Heel toe vs heel toe double de clutch

[Spranga]

l

Its not that hard even on my old box but fiddling with the clutch made it better (although its gone worse again for some reason).

Maybe your syncros are rooted and you need to ddc

[marcusus]

Right, let the fun begin

lol marcus, you're wasting time with the double clutch. Just practice doing normal heel toe before the next track day, its twice as quick.

I'd say double declutching would be a better use of time on the street because you have all the time in the world. And since a double de clutch encompasses a simple heel toe, learning to the the harder one better will result in doing the easy one better.

In terms of my speed, I notice that when I do my double de clutch, it is a a bit slower, but only because I'm taking my time with it more. If I really want to slap it in, I haven't found a difference in time. If anything I'm quicker because I'm used to that method. This can be put down to practice though.

You are effectively shifting twice. I don't know about you but I don't have time to do that when I'm braking, or another brain to think about it.

You might be shifting twice, but if it becomes second nature, there's no need to think about it at all. As for time to do it when braking, you've got the same amount of time on the brakes anyway, so what difference will it make? Especially if I'm doing it at the same speed as a heel toe?

If you have enough time to do that then maybe you aren't braking late enough for the corner. Also try staying in 3rd on the back straight rather than 4th, I find I can concentrate on braking hard and corner entry only shifting once rather than twice, also don't waste time shifting up for no reason unless you are on the limiter well before the braking point. Although to think about it, I hit my 7400 limiter so your car should get there a little quicker and you might have to shift, dunno about the diff ratio, also depends on fishhook exit speed since its flat from that exit.

I stayed in 3rd the entire time on the back straight, even though Kevin from the club suggested I be in 4th for that section. I thought it wasn't worth me changing up to wipe speed off that I wouldn't be able to gain back due to lack of road before the last turn.

As for braking late enough, I very much doubt that I'm near where the correct braking spot is, but of course that was my first time at Wakefield so I have much to learn about the track and the limits of my car. That being said, I found going from 3rd to second a breeze because of the double de clutch.

About the extra effort, get a better shift knob or fix your clutch so that its smoother. Its not that hard even on my old box but fiddling with the clutch made it better (although its gone worse again for some reason). Shifting normally without rev matching makes it much much harder to get into gear, rev matching makes it easier, haven't tried double clutching.

Ah hah! You haven't even given the double clutching thing a go! Give it a shot and see how smooth it is to change gears compared to just standard shifting and your heel toe without double de clutch. During my experimentation I found if I was fairly high on the revs in 3rd and did the heel toe without the de clutch, it needed a bit more coercing to get it into gear, whereas with the double de clutch it just slides in. And as mentioned, that means more time with my hands on the steering wheel which can only be a good thing.

If you find its just too hard to get into gear and you are braking on the very limit and you have plenty of time to double clutch then sure use it but at your stage I recommend normal heel toe.

The effort over isn't so much that I can't do it. It's just more that if there's an easier (and possibly better) way, why not use that? I don't see how using the full double de clutch can be anything but beneficial. Not saying that normal heel toe isn't, but the full thing would be more beneficial than a cut back version yes?


That was fun

[Sasso]

Spranga lol, I don't think its my synchros because it does it in every gear indicating a clutch disengagement problem.

OK here we go...

On the street do what you like to entertain yourself but there's no point, that is why they invented synchros.
Learning the harder one will result in doing the harder one better, practicing the easier one will make it much quicker and easier than the hard one.

How can there not possibly be a difference in time between the two? You have to do the same thing twice! So at BEST it takes twice as long.

Yes you should be on the brakes as long as me or shorter but I'm saying based on your last track day you weren't, to do low 80's you must have been braking like a grandma, and thats fine and expected for your first time, but what I'm saying is you might have time to do it now, but when you start getting better under brakes you will probably half your braking distance and time and you won't have time to double clutch.

I did a bit of playing with a simulator program my dad has that estimates every detail of a lap around a track, in this case wakefield, everything is adjustable so I put most of the mx5's details including gear ratios. It was pretty damn close to my car and times. I looked at braking points and speeds and they seemed very accurate too.

Lets say you are going down the back straight at wakefield, just shifted into 4th because you're not crazy like me and don't rev 'till the valves pop out and dance on the bonnet (or have a 1.8 ), you brake after the last marker going from 135 down to 70 in a matter of 3 seconds, in that time you down shift twice to 2nd, get your line right, turn in then feed in the throttle, apex late just where the ripple strip ends (the big dip where you can get air like kula's car) and unwind as wide as you can to the edge of the track onto the straight.

Now how can you tell me that you can do effectively 4 shifts in 3 seconds? And realistically its less than 3 seconds because you can't be shifting the whole time you're braking, you need time before and after shifting firstly to let the car speed down so you don't blow you're engine when you rev to 8k by downshifting too soon, and you can't be shifting too late because you would have started to turn and get the car settled to turn hard, and if you let the clutch out then there is much more risk of losing it.

So if you are braking as hard and as late as possible then you don't physically have time to double clutch. Just imagine you're flying down the straight at eastern creek, you take the first turn flat in 5th and arrive at the slow turn 2 in 5th at 180km/h. You brake hard after the last marker and shift down into second gear and start turning in while keeping full brakes all within a matter of seconds. There is no way in hell you're going to push the clutch in and out 6 times! without stuffing up, then have to do it for the hairpin from 4th to second and last turn 4th to 3rd and keep it up for 20 minutes.

Seriously its a waste of time I'm telling you. My dad (race engineer and gearbox designer) said the whole point is to whack it in gear as quickly as possible, and some people do it so quick they don't even use the clutch, they just blip and slam it in, breaks the hell out of the synchros but they go home after and rebuild it so doesn't matter. We use the clutch and let they synchros do their work.

I haven't tried dc because like I said before, I don't drive a truck. And I don't have a problem with the force required to get it into gear. I don't want to waste my time learning an outdated technique that won't help me go faster. The only time I think it would be useful is in VERY slow corners or rally where you need to shift into first. (Does first have a synchro?) But I hardly do that and its still possible to do with normal heel toe (To the detriment of my parent's sleep when I come home late).

Crap hit max character count....

[Sasso]

...

Better in terms of it might make your synchros last a little bit longer but not by much since normal rev matching saves them too. If you wanted to save your gearbox you wouldn't be racing.
But better in terms of racing technique then no, its worse because its not necessary, it wastes time and give you extra work so tires you out, and it makes you do more multitasking as you should be concentrating on the corner, more to do is worse, just imagine also having to look out for other cars overtaking or lining up the car in front to overtake.
Its not the cut back version its the replacement.


So I hope that gave you a bit to think about and hope you get practicing and realise that downshifting time is limited only by how quickly you can smash the lever across the gates.

You're right, that was fun...



And for those interested, according to the simulation software if you put a 6speed paddle shift gearbox in your car that reduces your shift speed from 500ms to 50ms then your car accelerates a fair bit quicker. So much time is lost shifting its amazing. The gear ratios and shift speed took 2 seconds off the wakefield laptime, that's quite impressive.

[Spranga]

I don't think its my synchros because it does it in every gear indicating a clutch disengagement problem.

Agreed, thanks for the extra information. Fifth gear is stuffed right?

On the street do what you like to entertain yourself but there's no point, that is why they invented synchros.

Yes to make it easier for grandma to drive to the shops.

Learning the harder one will result in doing the harder one better, practicing the easier one will make it much quicker and easier than the hard one.

Is this a rule for everything in the world or did you just make it up for this post?

How can there not possibly be a difference in time between the two? You have to do the same thing twice! So at BEST it takes twice as long.

On the track braking generally takes longer than the difference in time it takes to ddc compared to not ddc as we are talking about 10ths of a second difference. When was the last time you had to brake for shorter than half a second and change down a gear? Therefore although the process of ddc requires more time than not doing it there is no actual lap time lost as you are hard on the brakes throughout the gear change with both methods

Yes you should be on the brakes as long as me or shorter but I'm saying based on your last track day you weren't, to do low 80's you must have been braking like a grandma, and thats fine and expected for your first time, but what I'm saying is you might have time to do it now, but when you start getting better under brakes you will probably half your braking distance and time and you won't have time to double clutch.

Directed at Marcus I assume??? Many more variables to consider here mate. ... this is a huge assumption to make without sophisticated telemetry.

I did a bit of playing with a simulator program my dad has that estimates every detail of a lap around a track, in this case wakefield, everything is adjustable so I put most of the mx5's details including gear ratios. It was pretty damn close to my car and times. I looked at braking points and speeds and they seemed very accurate too.

Does it have an input for ddc or not ddc??? Didn't think so.

you brake after the last marker going from 135 down to 70 in a matter of 3 seconds, in that time you down shift twice to 2nd,

You are wasting time shifting down twice. Ddc and shift to the gear you need to exit the corner. Wasted effort otherwise.

Now how can you tell me that you can do effectively 4 shifts in 3 seconds?

See above. There is no need to do this. Go straight to the gear you need.

you need time before and after shifting firstly to let the car speed down so you don't blow you're engine when you rev to 8k by downshifting too soon, and you can't be shifting too late because you would have started to turn and get the car settled to turn hard, and if you let the clutch out then there is much more risk of losing it.

I can manage this without over revving every time and my ddc avoids any driveline shunt that will knock the rear end out (although this is unlikely in most circumstances).

[Spranga]

So if you are braking as hard and as late as possible then you don't physically have time to double clutch. Just imagine you're flying down the straight at eastern creek, you take the first turn flat in 5th and arrive at the slow turn 2 in 5th at 180km/h. You brake hard after the last marker and shift down into second gear and start turning in while keeping full brakes all within a matter of seconds. There is no way in hell you're going to push the clutch in and out 6 times! without stuffing up, then have to do it for the hairpin from 4th to second and last turn 4th to 3rd and keep it up for 20 minutes.

As above. Change from the gear you are in to the gear you want on exit. Who said you have to do this with ddc and not without? I think you made this up lol? Nothing to do with ddc?

Seriously its a waste of time I'm telling you. My dad (race engineer and gearbox designer) said the whole point is to whack it in gear as quickly as possible, and some people do it so quick they don't even use the clutch, they just blip and slam it in, breaks the hell out of the synchros but they go home after and rebuild it so doesn't matter.

No ddc on the upshift, just downshift because the speed differential between engine and gearbox is not very different during acceleration. Ddc while upshifting would take longer as the amount of time sending drive to the wheels is reduced. Ddc while braking does not effect the lap time because you are braking and not accelerating. Do you get it yet? No time lost.

...
Better in terms of it might make your synchros last a little bit longer but not by much since normal rev matching saves them too.

How does the gearbox speed match the engine speed if you have not revved it in neutral? Syncros are still working and therefore wearing.

If you wanted to save your gearbox you wouldn't be racing.

I like racing and my gearbox.

give you extra work so tires you out, and it makes you do more multitasking as you should be concentrating on the corner, more to do is worse, just imagine also having to look out for other cars overtaking or lining up the car in front to overtake.

I can imagine this actually as I have competed in several race events at EC involving stints of about 60 minutes each. It is second nature. I can ddc while trying to get through turn 2 at EC with 10 other crazy blokes. And no I have never had sore legs after an event.

So I hope that gave you a bit to think about and hope you get practicing and realise that downshifting time is limited only by how quickly you can smash the lever across the gates.

Are we talking about downshift time? Yes it is faster to downshift without ddc but under braking it makes no difference. Are we getting through?

[marcusus]

you brake after the last marker going from 135 down to 70 in a matter of 3 seconds, in that time you down shift twice to 2nd,

You are wasting time shifting down twice. Ddc and shift to the gear you need to exit the corner. Wasted effort otherwise.

[/quote]
Spranga. Basically everything I was going to say as well. However, of special note was this point.

Gerard, if you're in 4th on the back straight at Wakefield, do you go to 3rd then second? If you double declutch, you can go from 4th to 2nd no dramas so long as you don't hit the rev limiter when you want to be in second. How much time do you save not having to do that extra shift? How much time can you gain because you're at a higher speed in a higher gear before you need to start the downshift process?

Who else has an opinion on this? This is getting interesting

[Sasso]

Geez, out in full force, where's my backup?!?

Yah fifth gear synch is broken because for some reason I have a vibration at redline that makes it hard to get into gear, so when I went to shift to 3rd I'd hit 5th, do that about 6 times over two trackdays and bye bye 5th gear synchro, its such a pain to drive on the street now because if you don't time the upshift it crunches as it goes in.

Yes to make it easier for grandma to drive to the shops.

Yes and to make shifting quicker and easier so you can concentrate on other things.

Is this a rule for everything in the world or did you just make it up for this post?

Just some logic, not for everything, usually the hard way is better but not necessarily in this case.

On the track braking generally takes longer than the difference in time it takes to ddc compared to not ddc as we are talking about 10ths of a second difference. When was the last time you had to brake for shorter than half a second and change down a gear? Therefore although the process of ddc requires more time than not doing it there is no actual lap time lost as you are hard on the brakes throughout the gear change with both methods

Actually its not 10ths of a second it would take about 500ms to complete and for ddc a whole second.

Directed at Marcus I assume??? Many more variables to consider here mate. ... this is a huge assumption to make without sophisticated telemetry.

Well you just need a bit of thinking, if he is about 7 seconds slower than say my time, his car is just as quick on the straight, so he'd losing his time in the corners, and more specifically corner speed (due to bad line or just has't found the limit yet), corner speed is related to corner entry speed which is purely related to braking, the more speed you need to lose the longer you need to brake. Not to mention that he would be braking too early and not just to much. I think its quite safe to assume that even without telemetry.
Now that extra time he is braking is allowing him to complete his ddc in time for the corner, but when he gets better he will be braking much later and shorter so he will be stripped of time.

Does it have an input for ddc or not ddc??? Didn't think so.

It assumes you can downshift. You are right in saying that if you can downshift intime for the corner it doesn't matter what way you do it but there's more to it than that. The software doesn't simulate concentration levels it just simulates the best possible laptime the car can do, and assuming the driver is perfect.

You can just shift once into the gear you need but doing all this downshifting and gate jumping is just interfering with you braking, you need to concentrate as much as you can on braking as hard as you can and modulating the pedal, and corner entry line and everything else, downshifting is the last thing you want to be spending time doing.
Braking and cornering takes more concentration than you have available so fancy shifting is just taking that away (even if its second nature its still robbing your of processing time). Just imagine how much better you could brake and turn if you didnt have to worry about downshifting.
And that is why I leave my car in 3rd going down the back straight, it means I can concentrate on braking most of the time and shift once to 2nd which is a quick little blip and whack into gear.

Also, spoke to my dad, he said ddc over rev match it wont necessarily make any difference to the wear of the synchros. They are still working no matter what because they are there and constantly lining up the gear, even when you're ddcing. No racing driver would ddc except for the ones in the 60's when they had no synchros so whats the point of going out and doing it if there is no advantage and most likely a disadvantage (reduction is baking and cornering performance), or are you just trying to prove a point?

[Sasso]

prove a point?


Also spranga, I was watching your eastern creek video on youtube and, I'm a bit confused because it doesn't even sound like you were rev matching at all, you would hit the throttle and engine would rev, then revs would drop, then you let the clutch out and revs would rise again. To me that defeats the purpose because the engine is putting pressure on the rear wheels, and since your car didn't lose control and lock the rears I think I can safely say you weren't braking on the limit. Were you ddcing because it looked like it was taking too long and the revs would drop by the time you get it into gear and release the clutch (for the second time).


Marcus, like I said above, I stay in 3rd on the back straight for 2 reasons, the first one is so I don't have to downshift twice, downshifting interferes with braking and I find I can pull up quicker and brake later when I use all effort on modulating brakes then quickly shifting to 2nd before I turn in. Secondly because you waste half a second shifting to 4th for about one second then have to start braking, so all that time is lost and I don't believe you are going faster, staying in 3rd gives you half a second more time on the throttle and keeps you in a gear with better acceleration so you should reach a higher speed.

Jumping gates is fine, and it can be done without ddc too, but at your level I don't recommend it, it just adds to the learning, it works in the same way as learning to drive on the streets starting in a manual or in auto. In the auto can you learn to drive easier but in manual you have to learn both things at the same time. And I'll say that even though you think its second nature and doesn't affect your braking, it most probably does and there is much you can gain out of braking.

I'm not going to stop you from ddcing but since you did ask, I am going to tell you again that there is no point and you're just hindering your learning to drive on the track by doing it. That's what I believe but its up to you if you want to hear or not. I'm not trying to be boastful, even I have a long way to go, I just know ddc isn't the way, but I am a fair bit more experienced and quicker on the track, I have been in your position and I can say that its the last think you want to be doing is complicating the downshifts, if you came and smashed my lap time using ddc then I would't think its affecting your driving, but until then my suggestion stands.

Heaps of ppl have opinion on this and they posted before saying ddc was pointless. However I too would like to hear what other ppl have to say in more detail perhaps.

[JBT]

I think you've covered it all Sasso . Yes, double declutching is a waste of time.

[Spranga]

Also spranga, I was watching your eastern creek video on youtube and, I'm a bit confused because it doesn't even sound like you were rev matching at all, you would hit the throttle and engine would rev, then revs would drop, then you let the clutch out and revs would rise again.

My car has a stock exhaust so you can only hear the engine in the video when it is under load. So I have no idea how you can tell what the revs are doing or when the clutch is going in or out as you cannot see my legs or most of the tacho.... more assumptions perhaps????

To me that defeats the purpose because the engine is putting pressure on the rear wheels, and since your car didn't lose control and lock the rears I think I can safely say you weren't braking on the limit. Were you ddcing because it looked like it was taking too long and the revs would drop by the time you get it into gear and release the clutch (for the second time).

More wild assumptions....

[Spranga]

but at your level I don't recommend it, it just adds to the learning,

Mate I find this an astonishing comment. There are some fantastic drivers on this forum but I am sure none of them would consider rating other forumites driving with such superficial analysis. I don't claim to be the best driver on the forum and I would certainly not cast judgment on the skills of others without a very sound reasons.

even I have a long way to go,

Not a good look no matter how good you are...

[marcusus]

On the track braking generally takes longer than the difference in time it takes to ddc compared to not ddc as we are talking about 10ths of a second difference. When was the last time you had to brake for shorter than half a second and change down a gear? Therefore although the process of ddc requires more time than not doing it there is no actual lap time lost as you are hard on the brakes throughout the gear change with both methods

Actually its not 10ths of a second it would take about 500ms to complete and for ddc a whole second.

But that's not the point. Re read it. The point is that you're on the brakes for 3 seconds. If you're spending 1 second changing gear (irrespective of ddc or non ddc) it means you're braking for more time than changing gear. What you're trying to do is slow the car down via braking, not via engine braking. The gear is only for your exit speed. So if the braking is taking a longer time than a gear change, what difference does it make if you do a smoother change by doing a ddc or a non ddc? You're still braking by the same amount because you're still heel toeing.

Now that extra time he is braking is allowing him to complete his ddc in time for the corner, but when he gets better he will be braking much later and shorter so he will be stripped of time.

Not necessarily. And who's to say my double clutch isn't fast enough anyway? As long as it's within the time I'm on the brakes I have no problem. Of course the rest of the points in that previous paragraph of yours are irrelevant to this discussion because that's related to my track experience specifically, and can't be reduced down purely to me using ddc or non ddc.

You can just shift once into the gear you need but doing all this downshifting and gate jumping is just interfering with you braking, you need to concentrate as much as you can on braking as hard as you can and modulating the pedal, and corner entry line and everything else, downshifting is the last thing you want to be spending time doing.

You just contradicted yourself
Less time spent downshifting = shifting from 4th to 2nd.
More time spent downshifting = shifting from 4th to 3rd then 3rd to 2nd.
If you ddc, you only need to do this stuff once, rather than twice, thus allowing you more time to concentrate on braking and everything else, as you put it. If you don't ddc, you'll have more to do on the gears which will result in less time for everything else.

Braking and cornering takes more concentration than you have available

I don't know about that... we don't understand the brain well enough at this point in time to make assumptions like that. I personally don't think track driving is so intensive that we're out of thinking capacity. Yes all my attention is on the track, but I don't think adding in an extra (subconscious) foot movement is going to add a significant amount of brain concentration.

Just imagine how much better you could brake and turn if you didnt have to worry about downshifting.

The same is true for both ddc and non ddc, so it makes no difference to this debate. In the end, we all still need to perform a gear down operation, so this part is common for both methods and can't be factored into the debate.

And that is why I leave my car in 3rd going down the back straight, it means I can concentrate on braking most of the time and shift once to 2nd which is a quick little blip and whack into gear.

I would use 4th if I was going fast enough to make gains on the speed wipe in an upshift, but because I'm still new to Wakfield and the track, I decided against it. So again this is too subjectively based around the track itself rather than on the theory of ddc vs non ddc.

Also, spoke to my dad, he said ddc over rev match it wont necessarily make any difference to the wear of the synchros. They are still working no matter what because they are there and constantly lining up the gear, even when you're ddcing. No racing driver would ddc except for the ones in the 60's when they had no synchros so whats the point of going out and doing it if there is no advantage and most likely a disadvantage (reduction is baking and cornering performance), or are you just trying to prove a point

That's a bit better
Fair call there. Of course you'd better explain what your dad does to put it in context ;)

[marcusus]

Marcus, like I said above, I stay in 3rd on the back straight for 2 reasons, the first one is so I don't have to downshift twice, downshifting interferes with braking and I find I can pull up quicker and brake later when I use all effort on modulating brakes then quickly shifting to 2nd before I turn in. Secondly because you waste half a second shifting to 4th for about one second then have to start braking, so all that time is lost and I don't believe you are going faster, staying in 3rd gives you half a second more time on the throttle and keeps you in a gear with better acceleration so you should reach a higher speed.

You're repeating yourself. See above.

Jumping gates is fine, and it can be done without ddc too, but at your level I don't recommend it, it just adds to the learning, it works in the same way as learning to drive on the streets starting in a manual or in auto. In the auto can you learn to drive easier but in manual you have to learn both things at the same time. And I'll say that even though you think its second nature and doesn't affect your braking, it most probably does and there is much you can gain out of braking.

I have no problems in improving all of my technique incrementally. I'd rather do that than learn one thing completely, then start learning another technique from scratch. Best to learn it all together so it all moves together at about the same level. That way your skill in one area won't outstrip your skill in another. Consider what would happen if you learnt heel toe long long long after you'd been on the track. You would be so used to your method of turning in and everything that when you learnt heel toe, you would lose time on the track. If you do it all at once, everything moves forward by the same amount (in theory). Thus, my track times theoretically shouldn't go down. Unless of course there's another tricky technique that I haven't learnt about yet

I'm not going to stop you from ddcing but since you did ask, I am going to tell you again that there is no point and you're just hindering your learning to drive on the track by doing it. That's what I believe but its up to you if you want to hear or not. I'm not trying to be boastful, even I have a long way to go, I just know ddc isn't the way, but I am a fair bit more experienced and quicker on the track, I have been in your position and I can say that its the last think you want to be doing is complicating the downshifts, if you came and smashed my lap time using ddc then I would't think its affecting your driving, but until then my suggestion stands.

This is a good debate. I dont' think you're boasting or doing anything silly like that at all. It's simply a group of drivers that enjoy the track having a good debate about the merits of ddc vs non ddc.

However I'm gonna stick with the ddc. After all, now that you've issued a challenge, I have to practice with ddc and prove you wrong ;)

Mind you, I doubt there will be a huge time difference due to one or the other. I daresay the important bits of track driving are the simplest ie good lines good braking. Everything else is just us showing off

[Sasso]

Also spranga, I was watching your eastern creek video on youtube and, I'm a bit confused because it doesn't even sound like you were rev matching at all, you would hit the throttle and engine would rev, then revs would drop, then you let the clutch out and revs would rise again.

My car has a stock exhaust so you can only hear the engine in the video when it is under load. So I have no idea how you can tell what the revs are doing or when the clutch is going in or out as you cannot see my legs or most of the tacho.... more assumptions perhaps????

To me that defeats the purpose because the engine is putting pressure on the rear wheels, and since your car didn't lose control and lock the rears I think I can safely say you weren't braking on the limit. Were you ddcing because it looked like it was taking too long and the revs would drop by the time you get it into gear and release the clutch (for the second time).

More wild assumptions....

Please don't take offence I wasnt trying to have a go at you, your driving was pretty good I thought, its just something I noticed the first time I watched the video.
Its just a bit of diagnosing, to help improvement.
They're not wild assumptions they are educated inferences based on the data and my experience.
Turn up your speakers you can always hear the engine humming, the intake induction it sounds like, unless thats some other random noise that sounds exactly like an engine.
Watch the first 30 seconds, braking for first second corner, you blipped, heard that, then goes dull and at 25-26 seconds you hear the hum increase in pitch/volume and then drop slightly then hear you hit the throttle at a pitch that matches where the hum left off. That hum sounds exactly like you letting out the clutch and raising the engine revs using the wheels. I only watched 2 laps and you seemed to do it every time, but I'm not sure if you changed your technique later in the vid (my internet sux).
That is a safe assumption given that the sound im hearing is the engine and it sure as does sound like it, I have no idea what else it could be.

As for not locking the rears, its very common and it the reason you need to rev match in the first place. If your brakes a setup correctly and you are braking on the very limit, if you give any input to the rear wheels you will sent straight off.

Here is a situation where you have to heel toe and will struggle to ddc or just let the clutch out:
I found that going down the back straight at eastern creek arriving at the second last corner (kink to the right and then turn hard left), I'd be in 4th and have to downshift to 3rd because I'd hit the 3rd limiter before the corner, you take the right hander flat then just before you turn left you stab the brakes hard and short and turn, but you have to downshift in that time of literally a second on the brakes, while turning slightly at high speeds, if I don't rev match and slowly let out the clutch the rear dont lock but slip and lose traction, gets all sideways and I lost it going into the fast left and flew off the track. Then I started to revmatch there and it made the braking SO much more stable. I don't think you could ddc in that short amount of braking time, and you can't just stay in 3rd.

Matching the revs is very important, did you see that skyline at ec twilight night completely wrecked because he downshifted at the end of the straight, lost the rear, hit the inside wall and ploughed into the tyre barriers at the end of the straight going extremely fast.