NOTE: I posted this on www.legacygt.com to demonstrate what rev-matching is.. so the information was geared (no pun intended) towards the 2005 Legacy GT 5speed, but it shouldnt be too different to today's 5 speed cars with similar redlines). Enjoy:



I decided to post this up since I had a few members asking me if I had problems doing rev matching for many reasons (due to drive by wire, the dual mass flywheel, etc etc).. so I decided to come up with a quick and easy way to:

1) explain what rev matching is all about

2) science behind rev matching

3) the science vs "art form" to rev matching

4) Xenonk's tips on how to rev match better


Part 1:
Rev matching is all about matching the speed of the car to the speed of the transmission's spinning rate of the chosen gear. We all know that the car moves along the road and we shift to and from gears all the time and we get that occasional jerk from letting out the clutch either too fast or we apply the gas too much. The idea of rev-matching is to lessen that motion because you are forcing the transmission to spin to the correct matching spinning speed of the tires by playing with the throttle while the clutch is pressed in. A simple example is like waiting for the right moment to jump into a double dutch jump rope.. if you dont time your clutch release at the right time (or moving into the jump of double dutch jump rope) you can slam gears or grind gears (or get hit by the rope).

The reason why you want to rev match is because:
A) less wear on the gears/synchros in the tranny
B) less wear on the clutch
C) less weight transfer (or upsetting the car's balance during gear shifts)
D) fastest acceleration without wheel spin from a rolling start

Part 2:
here's a chart I put up for the BL/BP Legacy GT's gearing RPM vs MPH:


Hopefully this chart is self explanatory for most of you. As you can see from the chart, I plotted out a semi accurate chart of the Legacy GT's 5spd gearing for some demonstration purposes.

Rev matching based on car speed:
If you look at the 75mph example line as our first example, you can see that when you are traveling at 75mph in 5th gear, your engine speed is around 3150 rpms (circled "A"). If you were to shift into 4th, you would need to rev-match your motor to around 4500 rpms to travel that same 75mph. When you do the rev-match correctly, the car shouldnt lose or gain speed, only the motor should jump from 3500 rpms to 4500 rpms (marked "B").

Makes sense? What about 75mph in 3rd gear, what would the rpms be? According to the chart (circled "C") it should be near 6000 rpms!! Becareful now! What if you were traveling at 75mph and you want to drop the car into 2nd gear? "OH NO!, the car doesn't rev past redline at 6500 rpms", you're right, at 2nd gear doing 75mph, your motor has to be able to rotate well over 8000 rpms to have a smooth shift (but Im sure something will break or blow up if anyone is crazy enough to do that on a stock transmission).

Rev matching based on picking your rpm levels (commonly known as heel-toe):
You can see from the "3500 rpm example" that we are using a known rpm instead of speed. Say you are traveling on 5th gear at 3500 rpms, you should doing around close to 80 or slighty higher [according to the chart of course] (circled "1"). In a braking situation where you would use braking AND a rev match (also known as "heel toe" shifting), you can see that in order for you to shift into 4th at 3500 rpms, you need to slow the car down foremost to 60mph (circled "2"). Of course you can rev match and shift and then brake, but most high performance drivers wouldnt opt this technique because you will hit the redline limit as we discussed before. Brake first, then rev match/heel toe so that your engine will see you through the end of the turn.


Part 3:
It's all fine and dandy that you can use the chart as a guideline, but it's by no means that anyone can get everything down to an exact science of being able to rev the motor to exactly 3495 rpms to match the speed of the car that is going 64.1583 mph. All cars are different with engine redlines and different transmissions with different gear ratios. No one is going to sit there and spit out every plot out for you just so that you remember what speed the car is going and what gear it is in to be a certain rpm.

So where's the art in it? It's the driver that is all in sync with the motor and the tranny. Remember, the driver is the conduct that controls the engine's speed using the throttle at the same time the driver can also control the speed of the car using the brakes.. you can easily use one or the other or BOTH to find the exact "window of opportunity" to where both the transmission speed meets up with wheel speed. It's an art form simply that it's all based on the drivers inputs to make the results come out the way they wish to come out. Think of it as a dance with two feet in unison. When you drive other cars, you shouldnt have to worry if the car has a tachometer or not. Your senses of touch, seeing and hearing should give you everything you need to know how to rev match properly.


Part 4:
Tips:
1) try not to look at the tach so much and worry about the science behind it.. you just need to know the concept that you are trying to match the speed of the transmission (engine) to the speed of the car (wheel spin speed). Use your ears and train them to hear what 3000 rpms sound like, or 2000 or even 8000 rpms if you dare (if you have a car that has a 11,000 rpm redline). Turn off the radio and listen to your wonderful motor for once.

2) Speed. Train your body to know what zero acceleration is like and force your body to be more aware of what the car feels like in each gear at the same traveling speed.. practice at a safe cruising speed of 40 mph on an open straight highway. Teach yourself to know what it feels like when you are each gear and feel for how hard the motor is working to move the car.

3) Practice. Be conceous of your mistakes and know why the jerk is still there.. ask yourself "did I miss my "window of opportunity?" or "did I over rev or under rev the motor to the gear I am matching?"



This lesson is just a basic coverage of what rev-matching is about and how it can be done by the science and by an performing art.

Post questions and I'll do my best to answer them here. Thank You.

 

I find it pretty funny how many people have responded to this topic. For all the nuckel heads that want to know what BOV to put on their stock EVO. You would think more people would want to learn a little bit on how to drive the damn thing. Thank you for the info, Heal toe is one of those thing that still alludes me, but I am working on it. Thanks again

 

I'm currently at the track ( www.virclub.com ) and I'll post some videos from today of my heel toe and some other videos of me passing the vettes a few vipers my GT is stock, just has suspension, brake pads and race tires.

 

Love the use of AutoCAD. Are you a CAD operator? That's what I do.

 

beautiful write-up

 

Just one thing to add...

If you make a serious effort to rev match every shift, all of the time, not just some of the time, but ALL of the time, it will become an automatic action and you'll also get really good at it. The same goes for heel-and-toeing.

When learning to drive a manual transmission car, you go through phases... First, you're actively thinking about everything, and every shift is an adventure. Soon, the shifter H-pattern and gear selection become more or less automatic. Then soon you will find that you're no longer thinking about the clutch pedal -- you're just doing it, but you may have some bad habits like pressing or holding the clutch pedal down when you shouldn't, or letting the clutch out slowly to avoid the "jerk" when it engages. Many people stay at that level their entire lives -- I did for ten years. If you're driving a 90 HP FWD econobox, you're probably never going to see any reason to change.

But to really get the most out of the manual transmission, you'll need to move up the learning ladder and probably unlearn some bad habits as well. The reason that clutching, shifting, and mentally choosing the correct gear became automatic for you is because you did them all the time. If you want rev-matching and heel-and-toeing to become automatic, do them all the time as well... And like xenonk wrote, be conscious of your mistakes and work to minimize them.


After a while, you'll end up like I am today, where the idea of not rev-matching a shift just makes you uneasy -- I'd put a non-rev-matched shift in the same category with intentionally grinding gears.

 

yes, been close to 11 years, more like 12 soon.


rev-match is essential of keeping your tranny happy.. Im very suprised that everyone (either a Subaru or an Evo) that many people say that they have a weak tranny.. I personally think it's the driver.. as it's the driver's job to understand that this isnt some 2-wheel drive car, you are actually coming close to doubling the resistance because of AWD. You have that much more resistance to overcome to get the tires to start rolling.. people that don't take their driving seriously isnt making an effort to understand what the car needs and capable of doing. If you want to drop the clutch, that's fine, just don't expect it anything to last with driver-neglect.

 

So it isn't as beneficial on FWD cars?

 

nice

 

What I meant by my statement above (about 90 HP FWD econoboxes)...



In a 2WD car, if you don't rev-match your shifts, it can only put about half as much stress on the transmission/engine, because it only takes about half as much force to break loose the drive wheels, when compared to an AWD car.

Furthermore, most 90 HP FWD econoboxes have an open differential, meaning that you don't even have to break both front drive wheels loose -- only one of them needs to break loose to protect the transmission/engine from stress. And 90 HP FWD econoboxes usually have skinny little all-season tires that break loose pretty easily. And when you do break that one tire loose, the car exhibits understeer which is not particularly dangerous.

So with very little chance to damage the car due to an un-rev-matched shift, the only incentive to rev match is to make downshifts feel smooth -- but you can do that by just letting the clutch pedal out slowly and smoothly. The transmission can bring the engine up to speed for the lower gear. And given the smaller lower-revving engines we're talking about, that's not such a terrible way to do it -- it's clutch abuse for sure, but other than an earlier-than-normal clutch replacement, probably not going to cause any problems.



I drove FWD manual econoboxes for pretty much the first 10 years of my driving, and pretty much drove it the way I discussed above. Then I bought an '82 Porsche 928 (RWD) with a manual transmission and with a 2nd gear synchro which was essentially totally worn out. So I had a crash course not only in rev-matching but in double-clutching (but that's a subject for another thread)...


To summarize, I wouldn't say that rev matching isn't useful on a low-powered FWD car. But the possible consequences of not doing so are fairly minor.

 

Funny to come across this on the Evo forums too. I am driving a Nissan Altima SE-R right now (and preparing to buy my first Evo soon). My SE-R is the first 6spd manual I have ever driven, and for some reason the gearbox on the Nissan is really rough. It's a problem everyone who drives the VQ35DE engines mated with manual transmissions complains about.

Anyway, when I got the SE-R and started driving it, I realized that if I actually drive better (rev matching mostly, with a bit of heel-toe downshifting and occasional double clutching), the car not only performs better, but the gearbox feels a lot smoother. I think a lot of us ended up learning how to drive a manual on a car that wasn't as much of a precision instrument as the Evo is. Or as my SE-R is. I, for one, learned how to drive a stick on a Chevette back 20 years ago. Big difference!

Anyway, even without heel-toe downshifting on the corners, rev matching makes a huge difference in how smooth the car drives and it really does reduce the wear on the transmission in the long term.

 

youre funny.