School me on Rev hang

Snail

Banned
So Rev hang is the new norm in order to reduce tailpipe emissions by ensuring combustion is complete in a controlled reduction in engine speed. It dulls the whole driving experience when paired with a manual trans (which is the only way to go) and often results in grinding 2nd gear due the the large ratio difference between 1st and an engine speed too fast for smooth synchromesh engagement.

It's a pain in the ass, but it's better for the environment so...yeah. We either live with it or we tune it out at the detriment to greater tailpipe emissions.

...but I had a couple of questions. Why is rev hang much worse on certain engines, and how on earth do quick-shifting automatics reduce engine speed so quickly and pass emissions? I'm not even talking about the farting autos out there (which I assume fart to burn off NOx); just the regular torque converters fitted to normal or higher performing engines. Many of these automatics shift gears in a small fraction of the time it takes from physically shifting from 1st to 2nd in a manual and yet we're grinding gears because of emissions. Is there a way to have an engine behave like it was bolted to an auto with its engine speed agility + emissions friendliness? There's something I'm not understanding here.

Thanks
 

Enjoy.

Manufacturer will put in more effort to tune out rev-hang based on price-point/market.
Example: The Si has much worse rev hang than the Type R.
 
Didn't we just have this thread last month or two months ago?

Sent from my EML-L09 using Tapatalk
 
Didn't we just have this thread last month or two months ago?

Sent from my EML-L09 using Tapatalk

sorry, didn't remember seeing it and didn't bother searching; a mod can merge the threads if they'd like I'd be happy with that.
 
My guess:
Avec les transmissions auto, le changement de vitesse est synchronisé avec le régime moteur. Lorsque le moteur approche le shift point (ou quand tu enclenche la vitesse supérieur), le moteur doit coupé l'admission en essence un brin avant de changé de rapport brûlant l'essence "en trop".

Pour le gear grinding en 2e... j'ai jamais eu ça avec mes voiture...
 
So Rev hang is the new norm in order to reduce tailpipe emissions by ensuring combustion is complete in a controlled reduction in engine speed. It dulls the whole driving experience when paired with a manual trans (which is the only way to go) and often results in grinding 2nd gear due the the large ratio difference between 1st and an engine speed too fast for smooth synchromesh engagement.

It's a pain in the ass, but it's better for the environment so...yeah. We either live with it or we tune it out at the detriment to greater tailpipe emissions.

...but I had a couple of questions. Why is rev hang much worse on certain engines, and how on earth do quick-shifting automatics reduce engine speed so quickly and pass emissions? I'm not even talking about the farting autos out there (which I assume fart to burn off NOx); just the regular torque converters fitted to normal or higher performing engines. Many of these automatics shift gears in a small fraction of the time it takes from physically shifting from 1st to 2nd in a manual and yet we're grinding gears because of emissions. Is there a way to have an engine behave like it was bolted to an auto with its engine speed agility + emissions friendliness? There's something I'm not understanding here.

Thanks

Unlike on a manual trans car, the automatic car's throttle doesn't have to momentarily close on the upshifts. IE it could remain WOT. The transmission deals with the engine speed variations on it's own through the torque converter and there are no significant changes in air/fuel ratio to contend with.

That's my take on it anyways.

Rev Hang shouldn't have any impact on gears grinding. That's probably more to do with clutch delay valves or improper user input.
 
Unlike on a manual trans car, the automatic car's throttle doesn't have to momentarily close on the upshifts. IE it could remain WOT. The transmission deals with the engine speed variations on it's own through the torque converter and there are no significant changes in air/fuel ratio to contend with.

That's my take on it anyways.

Rev Hang shouldn't have any impact on gears grinding. That's probably more to do with clutch delay valves or improper user input.
Someone got upset with me once for removing a clutch delay valve during a brake fluid flush (also includes clutch bleed) lol

Sent from my EML-L09 using Tapatalk
 

oh wow only a couple of months ago. lol

thanks I'll try to be more diligent next time

J'ai jamais vu ca grinder une gear a cause du rev hang. What ?

t'as absolument raison; c'est moi qui est mélangé.

Unlike on a manual trans car, the automatic car's throttle doesn't have to momentarily close on the upshifts. IE it could remain WOT. The transmission deals with the engine speed variations on it's own through the torque converter and there are no significant changes in air/fuel ratio to contend with.

hmmm. That's interesting. I would still think there are unburned gasses to be dealt with but yeah that makes sense.

Rev Hang shouldn't have any impact on gears grinding. That's probably more to do with clutch delay valves or improper user input.

You're 100% right; I do get gear grinds (clutch pedal 100% depressed) but I assume it probably the wide ratio spread and the synchromesh not doing its job. This happens at any temp; not just startup. Why do older manuals not seem to have this issue but many recent manuals do? It shouldn't have anything to do with a clutch delay valve either because engine and trans are completely disconnected when the grind happens. Anyhow, a little off topic.

My guess:
Avec les transmissions auto, le changement de vitesse est synchronisé avec le régime moteur. Lorsque le moteur approche le shift point (ou quand tu enclenche la vitesse supérieur), le moteur doit coupé l'admission en essence un brin avant de changé de rapport brûlant l'essence "en trop".

Pour le gear grinding en 2e... j'ai jamais eu ça avec mes voiture...

j'entend surtout parler de grind avec des transmissions 6 vitesses (récentes) et presque jamais avec des 5 vitesses (à moins qu'elle a beaucoup d'usure). Le Civic mk10 avec le K20 à mon cousin fait ça, les Type R ont beaucoup de problèmes, les Sportwagens 6MT AWD. Mais effectivement ça n'a rien à avoir avec le rev hang. Peut-être plus de momentum interne? Je ne sais pas.
 
I have appalling rev-hang on the Saabaru. 2.0H Turbo WRX engine tuned with full STi 3" exhaust line and no cats. It's ridiculous and I find it dangerous a bit because the tune removes the cut-off (if there is one I haven't found it yet... lol) and shifting high still gives a 200-400RPM rev boost/hang after releasing the gas pedal.

But bloody hell the Saabaru is fun to drive...
 
I have appalling rev-hang on the Saabaru. 2.0H Turbo WRX engine tuned with full STi 3" exhaust line and no cats. It's ridiculous and I find it dangerous a bit because the tune removes the cut-off (if there is one I haven't found it yet... lol) and shifting high still gives a 200-400RPM rev boost/hang after releasing the gas pedal.

But bloody hell the Saabaru is fun to drive...
Be careful with that 2nd gear synchro, I've changed so many of those..
 
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