Probably a dumb C7 tranny question
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Not sure this makes sense where unlike a manual you're not lifting off the clutch or gas, with the auto you just keep your foot into it and hit the paddle shifter moving up the gears......
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Not a dumb question in the least. As for some replies you may get, well...
I'm not sure about the C7 automatic, but I think it does. I would hope so.
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Rev matching a paddle shift downshift serves the same purpose of rev matching a manual stick downshift...to get the engine speed matched to what it needs to be in the next gear.
I'm not sure about the C7 automatic, but I think it does. I would hope so.
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Rev matching a paddle shift downshift serves the same purpose of rev matching a manual stick downshift...to get the engine speed matched to what it needs to be in the next gear.
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Okay, so let me ask the following: other than on the track where you sometimes don't want a downshift to slightly slow your forward momentum, why would anyone care if the C7 has rev matching at all?
I grew up in an extremely mountainous area, and I would intentionally use downshifts to help slow the speed of the vehicle. I never blipped the throttle because I WANTED the engine to help slow the vehicle. Also, I know this did no damage to the engine or transmission because an old GMC S-15 pickup went through this downshift-to-help-save-some-brakes treatment for over 230,000 miles and was still going stong when my sister totaled it during a rain. Also, for every other manual transmission vehicle I have driven, I drove it that way, and never had a problem.
So, my question is, other than in a high performance scenario where someone needs to downshift and still not lose any forward momentum, why is rev matching needed?
I grew up in an extremely mountainous area, and I would intentionally use downshifts to help slow the speed of the vehicle. I never blipped the throttle because I WANTED the engine to help slow the vehicle. Also, I know this did no damage to the engine or transmission because an old GMC S-15 pickup went through this downshift-to-help-save-some-brakes treatment for over 230,000 miles and was still going stong when my sister totaled it during a rain. Also, for every other manual transmission vehicle I have driven, I drove it that way, and never had a problem.
So, my question is, other than in a high performance scenario where someone needs to downshift and still not lose any forward momentum, why is rev matching needed?
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Simple answer is to not wear out the clutch.
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Also, to sort of answer the OP's question to the best of my ability, rev matching is meant to change the RPMs of your engine based on a function of your present speed, and the gear to which you are moving. At whatever speed MPH your car is moving, your wheels will have a certain RPM based on that present MPH and the circumference of your wheels. That RPM of your wheels will go through the rear diff, and result in a RPM value for your driveshaft to your transmission. Then your transmission has a different gear ratio for each gear 1-7, and these ratios are used to mate the RPM from your driveshaft to your engine.
Now, what happens during a shift is that as you move from one gear to another, your overall speed of the car in MPH does not change (well, only very, very slightly during the instant when the shift happens, but we can neglect that for this conversation). However, the gear ratio of the transmission does change. The result is that the engine RPM must change from what it was before the shift to a new RPM after the shift. The whole idea of REV matching is to have the engine already at the correct RPM an instant before the transmission reengages from a shift instead of an instant later.
Now, can you answer the question for yourself?
Now, what happens during a shift is that as you move from one gear to another, your overall speed of the car in MPH does not change (well, only very, very slightly during the instant when the shift happens, but we can neglect that for this conversation). However, the gear ratio of the transmission does change. The result is that the engine RPM must change from what it was before the shift to a new RPM after the shift. The whole idea of REV matching is to have the engine already at the correct RPM an instant before the transmission reengages from a shift instead of an instant later.
Now, can you answer the question for yourself?
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Okay, that makes sense, but how much wear are we really talking about here? Why did I get by all those years in really mountainous areas and never have clutch problems? GMC vehicles are built like tanks?
I guess I should also mention that I always hit every gear on the way down, and had a good enough feel for the vehicle to know that the next downshift would not send the engine RPMs too high for the speed I was at.
Edit... Hum, now that I think about it, maybe I did have to have the clutch replaced on that old S-15, but just thought of it at the time as normal maintenance...
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Best example I can recall is my old Toyota 4x4. Original clutch lasted 160k miles. Most folks were getting half that. I did plenty of downshifting and drove it hard (well, as hard as you can for the old 22R-E that was in it) but I did blip the throttle on downshifts to match RPMs as close as possible.Okay, that makes sense, but how much wear are we really talking about here? Why did I get by all those years in really mountainous areas and never have clutch problems? GMC vehicles are built like tanks?
Edit... Hum, now that I think about it, maybe I did have to have the clutch replaced on that old S-15, but just thought of it at the time as normal maintenance...
Since the clutch disc is faced with friction material, much like brakes (different materials I'd expect), any time you are slipping the clutch to start moving or during shifting when the transmission input shaft and engine speed aren't matched, you'll wear the clutch. Upshifts aren't as bad since they would typically have a speed mismatch measured in 10's or 100's of RPMs. Downshifts RPM mismatches would be on the order of 100's to 1000s of RPMs. From those generalizations the amount of wear on a downshift with no rev match (blipped throttle or otherwise) could see up to 10 times the wear of a normal upshift.
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Don't overthink it guys (and gals), the reason for rev matching has nothing to do with wear and tear, it's to prevent the rear of the car from becoming unsettled as it down shifts. It's why a performance driver learns how to heel-toe and why motorcycles have slipper clutches.
And yes, the auto on the C7 rev matches on manual (paddle) downshifts. If you watch the tach as you downshift you will see a blue line appear? That's the RPM the computer used to "match". It doesn't do it in full auto mode. Also remember the OP asked about the auto trans, not the manual. However, the same logic holds true for the rev matching on the manual, it's not for wear and tear, it's purely a performance issue.
And yes, the auto on the C7 rev matches on manual (paddle) downshifts. If you watch the tach as you downshift you will see a blue line appear? That's the RPM the computer used to "match". It doesn't do it in full auto mode. Also remember the OP asked about the auto trans, not the manual. However, the same logic holds true for the rev matching on the manual, it's not for wear and tear, it's purely a performance issue.
Thanks Mark, I think you probably hit it right........while I rarely drive my SMG M6 hard enough to really need the rev-matching feature, I sure enjoy the sensation of being a better driver than I am.......and while I've never really been a Corvette sort of guy (though I never doubted their capability) I will be putting in my order for a LRG Z51 in a week or so. Will be selling my M6 and my beloved NSX for the C7, hope I'm not making a mistake. Enjoying the forum for sure!
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