High speed neutral coasting - 986 Forum - The Community for Porsche Boxster & Cayman Owners

kk2002s · 09-17-2015, 04:13 AM

I do put the trans in neutral and coast at speed when the situation is there and it's a longer downhill run.
Typically it is when I'm following someone and they're going to slow, so if I remain in gear, I'm doing a lot of engine braking.
I think prolonged engine braking is a bad thing.
I have also done it on long downhills to cool, bring down the temp. It works. It also gets some RPMs out of the auxiliary items (Alternator, power steering)

Trade off is that you do have to brake more especially following someone

I don't do it to save gas.
My main motivation is either cool down and reduce RPMs on the auxiliaries
OR
Not do prolonged engine braking

Is this bad for the Trans/Clutch what ever??
I know it's bad for the brakes but they are cheap, relatively

fridsten · 09-17-2015, 04:30 AM

Engine braking is not bad for the transmission, clutch or engine. It doesn't add any significant friction wear and since the power stroke is eliminated, the most demanding energy load on the engine is gone as well.

What engine breaking does, though, is make it possible for the fuel injection to shut off completely, which means that the engine doesn't consume any fuel at all, as opposed to when it's running on idle while coasting. It also, as you pointed out, save the brakes.

Engine breaking is highly recommended.

Edit: As a matter of fact, since there's no combustion going on, and fresh cool air gets sucked into the cylinders, it also helps cooling the engine.

BIGJake111 · 09-17-2015, 06:34 AM

I used to do this fairly often.

But my brakes are getting worn (changing pads this weekend) but in the mean time I've been engine braking to save brake wear. Engine braking through the gears to third is really efficient and leaves me only needing to brake the car from about 30 to zero which takes nothing.

I'll continue to engine brake even after I get new pads.

rick3000 · 09-17-2015, 06:44 AM

In the situations you describe, I always stay in gear (maybe a higher gear at a lower RPM) simply because I want to have the ability to accelerate if I encounter something unexpected. I personally think coasting for long periods of time is dangerous, and as fridsten describes doesn't really offer any benefits.

The Radium King · 09-17-2015, 07:02 AM

brakes are for braking, designed to turn rotational energy into heat and ablation of the brake pads. the engine is a highly complicated, lightweight, rotating device designed to produce power. i'd suggest that using your engine to absorb energy is not a good idea. one of the first things they teach at performance driving school is to not engine brake. not only is it hard on the vehicle, it can upset vehicle balance and weight distribution because the braking is occurring at the rear instead of (primarily) at the front where it is supposed to happen.

kk2002s · 09-17-2015, 07:35 AM

I remember reading not to long ago that Engine braking generates a much higher vacuum within the engine which places an unusually high demand on the AOS
It does place strain on the Clutch and drive-train, basically opposite of acceleration or steady driving

Also with the thought behind the smaller under drive pulley reducing RPMs on accessory items, idling certainly does that

This is something I think about when I take long trips into mountainous area where I'm driving 4- 8 hours at a time and any releaf I can give to the car is a plus

fridsten · 09-17-2015, 07:57 AM

Here's a pretty good source of information.
http://mechanics.stackexchange.com/questions/678/least-wear-and-tear-most-fuel-efficient-method-of-coasting-in-a-manual-transmis/681#681
It might not be recommended for performance driving, but that's not what we're discussing here. Also, engine braking near the redline is not a good idea.

landrovered · 09-17-2015, 10:25 AM

I coast regularly, gears are for going and brakes are for stopping. All this vroom vroom vroom downshifting coming to a stop sign is bad for the clutch. I simply kick it into neutral, coast til I brake and then rev match if I need to roll through a stop or put it in first to take off from a stop sign. Once you give up the rowing down through the gears it seems silly why you did it in the first place. Brake pads are a lot easier and cheaper to replace than a clutch.

JayG · 09-17-2015, 11:56 AM

Quote:

Originally Posted by landrovered

I coast regularly, gears are for going and brakes are for stopping. All this vroom vroom vroom downshifting coming to a stop sign is bad for the clutch. I simply kick it into neutral, coast til I brake and then rev match if I need to roll through a stop or put it in first to take off from a stop sign. Once you give up the rowing down through the gears it seems silly why you did it in the first place. Brake pads are a lot easier and cheaper to replace than a clutch.

Yup, that is the proper way to do it. That is exactly what I told my wife when we bought the Boxster for her. She was used to downshifting to slow down from when she had a Celica GT years ago.. She got all pissed off and said she was not going to drive the car so I was stuck driving it. I'm such a good husband that I said OK, If you insist, Ill drive it, you drive the Passat. The only problem (?) is she then started looking for a 911 with a Tip. 6 months later she fond the one she wanted and now we have 2 Porsche.

If cornering, practice your heal/toe downshifting

fridsten · 09-17-2015, 12:03 PM

To each their own, I guess.

Jamesp · 09-17-2015, 02:08 PM

I don't know which is best, but I coast most of the times. I found the assertion that the fuel is shut off completely during downshifting curious. Seems like the fuel to air ratio would be maintained even if the engine is spinning down with the throttle plate closed.

JayG · 09-17-2015, 02:57 PM

brake pads and rotors ~ $400 - $800 and DIY
Pads only ~$100-$400 definitely DIY

Clutch $!200-$2000 not DIY

You choose

lkchris · 09-17-2015, 03:11 PM

Normally don't downshift to slow, but do want to be in a gear that will give me acceleration should I need it. This moreso on a motorcycle.

jb92563 · 09-23-2015, 06:33 AM

Ugh...really?!!! going to neutral in a Porsche at speed!!!
I can hear Ferdinand crying in his grave.

Its simple. If you want to remain in control of your car and be ready to respond to sudden events like road debris, animals, distracted drivers, Ferraris etc, then you leave the car in gear so you can use the power and brakes to control the balance and traction while doing what ever fancy maneuvering is necessary.

If you are in neutral you do not have this same level of control.

Take a Porsche performance driving school and learn how to take advantage of all the wonderful capabilities of you car and stop driving it like a Wheelbarrow.

More safety and skill is better for you, your car, and the folks around you...you owe it to yourself and your family.

I know folks will have other strong opinions, but take the driving school and then we'll see if you change your mind.

As for wear and tear on the clutch, nope, not if you are doing it well.

As a matter of fact the plate friction material mostly gets abraded in one direction, but when using engine braking the material gets abraded in the other direction as well which prevents the surface from glassing over. In effect you are reconditioning the surface and making it better gripping so engine braking is actually good for it.

I have NEVER worn out a clutch in any of the 5 stick shifts I have driven daily in the last 40 years, and I always use engine braking. I also touch the break to light up the tail lights when cars are close behind when engine braking.

Ray