The Big Problem With Modern Manual Transmissions - Rev Hang

Hello everyone and welcome! Today is my YouTube Birthday, and Engineering Explained is officially 9 years old! Thanks for joining in, I really appreciate it! As for the video, I have wanted to make a video on rev hang for a long time, but wanted to make sure I had it right. I've discussed this with numerous powertrain engineers, read through academic literature that relates to the subject, and boiled it all down in this video. Quite excited about this one, hope you enjoy!!

It doesn't matter how hard or soft I shift, there's still a jerk in the driver's seat.

The answer to any modern car problem: “it’s to control emissions”

I surprisingly understood everything. And I'm a dentist. As they say.. if you can't explain it to a ten year old, you don't probably understand it yourself.

You failed to mention that cable driven throttles usually have some mechanical non linearity built into them. If you look at the part the cable goes around, you will notice it's oval. Otherwise good video. I have just converted my car to drive by wire with an aftermarket ecu, and can confirm no rev hang, it's all in the tuning, as you say, it's a deliberate thing built into Oem cars, not a limitation of the technology in general. Electronic throttle, when you can set it up yourself is awesome.

I had a throttle body freeze up while going down a hill in winter, now THAT was some rev hang...

good thing that my throttle is cable operated then again my scooter doesnt have any gears...

Idk why I'm watching this, my car is carbed.😂

I would love to see a modern engine with today's materials and tolerances ran with all mechanical/carb then converted to all electronic and see the actual mpg differences and emissions.

I’ve seen mechanical throttle bodies with a “cammed” lever so that the airflow increase is more proportional to input at the accelerator pedal.

I don't know why I'm watching this, I can't even afford to fix the suspension in my 1993 Audi 80. Edit: As of last month, sadly she is deceased, had a crash at a car meet, front ended up totalled, wrecked intercooler. Spent some good years with her, Rest in Peace.

You totally nailed it. I used to do emissions testing at Ford back in the 80s when cars were transitioning to 3-way catalyst necessitating, prior to EFI, feedback carburetors to attempt to control to stoich AFR. But with carbs there were all sorts of AFR excursions during transient tip-in tip-out modes, and on a tip-out, all the wet fuel clinging inside the intake manifold suddenly vaporized and sent this huge HC spike which blew through the oxidation catalyst. Remember dashpots on the carburetor? This slowed the closing of the throttle to it's idle setting to attenuate the fuel vaporization rate, the first form of rev-hang. But even on my 93 Mustang with EFI and cable actuated throttle, it has the annoying rev-hang, but this is the idle speed control valve acting, like drive-by-wire throttle, to bypass air to achieve the same emission control goal. Just some retro perspective to ponder. The guy below said it succinctly, 'it's to control emissions'. Today, there are regulations to be met, vastly more stringent than the 80s. Give credit to the engineers that achieve them and build engines like the Coyote, LT6 and Hellcat.

I would love to see you take a shot at tuning a car. With all of your knowledge, that may be interesting to watch.

4:07 This engine is super clean.

Literally couldn't be a more intuitive and thorough explanation. That was an amazing video.

My dad has a 19 Subaru Impreza, It's the first car I've driven to have so much rev hang that I needed to learn how to drive "around" the hang. I thought it was just a crazy heavy flywheel! Great video! I'll have to check it out later lol

Me: presses pedal to 25% hoping for 50% air Gets 25% air. :O

Every video I see like this just gives me another reason to hang on to my 90's cars.

I had a carbureted vehicle with a vacuum dashpot actuator to accomplish the delayed throttle butterfly closure, too. That general system was not exactly uncommon toward the end of the days of carburetors on on-road automobiles. It’s also interesting the discussion about how one could use electronic throttle control to make the relationship between pedal position and delivered power more linear. Why I think it’s interesting is that we don’t see that actually done. What we see instead is that electronic throttles are programmed to provide ridiculously overdone tip-in, because that makes people think their car is really fast.

"Can remove driving jerk..." shows himself driving