rev matching???
Newbie
Joined: Sep 2003
Posts: 24
Likes: 0
From: MD
actually, NightShifter did miss the entire point by a long shot. Although he explained a very good reason about NOT to downshift during a 1/4 drag, rev matching and double clutching should be only used for downshifting (I cant see another real reason other than just shifting from different gears or when the car is coasting down the street in neutral and you want to put it back into gear).. anyone even mentioning revmatching and double clutching with 1/4 drag in the same sentence needs to check their driving IQ.
Not to insult NightShifter's intellect and with all due respect, do even know what rev matching and double clutching was even used for? Also, I can tell you right now why you still havent figured out why you have trouble from your upshifts and I can easily tell you about everything else that you see that are problems are really easy to solve or at least understand of how it works. Also, your "gear math" is very vague, but I will give you the benefit of the doubt and assume your "5100" rpms is based on 2nd gear traveling at the top speed of 1st gear and not so much of 1st gear's gear ratio.. it's kinda stupid to take the car past the 'sweetspot' of the motor. [Sweetspot is the range in the RPMs between peak torque and peak hp.. going beyond that is actually slower, which if you did 4 shifts and you even lose .1 seconds from overreving, there's your .5 seconds in difference].
Revmatching is mainly used for matching shifts during downshifts (or neutral coasts back into gear, aka exaggerated double clutching).. if you wanted a faster engine response from upshifts, you get yourself a lightweight racing flywheel which are quick reving going up and down (since there's less mass to rotate and less momentum/intertia to keep the engine from free-rolling). It allows the motor to drop faster in rpms to get to the next gear. And no, you DONT want the motor to bounce off the redline/rev limiter when going up the next gear, you are only abusing the tranny that way from creating a difference in forces (positive force generated by the motor vs negative forces such as friction from tires and drivetrain that wants to stay at rest, please read your 3 Newton's Laws of physics). Do it enough times where the flywheel is spinning faster vs drivetrain that wants to go slower results the tranny/diff/drivetrain being the middle-man of a lot things breaking. If you are bouncing off the rev-limiter, your hard-on/adrenaline needs to back off and let off the throttle some so that you can hold the rpms to the exact rpms of the next gear. A good practice excercise to do this is when you are going in and out of the same gear to neutral and back all while keeping the rpms exactly the same. The car should not jolt when you let off the clutch (and you do NOT ride the clutch, it should be a quick clutch-in-clutch out all in a matter of .3 seconds, same speed/timing as a blink of an eye) as you drive down the road. If you are really good, you dont even need to push in the clutch (aka clutchless shifting by using rev-matching). Basically, any over-reving/rev-limit hitting that causes "bouncing" comes from driver error first... I refuse to believe that every new car has a crappy clutch.. it's the driver's responsibility to control the throttle to the right amount to match the rpms or at least hold the throttle so that the rest of the drivetrain can match the rotational speed. How many of you guys even practice holding the throttle at 3k rpms at a red light in neutral without going over or stopping short of 3k rpms? Of all the students I teach, only 2% get it right the first time, and I have taught well more than 100 people for high performance driving schools.
Double Clutching was used back in the days where cars and trucks DIDN'T have syncros in the tranny (normally found in 1/2, 3/4, and sometimes 5/6, which result in pushing in the clutch twice to shift from one gear to the next. Some people still do double clutching (especially downshifting) to have less wear from the syncro doing all the work to have a better match for all the helical gears (curved/twisted gear teeth as opposed to straight cut/star shaped gear teeth for quick meshing.. also known to have in every manual car as a reverse gear). Because of the curved gears, this required some help of the driver to match the rotional speeds of the gears to be the same and less damage when shifting. "So why have curved gears?" Helical gears are quiet for better interior driving comfort.. not sure if anyone here even have a PPG or dog-box tranny, but basically if you swapped out all your forwarding gears to straight cut, your car would sound just as if you were in reverse gear (that high winding/whiney noise). In a dog-box tranny, you can slam gears all day long as they wont have a problem with needing to really syncronize since the meshing window/"window of fitment" is larger area to fit the gears together.
As for the 1/2 and 3/4/5 shifting, if you ever got the chance to look at your gear ratios, you can see that 2nd gear is sometimes 1/2 the teeth count than 1st gear. The syncro needs the time to get all the timing of teething right hence you just can't shift it hard or fast right into it (unless you want to break something).. and of course, stomping and keeping the throttle down is only making the difference in rotational speeds from the tranny vs flywheel gets only worse to match. That's like the same analogy as you trying to grab on a moving car while standing still vs grabbing on the car WHILE you are running.. you have a better and easier chance to grab onto the car if you were moving at the same speed as the car is rolling. If we exaggerate the example a little bit, let's see you try to grab a car going by at 50 mph vs 5 mph.. I think it's less pain on your hands to try to grab the 5mph one.
And one more thing, power shifting is bad on the tranny, it's not going to make you go any faster other than you breaking the tranny faster. And all for what? A gain in .2 to .3 seconds in the 1/4? I rather have consistent smooth shifting and not beat up the clutch and take the loss of .3 seconds.. I know how long .3 seconds takes (which is really a blink of an eye)... I do autocrossing A LOT and my races comes down to a difference of .001 seconds.. try watching the overlapping-ghost videos on that and I bet you can't even tell the difference then. And to give you an idea of what .3 seconds mean in real life, the conversion is:
1.467 feet per second = 1 mph
so if you were doing 110 mph for your traps, you are doing 161.3 fps, and you multiply that by .3 seconds which is 48.39 feet that you traveled.. which is roughly 3 to 4 car lengths IF the other car was also travelling the same trap speed. So if two Evos ran the same trap speed, but one car was .3 seconds faster due to driver error in launching the car or was sleeping at the line, expect to see somewhere of the faster Evo being around 3 to 4 car lengths ahead (sport compact cars around around the 12 to 15 feet overall length). If this was on a road-course or at a drag strip, a really great driver will catch up 3 car lengths under braking and cornering or an unlucky launch by bogging the motor is all you need to catch up.
If anyone wants to question my knowledge, I've done about 5 years of racing and taught myself how to drive stick. I also have driven over 250,000 miles for the past 10 years, along with 6 years of high performance driving [over 5000 miles of road-course track driving, a drag racer would have to do over 20,000 passes and also downshift 20,000 times to come to the numbers I get just for track driving]. Im getting to the point where Im about to take some stunt driving schools and rally/off-road performance driving schools and learn more about 180s, 360s, 720s, perpendicular parking (parallel parking coming in head-on towards the curb) as well as learning O'Neil shifting for rally/loose pavement situations... O'Neil shifting is left-foot braking with a rev-match downshift without using the clutch. Anyone got that? If not, google it up.
My two race cars (both with over 55,000 miles and both on stock transmissions and the original clutch):
http://www.xanga.com/xenonk
Ok, class dismissed.
Not to insult NightShifter's intellect and with all due respect, do even know what rev matching and double clutching was even used for? Also, I can tell you right now why you still havent figured out why you have trouble from your upshifts and I can easily tell you about everything else that you see that are problems are really easy to solve or at least understand of how it works. Also, your "gear math" is very vague, but I will give you the benefit of the doubt and assume your "5100" rpms is based on 2nd gear traveling at the top speed of 1st gear and not so much of 1st gear's gear ratio.. it's kinda stupid to take the car past the 'sweetspot' of the motor. [Sweetspot is the range in the RPMs between peak torque and peak hp.. going beyond that is actually slower, which if you did 4 shifts and you even lose .1 seconds from overreving, there's your .5 seconds in difference].
Revmatching is mainly used for matching shifts during downshifts (or neutral coasts back into gear, aka exaggerated double clutching).. if you wanted a faster engine response from upshifts, you get yourself a lightweight racing flywheel which are quick reving going up and down (since there's less mass to rotate and less momentum/intertia to keep the engine from free-rolling). It allows the motor to drop faster in rpms to get to the next gear. And no, you DONT want the motor to bounce off the redline/rev limiter when going up the next gear, you are only abusing the tranny that way from creating a difference in forces (positive force generated by the motor vs negative forces such as friction from tires and drivetrain that wants to stay at rest, please read your 3 Newton's Laws of physics). Do it enough times where the flywheel is spinning faster vs drivetrain that wants to go slower results the tranny/diff/drivetrain being the middle-man of a lot things breaking. If you are bouncing off the rev-limiter, your hard-on/adrenaline needs to back off and let off the throttle some so that you can hold the rpms to the exact rpms of the next gear. A good practice excercise to do this is when you are going in and out of the same gear to neutral and back all while keeping the rpms exactly the same. The car should not jolt when you let off the clutch (and you do NOT ride the clutch, it should be a quick clutch-in-clutch out all in a matter of .3 seconds, same speed/timing as a blink of an eye) as you drive down the road. If you are really good, you dont even need to push in the clutch (aka clutchless shifting by using rev-matching). Basically, any over-reving/rev-limit hitting that causes "bouncing" comes from driver error first... I refuse to believe that every new car has a crappy clutch.. it's the driver's responsibility to control the throttle to the right amount to match the rpms or at least hold the throttle so that the rest of the drivetrain can match the rotational speed. How many of you guys even practice holding the throttle at 3k rpms at a red light in neutral without going over or stopping short of 3k rpms? Of all the students I teach, only 2% get it right the first time, and I have taught well more than 100 people for high performance driving schools.
Double Clutching was used back in the days where cars and trucks DIDN'T have syncros in the tranny (normally found in 1/2, 3/4, and sometimes 5/6, which result in pushing in the clutch twice to shift from one gear to the next. Some people still do double clutching (especially downshifting) to have less wear from the syncro doing all the work to have a better match for all the helical gears (curved/twisted gear teeth as opposed to straight cut/star shaped gear teeth for quick meshing.. also known to have in every manual car as a reverse gear). Because of the curved gears, this required some help of the driver to match the rotional speeds of the gears to be the same and less damage when shifting. "So why have curved gears?" Helical gears are quiet for better interior driving comfort.. not sure if anyone here even have a PPG or dog-box tranny, but basically if you swapped out all your forwarding gears to straight cut, your car would sound just as if you were in reverse gear (that high winding/whiney noise). In a dog-box tranny, you can slam gears all day long as they wont have a problem with needing to really syncronize since the meshing window/"window of fitment" is larger area to fit the gears together.
As for the 1/2 and 3/4/5 shifting, if you ever got the chance to look at your gear ratios, you can see that 2nd gear is sometimes 1/2 the teeth count than 1st gear. The syncro needs the time to get all the timing of teething right hence you just can't shift it hard or fast right into it (unless you want to break something).. and of course, stomping and keeping the throttle down is only making the difference in rotational speeds from the tranny vs flywheel gets only worse to match. That's like the same analogy as you trying to grab on a moving car while standing still vs grabbing on the car WHILE you are running.. you have a better and easier chance to grab onto the car if you were moving at the same speed as the car is rolling. If we exaggerate the example a little bit, let's see you try to grab a car going by at 50 mph vs 5 mph.. I think it's less pain on your hands to try to grab the 5mph one.
And one more thing, power shifting is bad on the tranny, it's not going to make you go any faster other than you breaking the tranny faster. And all for what? A gain in .2 to .3 seconds in the 1/4? I rather have consistent smooth shifting and not beat up the clutch and take the loss of .3 seconds.. I know how long .3 seconds takes (which is really a blink of an eye)... I do autocrossing A LOT and my races comes down to a difference of .001 seconds.. try watching the overlapping-ghost videos on that and I bet you can't even tell the difference then. And to give you an idea of what .3 seconds mean in real life, the conversion is:
1.467 feet per second = 1 mph
so if you were doing 110 mph for your traps, you are doing 161.3 fps, and you multiply that by .3 seconds which is 48.39 feet that you traveled.. which is roughly 3 to 4 car lengths IF the other car was also travelling the same trap speed. So if two Evos ran the same trap speed, but one car was .3 seconds faster due to driver error in launching the car or was sleeping at the line, expect to see somewhere of the faster Evo being around 3 to 4 car lengths ahead (sport compact cars around around the 12 to 15 feet overall length). If this was on a road-course or at a drag strip, a really great driver will catch up 3 car lengths under braking and cornering or an unlucky launch by bogging the motor is all you need to catch up.
If anyone wants to question my knowledge, I've done about 5 years of racing and taught myself how to drive stick. I also have driven over 250,000 miles for the past 10 years, along with 6 years of high performance driving [over 5000 miles of road-course track driving, a drag racer would have to do over 20,000 passes and also downshift 20,000 times to come to the numbers I get just for track driving]. Im getting to the point where Im about to take some stunt driving schools and rally/off-road performance driving schools and learn more about 180s, 360s, 720s, perpendicular parking (parallel parking coming in head-on towards the curb) as well as learning O'Neil shifting for rally/loose pavement situations... O'Neil shifting is left-foot braking with a rev-match downshift without using the clutch. Anyone got that? If not, google it up.
My two race cars (both with over 55,000 miles and both on stock transmissions and the original clutch):
http://www.xanga.com/xenonk
Ok, class dismissed.
Last edited by xenonk; Dec 19, 2006 at 04:57 PM.
i think it's funny how these pointless threads get drawn out for so long. there's one guy who actually answered the question on the first page in like 2 sentences. nobody else has really said anything worth paying attention to, and a lot of the stuff said here just makes no sense at all.
After reading all of this and seeing many good points and many more bad ones I thought I would throw in the one bit of info that made me want to learn how to rev match.
When you are driving closer to 10/10ths traction and control are are dear. It is even more dear when trying to change direction which often happens when your slowing into a corner and twisting the wheel. This also means that you will most often need to press in the clutch and downshift to come out hard after hitting the apex.
The problem as I understand it is without rev matching when you grab that gear and pop the clutch the whole drivetrain attempts to spin up to speed which is bad but even worse in that it could easily push the contact patches of your tires past their limit resulting in you and your car swapping ends and going into the grass or worse.
By blipping the gas and raising the revs as the clutch is in you can eliminate the jolt, save your drivetrain and keep your car under control which are good things all. You can also impress your friends and be the envy of all the folks who wreck their cars because they think that learning to be a better driver is silly.
When you are driving closer to 10/10ths traction and control are are dear. It is even more dear when trying to change direction which often happens when your slowing into a corner and twisting the wheel. This also means that you will most often need to press in the clutch and downshift to come out hard after hitting the apex.
The problem as I understand it is without rev matching when you grab that gear and pop the clutch the whole drivetrain attempts to spin up to speed which is bad but even worse in that it could easily push the contact patches of your tires past their limit resulting in you and your car swapping ends and going into the grass or worse.
By blipping the gas and raising the revs as the clutch is in you can eliminate the jolt, save your drivetrain and keep your car under control which are good things all. You can also impress your friends and be the envy of all the folks who wreck their cars because they think that learning to be a better driver is silly.
After reading all of this and seeing many good points and many more bad ones I thought I would throw in the one bit of info that made me want to learn how to rev match.
When you are driving closer to 10/10ths traction and control are are dear. It is even more dear when trying to change direction which often happens when your slowing into a corner and twisting the wheel. This also means that you will most often need to press in the clutch and downshift to come out hard after hitting the apex.
The problem as I understand it is without rev matching when you grab that gear and pop the clutch the whole drivetrain attempts to spin up to speed which is bad but even worse in that it could easily push the contact patches of your tires past their limit resulting in you and your car swapping ends and going into the grass or worse.
By blipping the gas and raising the revs as the clutch is in you can eliminate the jolt, save your drivetrain and keep your car under control which are good things all. You can also impress your friends and be the envy of all the folks who wreck their cars because they think that learning to be a better driver is silly.
When you are driving closer to 10/10ths traction and control are are dear. It is even more dear when trying to change direction which often happens when your slowing into a corner and twisting the wheel. This also means that you will most often need to press in the clutch and downshift to come out hard after hitting the apex.
The problem as I understand it is without rev matching when you grab that gear and pop the clutch the whole drivetrain attempts to spin up to speed which is bad but even worse in that it could easily push the contact patches of your tires past their limit resulting in you and your car swapping ends and going into the grass or worse.
By blipping the gas and raising the revs as the clutch is in you can eliminate the jolt, save your drivetrain and keep your car under control which are good things all. You can also impress your friends and be the envy of all the folks who wreck their cars because they think that learning to be a better driver is silly.
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From: chicago, michigan, arkansas
.....Revmatching is mainly used for matching shifts during downshifts (or neutral coasts back into gear, aka exaggerated double clutching)....
...Double Clutching was used back in the days where cars and trucks DIDN'T have syncros in the tranny (normally found in 1/2, 3/4, and sometimes 5/6, which result in pushing in the clutch twice to shift from one gear to the next....dismissed.
...Double Clutching was used back in the days where cars and trucks DIDN'T have syncros in the tranny (normally found in 1/2, 3/4, and sometimes 5/6, which result in pushing in the clutch twice to shift from one gear to the next....dismissed.
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