased stopping power with the car in neutral, or with clutch in, as the engine isn't driving the wheels anymore, so less resistance.
Stalling, IMO, is not likely, but is possible. If you are dropping into neutral for a stop at 50/60mph I'm presuming that you are still above idle when you begin applying the brakes ... also I don't think you could stall a race car that easily either doing this as I would imagine idle would be well above stalling point. If you have an older vehicle which has a somewhat erratic idle, or for example the AC is draining power, then there is the possibility that you will dip just enough to get a stall. On a healthy engine I wouldn't imagine it happening anywhere near often.

On decel, the engine is not driving the wheels. It is adding resistance and as such is actually assisting the brakes. Depending on conditions, this may not be significant, or it can be very significant.

Originally posted by Big Jim:
On decel, the engine is not driving the wheels. It is adding resistance and as such is actually assisting the brakes. Depending on conditions, this may not be significant, or it can be very significant.

But surely, unless you a braking extremely softly, when applying braking power you are working against power sent from the engine to the transmission, even though that power is dropping it is still there. I can understand it assisting in slow braking but in fast braking, especially emergency braking, clutch in is best as there is no power being sent from the engine.
At least this is the way I see it in my mind, the physics of this makes sense to me.

I kind of do both, depending on what the situation calls for. Sometimes I engine break till about 1000-1500, sometimes the distance from one acceleration to a stop is so short that I just leave it in the same gear till neautral or just go to neutral right after the acceleration.

XL

Originally posted by Christian:

Originally posted by Big Jim:
On decel, the engine is not driving the wheels. It is adding resistance and as such is actually assisting the brakes. Depending on conditions, this may not be significant, or it can be very significant.

But surely, unless you a braking extremely softly, when applying braking power you are working against power sent from the engine to the transmission, even though that power is dropping it is still there. I can understand it assisting in slow braking but in fast braking, especially emergency braking, clutch in is best as there is no power being sent from the engine.
At least this is the way I see it in my mind, the physics of this makes sense to me.

Once you lift your foot off the gas pedal, the power generated from the engine turns from propelling the car (positive power) to slowing the car (negative power). Surely you can feel that as you lift the throttle. While this is happening, the engine is assisting braking all the way down to engine idle.

Exactly.

In fact, pressing the clutch in is actually creating (in some small aspect) MORE work for the brakes. More control, sure, I won't argue the uses in the performance aspect (nascar, etc, as stated above).

Ray

i usualy do both, mostly double clutch into 3rd and use engine and breaks to slow it till its close to idle then i put in clutch or take it out of gear. My dad told me when you are engine breaking you are getting as good or better gas milage as idle. Also the only time i dont engine break is in snowy weather because it can lock the tires up and thats not good.

i have a habit of coasting in neutral....then again if you seen me drive it would make you go crazy!

sometimes i shift 1-3-5 or start in first, wind it out then shift to 5th

i have no set method of driving

the reason for being like this.....i didnt have anyone teach me to drive stick. i taught myself on my car with a 3L, torsen, spec stage 3, and a spec flywheel, talk about a good starter car eh?

i didnt have a parent teach me to where i had to drive "normal" and i didnt have a slow beater either. i never had anyone to form me into a habit or style of driving. do to the nature of my car is why i drive totally random and crazy

offtopic:

1-3-5, and 1-5 is REALLY hard on the synchros if you aren't PERFECTLY rev-matching when you shift.

/offtopic

Originally posted by mvr:
i usualy do both, mostly double clutch into 3rd and use engine and breaks to slow it till its close to idle then i put in clutch or take it out of gear. My dad told me when you are engine breaking you are getting as good or better gas milage as idle. Also the only time i dont engine break is in snowy weather because it can lock the tires up and thats not good.

i actually do the opposite for winter. i thought the whole point was the control that an mtx will give u. i'd rather go down a snowy hill in 2nd or 3rd and let the engine get me down the hill at a more controlled constant speed rather than trying to brake the whole way down and hope to not brake too much to cause the tires to lose grip and slide.

i usually brake to a stop in gear then when i'm kinda close i pop it into neutral. so some of u guys will sit at a light with the car in gear holding the clutch down? hope u dont get a tired foot holding the clutch pedal and then let the car lunge forward into the car in front of u after your foot pops up.

its an SVT clutch, not a Corvetter Racing clutch, etc.

It isn't like its HARD to hold down.

MY 65 Chevy flareside had a clutch so hard to press that I, and my sister (when I was younger, before it was handed down to me) stepped on it, and WE went UP. You LITERALLY had to hold the steering wheel, and pull yourself downwards (Even as a grown man..) to get it down.

Once down it was fine.. but that halfway point was like trying to hold a compound bow halfway pulled back! Talk about a quivering leg! (God forbid you get stuck on a hill!)

edit:
8inch steering wheel, and no PS, either.
All out drag machine, but not much else!
Passed anything but a gas station. (about 3mpg, or less, with a 10 gallon tank behind the seat)
Caddy 472, Dual Holley 850 double pumpers, et al.
/EDIT

Ray

I rev match and heel-toe when I downshift, I don't like putting the car in neutral I like to have it in gear so I can just accelerate if I have to. The only time I really let the car coast in neutral is if I'm in a residencial zone and coming to a stop at a stop sign since the speeds are so low in a residencial zone.

Aaron

Originally posted by Big Jim:

Originally posted by Christian:

Originally posted by Big Jim:
On decel, the engine is not driving the wheels. It is adding resistance and as such is actually assisting the brakes. Depending on conditions, this may not be significant, or it can be very significant.

But surely, unless you a braking extremely softly, when applying braking power you are working against power sent from the engine to the transmission, even though that power is dropping it is still there. I can understand it assisting in slow braking but in fast braking, especially emergency braking, clutch in is best as there is no power being sent from the engine.
At least this is the way I see it in my mind, the physics of this makes sense to me.

Once you lift your foot off the gas pedal, the power generated from the engine turns from propelling the car (positive power) to slowing the car (negative power). Surely you can feel that as you lift the throttle. While this is happening, the engine is assisting braking all the way down to engine idle.

Okay, I may be a little slow here on this one

If the engine is still producing power then even if that is less than the power required to propel the car at the same speed (hence engine braking), would that power still not be put to the wheels (even if it is less than required for propulsion) meaning that when you brake ... you are braking not only the velocity/momentum of the vehicle but also the revolutions of the engine ... whereas if you brake clutch in/in neutral you are braking against purely the velocity/momentum of the vehicle ... my understanding of physics, back from A-levels 15+ years ago, so it is a little shoddy!

I can picture this scenario ....
Say at 50mph you need 10% disc braking to stop in distance x, if you apply engine braking you would need only 5% (making up numbers here) as the engine braking allows for 5% braking power ... which is why we brake with engine engaged.

But I don't see this ...

If I want to perform an emergency stop (slam on brakes as kid jumped in road) ... my aim is to stop as quickly as possible. At this point I imagine that removing engine power from the scenario would reduce braking, as the engine is rotating it is producing power, which goes to the wheels which causes forwards momentum (even if it is less), which means I have to apply more braking force to the wheels ...

Sorry to turn this into a school lesson, just I don't quite get it.

Cheers,

Christian./

to make a quick stop(kid jumps infront of ya) put it in the lowest gear that u can and hit the brakes. DONT be goin 50mph and then o sh!t and brakes and put it in 1st no.not what im saying. . in my past experience ive dropped the gears and hit the brakes and it helped me slow down alot then just clutch in and hit the brakes...others will understand what im saying hopefully and explain it better

well if im not mistaken when you are engine breaking in snow the engine could cause the tires to lock up. i would try to explane further but i would make myself look like an idiot. id rather take my chances with the antilock.

i have no idea about the snow cuz it never snows in ga. or macon atleast. but i kno on dry pavement the brakes and using the engine helps you slow down as quick or quicker. ive been ther done that kinda thing.

Christian:

For an emergency stop, you're supposed to press the clutch to the floor and hit the brakes as hard as you can (assuming you have ABS).

Originally posted by Christian:

Originally posted by Big Jim:

Originally posted by Christian:

Originally posted by Big Jim:
On decel, the engine is not driving the wheels. It is adding resistance and as such is actually assisting the brakes. Depending on conditions, this may not be significant, or it can be very significant.

But surely, unless you a braking extremely softly, when applying braking power you are working against power sent from the engine to the transmission, even though that power is dropping it is still there. I can understand it assisting in slow braking but in fast braking, especially emergency braking, clutch in is best as there is no power being sent from the engine.
At least this is the way I see it in my mind, the physics of this makes sense to me.

Once you lift your foot off the gas pedal, the power generated from the engine turns from propelling the car (positive power) to slowing the car (negative power). Surely you can feel that as you lift the throttle. While this is happening, the engine is assisting braking all the way down to engine idle.

Okay, I may be a little slow here on this one

If the engine is still producing power then even if that is less than the power required to propel the car at the same speed (hence engine braking), would that power still not be put to the wheels (even if it is less than required for propulsion) meaning that when you brake ... you are braking not only the velocity/momentum of the vehicle but also the revolutions of the engine ... whereas if you brake clutch in/in neutral you are braking against purely the velocity/momentum of the vehicle ... my understanding of physics, back from A-levels 15+ years ago, so it is a little shoddy!

I can picture this scenario ....
Say at 50mph you need 10% disc braking to stop in distance x, if you apply engine braking you would need only 5% (making up numbers here) as the engine braking allows for 5% braking power ... which is why we brake with engine engaged.

But I don't see this ...

If I want to perform an emergency stop (slam on brakes as kid jumped in road) ... my aim is to stop as quickly as possible. At this point I imagine that removing engine power from the scenario would reduce braking, as the engine is rotating it is producing power, which goes to the wheels which causes forwards momentum (even if it is less), which means I have to apply more braking force to the wheels ...

Sorry to turn this into a school lesson, just I don't quite get it.

Cheers,
Christian./

You are almost there. If it is producing less power than required to propel the car it is engine braking and that engine braking is assisting in stopping the car.

When I slow down from say 55mph I almost always brake a little and downshift to slow down. If I'm going slower sometimes I don't even use the brakes until I'm going 15 or less.

I got over 100,000 miles on my brake pads (backs went first for some reason), and I'm still on the original clutch. So I think as long as you're not slamming it into first at 55mph or popping the clutch, you should be fine either way.

I've also gotten pretty good at upshifting from 3->4 and 4->5 without clutching.

Originally posted by mvr:
well if im not mistaken when you are engine breaking in snow the engine could cause the tires to lock up. i would try to explane further but i would make myself look like an idiot. id rather take my chances with the antilock.

Yes, esp when going down a hill it's not smart to downshift where your RPM goes say 4000+. Under normal conditions, the pavement doesn't allow any slippage , of course. Under slippery conditions the engine braking (normally allowed because there's friction from the pavement) allows the tires to lose traction and thus create what you called "lock up" but more appropriately be lose traction, like you do when you accelerate in snow.

This can happen in automatics too, if they gear down to a high RPM. My Mech teacher told us about him driving in the snow and a Grand Prix decides to gear down on hwy(no brake lights lit) and it loses traction and kareens into the barrier.

Originally posted by Rishodi:
Christian:

For an emergency stop, you're supposed to press the clutch to the floor and hit the brakes as hard as you can (assuming you have ABS).

Say you don't have ABS (<--me), wouldn't braking w/o lockup and stalling the engine (don't engage the clutch) stop you quicker?

Originally posted by Big Jim:

You are almost there. If it is producing less power than required to propel the car it is engine braking and that engine braking is assisting in stopping the car.

Okay, that I get. However for maximum braking would the power not be cumulative to the momentum as it is still creating some momentum ... and if you are braking hard, once the velocity drops (if dropping quickly) to match the velocity that the engine is trying to produce, further hard braking is going to be working against the engine too, as the engine is not dropping quick enough to match the drop in velocity, so you're (from that 'sweet spot') braking against both the momentum of the car and the engine's power output (even though it is dropping) ?

Originally posted by Christian:

Originally posted by Big Jim:

You are almost there. If it is producing less power than required to propel the car it is engine braking and that engine braking is assisting in stopping the car.

Okay, that I get. However for maximum braking would the power not be cumulative to the momentum as it is still creating some momentum ... and if you are braking hard, once the velocity drops (if dropping quickly) to match the velocity that the engine is trying to produce, further hard braking is going to be working against the engine too, as the engine is not dropping quick enough to match the drop in velocity, so you're (from that 'sweet spot') braking against both the momentum of the car and the engine's power output (even though it is dropping) ?

Yes. The engine is creating resistance to the car's motion above idle speed, since the air in the cylinders is being compressed. As demon stated, there is no fuel coming out of the injectors when coasting. No fuel means no power. None. You are compressing air in the cylinders, and letting it out the exhaust. This take a lot of energy from the kinetic energy of the car, slowing you down. Even in a car with the injectors spitting fuel at idle speed, the force it takes to compress the non-firing cylinder that revolution is less that the force created by the firing cylinder. Thus, the engine produces DRAG on the trans. You can feel this when the transaxle clunks upon letting off the gas. This is the gears locking in the opposite direction: the wheels are now pushing the engine. Once you get down to idle speed, the amount of energy created by the firing cylinder is exactly equal to the energy expended compressing the non-firing cylinder, so it's a wash. Coast lower than idle, and you're going to be hurting your deceleration, as well as probably stall the engine, unless you hit the clutch soon!

Hope that helps. The key is: the engine takes power too, it doesn't just make it. Whether the TOTAL amount of power coming from the engine is positive or negative depends on whether it is above or below the speed it would natually spin with a given amount of throttle.

so, what i'm getting from all this is that it is better to coast in gear for various reasons. the one that catches my attention is that by doing that the injectors cut off the fuel going to the engine, so the cylinders aren't firing. When coasting in neutral the engine goes down to idle which means the injector is sending fuel to the cylinders and some gas is actually being used.

therefore, at least in theory according to the posts in this topic, it is cheaper on gas to coast in gear instead of coasting in neutral. i had no idea the engine could actually run without there being gas being ignited in the cylinders.

this brings up a question. theoretically, can you turn the ignition to the off position and coast in gear? wouldn't this make sense since there's no gas flowing into the cylinders? i know that it would affect other parts of the engine like power steering and braking, but consider just the motor.

now, back to the argument about engine momentum. i still agree that if you coast in gear and have to slam on the brakes that you would be braking against the velocity and the engine rotation because engine can decel only at a certain rate. if you brake at a greater rate than the engine can decel than you are actually also braking against the engine momentum. which would make sense to put the clutch in for slam braking, right? please clarify.

Is it better to clutch for a panic stop? Maybe, but not for that reason. The engine has some inertia, but I doubt the car can stop faster than the engine. The car takes a very long time to stop, the engine natuarally drops in revs pretty quickly. I always hit the clutch at some point during a panic stop because I don't want to stall the car. Also, the extra braking power from the engine (I think it probably does provide resistance, even on fast stops) will bias the brakes even more to the front. They are reasonably well-biased from the factory, but err on the side of too much front. If you have a lowered, more stiffly sprung, or more rear-biased car, more front braking power isn't needed. Besides, once you peg the brakes, you have all the power you need to stop. Those discs can lock up very sticky tires without too much of a problem. But that's all academic. Really:

It's a non-issue. Leaving the clutch engaged until you are about to fully stop (or are in a spin) is the best idea, just to keep vacuum pressure up. Downshifting through the gears isn't a bad idea, partly to keep the revs (and vacuum, and engine braking power) up, and also to be able to floor it if some idiot comes barreling in behind you. It won't take long for a good driver to get it into gear and go, but any time at all can be too much in an accident situation.

Originally posted by Christian:

Originally posted by Big Jim:

You are almost there. If it is producing less power than required to propel the car it is engine braking and that engine braking is assisting in stopping the car.

Okay, that I get. However for maximum braking would the power not be cumulative to the momentum as it is still creating some momentum ... and if you are braking hard, once the velocity drops (if dropping quickly) to match the velocity that the engine is trying to produce, further hard braking is going to be working against the engine too, as the engine is not dropping quick enough to match the drop in velocity, so you're (from that 'sweet spot') braking against both the momentum of the car and the engine's power output (even though it is dropping) ?

Sometimes theory can only go so far in explaining physics. Now it is time to go gather some empirical data to see what really happens. In other words, go experiment on stopping using both engine braking and brakes in various combinations. I think that may be the only way for you to fully see just waht is happening.

The Wright brothers had incorrect theory when trying to make their first flying machine. They had to determine the correct theory on their own to make it actually fly. You can do the same. See for yourself.

Thanks for the lesson

Now I get it, would have understood much quicker if I had re-read the original posts for ...

Originally posted by DemonSVT:

When you are coasting in gear the PCM shuts off the injectors in series. You are basically getting free mileage for no real fuel spent. The exhaust will be flat out lean. Engine braking (extreme vacuum) is by far the most efficient state an engine can be run in.

Then I wouldn't have run in circles until 95sleeper pointed it out again and it sunk in!

Cheers all !