2 ms·

The rev hang or skip shift isn't about unburnt hydrocarbons, it's about efficiency standards. It's a different problem - emissions efficiency is one thing and e

The rev hang or skip shift isn't about unburnt hydrocarbons, it's about efficiency standards. It's a different problem - emissions efficiency is one thing and emission compound/type restrictions are another.

jeffbee 2y ago
Incorrect. The engine speed hold is there to optimize mixture while the engine decelerates, instead of just slamming the throttle shut. Depending on where the fuel is injected, cutting off fuel and air instantly leads to either too much fuel or too much air in the cylinders. The electronic rev hang corrects this to reduce NOx and unburnt fuel. It does not improve fuel efficiency.
- giantg2 2y ago
  I guess if it's not DI, but what new cars aren't DI these days? If you have a DI engine doing rev hold, it's not about mixture ratio.
  - jeffbee 2y ago
    The difference between DI and port injection is only which thing is escaping the catalytic converter. With port injection the engine is rich after lifting off the throttle, and hydrocarbons escape. With direct injection the engine leans out, and NOx escapes. In both cases the rev hang exists to keep the emissions system in its effective air/fuel ratio range. Every hanging MT car I ever owned was DI.
    - giantg2 2y ago
      That's very odd. DI should only be firing a full shot injector as the air is coming in, or already came in. It really shouldn't lean out. If your DI car had rev hang, it's for other reasons. https://www.roadandtrack.com/new-cars/car-technology/a32958665/the-annoying-rev-hang-in-modern-manual-cars-is-there-for-a-reason/ https://www.roadandtrack.com/new-cars/car-technology/a329586...
      - jeffbee 2y ago
        We were discussing the 2015 WRX after all, it is port injected. The guy who wants to delete the rev hang from his VA WRX is advocating to blowing unburnt gas right out of the tailpipe, like a psycho.
        giantg2 2y ago
        Not true. Without rev hold it actually can go lean. The main reason for rev hold is to reduce oil vaporization. https://www.carthrottle.com/news/what-rev-hang-and-why-do-petrolheads-hate-it https://www.carthrottle.com/news/what-rev-hang-and-why-do-pe...

jeffbee 2y ago

Incorrect. The engine speed hold is there to optimize mixture while the engine decelerates, instead of just slamming the throttle shut. Depending on where the fuel is injected, cutting off fuel and air instantly leads to either too much fuel or too much air in the cylinders. The electronic rev hang corrects this to reduce NOx and unburnt fuel. It does not improve fuel efficiency.

giantg2 2y ago
I guess if it's not DI, but what new cars aren't DI these days? If you have a DI engine doing rev hold, it's not about mixture ratio.
- jeffbee 2y ago
  The difference between DI and port injection is only which thing is escaping the catalytic converter. With port injection the engine is rich after lifting off the throttle, and hydrocarbons escape. With direct injection the engine leans out, and NOx escapes. In both cases the rev hang exists to keep the emissions system in its effective air/fuel ratio range. Every hanging MT car I ever owned was DI.
  - giantg2 2y ago
    That's very odd. DI should only be firing a full shot injector as the air is coming in, or already came in. It really shouldn't lean out. If your DI car had rev hang, it's for other reasons. https://www.roadandtrack.com/new-cars/car-technology/a32958665/the-annoying-rev-hang-in-modern-manual-cars-is-there-for-a-reason/ https://www.roadandtrack.com/new-cars/car-technology/a329586...
    - jeffbee 2y ago
      We were discussing the 2015 WRX after all, it is port injected. The guy who wants to delete the rev hang from his VA WRX is advocating to blowing unburnt gas right out of the tailpipe, like a psycho.
      - giantg2 2y ago
        Not true. Without rev hold it actually can go lean. The main reason for rev hold is to reduce oil vaporization. https://www.carthrottle.com/news/what-rev-hang-and-why-do-petrolheads-hate-it https://www.carthrottle.com/news/what-rev-hang-and-why-do-pe...