[buzylivn]

Have a 2014 C7 Stingray. When I use REV MATCH- Engine will rev in some gears (2,3, & 4) when I push the clutch in - not even having shifted to a lower gear yet! Does not happen all of the time. This happens more so when going from 3rd gear to 2nd gear. Another quirk is when I place the gear over to second but not in the gear yet it will rev up BEFORE I even have the gear locked in AND the clutch engaged. IS THIS NORMAL?

Some may recall this car had a leaking transmission at 300 miles. GM replaced the whole transmission, which I appreciate. Does this have anything to do with the transmission being replaced meaning something was not set correctly? Car now has 4300 miles.

Appreciate any direction, so I can inform the mechanic.

 

[rdslon01]

Have a 2014 C7 Stingray. When I use REV MATCH- ... [cut] ... Another quirk is when I place the gear over to second but not in the gear yet it will rev up BEFORE I even have the gear locked in AND the clutch engaged. IS THIS NORMAL?

For the second item you mentioned (the one I copied above), I do believe this is completely normal. The engine is supposed to rev match as soon as it thinks it knows where you are going. So, if you approach second, it will rev match for second even before you get it into second.

As for the other issues, I do not know. Hopefully someone else can help.

 

[Mobius]

Let me start by saying that I love the Rev Match feature, and I use it consistently. It adds another interesting dimension to the C7, and there are occasions when the engine may rev slightly and unexpectedly as a shift is in progress (as the car works to guess the gear your headed for), but RPM is immediately corrected in almost all instances when the next gear is selected.

Here's my interesting issue with Rev Match, which occurs infrequently, but I'd like to understand the root cause issue (if possible).

http://www.stingrayforums.com/forum...950-some-issues-i-am-seeing-26.html#post88040

 

[abshapiro]

Mobius -

I make my 1-2 and 2-3 up shifts at 3000 rpm without rev match. This is the sweet spot for the type of city driving I do and my body timing on clutch, shift and accelerator. The shifts are smooth and I can't notice any rpm mismatch or jerkiness. I will pay more attention to this over the next day and also turn on rev match to give you a better answer.

Art

 

[Mobius]

I have another idea that I'll explore...

I have a CAGS bypass installed.

If the CAGS system communicates with the ARM system, it might lead to some "inconsistent" RPMs when a 1-4 skip-shift is ordered by the CAGS system, but the operator is slipping it into 2nd gear instead.

I'm not sure this is a strong possibility in my case, since I generally shift at RPMs above the CAGS threshold, but maybe I'm not always above the threshold...

I'll monitor shift RPM more closely when the ARM "anomaly" occurs, and see if CAGS might be in play.
.
.
Some additional ARM details (pg 9-32 of C7 manual):

ARM will also:
. Be active above 32 km/h (20 mph).
. Match engine speed up to 5400 rpm.
. Not operate when the accelerator pedal is applied.
. Be disabled when the coolant temperature is below 0°C (32°F).

 

[53Vette]

I use rev match all the time. I love it. On the track it is so smooth.
On the road it will rev sometimes before you fully engage the next lower gear.

 

[abshapiro]

I only have 2100 miles on the car so I’m still somewhat in the learning to drive it mode. I turned on rev-match and now wonder why I haven’t been using it for daily driving. The only time I use it is when I drive the twisty back roads on a Sunday morning for enjoyment. I do have a CAGS eliminator installed. I did the 1-2 and 2-3 up shifts at various RPMs and all shifts were smooth with no increase blip in RPM. The only time I experienced an RPM increase blip is when I shifted at 18 mph when the display indicated CAGS was engaged and I shifted from 1-2 and not 1-4.

 

[53Vette]

Rev match is for down shifts only.

 

[Mobius]

Rev match is for down shifts only.

From Owner's Manual,

"Vehicles equipped with a manual transmission have Active Rev Match (ARM). ARM aids in smoother shifting by matching the engine speed to the next selected gear. By monitoring shift lever and clutch operation, ARM adjusts engine speed to match a calibrated value based on gear selection. On upshifts and downshifts, engine speed will be increased and decreased to match vehicle road speed and transmission gear position. ARM is maintained for a few seconds between shifts, then deactivates if the shift is not completed."

 

[53Vette]

I'm going to have to try screwing up my up shifts to see what it does. I've never seen it do anything so far.

 

[phantom]

Mine matches downshifts only, also!

 

[corvettrob]

Mine down shifts only !! Works perfect !!!

 

[rdslon01]

It is much easier to code a rev-match which matches on both upshifts and downshifts. Why is this the case?

If you match both ways (both upshifts and downshifts), what the car's computer needs to have and know include:
-the gear ratios (easy to have in a table),
-what your speed is (easy since this is known to the car),
-which gear you are approaching (not so easy, but they did it).

If you want to only match on the downshifts, then, in addition to all the above, you also need to know:
-what gear you were in previously (easy enough if you store this information in memory - but you also have to write the code to determine when this "previous gear memory" should be overwritten - does it get overwritten after you enter a transmission gear's gate, or only after you have done this plus let out the clutch?),
-then compare that to what gear you are going toward to see if the new one is lower or higher than the previous one,
-then probably also mix in data on if you are speeding up or slowing down (which probably also requires some memory and speed comparisons, with some intelligent algorithms built around the exact time intervals of when those comparisons would be done, probably as a function of speed), and
-then after all of that extra trouble, determine whether to rev match or not.

The engineers would have to be out of their minds to go to all that extra trouble just to know when to disable rev match for upshifts.

It is much easier to just do it for both upshifts and downshifts when rev match is turned on, instead of going to all the extra trouble of disabling it for upshifts.

 

[mjw930]

FYI, the Tremec has a Hall effect sensor built into the trans that tells the computer which gate you are selecting. The time between moving into the gate and actually selecting the gear and releasing the clutch may seem short to us but in computer time it's an eternity so rev matching is fairly easy from a programming point of view.

Also, I've played around and RPMs change as you select different gates, it's pretty cool.

 

[rdslon01]

a Hall effect sensor built into the trans that tells the computer which gate you are selecting.

This may not be very difficult, but everything required to do that ^ does not seem so simple to me.

 

[Curahee]

Rev match is for down shifts only.

Nope. See owners' manual page 9-32.

 

[Petercwelch]

Presumably listening to increases in RPM is more noticable than listening for RPM decreases. May explain why rev match with upshifts seems not to work.

 

[rdslon01]

Presumably listening to increases in RPM is more noticable than listening for RPM decreases. May explain why rev match with upshifts seems not to work.

I think you are correct. Also, people are used to hearing the RPMs decrease when they upshift and let off the gas. They are just not noticing that that decrease is now being very well controlled instead of a free fall.

 

[mjw930]

If you want to prove to yourself the rev matching works in both directions move the shift lever quickly between gears. If done quickly enough you can play a tune with the RPM's without ever touching the throttle. The easiest shift is 3 - 4, just slide it over to the 2nd gear gate then back to the 4th gear gate and listen to the RPM's change.