2018 S4 engine braking
04-17-2018, 04:30 AM
#1
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2018 S4 engine braking
I have a 2018 S4 equipped with a 8 speed tiptronic transmission. The upshifts are super fast.
The downshifts, although equally fast have very little engine braking effect. It sounds great but I can shift from 5-4-3 and feel very little braking effect.
My previous B8 with manual tranny had amazing engine braking
Does Audi adjust the valves timing to deliberately reduce engine braking on the 2018 S4.
The downshifts, although equally fast have very little engine braking effect. It sounds great but I can shift from 5-4-3 and feel very little braking effect.
My previous B8 with manual tranny had amazing engine braking
Does Audi adjust the valves timing to deliberately reduce engine braking on the 2018 S4.
04-17-2018, 07:03 AM
#2
AudiWorld Senior Member
The new V6T in this S4 has a Miller cycle (aka B cycle), which uses variable valve lift to effectively make the power stroke longer than the compression stroke. I'm not sure what affect if any this has on engine braking, but it is indeed a change from the previous S4's engine. The addition of a Miller cycle allows more power without a negative fuel economy hit.
04-17-2018, 09:45 AM
#4
AudiWorld Senior Member
On many high end sportbikes e.g. BMW S1000RR and many Ducatis, the amount of engine braking is user selectable. It is generally considered "better" or at minimum advantageous to have *less* engine braking, and so engine braking decreases as your progress further towards "race" settings, for a couple of reasons I'll describe below.
1. Engine braking applies to the drive wheels only, in a way that is proportional to the drive wheels. On a motorcycle, this is your rear tire: the one you do almost 0% of your braking with especially in a performance riding scenario (in fact if you watch MotoGP races, you'll often see Rossi and Marquez come into the corners with their rear wheel a full inch off the ground thus providing no braking at all, and their front rotors glowing orange). On a car, the front brakes still do the lion's share of the work (there is a reason that front brakes are always larger and on some cars like RS3 only the front rotors are available as ceramic, after all) and on a 60-40 rear-biased car like our S4s, the back-torque applied through the rear-wheels provides minimal advantage and, theoretically, could be the 0.1% that causes a lockup at the limit.
2. Engine braking is not something you can modulate. It is a much less direct way of decelerating a vehicle than a brake pedal.
3. ABS and ESC systems can not -- at least in our cars -- modulate engine braking to counter its effects either.
Anyway, sorry for the wall of text but my point is when you say "proper downshift feel," I think you might have it backwards?
Edit/afterthought: I will admit that for normal, legal street driving it is entirely a preference thing. An appreciable bit of engine braking is certainly useful to have in the mountains for example, and this car doesn't have enough to resist a rather substantial piling on of speed as you descend a pass. On the flip side, the fuel penalty could be quite harsh and the driving experience quite annoying if engine braking were present to such a degree that it slowed the car when driving along flat roads in S mode enough to where you had couldn't really coast but rather had to keep your foot on the gas most of the time, and I think it could be argued that the current amount this S4 has is about as high as I'd want to go in that regard.
1. Engine braking applies to the drive wheels only, in a way that is proportional to the drive wheels. On a motorcycle, this is your rear tire: the one you do almost 0% of your braking with especially in a performance riding scenario (in fact if you watch MotoGP races, you'll often see Rossi and Marquez come into the corners with their rear wheel a full inch off the ground thus providing no braking at all, and their front rotors glowing orange). On a car, the front brakes still do the lion's share of the work (there is a reason that front brakes are always larger and on some cars like RS3 only the front rotors are available as ceramic, after all) and on a 60-40 rear-biased car like our S4s, the back-torque applied through the rear-wheels provides minimal advantage and, theoretically, could be the 0.1% that causes a lockup at the limit.
2. Engine braking is not something you can modulate. It is a much less direct way of decelerating a vehicle than a brake pedal.
3. ABS and ESC systems can not -- at least in our cars -- modulate engine braking to counter its effects either.
Anyway, sorry for the wall of text but my point is when you say "proper downshift feel," I think you might have it backwards?
Edit/afterthought: I will admit that for normal, legal street driving it is entirely a preference thing. An appreciable bit of engine braking is certainly useful to have in the mountains for example, and this car doesn't have enough to resist a rather substantial piling on of speed as you descend a pass. On the flip side, the fuel penalty could be quite harsh and the driving experience quite annoying if engine braking were present to such a degree that it slowed the car when driving along flat roads in S mode enough to where you had couldn't really coast but rather had to keep your foot on the gas most of the time, and I think it could be argued that the current amount this S4 has is about as high as I'd want to go in that regard.
Last edited by mplsbrian; 04-17-2018 at 10:16 AM.
04-17-2018, 10:52 AM
#5
AudiWorld Senior Member
Keep in mind that the B9 transmission has a torque converter. If the TC is not in lockup mode, it will allow some bit of freewheeling when the wheels try to turn the engine. The B9 does provide a fair bit of engine braking on downhills, but the "engagement" seems much smoother do to that TC. With the dual clutch the engagement was much more abrupt.
04-17-2018, 01:08 PM
#6
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I spoke with the senior tech at my local Audi dealership, he drives a similar vehicle. He confirms that the TC will not lock up when the wheels try to drive the engine (during downshifts) and the TC will tend to allow slippage. this is specific to the 8 speed trans without a dual clutch.
His general comment was although the car is marketed as a sports performance sedan, fuel economy for general driving trumps performance.
His general comment was although the car is marketed as a sports performance sedan, fuel economy for general driving trumps performance.
04-17-2018, 02:02 PM
#7
AudiWorld Senior Member
I spoke with the senior tech at my local Audi dealership, he drives a similar vehicle. He confirms that the TC will not lock up when the wheels try to drive the engine (during downshifts) and the TC will tend to allow slippage. this is specific to the 8 speed trans without a dual clutch.
His general comment was although the car is marketed as a sports performance sedan, fuel economy for general driving trumps performance.
His general comment was although the car is marketed as a sports performance sedan, fuel economy for general driving trumps performance.
What you say about how the S4 is marketed vs. what it is is also definitely true. Consider that you can get a pretty nasty track monster of a Corvette for about the same money. Most people daily these things to work and open them up once in a great while on the weekend on and I’m no exception.
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04-17-2018, 02:31 PM
#8
AudiWorld Senior Member
I'm perfectly ok with this. I don't necessarily care about fuel economy, but I do care about driving comfort since 90% of the time it's just a daily driver for me. However, I do think that when the car is in Dynamic/S mode, the engine braking seems more pronounced, so perhaps they tune the lockup clutch to engage differently in that mode.
04-17-2018, 07:22 PM
#10
AudiWorld Super User
The ZF8 in the S4 is programmed to freewheel when coasting. It deliberately doesn't engine brake and instead makes the transmission not drag the engine so the car can coast under its own momentum and save fuel. I haven't driven an S4 yet, but I've extensively driven the RS5, which doesn't have the freewheeling and engine brakes properly.
