I think he just didn't say what he wanted to. We'll see.

Jeez, what are we all doing this late at night? We really need to go to sleep.

 

Well, we're just about to go out to dinner. However, I am on the other side of the world from you guys.

 

BlackhawkRA's post was very good , but for the ADD I'll try to add to it and shorthand it.

When you upshift normally, the engine will drop speed. when you let the clutch out, you can naturally time it to engage at just the right time to give you a perfectly smooth shift. (say from 3rd to 4th, when the engine needs to drop 500rpm for a given speed).

Rev matching allows you to just the opposite, when you downshift. The engine needs to speed up instead of slow down. To do this, blip the throttle to speed up the engine when the clutch is disengaged. Shift to the lower gear. When you let the clutch out for the lower gear, the engine will be spinning at a higher rpm, (whatever is dictated by the lower gear) and you don't get the jerky lurch. This is the same "single-clutch downshift" BlackhawkRA was talking about.

Heel/toe is used to brake at the same time the above is being done. Your right foot presses on the brake pedal, and the side (or heel) of your foot swings over and blips the throttle to rev match. This is extremely useful on a track for getting into the right gear while you're braking into a corner. So, when you exit the corner, you're good to go, no more playing with the shifter.

Double clutching is much more technical, and it's only to prevent wear on the transmission during downshifts by engaging the clutch in neutral while the engine is rev matched. It is used with heel/toe braking and rev matching to allow the engine to speed up the first half of the tranny instead of it's internal synchros. High rev shifting (especially downshifting) causes excessive synchro wear.

Many racing transmissions or "dog boxes" won't have synchros, because they add weight, and its one more thing to go wrong. Those guys need to double clutch and rev match everything, which is good because it prevents disrupting the car's balance.

 

Thanks, I was actually about to do that, but after writing like a half page refuting all the crap I saw on this thread, I realized I was most likely confusing those three terms. After reading your explanation as well as Wheelhous's summary, I have come to the conclusion that rev matching is a part of the heel-toe and double-clutching techniques, and is virtually useless by itself (why would you need to rev match if you aren't changing speed?), and heel-toe is the standard method of matching revs while braking, this the need to simulate having three feet. Finally, I'm not sure exactly how to double-clutch or when it would be needed over heel-toe, but I'll start reading the details soon.

I must correct you in one thing, though. In most autocross situations, you only shift once (1-2) then you never shift again. But in the few cases where you actually get up to 3rd (or if you're racing an AM car), I can see where that would come in handy)


How did you know?

 

Absolutely correct.

I do this all the time. Most typically its when I'm cruising, and need more power to pass someone or conquer a steep hill. If the gear is too tall, you have to donwshift. I almst always rev match my downshifts, but they're not all for the purpose of slowing down. I'll rev match if I'm slowing very casually for a slow turn. I'll brake lightly, rev match at low rpm, continue braking slowly, enter the turn and accelerate. You don't need to heel/toe in order to rev match unless you need to brake and downshift at the same time.

Once you fully grasp the technical ins and outs of just how a transmission works and just what's going on, only then double clutching will fully make sense.

 

yeah waist of time i think

 

Thanks Wheelhaus, that made complete sense. Even using rev matching without braking. I never stopped to realize that I do that frequently, going up hills, pasing lanes, etc. I spent most of today trying to heel toe while driving back from the beach. Thanks!

 

13 seconds is a good time for a stock evo 8 here in AZ.


I've never even done it a track. I was presenting an alternative from racing from a roll while still in lag. That's all. I'm not saying "clinical studies have shown.....blah blah blah....."

 

Glad to hear that you understand the practical uses... as you've found out, rev matching can be used when you're cruising (not accelerating) and you wanna down shift to pass, or when you're coasting in N and you wanna kick it into gear quickly and smoothly, such as when the light turns green before you've stopped completely. Heel-toe will take a little practice, but it seems like you'll get it down real quickly. Good luck bro.

 

lol double clutching

1) you dont need to do it, thats what synchros are for

2) dont do it

 

Why would you resurrect a good thread just to post crap like this? Read the thread and grow up.

It IS needed in some transmissions, not all are equipped with synchros. And in a synchro'd tranny, it still helps to reduce wear. which is ESPECIALLY a good idea considering the Evo tranny is prone to synchro and shifting problems. Besides, learning to do it can help to make you a better driver because you become more connected to the car.

 

lol is right. Have you ever rebuilt a gearbox? It's a bit of work (and expense) to go through just to replace synchros that could have been saved by matching. Two points extrapolated from my post here months ago:

1) If you rev-match downshift with the clutch disengaged (not a double clutch), you still don't match the input shaft and output shaft speeds. Remember the clutch plate is on the input shaft and needs to be accelerated by the engine itself.

2) Double clutching is not just for the track. It preserves synchros under proper street driving dramatically compared to not doing it. Even for hard steel, triple-cone pieces. This point amplifies when you have relatively weak synchros like our Evo units...

 

What I don't understand is, if you have a fully functioning clutch master & slave cylinder, why would two clutch pumps be any different than one clutch pump? The amount of fluid being displaced per pump should be the same. So if you adjust your clutch pedal right, would you still need to double clutch?

 

It has nothing to do with the fluid or pumping. The reason is in point 1 from my post above. To state it another way:

When downshifting, the input shaft speed needs to match the output shaft speed (connected to the wheels). With the clutch disengaged, the clutch plate/input shaft assembly spins free. The only way to speed it up to match the output is to engage the clutch and blip the throttle.

Absolutely required in some gearboxes, the best way to do it in most gearboxes.

 

^ you must not have read the thread, or you're trying to get flamed...

Let me try the cliffnote version instead of replying with "read the thread".

the transmission had two different halves that are always connected to each other (all the gears are always engaged). the gears are always meshed, but the gears on the output shaft are free spinning on the shaft. when you "select a gear" you're engaging THAT gear to the shaft. The rest remain free-spinning. The two halves are 1: the input shaft that has the clutch, and 2: the output shaft that's always connected to the drivetrain.

The engine needs to rev up for a downshift. so you can blip the throttle for this to match speed to the drivetrain. You can only do this when the clutch is disengaged.

When you disengage the clutch and select the lower gear, the synchros are forcing the next gear to spin the input shaft faster (clutch). (Ever wonder why the clutch speeds up? Thats why.) This way, when you engage the clutch it feels smooth with a rev match. The lower gear needs a higher rpm on both sides for a smooth lurch-free getaway.

the problem:
using the synchros to speed up the input shaft causes excessive wear, especially on downshifting where things are being forced to speed up. It's one thing to match speeds as they're slowing down (upshifting for the next gear) as it's MUCH easier.

When you rev match, you can use the engine to speed up the input shaft instead of forcing the synchros to do this for you.

1: Clutch off and rev match (this sets the speed of engagement)
2: Clutch on in neutral (this is when the input shaft is matches to the higher engine rev)
3: Clutch off and in gear (it slips in easily because the synchros have no work to do)
4: Clutch on gas it and go in your lower gear.