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Rev matching, down shifting and heal toe, MANUAL TRANS ONLY

TURTL3

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When you guys rev-match downshift do you guys let off the clutch pretty fast? This is my first manual car and after countless harsh over and under revving tries I found that letting off the clutch a little slower helps make the downshift smoother but not sure if doing it that way is defeating the purpose of rev matching?
It's making your downshifts smoother, hardly defeating the purpose! :thumbsup:

The clutch isn't a on/off affair. You're matching the speeds of the transmission and the engine. Unless you rev match at the exact perfect RPM every single time (impossible for a human), you'll need to modulate how fast you let off the clutch based on the situation. If you slowed down your clutch action and you're getting better rev matching results, you're on the right track my friend.
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TURTL3

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Curious to know...what's the point in blipping (which I understand as pulsing the throttle to a know RPM, then let go), if one can just rev-match (hold the known RPM) when down shifting?

Maybe I'm getting the terminology wrong here...but I always hold the RPM before smoothly letting go of the clutch, what would be the advantage in just pulsing it before letting go of the clutch?
But how do you downshift smoothly by holding a RPM? If you're downshifting, your revs should jump up, which means if you're holding a steady RPM, you're going to get driveline shock. Are you saying you're basically slipping out the clutch?

So, the way I'm understanding your post, say you're in 5th going 2K rpm. You want to downshift to 4th and let's say doing that will make the revs jump .5K rpm to 2.5K rpm. You clutch in, and hold the gas at 2K rpm and then bring the clutch out as you're holding the throttle at 2k?
 

TexasRebel

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Curious to know...what's the point in blipping (which I understand as pulsing the throttle to a know RPM, then let go), if one can just rev-match (hold the known RPM) when down shifting?

Maybe I'm getting the terminology wrong here...but I always hold the RPM before smoothly letting go of the clutch, what would be the advantage in just pulsing it before letting go of the clutch?
"Blipping" the throttle is a very quick attempt at rev-matching on a downshift. If you were to downshift and engage the clutch without touching the throttle the engine would begin to drop to idle and the clutch will do the work to bring the engine up to speed instead of expanding gasses in the cylinders. This is just extra, unnecessary, wear on the clutch.

Keep in mind, some of these techniques were developed with, by, and for, racing clutches which are much different than the OE clutch in a Mustang. Some racing clutches do begin to become more of a "toggle switch" affair which allows for quicker shifting while moving, but makes starting a pain (which is an acceptable trade off on a road course as you don't intend on starting from a stop very often).
 

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There are many situations to rev match. Sometimes people just downshift to utilize engine brake. That's when you just blip it so you don't accelerate when you release the clutch. Sometimes people want to drop a gear and go, that's when you press on the gas pedal raise the rpm to the matching rpm then release the clutch and accelerate. You don't let go the gas pedal in that situation. There are times when you REALLY want to accelerate from a high gear to low gear, you simply WOT the pedal before relaseing the clutch for a perfect engagement For example from 5th gear to 2nd.
There are many uses for the gas pedal.
 

Rebellion

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But how do you downshift smoothly by holding a RPM? If you're downshifting, your revs should jump up, which means if you're holding a steady RPM, you're going to get driveline shock. Are you saying you're basically slipping out the clutch?

So, the way I'm understanding your post, say you're in 5th going 2K rpm. You want to downshift to 4th and let's say doing that will make the revs jump .5K rpm to 2.5K rpm. You clutch in, and hold the gas at 2K rpm and then bring the clutch out as you're holding the throttle at 2k?
Basically yes...let's say, I needed 5k RPM to do the same speed at a lower gear, just rev up to 5k and let go of the clutch. Of course, you put the throttle after you get out of gear.

What I understand is that when you blip, you let go of the throttle and then let go of the clutch...why do I have to let go of the throttle, just hold it in the desired RPM.
 

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Rebellion

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There are many situations to rev match. Sometimes people just downshift to utilize engine brake. That's when you just blip it so you don't accelerate when you release the clutch. Sometimes people want to drop a gear and go, that's when you press on the gas pedal raise the rpm to the matching rpm then release the clutch and accelerate. You don't let go the gas pedal in that situation. There are times when you REALLY want to accelerate from a high gear to low gear, you simply WOT the pedal before relaseing the clutch for a perfect engagement For example from 5th gear to 2nd.
There are many uses for the gas pedal.
Yes, exactly...it would be your 2nd and 3rd scenario, no need to actually pulse the throttle, just rev up to the desired RPM. On the first scenario, I let go of the throttle after rev matching, of course, stupid coyote does have a engine brake delay, takes like a second before it actually down revs.
 

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It's making your downshifts smoother, hardly defeating the purpose! :thumbsup:

The clutch isn't a on/off affair. You're matching the speeds of the transmission and the engine. Unless you rev match at the exact perfect RPM every single time (impossible for a human), you'll need to modulate how fast you let off the clutch based on the situation. If you slowed down your clutch action and you're getting better rev matching results, you're on the right track my friend.
Thanks for all the good info. When you let off just pretty slowly, is it still "riding the clutch" and harmful? Or is it not really that much of an issue since it's just a small amount of time?
 

Rebellion

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Thanks for all the good info. When you let off just pretty slowly, is it still "riding the clutch" and harmful? Or is it not really that much of an issue since it's just a small amount of time?
If the rev matching is more or less on point, there shouldn't be much wear and you'll be releasing it quicker (of course there will be a wee bit of wear, but that's what is supposed to do). The farther away you are from the right RPM, the more wear there would be, either the clutch or synchros will get a beating.

For me, the biggest helping factor has been the aftermarket exhaust..let's me know the RPM without looking and thinking.
 

TURTL3

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Thanks for all the good info. When you let off just pretty slowly, is it still "riding the clutch" and harmful? Or is it not really that much of an issue since it's just a small amount of time?
As long as it's a gradual slow, release, then no. Riding the clutch is when say, you hold the clutch in the bite point for a long time or if you hold the clutch in when waiting for a stop light (wears the throw out bearing), or if you're holding the clutch in the bite point to hold the car steady on a hill (NEVER do that), or if when you're coming up off a start and you keep the clutch engaged when you've already got a enough revs to drive freely without the clutch engaged.

I always try to make the clutch release a gradual, fluid motion. If you do that slowly, but in a fluid motion, its no more wear on your clutch than normal. Think about when you take off from a start. If you just dump the clutch the car is going to jerk and go into drive line shock (light up the tires, smoke everywhere, maybe a code brown :D). That's way more wear on your clutch than say slowly releasing the clutch, giving it a little gas, and feeling when it bites so you know when you can fully come off the clutch.

A lot of this is feel. If I were to hop in your GT350 (offering? haha) I would have to get used to your shorter gears and how much faster your car revs than my 3.7 But despite that, my mechanics don't change. I just feel how the trans and engine react at different RPMs, but I'm always focused on a linear clutch release.



Now if you mean to light up the tires, by all means dump that clutch! :headbang:

Also, keep in mind, sometimes you may need to let the clutch out faster. The general rule is, slower speeds and lower revs, slower clutch release and vice versa for faster pulls/higher revs.

Doing a 30-80 pull? Or just driving fast? Everything is going to spin faster, and you'll have to release the clutch a little faster, but make it smooth. You can make the motion faster, but make sure its linear. If you do it too quick, the whole car will buck.
 

altjx

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Very cool information. Thanks a ton guys! Seriously. This thread is probably the most helpful one I've run across :D
 

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ForTehNguyen

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I've tried heel-toe a few times but the PP brakes are so touchy I end up braking way too hard when I blip the throttle. May not be as much of an issue on the track because you probably do brake pretty hard all the time.

For regular street use I brake, blip/down shift, brake more if needed and repeat as necessary. If I'm coming up to a stop light I'll brake/blip/shift 6-5-4 and then stay there to the light.
need to do the spacer mod for the gas pedal, it makes the gas pedal more flush with the brake pedal during braking. It helps immensely. And very cheap modification.
 

TexasRebel

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another point of clarification that may be leading to confusion on this thread:

clutch engaged = pedal out
clutch disengaged = pedal pressed

"Release the clutch" is somewhat ambiguous as many people say this to mean "release the clutch pedal" which is not incorrect. However, engaging the clutch pedal releases the clutch.
 

Norm Peterson

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Granny Shift: attempting, sometimes successfully, to shift out of and into gears while leaving the clutch engaged by modulating engine speed. Don't.
That's not 'granny shifting'. Drivers of 18-wheelers call it 'floating gears'.

Road course drivers may get closer to doing this than they realize . . . by not getting the clutch 100% fully released from time to time.

I can do this with pretty good reliability/repeatability, but I don't make a habit of doing so. Just knowing I can if I have to in case of clutch failure out on the road is good enough now.


Norm
 

Norm Peterson

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Curious to know...what's the point in blipping (which I understand as pulsing the throttle to a know RPM, then let go), if one can just rev-match (hold the known RPM) when down shifting?
Holding the engine revs up with the clutch fully disengaged can let the input shaft and countershaft slow down well below where the synchros want them to be, where they'll make the synchros have to speed them up (and work a little harder in the process) to get the shaft speeds matched. This can even happen on an upshift if the weather is cold enough and the gear lube stiff enough, and you don't run 1st gear out quite far enough because its oil is cold and a little stiff.

A fully synchronized transmission only accomplishes synchronization for the gear being shifted into. Constant mesh (what I think TexReb is thinking of) is something entirely different.


Maybe I'm getting the terminology wrong here...but I always hold the RPM before smoothly letting go of the clutch, what would be the advantage in just pulsing it before letting go of the clutch?
Don't you lift off the throttle for easy/normal upshifts? Same thing, really, that while you're moving the shift lever you're letting the input side revs decay to match what the new gear wants. Only for a downshift the revs are too low to begin with so you have to kick them "upstairs" first so they can fall back.


Norm
 

TexasRebel

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floating gears is granny shifting and it's not good for anything. The term comes from the line of thought that a grandma would be too old/lazy/weak to push the clutch pedal for every shift and/or fully disengage the clutch when she does.

The inertia of the vehicle against the moment of inertia of the engine puts a huge strain on synchronizers and the input shaft. This is how shafts shear and gears lose teeth. Sure, if you get the engine speed pretty close the collar will drop right into the dog teeth, but get it wrong and the worst case is you could be walking. Especially with a high-torque diesel. If you really wanted to you could get your vehicle rolling from a stop without the clutch, using only the synchronizers, but with the increased wear on the synchros, you'll either learn why double clutching is necessary or how to rebuild a transmission in short order.

Road course racers do get very close to doing this, and ideally they could shift without clutching. In reality they do more of a modified double-clutch rev-float. The clutch releases torque from the input shaft to shift to neutral and as the clutch engages the rev-matched engine brings the input shaft RPM up to where the collar will drop into the dog teeth.

Disengaging the clutch while shifting creates 3 independent rotating assemblies: engine, transmission input, and transmission output. The transmission input has very little mass and a low moment of inertia. Synchronizers are designed to speed/slow this small rotating assembly to match the corresponding rotational velocity of the transmission output to allow the proper gear to engage. Synchronizers are tiny wet clutches. The huge dry clutch you operate with your foot then matches the rotational velocity of the engine to the transmission input.
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