blazed54

iTrader: (1)

I know this thread has been beaten to pieces but i couldn't find anything pertaining to my particular question. So sorry if it's been covered before

I'm gonna go out on a limb and assume that not all of us (myself) included can shift like a god and get our rev matches to the perfect rpm everytime. But, that with a little practice, people like me can get it within 500 rpms almost every time.

So my question is, when rev matching is it better to over rev, or under rev? Which would put less strain on the syncros (if it makes any difference at all) overreving the engine slightly and letting the syncros match the rpm down to the proper speed, or under revving it and letting the syncros bring it up to the proper speed.

I know it seems like such a trivial thing but if i makes a difference i'd like to know about it so i can be a better driver. Thanks for any input even if it's to flame cause i couldn't find an answer to my topic by searching hehe. thx

FastZ33

iTrader: (29)

neither r good, but over is bettter then under

Kolia

iTrader: (2)

I'd say a slight over rev is preferred. It feels better.

But in truth, either might have the same effect on the drive train.

Don't sweat it too much. It's when you start really pay attention that you'll start to mess up your shifts! Lol

davidv

iTrader: (2)

Rev-matching is overrated. Drive 100,000 miles with a manual transmision, and it will became natural and barely noticeable.

FastZ33

iTrader: (29)

^^^ dont wanna hold a cup of coffee while i sit passenger with him lol

Jokestrap

In a highly modified car, no, but in normal circumstances, most manual cars can be driven to feel like autos with practice. That is what he meant...

Spike100

Good question, and not trivial...

When missing the rev-match (and it’s not always easy to do a “perfect” rev-match), over-rev is preferable to under-rev since an over-rev places less stress on your drive train and feels more smooth than an under-rev (which usually feels “jerky”).

--Spike

HKS-Z

iTrader: (1)

do you use this method in normal everyday driving?..i only rev-match to take off from rolling, rev matching kills your mpg,but it sounds cool!

silver350tn

iTrader: (6)

it may be just me but i use rev-matching to down shift before coming to a stop, its a waste of gas but its fun it just takes practice

roast

iTrader: (2)

Sounds like you're trying to hold the throttle at a specific RPM. I'm a professional grade driver, and even I cannot do that perfectly every time. That's not how you should be revmatching. Blip the throttle instead. As the RPM shoot up, you have the engines momentum going in the direction you want it, so even if you don't let out the clutch at the perfect time, as long as you let out the clutch a little early they will "suck together" without much notice.

Unless you're double clutching (not much reason to), it makes no difference. The point of revmatching is to synchronize the engine speed with the rest of the drivetrain for smooth/seamless shifts. A synchro is designed to allow you to move the shifter into a gear without having to double clutch... it really has nothing to do with revmatching.

I1DER

I would think the over/under preference for revving would depend on whether you are shifting up or down-shifting to brake.

If you are down-shifting to brake, over revving isn't going to help that...or am I missing something?

I wholeheartedly agree that after time in a particular car, your ears and brain are going to automatically rev match if you pay attention from the beginning.

I down shift all the time for breaking. I've put 319,000 miles on my old Pathfinder and it has the original clutch and 2nd set of brakes. Yep, both systems need to be redone(Z gets all the attention), but the transmission is fine and has never been worked on. It's had rugged use too, including pulling boat trailers up soft beaches. As I've said many times, the last thing I double-clutched was an old farm tractor decades ago.

2005daytonaZ

iTrader: (3)

Hmm...I always rev match when I'm driving...and for the ones worried about gas mileage...can it really have that big of an effect?

Spike100

That's just a great explanation (the best I've read on this Forum). Nice job!

--Spike

blazed54

iTrader: (1)

Yes thank you that makes perfect sense to me now. So i guess what you're saying is that it doesn't matter if I over rev or under rev as long as it's heading in the right direction. Example (if you over rev then don't let the clutch out till it's back on the way down and vice versa). As for rev matching i mainly do it to engine brake while going down hill. Engine braking actually saves gas when the alternative is to coast in neutral while braking.

I1DER

I wouldn't let anybody that coasts in neutral while braking drive my car, including a dying wealthy relative. They have less control and apparently don't care. They probably wouldn't put me in their will anyway.
It doesn't save gas as you mentioned.

+1 for roast and a comprehensible explanation.

Spike100

Roast’s description of rev-matching is so clear that I think we all can understand the concept. Notice that he wisely removes the term “double-clutching” from the paradigm since this has nothing to do with rev-matching. He uses the term “blip” (kicking the accelerator pedal while the clutch pedal is depressed to bring RPM’s up quickly).

Consider this scenario: You are on a section of the track where you are running a straightaway that goes to a gentle left radius turn, followed by a short straightaway, followed by a tight right radius turn.

OK… let’s run this.

You’re on the straightaway with good speed and approaching the left turn. If your speed is too high, you may want to tap the brakes, but braking is done before you hit the turn. As you approach the turn, you depress the clutch pedal, blip the accelerator pedal while selecting the next lower gear, engage the clutch (pedal up), and begin applying gentle acceleration as you enter the turn. This is done and happens within a millisecond. As you approach the apex of the turn, you continue applying more power; and as you reach and leave the apex, you apply maximum power.

As you leave the first turn and enter the next straightaway, you should have plenty of speed as you approach the next turn. Again, if your speed is too high, you may need to tap the brakes (and you do this before entering the turn). As you approach and enter this turn, your technique is the same as described above: Depress the clutch pedal, blip the accelerator pedal while selecting the next lower gear, engage the clutch (pedal up), and begin applying gentle acceleration as you enter the turn. And again, it all happens within a millisecond. You begin progressively applying acceleration as you approach, reach, and leave the turn’s apex.

Fun stuff!

Disclaimer: Of course driving on the street is different. The concept is the same (you never want to be clutching or braking while inside a turn with RWD), but your speed would be lower and within safe limits while driving on the street. Of course if the roadway is wet, you would modify your driving to match existing conditions. VDC and TCS are very helpful on wet roadways.

Have fun, but drive sensibly and be safe.

--Spike

I1DER

When you downshift before going into a turn, you are enabling yourself to do 2 things missing in a higher gear. You are putting engine braking at your disposal and more power at your disposal for accelerating out of the lower speed corner. You rev match to make this smooth, not complicate things.

I highly recommend auto cross classes for the new guys/gals. The instructors will take much of the mystery out of a process that really is quite natural and sensible once explained.

Spike100

^^ I agree. 20 or 30 years ago, cars were RWD and many had MTs. It is becoming a lost art (driving a MT with RWD).

--Spike