Turbo Engine Braking
06-17-2017, 01:20 PM
#35
Originally Posted by MTNRIDE
I am, what you might call, a mature driver 73. I am an experienced driver with a few Porsches. My generation was introduced to the air cooled 911 world with standard transmissions. Being a spirited driver, I am used to working the gears in the bends and down shifting (engine braking) to keep RPMs up to hold speed and save undo wear on the brakes.
My 996 TT is a 6 speed standard shift. Although it isn't so necessary anymore to keep the RPMs up, old habits die hard. Cars behind me are always telling me my brake lights are out.
I don't find brakes to be my friend when looking to hold speed in a tight bend. I generally charge the bend, tap the brake lightly and push through the bend to accelerate out the other side. Probably what many do today.
Now, with a water cooled turbo, I'm asking whether or not engine braking/shifting down has any possibly harmful effects on the motor.
Without sharing the variety of answers I've gotten... Let's here you options.
My 996 TT is a 6 speed standard shift. Although it isn't so necessary anymore to keep the RPMs up, old habits die hard. Cars behind me are always telling me my brake lights are out.
I don't find brakes to be my friend when looking to hold speed in a tight bend. I generally charge the bend, tap the brake lightly and push through the bend to accelerate out the other side. Probably what many do today.
Now, with a water cooled turbo, I'm asking whether or not engine braking/shifting down has any possibly harmful effects on the motor.
Without sharing the variety of answers I've gotten... Let's here you options.
07-04-2017, 09:05 PM
#36
Instructor
Engine braking
Not sure I can address the issue of transmission wear but I can contribute something to engine braking.
One answer is that it depends on how "spirited" your braking is, your intent, and the circumstances.
When entering corners, especially tight corners, "trail throttle" can allow you to brake without shifting weight to the front wheels and/or it can also be used to apply brakes to the rear only allowing you rotate the car mid turn pivoting around the front wheels and allowing a better exit line when a regular line is unavailable or tighter/inside line is desired. It also can be handy in other situations. Biggest downside is the possibility of over revs and in some cases the reverse forces on the engine may break parts that are not as strong in that situation. In one car it had the tendency of breaking camshafts.
Those of you familiar with the "traction circle" know that a tire only has so much traction and you have to decide how you want to allocate it between braking, accelerating, and turning. Trail throttle allows you to allocate the majority of the front wheels traction to turning with none going to braking, especially when you take into consideration that most traditional braking ends up being on the front wheels. The example may vary slightly on AWD cars, can't say.
One answer is that it depends on how "spirited" your braking is, your intent, and the circumstances.
When entering corners, especially tight corners, "trail throttle" can allow you to brake without shifting weight to the front wheels and/or it can also be used to apply brakes to the rear only allowing you rotate the car mid turn pivoting around the front wheels and allowing a better exit line when a regular line is unavailable or tighter/inside line is desired. It also can be handy in other situations. Biggest downside is the possibility of over revs and in some cases the reverse forces on the engine may break parts that are not as strong in that situation. In one car it had the tendency of breaking camshafts.
Those of you familiar with the "traction circle" know that a tire only has so much traction and you have to decide how you want to allocate it between braking, accelerating, and turning. Trail throttle allows you to allocate the majority of the front wheels traction to turning with none going to braking, especially when you take into consideration that most traditional braking ends up being on the front wheels. The example may vary slightly on AWD cars, can't say.
07-04-2017, 10:07 PM
#37
RL Community Team
Rennlist Member
Rennlist Member
Not sure I can address the issue of transmission wear but I can contribute something to engine braking.
One answer is that it depends on how "spirited" your braking is, your intent, and the circumstances.
When entering corners, especially tight corners, "trail throttle" can allow you to brake without shifting weight to the front wheels and/or it can also be used to apply brakes to the rear only allowing you rotate the car mid turn pivoting around the front wheels and allowing a better exit line when a regular line is unavailable or tighter/inside line is desired. It also can be handy in other situations. Biggest downside is the possibility of over revs and in some cases the reverse forces on the engine may break parts that are not as strong in that situation. In one car it had the tendency of breaking camshafts.
Those of you familiar with the "traction circle" know that a tire only has so much traction and you have to decide how you want to allocate it between braking, accelerating, and turning. Trail throttle allows you to allocate the majority of the front wheels traction to turning with none going to braking, especially when you take into consideration that most traditional braking ends up being on the front wheels. The example may vary slightly on AWD cars, can't say.
One answer is that it depends on how "spirited" your braking is, your intent, and the circumstances.
When entering corners, especially tight corners, "trail throttle" can allow you to brake without shifting weight to the front wheels and/or it can also be used to apply brakes to the rear only allowing you rotate the car mid turn pivoting around the front wheels and allowing a better exit line when a regular line is unavailable or tighter/inside line is desired. It also can be handy in other situations. Biggest downside is the possibility of over revs and in some cases the reverse forces on the engine may break parts that are not as strong in that situation. In one car it had the tendency of breaking camshafts.
Those of you familiar with the "traction circle" know that a tire only has so much traction and you have to decide how you want to allocate it between braking, accelerating, and turning. Trail throttle allows you to allocate the majority of the front wheels traction to turning with none going to braking, especially when you take into consideration that most traditional braking ends up being on the front wheels. The example may vary slightly on AWD cars, can't say.
07-04-2017, 10:13 PM
#38
Instructor
Should have included engines and transmissions. Both were brought up in the thread but I think I really only addressed whether engine braking had a purpose and why you might use the engine rather than the brakes in some cases. Mostly a track or "spirited driving" thing.
07-05-2017, 06:16 AM
#41
Instructor
I think your on the right track for spirited driving. What your describing is staying on the throttle to the brake zone, tapping on the brakes is transferring the weight to the front for your turn in, giving your tires the traction they need to not push. How hard the "tap" depends on how much speed you need to scrub off for the corner at hand. I would say trail brake off smoothly till the car is turning and you get to the speed you want then use a maintenance throttle till your ready to put the power back on. Like everybody has mentioned if a down shift is required do a heal toe rev match with that tap. The danger would come from forcing the motor to rev without a blip on the throttle. Sounds like your enjoying the car!
For spirited driving, use everything you have.
Had to laugh. An entire thread devoted to braking, and not one person wrote anything about breaking. Then the heal and toe came up.
I try hard not to be a grammar ****, but I am afraid the internet is going to ruin what's left of the language.
07-05-2017, 12:19 PM
#42
"Your" = the possessive form of "you," e.g. something that belongs to you;
"You're" = a contraction of "you" and "are," e.g. "You're not serious, are you?"
"There" = a place one is referring to, e.g. "I'm going there."
"Their" = the possessive form of "they," e.g. "They discussed what would be the best thing to do with their house."
"They're" = a contraction of "they" and "are," e.g. "they're going to get on the airplane shortly."
:-)
07-07-2017, 08:21 PM
#43
Instructor
What is the huh? for, not sure if it's an honest huh or the sarcastic huh's that are difficult to id on the net. Happy to expound if it's an honest question. It's not something you would typically do on the street but he did mention tight corners.
07-10-2017, 01:40 PM
#45
Instructor
You're right of course, there is some forward weight transfer. It will be the least amount of transfer you can pull off short of turning the car sideways (which is part of it to scrub speed). I have found the forward weight transfer great for setting the front up for the pivot. It also saves your brakes which you usually have to manage as a limited and sometimes diminishing resource. Another consideration in how you execute this would be maintaining boost for the exit but I haven't tried this in a turbo car, I suppose you would need to make sure you're still in the powerband when you start the corner exit.
You are essentially pulling a power slide/drift with the rear braking using the engine rather than the throttle initially, then complete the slide/oversteer using throttle after you make most of the turn in and are exiting the corner. The transfer doesn't affect how much of your front tire's traction you are allocating for the turn in. Once you make the pivot you get on the gas. I've never actually had to think my way through it. To be fair I've not tried this with my P-car, only dedicated racecars you can powerslide in.
Some cars will simply throw you off the track sideways or backwards so YMMV. I had a Factory Five spec racer that I could never get to do this, it loaded up the rear suspension and then let it go all at once causing it to spin. My Legends car could slide and 4 wheel drift all day. Great fun. Sorry for the length.
You are essentially pulling a power slide/drift with the rear braking using the engine rather than the throttle initially, then complete the slide/oversteer using throttle after you make most of the turn in and are exiting the corner. The transfer doesn't affect how much of your front tire's traction you are allocating for the turn in. Once you make the pivot you get on the gas. I've never actually had to think my way through it. To be fair I've not tried this with my P-car, only dedicated racecars you can powerslide in.
Some cars will simply throw you off the track sideways or backwards so YMMV. I had a Factory Five spec racer that I could never get to do this, it loaded up the rear suspension and then let it go all at once causing it to spin. My Legends car could slide and 4 wheel drift all day. Great fun. Sorry for the length.
Last edited by lconn; 07-10-2017 at 01:59 PM.
