Revving issue during upshifts

[urbo73]

I guess it must be rev-"hang" Civic style! I've been driving manuals for 20+ years, and I've not seen this behavior on any of my prior cars. I've had it "hang" in the traditional sense (not go up as I said - just take a bit for revs to go down) on two cars, but not this "blip". It's strange because it only happens in 5-6. Oh well. I can get around it by lifting earlier, shifting slower, etc. Or just deal with it. It's not a big thing, just something that seemed quite odd to me.

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[TypeRD]

No my friend - rev hang results in rpm flair as the engine ecu is still injecting fuel when you've lifted off the throttle!

Yep, rev hang is an intentional “feature” due to emissions regulations. My ‘09 Si had it ; 8th gen Si’s were actually quite notorious for it and I got used to it. Check out this article.
https://www.carthrottle.com/post/rev-hang-explained-and-why-petrolheads-hate-it/

 

[urbo73]

Yep, rev hang is an intentional “feature” due to emissions regulations. My ‘09 Si had it ; 8th gen Si’s were actually quite notorious for it and I got used to it. Check out this article.
https://www.carthrottle.com/post/rev-hang-explained-and-why-petrolheads-hate-it/

"In extreme cases the engine speed will even rise slightly when the engine and transmission are disengaged."

I guess my 5-6 is an extreme case

TBH, the best cure for the rev-hang is the rev-match, as it will match rev even on the upshift to not jerk if you upshift too fast before the revs drop. When I do the 5-6 with rev-match ON, it's audible (the revving up I mention) but the shift is smooth even if very fast. With rev-match OFF, it's the same, but I have to shift slower to wait for RPM to drop properly. So leaving rev-match ON actually helps you upshift shift faster/smoother in this car.

 

[TypeRD]

Shifting from 5-6 is a pretty casual affair (for me) the vast majority of the time. I’m already up to the speed I want to be at in 5th. 6th is overdrive/ cruising gear. I doubt I’d even notice rev hang from 5-6 except maybe if I’m racing.

 

[tezzasaurusrex]

It can happen when upshifting between any gear as it is a result of the ecu continuing to inject fuel upon the release of throttle to cool down the combustion chamber (reducing NOx).

Try accelerating hard (WOT) in 2nd or 3rd gear but dont take it all the way to redline - just to around 5500-6000rpm - and release the throttle quickly without touching the clutch pedal. You will notice that the vehicle actually continues to accelerate for a split second after you've released the throttle which is where this rev-hang phenomenon takes place...

Now if one was to disengage the clutch during this moment - the rpm will flair upwards.

Literally happens in every modern car - manual or automatic. Its just less noticable in auto's cause the fluid friction in the torque converter takes up the rpm flair and you're never completely disengaging the transmission from the engine.

 

[CaryH]

Huh? I said 5-6. Not sure what you're talking about here. And BTW, to answer your own question, you can always upshift from 2-5 or 3-5. Think of accelerating hard onto the highway in 2nd or 3d, at high RPM, and you know you're at the speed where 5th or even 6th is fine to upshift to. Basic stuff really..

Wow I feel sorry for the fl5.....no where that u drive that u need to upshifit pal..unless your using the car for what it was intended to do...people are idoits.

 

[TypeRD]

@CaryH Your last 2 posts are really hard to follow, man. No need to upshift?

 

[urbo73]

Shifting from 5-6 is a pretty casual affair (for me) the vast majority of the time. I’m already up to the speed I want to be at in 5th. 6th is overdrive/ cruising gear. I doubt I’d even notice rev hang from 5-6 except maybe if I’m racing.

It's usually casual for me too, except in cases on the highway, where I downshift to 5th to pass and then back to 6th again. Pretty common for me.

 

[ScumbagRob]

@CaryH Your last 2 posts are really hard to follow, man. No need to upshift?

Yeah you don't just drive around in 1st everywhere?

 

[TypeRD]

Yeah you don't just drive around in 1st everywhere?

I have been driving manual all wrong for the last 22 years. That ends today.

 

[Icehawk]

This isn't rev hang IMO, my wife's '13 Si has terrible rev hang and it does what it says on the tin - revs drop slowly but there is no rev increase. I've had this happen numerous times with the CTR where the revs jump significantly when upshifting 5 > 6, it really feels more like a rev match miscalculation but urbo said it happens with it off too so /dunno.

When this happens in the CTR it doesn't "rise slowly" as that article describes it is a significant jump and it's immediate. It's what you would expect to happen if you flat foot shifted.

 

[TypeRD]

That’s true. @Icehawk Rev hang shouldn’t make the revs jump up between shifts. Rev hang, as I’ve experienced, is the revs “hanging” and not dropping right after clutch disengagement.

 

[tezzasaurusrex]

This isn't rev hang IMO, my wife's '13 Si has terrible rev hang and it does what it says on the tin - revs drop slowly but there is no rev increase. I've had this happen numerous times with the CTR where the revs jump significantly when upshifting 5 > 6, it really feels more like a rev match miscalculation but urbo said it happens with it off too so /dunno.

When this happens in the CTR it doesn't "rise slowly" as that article describes it is a significant jump and it's immediate. It's what you would expect to happen if you flat foot shifted.

That’s true. @Icehawk Rev hang shouldn’t make the revs jump up between shifts. Rev hang, as I’ve experienced, is the revs “hanging” and not dropping right after clutch disengagement.

Guys.. don't read into the terminology too deeply. Rev-hang is simply a term coined to interpret the condition of the engine rpm's not dropping as quickly as one would expect when releasing the throttle. The reason this happens is due to the engine ECU continuing to inject fuel to cool down the combustion chamber despite the ECU no longer reading a positive acceleration position command - this is the KEY cause and effect.

This phenomenon was commonly mistaken to be caused by modern fly-by-wire throttle systems which in the Type R world basically begun from the FN2R onwards. People would suspect that the throttle closure is being delayed as it takes too long for the electrical signal from the APS (acceleration pedal/position sensor) to be interpreted by the ECU and then command the throttle butterfly to close. This has been proven to not be the case as it can be mapped out via ECU tuning - which can achieve a cable throttle feel.

Other than flat shifting (continual throttle input between shifts), the rev-hang condition is the ONLY cause for the rpm's to flair up when you disengage the clutch (push the clutch pedal down) between shifts.

The following graphs plots RPM (red line magnitude over y-axis) over time (x-axis). You can see the red arrow represents the flair-up in rpm AFTER the throttle is closed - this happens on both graphs but of much greater duration on the former. The two graphs represent before and after rev-hang disabling. The blue arrow on the first graph showing the TPS command delays the throttle butterfly from completely closing despite the pedal being fully released (purple line).

Before:

After:

{QUOTE - K Tuner -

The blue arrow points out that the TPS and Throttle Plate take an almost identical path after the throttle has been released. With clutch engagement there is no longer a kick upward or hanging of the RPM beyond normal inertia. It is an immediate kick into high vacuum which slows things down and with this higher vacuum this will decelerate the vehicle faster as well.

As expected with higher vacuum it does make the transition into deceleration more aggressive and going from deceleration back into normal operation more aggressive as well. This can be adjusted with a new quick adjustment, Throttle Padding.}


Supporting evidence: http://www.ktuner.com/KTunerHelp/disable_rev_hang.htm

 

[urbo73]

Yeah, I get that. I'm just saying I've never experienced it like that in my prior non-Honda manual cars.

 

[Icehawk]

Agreed, it's bizarre behavior IMO unlike anything I've experienced before - thumbs down Honda.

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