Clutch helping to lower engine rpm under hard acceleration

[cat94]

Speaking with little experience driving cars with manual transmissions, and are performance oriented:

When accelerating and shifting aggressively, it feels like the clutch is helping to lower engine rpms when engaging. This is really only noticeable when shifting from 1st to 2nd.

Correct me if I'm wrong, but my guess is that this is because 1st gear is relatively short compared to the rest.

Should I be holding in the clutch slightly longer to allow engine rpms to fall appropriately by itself? In either case, the car is smooth and not jerky. When I wait though, it feels like I'm losing forward momentum. Also, by no means am I shifting like I have a racing clutch.

Is me using the clutch to drop rpms faster wearing out anything other than the clutch itself?

[mav1178]

You need to relearn how to shift. You need to change your shift timing based on how the RPMs drop.

Every engine type will be different.

If you have the clutch pedal pressed in, the engine RPM will drop naturally according to the rotating mass it has. Holding the pedal longer doesn't mean it will drop any faster, you just have to compensate for it.

-alex

[cat94]

Originally Posted by mav1178

You need to relearn how to shift. You need to change your shift timing based on how the RPMs drop.

Every engine type will be different.

If you have the clutch pedal pressed in, the engine RPM will drop naturally according to the rotating mass it has. Holding the pedal longer doesn't mean it will drop any faster, you just have to compensate for it.

-alex

Right, but holding the pedal longer means there is more time for the rpms to drop to match the gear.

My question is that it's possible to have the engine rpm drop faster via clutch engagement => quicker shift. Is this bad for the engine, or just wears the clutch?

[radroach]

Someone might be able to answer with a more accurate answer, I'd say it's more your engine rpms being forced back to whatever the next gearing speed is. If its just a couple hundred rpms then it's not going to matter anyway.

Just shift normally and don't overthink it, eventually you'll get good. Waiting for the rpms to fall before the next gear would develop a bad habit imo. Instead, I just let out the clutch a little slower and let it dampen the difference in engine rpms.

[churchx]

more time clutch held disengaged can be also too much time, if rpms drop below what's needed, and then you won't get your better shift. It needs to be just enough, for rpms to match ones that should be at set speed at specific target gear. Otherwise you just put all that work on synchros to equalise speeds, if too much rpms, then slowing down, if dropped too low, to sped up.
Also i wouldn't pursue quickest possible gear switch as goal. But i would pursue learning rev matching to lessen wear and lessen getting car balance out of whack if/when you release clutch pedal with mismatched engine rpm. You won't get much out of small portion of second less from forced gear switch. You will gain from not upsetting car balance/loosing grip/speed/worsening control with well rev-matched shifts.
RPM drops at somewhat same speed. There is inertia in rotational mass and then there are friction forces, force of continuously compressing air in cylinders, forces needed to drive pump/generator/AC and alikes. You can quicken rpm drop with lessening rotational mass, for example - fitting lightweight flywheel. I'd just leave it alone and simply would spend more time behind wheel to getting used to whatever you have, to hone heal & toe skills, to learn by instincts how long and how much throttle needs to be blipped by repeating it again and again.

[cat94]

Originally Posted by radroach

... Instead, I just let out the clutch a little slower and let it dampen the difference in engine rpms.

That's actually a pretty good description of what I'm doing.

Originally Posted by churchx

...It needs to be just enough, for rpms to match ones that should be at set speed at specific target gear. Otherwise you just put all that work on synchros to equalise speeds, if too much rpms, then slowing down, if dropped too low, to sped up...

Wouldn't this wear the clutch rather than the synchros?

Oddly, I'm more comfortable rev matching/heel toe than shifting at redline. Probably because there are more opportunities on the street to brake for turns, compared to WOT pulls.

[mav1178]

Originally Posted by cat94

Right, but holding the pedal longer means there is more time for the rpms to drop to match the gear.

My question is that it's possible to have the engine rpm drop faster via clutch engagement => quicker shift. Is this bad for the engine, or just wears the clutch?

I did not modify the clutch or shifter assembly in my BRZ and I had no problems shifting quickly/rowing through gears at the track. Ran close to 30 events in 3 years with the car... so based on what you wrote, I suggest you think of ways of modifying your shifting habits.

[cat94]

Originally Posted by mav1178

I did not modify the clutch or shifter assembly in my BRZ and I had no problems shifting quickly/rowing through gears at the track. Ran close to 30 events in 3 years with the car... so based on what you wrote, I suggest you think of ways of modifying your shifting habits.

I wasn't looking to modify anything, just looking to get some information so that I can figure out what I'm doing incorrectly and fix it.

The way I presented the topic seems to have been misunderstood, and I'm regretting now this thread altogether.

Entirely my fault. Thanks for taking the time to respond.

[D_Thissen]

Don't over think it.

[mav1178]

Originally Posted by cat94

I wasn't looking to modify anything, just looking to get some information so that I can figure out what I'm doing incorrectly and fix it.

The way I presented the topic seems to have been misunderstood, and I'm regretting now this thread altogether.

Entirely my fault. Thanks for taking the time to respond.

I brought up the modifying aspect because the engine RPMs will only drop at a certain rate. Holding the clutch longer will not change how the RPMs drop. What will change is if you are in a lower gear and you purposely let the clutch out earlier, so the difference in input shaft speed (engine speed) vs your gear speed (whatever gear you are in) will cause the two to suddenly match speeds, resulting in the jerking feeling you are writing about.

If you change your rotating mass by way of clutch, flywheel, or something else, then your engine RPMs will drop faster or slower depending on how much inertia you have in the rotating assembly.

I suggest you go look at videos of guys driving their cars at the track, to get an idea of how you can drive smoothly by simply changing your driving style.

-alex

[504]

I'll translate

Cat94 has observed that rpms drop quicker when he releases the clutch slowly which allows him to shift quicker but is worried that this might cause wear on the clutch.

He then moves on to ask if he should keep his clutch FULLY depressed for longer between shifts to reduce the slip time,



The clutch is designed to slip, that's its purpose. I wouldn't stress about the up-shift slip unless you're putting excessive throttle in it or holding the clutch too long

hope that helps

[cat94]

Originally Posted by 504

I'll translate

Cat94 has observed that rpms drop quicker when he releases the clutch slowly which allows him to shift quicker but is worried that this might cause wear on the clutch.

He then moves on to ask if he should keep his clutch FULLY depressed for longer between shifts to reduce the slip time,



The clutch is designed to slip, that's its purpose. I wouldn't stress about the up-shift slip unless you're putting excessive throttle in it or holding the clutch too long

hope that helps

Thanks, that's pretty much spot on.