Rev Matching.......Any How To's - The Unofficial BMW M5 Messageboard (m5board.com)

Tim W · 6th July 2005, 06:24

Gang:

Any How To's for rev matching? I have been trying to figure it out and am not coordinated correctly.

I have been engaging clutch, shifting to the lower gear, and then it is hard to coordinate when to blip and release clutch.

Any tips?

greg · 6th July 2005, 06:54

If you're WAY off, first learn how much RPM you need in the lower gear to get a feel for the range. Here's a hypothetical case for a 3-2 downshift.

1) Find a speed where your RPM in 2nd gear is toward the high end - let's say 5000 RPM. Note the MPH.

2) Upshift to 3rd, regain the speed you noted in step 1.

3) Now shift to 2nd, blip to somewhere just ABOVE 5000 RPM and release the clutch.

4) If you're practicing a braking maneuver you would be back off the gas after the blip. If you're preparing for immediate accelertion, use enough gas to keep the car from slowing down as you declutch and then roll the throttle back on.

Tim W · 6th July 2005, 07:02

Greg:

You want to have the RPM's above the Hypothetical 5000 RPM when the clutch engages right?

Some of my issue is that my M5 has the light wieght flywheel and things rev quick.

BmwNut · 6th July 2005, 08:54

The reason for blipping over the correct rpm is that it takes a little bit of time to get the clutch out once you have blipped. Gregs advice is spot on as always, as it is best to learn how to downshift to a given gear and rpm before experimenting. After sometime you will develop the feel for how much to blip for a given shift, and the numbers wont matter. Until that time, blip for the numbers that you remember.
When I blip the rpms go over where I need them to be, and then I pull the clutch out while the rpms are falling to the correct rpm. Do what works best for you, as I know some people who like to catch them on the way up, but I prefer catching them on the downswing.
If you shift, get it in the lower gear and then blip, I recomend sitting in the driveway with the car off to practice the motion. What works best is clutch in, then blip and shift at the same time. By sitting the driveway with the car off you can get used to the motion better, and at some point it will be second nature. You dont have to do this, but it saves time and is IMO easier.
There are quite a few great threads on this, so doing a search might help answer some questions. Hope this helps!

gsfent · 6th July 2005, 10:18

Quote:

Originally Posted by BmwNut

The reason for blipping over the correct rpm is that it takes a little bit of time to get the clutch out once you have blipped. Gregs advice is spot on as always, as it is best to learn how to downshift to a given gear and rpm before experimenting. After sometime you will develop the feel for how much to blip for a given shift, and the numbers wont matter. Until that time, blip for the numbers that you remember.
When I blip the rpms go over where I need them to be, and then I pull the clutch out while the rpms are falling to the correct rpm. Do what works best for you, as I know some people who like to catch them on the way up, but I prefer catching them on the downswing.
If you shift, get it in the lower gear and then blip, I recomend sitting in the driveway with the car off to practice the motion. What works best is clutch in, then blip and shift at the same time. By sitting the driveway with the car off you can get used to the motion better, and at some point it will be second nature. You dont have to do this, but it saves time and is IMO easier.
There are quite a few great threads on this, so doing a search might help answer some questions. Hope this helps!

Bren
Good post, but I will suggest you blip before you downshift, not after, otherwise you are working your synchros very hard. By blipping before the downshift, you are matching speeds for the differnt shafts and the gear lever should snick right into the lower gear if you do it right.
For people trying to learn the technique, 4th to 3rd is usually easier and can be done with a smaller rpm differntial, thereby making the downshift easier to accomplish smoothly.
Finally, I learned never downshift without braking, so I got int he habit of heel and toeing anytime I downshift and rev match ( I do occasionally downshift without rev matching, I am going to counselling to break the habit

).

Regards,
Jerry

BmwNut · 6th July 2005, 10:44

As a small point of clarification Jerry unless you double clutch you dont spin the input shaft of the tranny, so the internals dont get rev matched. Once the clutch goes in, it really doesnt matter when you blip as the engine and tranny are not connected anymore. Almost all of my downshifts are double clutches, and by blipping with the clutch out in neutral the input shaft turns the internals of the tranny to the correct rpm, and gears slot in buttery smooth like you mentioned. Hope that makes some sense.

HDClown · 6th July 2005, 14:25

Is it bad for the clutch/transmission to blip the throttle on a downshift but still leave your foot very slightly on the gas as you let the clutch re-engage? I've found this an easier way to get the clutch engaged smoothly. This is primarily in low RPM downshifting however. In the higher RPM range, doing a true blip with no foot on the gas until after the clutch engages is easier.

MEnthusiast · 6th July 2005, 14:43

I think you will burn a little bit more of the clutch doing that HDClown- but given that the clutch we have is considered a weak part you could look at this either as- work even harder to protect it so dont do this at all or its a consumable part like the tires and let the good times roll! My opinion is kind of a hybrid- I say take it easy on the clutch- but you only live once and its not too hard to replace the clutch.

I would add to the downshift discussion- be careful not to over rev the engine when you are first learning this. The rev-limiter will protect the engine from our lead footed tendencies when we are in a gear and approaching the redline, but it WILL NOT protect if you downshift and that shift calls for revs which are higher than the redline!

Also, Jerry, I think I understand your comment about always using the brake too, but what if you are just looking for passing power- you don't need the brakes for that- just rev match and go!

I do agree that the 4-3 downshift is probably the easiest to learn with- but speeds are higher than comfortable for some, try 3-2 when coming to a stop. Just look behind your car to be sure no one is tail-gating you. In time you will be able to fire off perfectly rev-matched downshifts without really even thinking too much about it- you are calibrating your brain to know when to do what. Soon you won't believe how easy it really is.

Now Tim, once you've mastered this, ask about heel-toe downshifting!

gsfent · 6th July 2005, 18:31

Quote:

Originally Posted by BmwNut

As a small point of clarification Jerry unless you double clutch you dont spin the input shaft of the tranny, so the internals dont get rev matched. Once the clutch goes in, it really doesnt matter when you blip as the engine and tranny are not connected anymore. Almost all of my downshifts are double clutches, and by blipping with the clutch out in neutral the input shaft turns the internals of the tranny to the correct rpm, and gears slot in buttery smooth like you mentioned. Hope that makes some sense.

Yes makes sense. I have done double clutches ( butter smooth as you say) and singles (almost as smooth with practice). I understand with clutch in the you have disengaged, but any time I have resistance on the stick a quick blip always lets it slip right into the lower gear. Maybe I am subconsciously doing a quick double clutch, I will have to pay more attention next time.
Regards,
Jerry

gsfent · 6th July 2005, 18:35

Quote:

Originally Posted by MEnthusiast

Also, Jerry, I think I understand your comment about always using the brake too, but what if you are just looking for passing power- you don't need the brakes for that- just rev match and go!

You are correct, I think I admitted to occassionally doing just that!! I was taught downshifting for track driving, so the "always use the brake" was part of the general rule. For passing power, drop down 2 (no brake needed) and call me in the morning!!

Regards,
Jerry