Engine braking

Kong76 said:

Might be a dumb question but during quarter mile runs and dyno pulls what is the correct method of release without harm? Engine braking or clutch in and neutral. It sounds like on many dyno pulls its clutch in and neutral. I have never tracked or dynoed a car. Like I said prob dumb no flaming.

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In the motorcycle world, it is mostly just let off the gas at the end of a run.

It seems mixed in the car world. I see some put clutch in at the end of a run. I asked one car Dyno guy why he did that and he said "I don't know" and shrugged.

Probably and old habit from old cars and dynos without brakes.

Twin Turbo said:

I agree, here in the UK we are taught NEVER to put the car in neutral whilst driving. Use both the engine and the brakes to slow down. If you come to a stop......put the clutch in, THEN put it in neutral and apply the hand (parking) brake.

I've seen many, many You Tube videos where someone will accelerate hard through the gears, get up to X-speed and then pop it in neutral. That seems an alien concept to me.

The other advantage of keeping it in gear......you have immediate control over the car should you need to accelerate out of a dangerous situation.

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Maybe this has already been asked, but why would you put it in neutral and applying the handbrake when coming to a stop? That would contradict keeping it in gear to accelerate out of a dangerous situation.

Unless you mean parking, and I still don't understand why people do that.

I almost feel an entire ocean isn't far enough away from somebody who uses the parking brake at a red light.

DrGrabster said:

Coming to a stop light I usually keep it in 1st gear with the clutch in until the car behind has stopped. Then if the lights look like they are not just about to change set the handbrake, pop the car into neutral and take left foot completely off the clutch pedal. This saves both throwout bearing and clutch plates. Plus it allows for any sort of hill start.

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Why parking brake. Can't you just hold the brake pedal?
The only time I use parking brake is when I can't press the brake pedal in neutral ie car running and I am not in it.
Otherwise I don't normally use it at all. I park with transmission in 1st. Maybe parking brake if on an incline to take the load off the drive train but still in gear.

Mustang_GT said:

Not to be offensive, but long term deperssing/holding of the clutch in puts undue wear/stress on the trust bearing. I only point this out for folks that go down long hills etc., holding in clutch the whole time at the traffic light etc. I have seen wiped out thrust bearings over the years.

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No offense taken, you have a good point and this is also true lol. Under the kinds of conditions like that, where I know I'm just coasting along and tapping some brakes I like to put it in neutral and take my foot back off of the clutch. At the light it's definitely in neutral with my foot off the clutch (if you don't want to take the time to put it in gear once the light is already green, you can easily be watching the cross-traffic's light to see when it's going yellow for them and get into 1st a second or two early). It's a simple matter to pop it back into gear when you need it. Just make sure if you're still coasting along like that, you put it into the proper gear haha.

DrGrabster said:

If you leave it in gear coasting down a hill you will save fuel. The injectors can just cut off. If you are coasting in neutral then the car has to keep the engine going by supplying fuel.

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Really... that's an interesting tidbit I'll have to experiment with and see how much of a difference it makes in my short little 9 mile commute. I do have a couple small hills over the course of my drive, but I wonder if they're enough to significantly make me see a difference. I'm going to give it a try next week once I re-fill my tank and see lol.

As someone who drove Fire Dept. apparatus (including snow conditions) and having had a CDL Class B license, you might want to avoid engine braking in snowy or other extremely low friction conditions as that may cause you to slide.

Better in those circumstances to put the vehicle in neutral and slightly tap the brakes.

DrGrabster said:

Coming to a stop light I usually keep it in 1st gear with the clutch in until the car behind has stopped. Then if the lights look like they are not just about to change set the handbrake, pop the car into neutral and take left foot completely off the clutch pedal. This saves both throwout bearing and clutch plates. Plus it allows for any sort of hill start.

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You aren't gonna wear the clutch out any noticeably faster if you hold it at a stop light. You're dealing with what is essentially a spring, built to be pushed thousands of times. Springs don't wear faster if they stay compressed than they would if they were pushed repeatedly.

Still, I don't understand why anyone would bother applying the parking brake at a light. That's just one more action to have to take to get moving again.

I only apply mine if I want to leave the car idling, or when I park the car in gear, simply so if someone in the car should happen to bump the shifter into neutral it won't cause an accident of some sort.

DrGrabster said:

Is America flat?

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Some parts yes, but the real issue is the younger drivers are too busy texting at lights and the older Americans are too lazy to lift that lever at lights.
Our fat feet do a fine job of keeping the car still.
(Parking brakes at lights is a bit strange)

DrGrabster said:

If you leave it in gear coasting down a hill you will save fuel. The injectors can just cut off. If you are coasting in neutral then the car has to keep the engine going by supplying fuel.

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ForTheHordeKT said:

Really... that's an interesting tidbit I'll have to experiment with and see how much of a difference it makes in my short little 9 mile commute. I do have a couple small hills over the course of my drive, but I wonder if they're enough to significantly make me see a difference. I'm going to give it a try next week once I re-fill my tank and see lol.

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Go into the fuel screen on the dash and watch your instantaneous mpg go up when coasting at speed in neutral. It does it even on flat land, probably does it on slight uphills too to a point. If I see a red light up in the distance I usually always coast up to it. Well I used to in my other stick shifts, but for some reason the novelty of having it in gear in the Mustang is still to fun for some reason.

PJR202 said:

You aren't gonna wear the clutch out any noticeably faster if you hold it at a stop light. You're dealing with what is essentially a spring, built to be pushed thousands of times. Springs don't wear faster if they stay compressed than they would if they were pushed repeatedly.

Still, I don't understand why anyone would bother applying the parking brake at a light. That's just one more action to have to take to get moving again.

I only apply mine if I want to leave the car idling, or when I park the car in gear, simply so if someone in the car should happen to bump the shifter into neutral it won't cause an accident of some sort.

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It's not about wearing the clutch, but the throwout bearing.

Bearings are designed for a number of cycles at a load. The throwout bearing is loaded when the clutch is disengaged. Sitting in gear with the clutch disengaged at a stoplight is pretty insignificant when you consider the tens of millions of revolutions the bearing is designed for. Trouble comes when drivers rest their foot on the pedal or remove the clutch assist spring entirely. This puts a higher load on the throwout bearing when the clutch is engaged and you will hit those tens of millions of cycles easily.

NoVaGT said:

There will be no difference. Or the engine braking would upset the braking balance of the car so much it would lengthen the stopping distances.

Using the brakes in a 100% ABS stomp mode means the vehicle's brakes are still doing all the work of slowing the vehicle. The brakes slow the vehicle much faster and harder than engine braking, so it could also be theorized that engine braking would actually increase braking distances, as the brakes would also have to over-come the inertia of the rotating mass of the engine.

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This is pretty much correct. The brakes on the car are set up balanced so that the rear versus the front all apply the most possible braking force at the limit. If you are trying to slow down as quickly as possible, brakes only are the way to go.

Yes, the car's antilock system will reduce the pressure on the rear brakes to try to prevent the rears from locking due to your engine braking. However, the engine braking doesn't provide additional slowing, because the rear brakes are configured to give as much slowing as there is traction available.

On the road course, good drivers do not use the engine to slow the car. What they do is called "rev matching" or "heel and toe downshift". This is the best way to pull off a downshift to avoid upsetting the car. Ideally the engine revs exactly match the rotational speed of the new gear being selected so that the engine DOESN'T slow the car. When the engine slows the car, it changes the car's balance and can cause the car to spin when on a road course and cornering near the limit of the tires' adhesion.

To answer the original poster's question, I think you could do a study of timing between coasting and using the engine to decelerate. However, there are far too many variables and to maximize engine braking you want to be in a gear where the engine is at very high RPMs. I don't think engine braking at mid RPMs is so bad for the engine, but I definitely wouldn't try downshifting into a gear that puts the engine near redline. Too many things can go wrong.

TexasRebel said:

It's not about wearing the clutch, but the throwout bearing.

Bearings are designed for a number of cycles at a load. The throwout bearing is loaded when the clutch is disengaged. Sitting in gear with the clutch disengaged at a stoplight is pretty insignificant when you consider the tens of millions of revolutions the bearing is designed for. Trouble comes when drivers rest their foot on the pedal or remove the clutch assist spring entirely. This puts a higher load on the throwout bearing when the clutch is engaged and you will hit those tens of millions of cycles easily.

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I respectfully disagree. I have the spring out, as do a ton of others. There is no weight coming from the 16th inch of slop in the pedal that would have any quantifiable effect on the life of the clutch.

PJR202 said:

I respectfully disagree. I have the spring out, as do a ton of others. There is no weight coming from the 16th inch of slop in the pedal that would have any quantifiable effect on the life of the clutch.

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We aren't talking about wear on the clutch, but the throwout bearing.
There is the weight of the clutch pedal. Say the weight of the clutch pedal adds force equal to the preload on the bearing... you've essentially halved the designed life of the throwout bearing.