Hello everyone and welcome! Today is my NOlocal 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!!

Jonathan Reed

Måned siden

Wow! Every time I watch EE, I learn more than had I read an auto magazine. It’s spectacular. I hope you continue to grow.

Brian ,Sweeney

2 måneder siden

What if when pressing in the clutch the revs don't just hang but slightly jump up?

Mitchoforza 0

2 måneder siden

Happy belated NOlocal birthday man

Rusty

3 måneder siden

Given what you have explained in this video I would love to know your technical views on the "sprint booster" product which is sold to improve throttle response and rev hang

doktermobiel

4 måneder siden

Congrats on the 9 year’s anniversary and thanks for providing us with so much insightful content

I’ve been learning on a modern manual car and I was wondering why my shifts were still jerky until I realized I wasn’t waiting for the revs to slowly go back down.

My mustang 2020 Has it and i hate it.

That's why I need to floor the accelerator all the time on electronic throttle. I expect with 25% of acceleration that 50% of torque.

Speaking about rev hang, this is the reason why I have to press my economy car's throttle even harder when I want to do heel-and-toe and rev matching techniques. It's obviously creating attention to other drivers since they hear the loud throttle blips, but at least I'll be able do smoother downshifting lol

Regarding the non-linearity of mechanical throttles, I have a feeling that something's not quite right - particularly the second graph, the torque vs. throttle. I understand that as you press the pedal harder and harder, you feel that the gain in torque is increasingly lower. That makes perfect sense. What doesn't seem to make sense to me is the red portion of the graph. I don't think the torque distribution actually looks like that. You may FEEL that it does when you push the pedal gradually, but I don't think it actually IS like that. What if you don't press the pedal gradually? What if you depress it directly to 50% of its travel? Won't you get 50% of the available torque? I think you will.

I hate rev hang!

So, are there any modern manual cars that don't have rev hang? Or is there a way to disable rev hang in modern cars so the driver can actually have control of the car? See, I thought the whole point of even having a manual car nowadays is to be in control of the vehicle and have fun, but with rev hang and synchrosizers in the transmission control is taken away from the driver 😢

now that we know what it is, how do we turn it off?

This dude is so clear and concise on difficult to describe subjects. I love it

Always great content, I own a 20 civic si and need to understand all its possible quirks on a educated level

The big problem with modern manuals is companies will no longer put the time and money into making them great again. They are just throw in options, to say you offer a manual, but you won't take the time to do them right. Big problem!

Woke AF

22 dager siden

Stick with Mazda and Porsche

القائم بأمر الله

22 dager siden

whats the best modern manual car do you think ?

Sooo..... Light weight fly wheels will cause more rev-hang? not sure what he meant by non/not heavy flywheels at 1:09

Problem is people do not care enough when driving. Everyone in the car scene knows you should not just gun it for best performance.

Why didn't he highlight the solution to this in most cases? Learn how to double clutch! The computer will pick up the neutral shift and close the throttle... with clutch systems now a days it's effortless to disengage the flywheel on a stock setup. Saying your leg gets tired doesn't work anymore lol

Mechanical throttle will still give you the best experience and connection with your car thought.

I'll stick to my cable operated throttle body on my stick car. Those benefits for electronic throttle don't appeal to me. My small SUV has the elect. throttle in an automatic which is fine for boat pulling and driving around the city.

The big problem with modern manual gearboxes are American drivers,I think it best if you stay with your Automatics.Problem solved!

It is easy to make the mechanical aperture linear with a spiral cable coupling

I think you can also bypass this with a gas throttle booster (i.e. Sprint Booster)?

So, sounds like the manual transmission is dead, forever. The complex technology needed to master the process requires complete control by a computer. Then, I suppose this leads to the development of "sport" and "touring" transmission settings in some vehicles, to offer different driving experiences.

still manual is the only way i go, you know because the environment :P

Couldn't an aftermarket tuner modify the program of the electronic throttle body to reduce rev hang? You would just be increasing the rate that the ETB tips out (close's) when you let off the throttle. Seems like that could even be added on OEM vehicles as a "sport mode" when crisper throttle response is desired.

I really enjoy your videos. As a car enthusiast, I feel it’s important for me to understand how cars and all their components work. Your videos make that easier for me!

Great, so more clutch wear and earlier failure and replacement. How about the emissions set free by producing more clutches??

Man I like your videos so much, even though I get bored about that part of mathematical calculations you always do.... still, you are a natural great teacher and I admire the energy and quality you put into your content. I will always support you no matter when you get boring. Congrats!

It seems like fuel injection and air sensing need to improve so rev hang doesn’t need to be necessary to reduce emissions

My rev hang is only there up to around 4500 rpm. After that, its not there. With rev hang, you don't shift slower. You just let off the clutch slower. Good for low acceleration consistency. For trying to reduce shift times, just shift above that rpm. More clutch rub at low rpm is nothing. But every car is different.

My 1970 BMW 2002 had a mechanical dash pot that caused the revs to hang. My Honda SI didn’t hang. At all.

Drive by wire systems are senseless. You can rectify mechanical throttle body input-to-flow with cam actuation.

That's why I stick to turbo diesels.

Why does this not impact the DSG?

Give me 10-x over boost & grind some off the synchro then dual plate clutch ~ this defeats my efforts to achieve traffic safety even though manual-cable to the TBI

If you have tip-out rev hang or overshoot during gear shift, that is because of poor calibration or no EMS specific software strategies. I guess that today the majority of the vehicles have automated transmissions and most engineers never have calibrated manual ones. In my time, clutch pedals had a switch or even linear position sensor. Also you do not mention catalyst O2 storage and O2 depletion strategies that can hadle fuel cut-off events to minimize emissions issues during manual gear change. Gear shift behaviour was always a major quality point in most vehicle manufaturer driveability evaluation criteria. I gues this has nowadays relaxed.

OMG YES. This has been a major pain in the ass with my car, first to second gear and the mf would just keep the revs high for 2 seconds. Like, who dafuq thought this was a good idea? Was one of the reasons i sold it early.

that very massive aggresive throttle body. what size is that?80mm?

You're a genius! Thanks for sharing your knowledge.

Good thing my 04 accord still has the manual old cable throttle body lol, any 06/07 accord has an electronic one

Bah, if you are in a sports car manual then emissions come second to driving/shifting experience. You'd still pass an emissions test during inspection because it's not like you are shifting gears during that test. Also electronic throttle bodies suck because when they error your car goes into limp mode and you have almost zero acceleration to get to where you were going.

Well, I reckon you're changing gears and using your clutch incorrectly. Never had a jerk from the car when changing gear.

Super clean 😉

Mine doesn’t have rev hang but it has an electronic throttle body. Maybe it’s more used in turbocharged cars or newer models

Could you not blip the throttle whilst the clutch on the upshift to better match the gear speed to the engine speed?

Well explained. Thank you. I've learn something on my car.

Clutch sensor has eliminated this issue to a big extent. But many cars still have this problem. However, peugeots with Bosch ECU don't have this issue very noticable

The first time I drove a "modern" car with an electronic throttle body I just stalled it the whole time. Muscle memory meant that I was used to using only a small amount of pedal travel when letting out the clutch to pull away. My conclusion? The "ideal" throttle response is whatever throttle response you're used to...

Luckily, most tuners are able to curb this idiotic feautre.

Did you just tell me rev hang was both a symptom and a benefit of electronic throttle bodies? 0:08 says it causes rev hang. 1:15 says that causes the car to jerk during shifting. 5:31 then contradicts the point of this video by saying it reduces shifting jerk. Did I miss something or is this a good spot to stop watching and disregard the video?

I love this channel!

I'd still take the mechanical throttle any day! You can work out how much the throttle will open whereas an electronic throttle could do anything, simple is almost always better...

I drove a mini one where the engine would rev up when you blooper the throttle. You had to press and hold in order to rev match. It was so strange

I think there were some problems in explaining the mechanical throttle here. If you say that from 10 to 20 it opens by 100%, and from 20 to 30 just 50%, that doesn't still mean it opens by smaller amount. I appreciate that the openness of the throttle will not necessarily directly correlate to how much more air flow or torque you get, and that the electronic control for the throttle still gives the advantage of being able to control it more precisely, but your explanation gave the impression that the amount the throttle opens by decreases with each 10 percent, which is just not true. And it's actually opposite because of how circular motion, with which the throttle opens, works. Let's assume that with every 1% of the travel of the throttle pedal the throttle valve itself also turns 1% of its way, so there is no change in how pushing the pedal opens the throttle. Say you can open it to a maximum of 90°, and when it's completely closed, it's at 0° (this of course is not completely realistic, but it's close enough to demonstrate my point), so 1% of opening equals to 0.9 degrees. Let's name the angle of the throttle valve as θ (theta), the maximum cross section area of the throttle at 90° as A and the cross section area at a given angle θ as a. So the area which lets air through is: a = (1 - cos(θ))A At 10% openness we have θ = 10*0.9° = 9°, so a = (1 - cos(9))*A = 0.0123A. So at 10% openness we only actually have 1.23% of the maximum throttle area. At 20%, a = 0,0489A, or 4.89% 30%: a = 0,109A, or 10.9% 40%: a = 0,191A, or 19.1% 50%: a = 0,293A, or 29.3% 60%: a = 0,412A, or 41.2% 70%: a = 0,546A, or 54.6% 80%: a = 0,691A, or 69,1% 90%: a = 0,844A, or 84,4% 100%: a = A, or 100% So we see that pedaling the throttle a little bit opens it by even a smaller bit, but as we open it more, the openness increases by ever bigger amount. So if we could directly correlate air flow and torque to the openness of the throttle valve, the curve you showed would be opposite. I'm not well enough versed in fluid mechanics to know how that goes, so I'm not saying it is like that. My point was to just show that the explanation you gave about throttle opening was very misleading, and it would still be so even if we had a throttle valve that increases the cross section area by equal amount for each percent of throttle pedal pushed.

Does a lighter weight flywheel reduce rev hang?

I get around this by not using the clutch.

You absolutely nailed it when you explain the advantages of electric throttle for the driver feeling part. Thank you so much!

6:20 - i have started the research on car emissions. and they do not provide anything for the outside world. The cloth industry provides the, most emissions. Do not let the big "wanks" lie to people. ALWAYS DO YOUR RESEARCH!

really really detailed explaination... great

mechanical

I HATE REV HANG!

Electronic throttle bodies for life - once you have a mechanical TB that falls off the guide and revs your motor over 8k rpm while trying to come to a stop in traffic and end up rear ending someone, you don’t ever go that route again. It’s something that never should’ve happened but now I can clearly see happening with any mechanical setup.

idk why but this guy reminds m e of David Bowie

I suppose that’s why some cars have active rev match

Subaru EA82 engines (and others, including my old 6-port 13B) mated to manual transmissions used a dashpot to prevent sudden throttle closure and thus reduce emissions. The dashpot was there to slow throttle closure, engaging around the 10% throttle mark and slowly allowing it to close to 0. There was no noticeable rev hang because the dashpot didn't engage until the throttle was nearly closed and if it took you that long to shift, you were probably going to have a choppy gearchange or come to a stop anyway.

Buy a lighter fly wheel works wonders

Better driving skills allows rev hang to be an advantage. Drive better......

all in the name of innovation.

My car haves a mechanical throttle body, after like a 70% pressed accelerator I really can't feel a difference between flooring it... Edit: it's an old chevrolet celta (never sold in the US), a 1.4L 103HP 1900 pound little hatchback!

They do it to avoid warranty claims for ruined catalytic convertors from going out of fuel air ratio limits. Catalytic convertors require the engine to burn rich to avoid NOX, thus selling more fuel to the Rockerfellers et all, in addition to the expensive convertors, so its win win for the oligarchs forcing us to buy from the company story by goverment force, all the while believing we are saving the enviroment. Water injection is used in power plants/aviation engines throughout history to to the same thing with better fuel efficiency.

I just thought my Compass was broken with how much the rev hang is.

TLDR: Engineers solving problems more easily solved with a simpler machine (electric motor)

But how much of a difference in emissions does that fraction of a second when the throttle body closes really make when you consider that the cat is already most likely up to temp? On top of that, how much of the emissions improvement is lost if the driver jerks the RPM's down on every shift?

Ford had Mechanical TBs designed to induce rev hang in the early 2000s. Supposedly, this was to burn unused fuel under engine deceleration, but I think it was just GARBAGE. I've been dealing with (yes, dealing with) mk1 focuses my whole car-bearing life and all I can say is that the zetec twin cam revs like a bike motor with a proper TB. EPA testing sucks, and I wish mfrs didn't have to tack on stuff like the early '00s fords had (these awful TBs) to create better data. My roommate at the time I had my last focus had to remedy the same problem on his v8 mustang. Come on, Ford! EDIT: The two vehicles I mentioned also had 10 ton flywheels. At the point these had reached, the flywhel DID cause rev hang.

Yeah, e-throttles COULD be more linear, but they AREN'T, because engineers deliberately make the throttle over-sensitive to small amounts of pedal travel, to trick the "double digit IQ" folks into thinking the engine is more powerful than it is.

For what it's worth, Ford was doing this on the 2.0L Capri - in 1974! There was an extra passage with a vacuum operated valve in the carburetor. When you let off the throttle, the carb vacuum would increase quickly and that would open the valve, dumping gas into the venturi. Crude but (perhaps?) effective.

Electric / thermal engine combo migh fix it

That rev-hang is programmed in by car makers to lower emissions , I learned this from a STAR cert. smog guy.

I have driven mechanical throttles that also suffer from the Rev hang. It's not as bad but it's there. A few I've had use the idle control bypass valve to eliminate sudden closed throttle decel. Reason I was given is cutting down on emissions. It wasn't super noticeable until I had the idle valve fail it it was like shifting a carburetor car. Let off and instant decel or rev down

I have a DCAT in my 20 Turbo Kia Soul. every time I drive it I think the engine is gonna blow up because of rev hang. The auto start stop is enough control. if there is a way to fix the broken throttle response issue AKA rev hang I'll gladly do the upgrade. I know when I want to go and when I don't. The Dual Clutch AT is great and I love the car just not the broken throttle issue

Just giving people an excuse for their poor shifting

4:08 I agree with the statement. That is the cleanest engine bay I have ever seen

what about carbureted engines?

I absolutely hated driving Detroit Diesels series 60 !! You had to use the jakes , and burp it up hills! Cummins was the best!

I've only ever noticed her opening up when I go "tip-in." Ba dum tss

I thought rev hang was a Toyota thing, all the modern stick shifts I’ve owned were Toyota cars or trucks. I guess i was wrong. Thanks for sharing.

lol, SUPER CLEAN!

The left throttle body he's holding is enough for 1000hp+ application.

I see your problem and it's only 20 seconds into the video. Shifting at 3,000rpm. Of course the car is going to want to keep the rpm up - it wants to play and is being a naughty little boy. Take it to 6,000rpm and show how different things are. What is probably happening is that the engineers have decided that most people take about 1/2 second to change gear. The difference in rpm between the two gears may be 800rpm, so the engineers make the rpms drop 800rpm in 1/2 second. They also decide, based upon lap times and other data, that manual transmission are by far slower than a semi-automatic box, so they design the manual transmissions for wannabe racers on public roads.

When I drive my brother's car (the only that has fuel injection, let alone electronic throttle) I just do the right foot move around one second before switching gears, so when I hit the clutch the throttle is already closing, and when I release clutch with the new gear it's already opening again.

Interesting how much stuff goes into airflow/mixture control. Run a 54 Chevy truck daily with a Weber 2 Barrel as economic/performance upgrade on the old carter single barrel. Throttle response is extremely smooth. Its eager to rev to its max. Revs drop...what you could call the natural rate. The engine runs a rich idle, lean low, rich middle and rich upper. The two barrel flows more air in the high bracket than the engine can use. The setup is 1000 parts less than a modern cars fuel/air management. Best...no clicks, whirrs or clacks like in a modern car, no surging, no hanging. If you have that - you dont want to drive a modern car - its way better.

I don't drive manual, but does rev-hang mean that one should adjust one's clutch timing? That is, waiting a bit longer until revs fall to the proper levels before engaging it rather than simply forcing the issue?

A mechanical throttle can be given an arbitrary torque curve by adding a cam or scroll to the throttle valve. However it’s a fixed curve, so you still don’t get the other benefits of an electric throttle.

this is so informative. Never knew electronic throttle had so many benefits. I have just written it off as newfangled over engineering. Especially with a stick shift I'm constantly tipping in and tipping out. Never knew that was creating more emissions.

Hey Engeering Explained....what about the early Honda Engines, When you were explaining something about the Port Injection, Honda has dual ports, another words early Prelude H22 had 2 butterflies. Try taking them apart, you will see. So the left over gas is still in those 4 ports, primary port and, the secondary ports. Can you explain this?

I like this guy

What I´ve learned is that process of my catalytic converter go cry cry and my exhaust go brap brap is called tap out. Cool.

I just consumed an enormous bowl of popcorn whilst watching this video! very interesting. Another advantage to electronic TB's is manual vehicles are less prone to stalling.

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.

Eric H

3 måneder siden

@Atarv Hegde All these things "help", I just wonder how much. 1-5-10 mpg. Something like a mid 70's slant 6, remade with all modern tolerances and materials comes to mind. That thing got nearly 20 mpg at 3.7L,,,, just at 125 HP, but it was a loose motor.

Atarv Hegde

3 måneder siden

Well EFI does help. I can't say the same about Electronics throttle body

double declutch, that saves the problem by increasing the shift time to let the rpm drop

Thats explain why my drive by wire car have more tork than my cable throttle car. Thanks.

Yeah I just added a pedal commander on mine, also it eliminated that rev hang...