Sorry if this question is a silly one, or even if this is where I should post it. I have been reading alot about drivers of their manual trans cars talking about "Rev Matching" and how important it is. I have driven a few manual cars over the years, but I'm not sure if I understand the meaning of rev matching. Maybe one of the experts here can explain exactly what that means in "laymans" terms that even I can understand.
Thanks

 

I'm not an expert and haven't taken any race driving classes, but my Uncle taught me to "rev match". Automatic transmissions perform this for you, but if you have a manual and want to down shift, you want to rev match for performance and keeping in control.

Say you are going 50 mph and in 5th gear and you want to accelerate quickly. I would perform a double clutch. First, hit the clutch and take the shifter out of 5th. Hit the gas to match revs at 50 mph for 3rd gear (say it's 4500 rpm). Then hit the clutch again while keeping 4500 rpm and stick the shifter to 3rd gear.

This way, you don't lose control of your car if you were just to decelerate quickly by just going from 5th, not rev matching and going to 3rd. You also don't jerk your car and have a smooth transition from 5th to 3rd gear.

This is just my 2 cents. There are probably some racers that have a better description.

 

There was another thread today talking about rev matching on up shifts. It is the same principle, when you shift up you want the engine rpm's to drop to the appropriate level for the next higher gear so you don't get any bucking or shuddering. Apparently the vette, at least for some people, is a little different and more difficult to "feel" that sweet spot rpm for the up shifts. You've driven manual trans cars before, you've done all this before without thinking about it. It just may take a little more practice with a vette. I haven't driven a manual trans C6 so I can't say what it's like.

 

I think I was the one who said that. I learned to drive on a car where as you upshifted, without your foot on the gass the tach would take so long to fall to the equivalent rpm band that I could time it so I dropped the clutch at exactly that second and feel no lurch. With the vette the issue was that I wasn't fast enough because the needle doesn't drop as far, so I end up holding the throttle in place manually. It'll probably not be an issue as I train myelf to be faster. I'm just slow. :P

 

Why do you double clutch? Isn't it the same as just reving it to correct RPM while just holding the clutch in the whole time?

 

I guess double clutching is a habit. Older cars didn't have good synchros like today's cars and you couldn't just single clutch.

Here's a video that might help explain rev matching and double clutching better.

http://forums.corvetteforum.com/show....php?t=2007217

 

Oops, wrong link:

http://www.youtube.com/watch?v=JcxHi...eature=related

 

Thanks! Now I know

Do people actually not rev match? Can't imagine anyone jerking the car every time they switch gears.

 

 

No, when you rev it at the correct RPM and hold the clutch in, the engine spins but nothing else. By letting off of the clutch while you rev in neutral, you spin the pilot shaft to the appropriate speed. Doing this keeps your synchros from having to do the work of speeding up your pilot shaft to match the output speed thus saving your synchros from alot of wear and tear.

Here is an experiment that you can try. Get along on the highway going oh, 65MPH. Now, lets say you want to giddyup, so downshift to third by simply letting in the clutch and pushing the stick into 3rd gear. Once in gear, you simply rev the engine to the appropriate RPM's and then let out on the clutch and get-er-done. BECAUSE you did not doubleclutch, when you tried to jam the shifter into 3rd gear, it was really difficult to do so. It will almost feel like it's fighting you and doesn't exactly want to go into 3rd gear. What you're feeling are your synchro's speeding up the pilot shaft to match 3rd gear which happens to be fairly high. This will create a good bit of wear and tear on your synchro and you'll find if you do this often it will wear out much faster.

NOW, do the same thing, only this time, before you jam it into 3rd, let out on the clutch pedal while in neutral and blip the gas to say 4000 RPM's. At the peak of the blip, push the clutch in and then shift into 3rd. You'll notice that it will glide right into gear with little effort. You used the engine to speed up the pilot shaft and thus removed the work that your synchro's would normally have done. You're transmission will last much longer if you do this when downshifting

 

I practice double clutching some but that's mostly for cars with unsynchronized manual transmissions. I don't even think about any more but I do rev-match constantly (except maybe at slow speeds down shifting into 1st). It just becomes second nature when driving a manual shift.

My problem is I can't heel/toe properly in the C6...the geometry of the pedals makes it near impossible for me. I keep the left edge of my right foot on the brake pedal and simply roll the right side of my right foot on the gas pedal to blip it. It took me a while to get used to this (especially under severe braking) but it works pretty well.

I did see a mod a long time back where someone modded the gas pedal...shimmed it out a bit in order to get a proper angle on it.

Love those racing transmissions...like Lou at LG runs...Formula 1 cars, etc....the computer automagically blips the throttle when you shift. Sweet!

 

I get more or less get smooth up shifts in the C6 Z51 by allowing the tach to drop by about 1000 RPM before letting out the clutch in the next gear. That is, if the tach is at 4K in 1st, clutch in, shift to 2nd, clutch out at ~3K rpm is fairly smooth. I'm sure a more knowledgeable forum member must have some more precise rpm numbers. Note: for civilized driving, not racing.

 

It's funny, because I do the same thing. Nothing is sweeter than hitting an off-ramp, downshifting mid turn with a perfect "rev match" and accelerating smoothly into traffic at the end of the ramp.

Ferrari has had a rev matching feature for a while now.

Great read found here:

http://www.autozine.org/Graveyard/html/Ferrari/360.html

 

Double clutching matches the speed of the transmission input shaft (that's after the clutch) to the output shaft (the driveshaft) so that the transmission doesn't have to speed up the engine when the clutch is engaged during downshifts while driving. Reving with the clutch held down does not speed up the tranny input shaft.

In the "old days" (pre synchronizers) this had to be done or the gears would grind (as they were revolving at different speeds). Synchronizers in the tranny have cone clutches to speed up the slower gear.

As the throttle needs "blipping" to rev the engine, this isn't possible to do while braking unless the "heel and toe" method is used. Here it is -

http://en.wikipedia.org/wiki/Heel-and-toe

 

Johnny O'Connell has a good description of heel/toe on his web site along with some other really good driving tips.

http://www.johnnyoconnell.com/2006/DrivingTips4.htm

 

Great! Thanks. That YouTube vid that Capn Crunch posted was good too.

 

Thanks for all the info! I do beleive that even I am starting to understand! Captain Crunch- thanks for the link to the Youtube video, a lot of really good and useful info there! That heel and toe technique looks a little difficult, I must say I never did that before. How many of you here do that? I guess rev matching, from what I can see, is mainly done when deccelerating and when you are cruising at a given speed and you want to downshift in order to accelerate quicker(does that make sense? )

 

With the newer transmissions of today, there is really no NEED to match revs, double clutch on the up or down shifts, heal-n-toe or wear fancy slippers......

It WAS needed hundreds of years ago when the clutches were crap, the transmissions were fragile and whole drive trains that were suspect..

Being 63 years old, and having lived through the aforementioned era, and understanding the original reasons, love the fact that I can still perform this archaic form of mechanical manliness....

I look at it as a long lost "ART FORM".

That and the fact that it absolutely blows the minds of the twenty somethings who run the local rice rocket shop next to my office.

"How do you DO that, old man"?

Practise kid........ practise......

"Why do you do that, old man"?

because.... I can...

ZOOOM

 

Eloquently said.

 

GREAT! Remember 60 is the NEW 50!