So about rev hang

invader

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Well
I thought the reason for rev hang was because the throttle doesn't close immediately after you step on the clutch due to emissions purposes? So what would a crank shaft pulley do....
A lighter crankshaft pulley will still help by allowing the rpm's to go down more quickly once the throttle valve does shut... We'll see how much of an improvement it yields in good time.





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dmitri

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Is it really that big of a deal? I don't remember rev hang specifically mentioned/complained about in any of the reviews -- although I probably missed something, plus I haven't watched all of them to the last minute... If I did miss something, please point me to the review that talks about it? TIA
 

pukemon

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Absolutely correct. You could have a crankshaft made out of toilet paper tube and a flywheel made out of paper plate and you'll still have rev-hang as long as the ECU prevents the throttle from snapping closed once you let off the accelerator in order to control emissions, which is the cause of the type of rev-hang in the context of the Civic.

Would you happen to know if rev hang helps with rev matching? Curious since I am not the greatest at it. I learned to drive stick buying a truck and having to drive it home. Actually only learned about rev matching about 5 years ago but was exclusively driving auto at the time. And only learned that not rev matching was bad for manual ~2013. Puts a big smile on my mug now not because of the smooth transition but because of the awesome acceleration.
 

pukemon

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Is it really that big of a deal? I don't remember rev hang specifically mentioned/complained about in any of the reviews -- although I probably missed something, plus I haven't watched all of them to the last minute... If I did miss something, please point me to the review that talks about it? TIA
Highly doubt reviewers will focus on this for many reasons. It's becoming more common for emissions and because of the negativity it implies and you most reviewers don't want to go that deep because they have access to pre samples of a popular enthusiast vehicle. Honestly, for the most part it doesn't bother me except for when I want to WOT. but I can understand why many don't want it there. On the plus side we do know for sure that tuners can tune better throttle response. Don't know why manufacturers would add latency in their sporty models. You're getting the sporty model for the fun factor. Why add something that takes away from that?
 

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Would you happen to know if rev hang helps with rev matching?
Rev hang and rev matching are opposite terms.

Rev hang is when the RPMs drop slowly after releasing your foot from the accelerator during an upshift. This can make the shift a bit jerky since the engine is speed is faster than appropriate for the next higher gear when you release the clutch. It also places a slight amount of additional wear on the clutch. The most offensive and pronounced form of rev hang is caused by emissions controls, but it can be caused by a heavy flywheel to a lesser degree.

Rev matching is when you increase the engine speed during a downshift, so that the engine speed is appropriate for the next lower gear when you release the clutch. Matching the engine speed to the next lower gear results in a smoother shift and less clutch wear.

Rev hang is bad - you don't want it.
Rev matching is good - you want it.

Some cars have automatic rev matching that automatically raises the engine speed for you during the transition to the next lower gear. Most vehicles - including the Si - do not, so you have to do it manually.

The answer to you question is: No. Rev hang makes rev matching on upshifts difficult to impossible unless you shift very slowly and wait until the engine speed falls.
 

pukemon

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OK. Thanks for the clarification. I was under impression that rev hang is/was revs basically stay or slowly drop. I'm assuming you're imyimg they drop more than I thought. Probably why I sucked so bad at rev matching in my SI's. I am getting much better with my GTI. I really haven't paid attention if there is hang or not. I just know I need to work on my timing better to get that badass smooth acceleration. I am still adjusting to the taller gears on the GTI. Different shifts definitely. I shifted slower on my SI when I wanted to downshift smoothly. Thanks for the details.
 

maddmatt02

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OK. Thanks for the clarification. I was under impression that rev hang is/was revs basically stay or slowly drop. I'm assuming you're imyimg they drop more than I thought. Probably why I sucked so bad at rev matching in my SI's. I am getting much better with my GTI. I really haven't paid attention if there is hang or not. I just know I need to work on my timing better to get that badass smooth acceleration. I am still adjusting to the taller gears on the GTI. Different shifts definitely. I shifted slower on my SI when I wanted to downshift smoothly. Thanks for the details.
No, you're right. Rev hang is the revs "hanging" or staying where they are and dropping slowly. Not that they do more than you thought. The rev hang on this thing doesn't bother me accelerating under WOT, accelerating during easy cruising (because lower revs/throttle position it isn't near as bad) or when rev matching downshifts during spirited driving. Only time it really annoys me is when you shoot out into a gap in traffic so you don't have to wait for 100 cars but there is a light right after so you were wot in 1st to 4k then you are now sitting in a line of stopped cars at a light and you are sitting there foot off the gas but your cars still at 4 grand dropping slowly.
 

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Rev matching is when you increase the engine speed during a downshift
Doesn't rev matching technically go both ways? You gotta give it some gas even when you're upshifting, especially if you took the previous gear to a high RPM. Unless, of course, you just pop the clutch at exactly the right RPM when the needle drops to it :p
 

ne0guri

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Honestly I don't even think I noticed the rev hang while I was test driving. I'll probably notice it more once I get mine, but I think it's minimal. Does shifting earlier in the band decrease the rev hang compared to shifting at red line?
 

maddmatt02

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Honestly I don't even think I noticed the rev hang while I was test driving. I'll probably notice it more once I get mine, but I think it's minimal. Does shifting earlier in the band decrease the rev hang compared to shifting at red line?
Yeah higher revs/more throttle it can be pretty bad... A little long winded but you can see the proof in my video of how bad it can be.
 

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