TumblingPanda

I have a 18' GS non-Z07 with manual transmission. On the track, the downshits are amazingly fast - I'm downshifting the fastest I physically can and the auto-rev-match works like a charm. However during upshifts, the revs are not falling down fast enough. I'm having to be deliberately slow so that the upshifts are smooth and I'm not destroying the clutch. This is the case for both 2 to 3 and 3 to 4. I haven't tried any other upshifts on the track! :P

Can something SIMPLE be done about this? Is this purely how the throttle controller is mapped or is this because the flywheel is too bulky and takes time to slow down?

EDIT: I've tried with the rev-match feature off as well and the behavior is the same. The revs aren't falling down quick enough for a fast upshift.

Avanti

Admittedly, I'm ignorant since I don't care for the rev-match feature and don't use it, but I thought that was exactly what it was suppose to deal with... yes, no???

TumblingPanda

I've tried with the rev-match feature off as well, and it is the same behavior. The feature can pull the rpm UP and HOLD it (presumably by opening the throttle), but what can it do to bring the rpms down quick enough? I'm beginning to think the rotational inertia of the engine is the culprit. Anyone else experiencing this?

BenCasey

You know.. weird stuff.. this reads like "I don't much care for microwaves and don't use them"

Why!?

But then I'm not a breast man, and my buddy thinks the world revolves around breasts. They look great in tank tops.

Rev match is amazing. Makes the car bark all the time. Bad *** downshifts hauling through the mountains. On the track it's a hoot to shift from 3rd into 1st on a 90 degree turn, decelerating from 80 to 30 with a perfect shift.

You might not know that the steering angle controls throttle. As you straighten out the steering wheel, the throttle opens up more. Yet another feature that someone, somewhere, doesn't like.

BenCasey

Panda man, I have not noticed this behavior, I'll keep an eye on it (car is in the body shop this week, I'll put this on my growing list of stuff to do).

I have 30,000 HARD miles on my car; daily silicon valley traffic, Sierra mountain passes, driving like a complete jerk on the freeway - never noticed. FWIW

DWillys

No lift shifting

The HACK

I think it's by design, most modern cars with drive-by-wire throttle control does this to burn off excess NOx. When you close off the throttle body too quickly, the excess unburnt fuel gets through to the CATs and whatever the cats don't handle, gets sent out into the atmosphere as NOx. Most cars made after 2000 with DBW leaves the throttle plate open momentarily during shifts so the extra air and fuel mix and burn-off. The only car that I've see that doesn't do this, is my German Iron that has an inline 6 with 6 individual throttle bodies. The individual, multiple throttle bodies are controlled electronically and some stay partially open, so the RPM can drop quickly because some of the throttle stay open to pipe in air for excess burn-off.

Anything with single throttle body will continue to hang the RPM on upshift because you can't completely close off the throttle body.

Wgg2017

TumblingPanda

Then is this something aftermarket throttle controllers like Vitesse controller will fix?

itch808

I also particularly find the rev hang issue annoying. Unfortunately seems pretty common on DBW cars. Most other cars seems only fixable with an aftermarket ECU flash or live with it.

C7&7

This is in the tune. Changeable if you're willing to get it retuned.

Shaka

Physics. Big 90' V8s have heavy crankshafts and they take a long time to rev up and slow down. People want fast shifts in their Autos and DCTs but if your car has this crankshaft, something has got to give. A F488 shifts faster than a LaFerrari. The closer the ratios, the less impact there is in fast shifts. An auto's torque converter will absorb this energy, but it will get very hot quickly.


Another thing, these gears are very heavy so even with rev matching, the syncros have to match the gear to shaft speed almost instantly. Inertia is a terrible thing. Rev matching is to save the timing chain for dumb drivers.
Downshifts are fast because the engine revs up faster than it slows down but the syncros have a harder job. It is not advisable to double declutch on new trannys because of the multi surface syncro packs. They will be damaged.




If you are not racing, let your brain decide the speed of the shifts. When you upshift, put some pressure on the lever. When it slips in easy, that is the correct speed and therefor RPM to shift. Try it.