15000 miles later

Topics relating to Advanced Driving in cars
IcedKiwi
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Re: 15000 miles later

Postby IcedKiwi » Wed Nov 09, 2016 4:22 pm

ChristianAB wrote:Thus, it will go like this: press the clutch, blip the throttle and simultaneously move the gear lever. Then quickly lightly press the throttle as you release the clutch pedal.


You can see why people were getting confused - Once you press the clutch in, the gearbox input shaft is completely disconnected from the engine. The input shaft, synchros and gear engagement cannot be influenced by the engine.
Could the blip be adding in a time delay that you don't notice due to having something to do and enjoying the sound which means you have a slower smoother engagement?

Agreed it could make the clutch engagement smoother if your rev's were falling away too much before, and maybe if you don't rev match perfectly it's smoother on a falling engine speed than pulling it up, but the blip shouldn't be able to effect the slotting into gear if the clutch is fully depressed.

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Mr Cholmondeley-Warner
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Re: 15000 miles later

Postby Mr Cholmondeley-Warner » Wed Nov 09, 2016 4:34 pm

Probably the revs were dropping too much, as superplum suggested, and just sustaining the right amount of throttle would also work, but is a tricky exercise. There's also a timing issue. If you wait forever, the revs drop too far and you have to bring them back up again.

Double-declutching works by reintroducing some momentum into the gearbox between the disengagement of the old gear and the engagement of the new one - the net result being that the ratios are more closely matched for speed when the engaging is done, and the synchro mechanism has less to do. This makes the gear lever slip into gear with less effort.

So Christian's problem is worse when his gearbox is cold, leading to notchiness between 1st and 2nd (my Boxster has a similar issue), and because the gear change takes longer, when the clutch is re-engaged, the rev matching is more crucial.

It's been a long time since I drove a 350Z (never driven a 370), but I do remember it being a difficult car to change gear in smoothly, having a very heavy clutch and a very sensitive throttle. I'm more used to cars like that now, but it's still a tricky combination.
Nick

devonutopia
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Re: 15000 miles later

Postby devonutopia » Wed Nov 09, 2016 8:38 pm

Strangely Brown wrote:Do you let the clutch in while you blip the throttle? If not, what does it achieve?


Sorry just seen this. Yes, the blip will be done with clutch depressed so its definitely not double declutching - only one clutch movement. All I am really doing is rather than letting the clutch engagement bring the revs up (which could be from close to tickover to 3000 rpm) I am bringing the revs up whilst clutch down and lifting the clutch to engage the gear when revs are around what they should be at that speed. It just seems to make things smoother.

My gearbox is a stock diesel box (in essence) but the clutch is a brutally tight paddle clutch and the flywheel is a steel single mass affair, so I do anything to make shifting a little more comfortable.

Under normal driving like you do with a diesel I rarely rev match. It tends to be something I do more when on a passionate bit of driving / trackday

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ChristianAB
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Re: 15000 miles later

Postby ChristianAB » Wed Nov 09, 2016 9:05 pm

IcedKiwi wrote:
ChristianAB wrote:Thus, it will go like this: press the clutch, blip the throttle and simultaneously move the gear lever. Then quickly lightly press the throttle as you release the clutch pedal.


but the blip shouldn't be able to effect the slotting into gear if the clutch is fully depressed.


I know it's hard to believe but that's how it is. In fact, just after starting the car, no amount of reasonable force will make the gear lever slot into 2nd, with the clutch fully depressed, unless the engine revs are manipulated. Again, hard to believe but I am happy to let anyone have a go and see it with their own eyes.

Initially, I suspected that even when the auto-blip is turned off, there might still be some trickery behind the scene which monitors temperatures, clutch, gearbox and engines rotational speed and actively 'resist' the engagement of a gear if you are too far off. But I went nowhere with that hypothesis, so I just focused on driving the car better.

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Strangely Brown
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Re: 15000 miles later

Postby Strangely Brown » Wed Nov 09, 2016 9:10 pm

That's not "blipping the throttle" with the clutch down. That sounds like a rev-matched gear change and, while it will have no effect on how easily the gear engages, it will certainly smooth out picking up the drive again.

What do you mean by..

Under normal driving like you do with a diesel I rarely rev match.


I always rev match in my/any diesel. Why would I not just because it's a diesel?

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ChristianAB
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Re: 15000 miles later

Postby ChristianAB » Wed Nov 09, 2016 9:12 pm

Mr Cholmondeley-Warner wrote:
It's been a long time since I drove a 350Z (never driven a 370), but I do remember it being a difficult car to change gear in smoothly, having a very heavy clutch and a very sensitive throttle. I'm more used to cars like that now, but it's still a tricky combination.


That's precisely why I love it. 8-)
Recently, I have been looking at mods to make the clutch even heavier, think 996 911 c2 heavy. Then I would be truly happy.

Gareth
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Re: 15000 miles later

Postby Gareth » Thu Nov 10, 2016 10:16 am

ChristianAB wrote:just after starting the car, no amount of reasonable force will make the gear lever slot into 2nd, with the clutch fully depressed, unless the engine revs are manipulated.

Have you tried a DDC without blipping?

Some of my more experienced friends tend to think that a DDC upshift only makes a difference by slowing things down; perhaps that's the issue.
there is only the road, nothing but the road ...

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ChristianAB
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Re: 15000 miles later

Postby ChristianAB » Fri Nov 11, 2016 12:08 pm

Gareth wrote:
ChristianAB wrote:just after starting the car, no amount of reasonable force will make the gear lever slot into 2nd, with the clutch fully depressed, unless the engine revs are manipulated.

Have you tried a DDC without blipping?

Some of my more experienced friends tend to think that a DDC upshift only makes a difference by slowing things down; perhaps that's the issue.


Yes, DDC without blipping is fine only when the car is warmed up, and you are right that it helps to slow things down. When the car is cold though, no chance.

Weirdly, maybe I am overthinking this: when the car is cold, I can always go straight into 3rd without issue, and the car has enough torque to make it an acceptable compromise.

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Mr Cholmondeley-Warner
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Re: 15000 miles later

Postby Mr Cholmondeley-Warner » Fri Nov 11, 2016 12:32 pm

Ummm - thinking theoretically here:

Christian has found that raising the revs while the clutch is disengaged helps the transition to second. The implication of this is that revs are falling too much while the clutch is down.

DDC on an upshift is a fairly pointless exercise, since usually we want the revs to fall for a higher gear, and re-engaging the clutch half way through (unless with a throttle input, which would be completely counter-intuitive), is only going to drop the revs even further.

I haven't driven the car, but I wonder if in fact the thinking is taking so long that actually, a quicker change would be better? (or learning to sustain the right amount of throttle during the change).
Nick


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