Welcome to the North American Subaru Impreza Owners Club Sunday May 19, 2019
Home Forums WikiNASIOC Products Store Modifications Upgrade Garage
NASIOC
Go Back   NASIOC > NASIOC General > Newbies & FAQs

Welcome to NASIOC - The world's largest online community for Subaru enthusiasts!
Welcome to the NASIOC.com Subaru forum.

You are currently viewing our forum as a guest, which gives you limited access to view most discussions and access our other features. By joining our community, free of charge, you will have access to post topics, communicate privately with other members (PM), respond to polls, upload content and access many other special features. Registration is free, fast and simple, so please join our community today!

If you have any problems with the registration process or your account login, please contact us.
* Registered users of the site do not see these ads. 
Reply
 
Thread Tools Display Modes
Old 05-16-2019, 11:34 AM   #26
Norm Peterson
Scooby Newbie
 
Member#: 498642
Join Date: Mar 2019
Chapter/Region: Tri-State
Location: corner barstool (TV reference)
Vehicle:
2019 WRX Limited
Dark Grey

Default

Quote:
Originally Posted by rtv900 View Post
^again, NO, synchros inside the transmission have less than no idea if you rev match with the clutch depressed, so that is a no, it makes no difference to synchros. The input shaft is disconnected from the engine, rev it to anything or don't rev it up at all, makes no difference.
You must have mis-read what I posted, or assigned what somebody else posted to me. I know all that, and I don't think I'd get it wrong.


Quote:
Double clutching is for synchros, or in reality, it is for NON synchronized transmissions and it is moronic to go through that ridiculous shifting procedure on a modern trans.
Just because you don't care to double-clutch a synchro'd transmission still doesn't make it wrong to do so. I can't help it if you or anybody else thinks it's too much bother when it really isn't all that much more. Then again most people really would rather do less than do any more than the minimum they can get away with doing, do easier rather than only a little harder, etc.


Quote:
You may as well put a hand crank on the front to start the motor so you can 'save' wear on the starter.
Ridiculous comparison.


Quote:
The comment was based on your previous statement implying that rev matching has anything to do with synchros, which it does not.
Double clutching is nothing more than rev-matching taken one step further. Double-clutching and its simpler cousin rev-matching are both about reducing rpm differences for smoother shift execution and reduced wear. Whether we're looking at rpm differences across only the clutch, or across the clutch AND across a transmission synchro, it's still about matching some input side rpm to what the output side needs the rpms to be at.


Quote:
So no, it isn't a small effect, it is no effect because there is zero connection between the input shaft and engine when you are clutched in and 'rev matching'
When you are clutch-in, it's all on the synchros, 100%, to speed up things on the input side of the synchro hub to match the rpm that the upcoming gear needs them to be at. That's still a form of rev-matching, except it's not you who's making it happen. And the way the synchros do their job absolutely does result in wear.

But feel free to continue either rev-matching, double-clutching, or doing neither.


Norm
* Registered users of the site do not see these ads.
Norm Peterson is offline   Reply With Quote
Sponsored Links
* Registered users of the site do not see these ads.
Old 05-16-2019, 11:53 AM   #27
rtv900
Scooby Specialist
 
Member#: 428511
Join Date: Aug 2015
Location: philadelphia
Vehicle:
2016 STI

Default

Quote:
Originally Posted by Norm Peterson View Post
If you rev-match your downshifts instead of using the clutch to drag engine revs up, the amount of additional wear is negligible. Synchros inside the transmission like you to do this as well, and that job's a bit more expensive than any clutch job.
Norm
^here is where you said that rev matching helps your synchros

How am I mis-reading this statement?

Quote:
Originally Posted by Norm Peterson View Post
You must have mis-read what I posted, or assigned what somebody else posted to me. I know all that, and I don't think I'd get it wrong.
I did not mis-read anything. You are saying rev matching has an effect on synchros (they 'like' you to do this)

again, NO, they don't 'like' it or 'dislike' it because it has ZERO effect on synchros

And yet again, this is exactly why people talk about how they double clutch when they are really just rev matching, because of misinformation like this
rtv900 is offline   Reply With Quote
Old 05-16-2019, 12:39 PM   #28
vlad11591
Scooby Newbie
 
Member#: 295970
Join Date: Sep 2011
Chapter/Region: Tri-State
Location: Hamilton, NJ
Vehicle:
2018 WRX
ISM

Default

clarification here guys. Am I rev-matching wrong if I don't take my foot off the clutch?
vlad11591 is offline   Reply With Quote
Old 05-16-2019, 12:39 PM   #29
Norm Peterson
Scooby Newbie
 
Member#: 498642
Join Date: Mar 2019
Chapter/Region: Tri-State
Location: corner barstool (TV reference)
Vehicle:
2019 WRX Limited
Dark Grey

Default

If you rev-match your downshifts instead of using the clutch to drag engine revs up, the amount of additional wear is negligible. Synchros inside the transmission like you to do this as well, and that job's a bit more expensive than any clutch job.
Quote:
Originally Posted by rtv900 View Post
^here is where you said that rev matching helps your synchros

How am I mis-reading this statement?
Keep in mind that that comment was aimed very narrowly at those who might use the clutch to drag engine rpms up. As would happen if you're using that technique to maximize braking due to engine friction/compression. I'd like to think that this doesn't happen all that often, but I suspect that would be an overly optimistic assumption.

Dragging the engine revs up by using the clutch and the car's momentum means that everything from the engine to the appropriate synchro hub is spinning slower than what the next lower gear needs them to be spinning at.

That then means that the synchros have to do all of the work getting everything from the clutch disc back to that synchro hub accelerated up to the necessary rpm.

Yes, you've at least disconnected the synchro from the flywheel, pressure plate, crankshaft, etc., but there's still those few rotating things downstream of the flywheel and upstream of the synchro that need the synchro to make their revs match what they need to be for the lower gear to engage. The slower-revving engine can't do that, the non-rev-matching driver isn't doing it, and there's nothing else left.


Norm
Norm Peterson is offline   Reply With Quote
Old 05-16-2019, 12:48 PM   #30
Norm Peterson
Scooby Newbie
 
Member#: 498642
Join Date: Mar 2019
Chapter/Region: Tri-State
Location: corner barstool (TV reference)
Vehicle:
2019 WRX Limited
Dark Grey

Default

Quote:
Originally Posted by rtv900 View Post
again, NO, they don't 'like' it or 'dislike' it
Synchro ring wear rates would be lower if you do double-clutch, or at least rev-match. Better? Sorry for trying to lighten the mood.


Norm
Norm Peterson is offline   Reply With Quote
Old 05-16-2019, 01:15 PM   #31
Norm Peterson
Scooby Newbie
 
Member#: 498642
Join Date: Mar 2019
Chapter/Region: Tri-State
Location: corner barstool (TV reference)
Vehicle:
2019 WRX Limited
Dark Grey

Default

Quote:
Originally Posted by vlad11591 View Post
clarification here guys. Am I rev-matching wrong if I don't take my foot off the clutch?
As in holding the pedal down when you kick the gas? That would be "rev-matching" but not "double-clutching". Either of those would be better than not doing anything at all with the throttle.


Norm
Norm Peterson is offline   Reply With Quote
Old 05-16-2019, 04:18 PM   #32
rtv900
Scooby Specialist
 
Member#: 428511
Join Date: Aug 2015
Location: philadelphia
Vehicle:
2016 STI

Default

Quote:
Originally Posted by vlad11591 View Post
clarification here guys. Am I rev-matching wrong if I don't take my foot off the clutch?
no, that is rev matching.

That is what more expensive manuals do now with a computer.
'active rev matching'

It blips the throttle and nails the revs dead nuts on the next gear.
The purpose is what Norm is saying, then the clutch doesn't have to pull up the engine speed and it makes for a super smooth downshift.

just doesn't have anything to do with synchros
rtv900 is offline   Reply With Quote
Old 05-16-2019, 04:24 PM   #33
rtv900
Scooby Specialist
 
Member#: 428511
Join Date: Aug 2015
Location: philadelphia
Vehicle:
2016 STI

Default

Quote:
Originally Posted by Norm Peterson View Post
Synchro ring wear rates would be lower if you do double-clutch, or at least rev-match. Better? Sorry for trying to lighten the mood.


Norm
ok, I can see you aren't going to give in on this so I'll just say it once more and then bail.

No, synchro wear would NOT be lower if you 'at least rev matched' because you have ALREADY put the shifter in gear while you were clutched in. So any rev you did has no affect at all.
The synchro did it's job while you were clutched in and it mated the input shaft to the output all by itself with no influence from the motor. You could have revved to 9000 and it would not have made a difference as the synchro doesn't even know.

I'm not saying rev matching doesn't technically save a minuscule amount of clutch wear because yes, then you don't need that friction to pull up the engine speed, sure.
But synchro wear, nope. Has no affect. Drive a non synchronized transmission and you can rev match until you are blue in the face and it won't make a lick of a difference.
rtv900 is offline   Reply With Quote
Old 05-16-2019, 04:52 PM   #34
jasonwrx86
Scooby Specialist
 
Member#: 472037
Join Date: Jul 2017
Chapter/Region: MWSOC
Vehicle:
2018 WRX Limited
CWP

Default

To make it simple. Anytime there is a rpm difference between the input shaft and the output shaft given the speed and gear you are selecting, you are wearing the syncro when they are being engaged. This is why skipping gears wear more on the syncros than going though the gears.
You can go from 1st gear at 6000 rpm to 4th gear at 2000 rpm, the 4th gear syncro has to take up 4000 rpm worth of inertia vs if you just go though 2-3-4 where each syncro will only take 1500rpm worth of inetia.
Same with down shift, if you go from 5th 2000rpm to 2nd at 4000rpm, the syncro has to do the same.
Now double clutching is when you manually rev up the input shaft to match the rpm of the output shaft given the speed and gear. That way the syncros don't have to speed up or slow down the rpm of the input shaft.
Technically, double clutching saves syncros both up and down shifts. However up shifts are less important because due to drag on the bearings and stuff, the input shaft will naturally slow down during shift.
But since syncro material has been improved dramatically over the years, they last a long time without double clutching.
And no, revmatching does not save syncros because you are still not manually matching the speed of the input and output shaft since the clutch is disengaged before you select the next gear. No amount of revving will change the input shaft speed before the syncro does.
Revmatching is to match the engine rpm to the input shaft of the transmission.
Double clutching is to match the input shaft to the output shaft of the transmission.

Last edited by jasonwrx86; 05-16-2019 at 05:00 PM.
jasonwrx86 is online now   Reply With Quote
Old 05-16-2019, 05:12 PM   #35
Norm Peterson
Scooby Newbie
 
Member#: 498642
Join Date: Mar 2019
Chapter/Region: Tri-State
Location: corner barstool (TV reference)
Vehicle:
2019 WRX Limited
Dark Grey

Default

Quote:
Originally Posted by rtv900 View Post
ok, I can see you aren't going to give in on this so I'll just say it once more and then bail.

No, synchro wear would NOT be lower if you 'at least rev matched' because you have ALREADY put the shifter in gear while you were clutched in. So any rev you did has no affect at all.
Please explain to me what you think makes the slower-revving clutch disc, input shaft, and at least the countershaft increase revs so that the revs between the synchro hub match that of the dog teeth on the face of the faster-spinning lower gear? This has to happen while you're putting the shifter in that gear, before it fully gets there. IOW, synchro ring operation happens before positive gear engagement - that's just how the arrangement works.

You're unwilling to believe me (even though I've had a few transmissions apart for various reasons), so I did an internet search on synchromesh transmission operation and got plenty of hits. Here's the description most applicable to this discussion, from http://enginemechanics.tpub.com/1403...ission-120.htm . While it's written in the context of upshifting, the mechanism works in precisely the same fashion when downshifting. Emphasis mine.

Quote:
The synchromesh transmission is a type of constant-mesh transmission. It synchronizes the speeds of mating parts before they engage to allow the selection of gears without their clashing. It employs a combination metal-to-metal friction cone clutch and a dog or gear positive clutch. These clutches allow the main drive gear and second-speed main shaft gear to engage with the transmission main shaft. The friction cone clutch engages first, bringing the driving and driven members to the same speed, after which the dog clutch engages easily without clashing. This process is accomplished in one continuous operation when the driver declutches and moves the control lever in the usual manner. The construction of synchromesh transmissions varies somewhat with different manufacturers, but the principle is the same in all.

So it's like I've been saying all along, that the synchros absolutely are involved. They have to be.

I'll give you that through good design (not all synchro mechanisms can claim this) synchro wear can be minimized. But not totally eliminated.


Norm

Last edited by Norm Peterson; 05-16-2019 at 05:25 PM.
Norm Peterson is offline   Reply With Quote
Old 05-16-2019, 08:51 PM   #36
blakep123
Scooby Newbie
 
Member#: 501696
Join Date: May 2019
Default

depends on car and RPM range id think
blakep123 is offline   Reply With Quote
Old 05-17-2019, 07:49 AM   #37
rtv900
Scooby Specialist
 
Member#: 428511
Join Date: Aug 2015
Location: philadelphia
Vehicle:
2016 STI

Default

Quote:
Originally Posted by Norm Peterson View Post
Please explain to me what you think makes the slower-revving clutch disc, input shaft, and at least the countershaft increase revs so that the revs between the synchro hub match that of the dog teeth on the face of the faster-spinning lower gear? This has to happen while you're putting the shifter in that gear, before it fully gets there. IOW, synchro ring operation happens before positive gear engagement - that's just how the arrangement works.
Norm
everything you copied and pasted from the internet is correct.

You aren't understanding regardless of how many transmissions you've had apart.
Rev matching has less than no affect on synchros, period.
rtv900 is offline   Reply With Quote
Old 05-17-2019, 08:29 AM   #38
Norm Peterson
Scooby Newbie
 
Member#: 498642
Join Date: Mar 2019
Chapter/Region: Tri-State
Location: corner barstool (TV reference)
Vehicle:
2019 WRX Limited
Dark Grey

Default

<sigh>

One of the synchros is involved in every shift before the gear you're going for is solidly engaged no matter what else you do or don't do. Synchro friction happens before dog engagement, always, and if synchro friction was negligible (what it would take for wear to truly be zero) the synchros would not work. How much friction happens is up to the driver and the shifting technique he prefers to use. Not every driver has much sympathy for the mechanical bits that make it possible to shift gears.

Next road trip I take, I'll try to pay attention to what's going on as I shift gears, even though I'm decades past having to do any such thing.


Norm
Norm Peterson is offline   Reply With Quote
Old 05-17-2019, 09:38 AM   #39
rtv900
Scooby Specialist
 
Member#: 428511
Join Date: Aug 2015
Location: philadelphia
Vehicle:
2016 STI

Default

No clue where you are going with that last post dude.
It's like you think I'm debating the job of a synchro.
I get that they are basically clutches for the input shaft to match to the output and they do their job just before the dog teeth come into play.
Hence non synchro transmissions grinding their dogs.

When you clutch in, you then push the shifter into gear. Whether you blip the throttle WHILE clutched in is meaningless to a synchro. Blip it or don't blip it, you aren't affecting the speed of the input shaft in ANY way.
Hence why I'm keep saying, blipping the throttle for a rev match while clutched in has less than no affect on a synchro because it won't affect the input shaft speed in any way what so ever.
The synchro has engaged that gear WHILE you are clutched in. It's job is done now.
Blip away dude. Won't affect your synchros.

You can say it does all day long. But it simply doesn't because they are disconnected.
rtv900 is offline   Reply With Quote
Old 05-17-2019, 09:41 AM   #40
rtv900
Scooby Specialist
 
Member#: 428511
Join Date: Aug 2015
Location: philadelphia
Vehicle:
2016 STI

Default

Quote:
Originally Posted by jasonwrx86 View Post
And no, revmatching does not save syncros because you are still not manually matching the speed of the input and output shaft since the clutch is disengaged before you select the next gear. No amount of revving will change the input shaft speed before the syncro does.
Revmatching is to match the engine rpm to the input shaft of the transmission.
Double clutching is to match the input shaft to the output shaft of the transmission.
^these three sentences are 100% correct

Double clutching is for synchros

Rev matching is just to have a smooth downshift that doesn't force the clutch to pull the motor up to speed.
rtv900 is offline   Reply With Quote
Old 05-17-2019, 09:09 PM   #41
Norm Peterson
Scooby Newbie
 
Member#: 498642
Join Date: Mar 2019
Chapter/Region: Tri-State
Location: corner barstool (TV reference)
Vehicle:
2019 WRX Limited
Dark Grey

Default

Quote:
Originally Posted by rtv900 View Post
No clue where you are going with that last post dude.
It's like you think I'm debating the job of a synchro.
You're the one who keeps insisting that double-clutching isn't worth your time and effort. Or makes any difference to the synchros.

But I suspect you're relying on a bit of clutch drag if you're getting gear engagement as smoothly and with as little force on the shift lever as you're trying to convince me is the case. In which case, what may be intended as simple rev-matching is effectively starting to behave a little like double-clutching without having to do a second 'down-up' on the clutch pedal . . . helping the synchros out a little.

Looks like the road trip came sooner rather than later. So I did pay attention to shifting force requirements using a variety of techniques. No surprise that the true double clutch method was the easiest and smoothest, that single clutching foot-to-the-floor-and-hold required the most force, and that various in-between methods had in-between results.


Norm
Norm Peterson is offline   Reply With Quote
Old Yesterday, 08:13 AM   #42
Norm Peterson
Scooby Newbie
 
Member#: 498642
Join Date: Mar 2019
Chapter/Region: Tri-State
Location: corner barstool (TV reference)
Vehicle:
2019 WRX Limited
Dark Grey

Default

Basically, the driver gets to choose whether to work the synchros in his car's transmission hard by making them do all of the work spinning up the input side bits, work them a lot less hard by doing some rev-matching at the synchros themselves by double-clutching or relying on clutch drag, or not work them at all by not downshifting.

Rev-matching, while more normally gets associated with the clutch, still applies as a concept to any other pair of rotating objects that need to be brought to the same rpm. I guess not everybody is thinking in terms of "concept" here. Only the obvious.


Norm
Norm Peterson is offline   Reply With Quote
Old Yesterday, 03:46 PM   #43
jasonwrx86
Scooby Specialist
 
Member#: 472037
Join Date: Jul 2017
Chapter/Region: MWSOC
Vehicle:
2018 WRX Limited
CWP

Default

Quote:
Originally Posted by Norm Peterson View Post
Basically, the driver gets to choose whether to work the synchros in his car's transmission hard by making them do all of the work spinning up the input side bits, work them a lot less hard by doing some rev-matching at the synchros themselves by double-clutching or relying on clutch drag, or not work them at all by not downshifting.

Rev-matching, while more normally gets associated with the clutch, still applies as a concept to any other pair of rotating objects that need to be brought to the same rpm. I guess not everybody is thinking in terms of "concept" here. Only the obvious.


Norm
I still don't see what your point is in the last 3 or 4 replies.
We have explained to you that single clutch rev matching will not save synchos compare to no rev matching because when you clutch in and select gear, the the input shaft is going to be spinning at the same speed regardless if you rev the engine or not because at that moment the input shaft is disconnected from the engine. When you select gear depending up or downshift, the synchro will either speed up or slow down the now disconnect input shaft to match the output shaft of the transmission given the new gear ratio. Now if you rev match, the engagement of the clutch will be seamless because there will be no rpm difference between the engine flywheel and the input shaft of the transmission when you engage the clutch.
Double clutch rev matching is based on above motion adding additional process of actually spinning up the input shaft by engaging the clutch and revving the engine before gear is selected. This way, the input shaft and output shaft of the transmission between the synchros are rev matched before gear is selected to reduce the wear on the synchro.
You can do a simple test, try putting in 1st gear when going about 10mph. You transmission won't let you because the synchro simply can't rev the input shaft to match the rpm. You can try rev matching by holding down the clutch and blip the gas, it still won't let you select gear. Now try double clutching by putting shifter in neutral, let out clutch and rev engine, then push in clutch and select 1st, this time the shifter will slide in smoothly because you have matched the input shaft speed so the synchro can engage.
jasonwrx86 is online now   Reply With Quote
Old Today, 07:19 AM   #44
Norm Peterson
Scooby Newbie
 
Member#: 498642
Join Date: Mar 2019
Chapter/Region: Tri-State
Location: corner barstool (TV reference)
Vehicle:
2019 WRX Limited
Dark Grey

Default

rtv has been insistent that the clutch is the only driveline component that should have revs matched. I disagree for a reason.


Norm
Norm Peterson is offline   Reply With Quote
Old Today, 10:25 AM   #45
jasonwrx86
Scooby Specialist
 
Member#: 472037
Join Date: Jul 2017
Chapter/Region: MWSOC
Vehicle:
2018 WRX Limited
CWP

Default

Quote:
Originally Posted by Norm Peterson View Post
rtv has been insistent that the clutch is the only driveline component that should have revs matched. I disagree for a reason.


Norm
I don't think that's what he said. He simply said single clutch rev matching does not save synchros compare to no rev matching. And I agree with him.
jasonwrx86 is online now   Reply With Quote
Old Today, 01:10 PM   #46
oichan
Scooby Specialist
 
Member#: 492327
Join Date: Oct 2018
Location: A garage in the Midwest
Vehicle:
2019 WRX / 16 STI
2017 Golf-R, etc

Default

Yeah, synchros is a different mechanism and rev matching has some impact to do with it. There is less friction yes.

When perfectly rev matched, you can enter a gate without clutch-in but that's because the synchro's are still doing its thing.
oichan is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

All times are GMT -4. The time now is 05:44 PM.


Powered by vBulletin® Version 3.7.0
Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
Powered by Searchlight © 2019 Axivo Inc.
Copyright ©1999 - 2017, North American Subaru Impreza Owners Club, Inc.