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Platystemon posted:Killing the engine like you did works (beware of losing hydraulic assist, of course), but sometimes people think they’re saving gas by putting the car in neutral and idling the engine, and that’s simply not true. You’ll coast faster, but the engine has to burn fuel to keep turning. If you coast in gear, your kinetic energy keeps the engine turning so it doesn’t have to burn any fuel. It does slow you down a little, but on many grades that’s fine or desirable. I can't imagine this is true with a carbureted vehicle. Air is still entering the engine, so it's still pulling fuel into the airstream.
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Jul 20, 2016 02:40
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Raluek posted:I can't imagine this is true with a carbureted vehicle. Air is still entering the engine, so it's still pulling fuel into the airstream. Yeah but how many hypermilers drive carbureted vehicles?
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Jul 20, 2016 02:50
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Platystemon posted:Yeah but how many hypermilers drive carbureted vehicles? I figured the guy you quoted who had the old Beetle probably had a carburetor or two on his 
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Jul 20, 2016 02:50
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Platystemon posted:Killing the engine like you did works (beware of losing hydraulic assist, of course), but sometimes people think they’re saving gas by putting the car in neutral and idling the engine, and that’s simply not true. You’ll coast faster, but the engine has to burn fuel to keep turning. If you coast in gear, your kinetic energy keeps the engine turning so it doesn’t have to burn any fuel. It does slow you down a little, but on many grades that’s fine or desirable. Not much in the way of assists on a 64 bug.
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Jul 20, 2016 02:54
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There's a guy in the motorcycle forum who blew up his transmission by coasting down a super long hill. If he had put it in neutral, it would have been fine, but he held the clutch in the whole time instead. This meant the engine was idling, and the transmission was still being driven at the full road speed. Most motorcycles share the oil sump and distribution system between the engine and the transmission. Idle-speed oil pressure + transmission at highway speed = bad news.
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Jul 20, 2016 03:38
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Sagebrush posted:There's a guy in the motorcycle forum who blew up his transmission by coasting down a super long hill. If he had put it in neutral, it would have been fine, but he held the clutch in the whole time instead. This meant the engine was idling, and the transmission was still being driven at the full road speed. Most motorcycles share the oil sump and distribution system between the engine and the transmission. Idle-speed oil pressure + transmission at highway speed = bad news. Why would he not just put it in high gear and let it make awesome burbling noises all the way down... ugh.
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Jul 20, 2016 03:47
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xzzy posted:Not much in the way of assists on a 64 bug. No locking steering column either. My first car was a neglected Beetle that broke down often. I could coast amazingly far down a highway or off the road and into a parking spot. The few times my current car has gone dead it's been startling how hard it is to control or push.
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Jul 20, 2016 05:10
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Raluek posted:I can't imagine this is true with a carbureted vehicle. Air is still entering the engine, so it's still pulling fuel into the airstream. It only applies to newer, fuel injected vehicles because the computer cuts fuel. But neutral/idle in a carbed vehicle is using less gas than engine braking, for the exact reason you bring up. Godholio fucked around with this message at 07:19 on Jul 20, 2016 |
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Jul 20, 2016 07:15
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Godholio posted:It only applies to newer, fuel injected vehicles because the computer cuts fuel. But neutral/idle in a carbed vehicle is using less gas than engine braking, for the exact reason you bring up. But the throttle plates are closed either way, and the power valve if so equipped won't be open, so I feel like engine braking and idling should be close of not equal on fuel use.
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Jul 20, 2016 17:20
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The higher negative pressure in the intake manifold should pull more gasoline out of the idle port downstream of the throttle valve, just like the choke normally does. Of course given how insanely complex carburetors got towards the end of their use in cars I would be shocked if most didn't include some sort of way to prevent that from happening, most likely a spring valve circuit to reduce idle flow when there is excessive vacuum. Shifty Pony fucked around with this message at 18:30 on Jul 20, 2016 |
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Jul 20, 2016 18:01
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StormDrain posted:But the throttle plates are closed either way, and the power valve if so equipped won't be open, so I feel like engine braking and idling should be close of not equal on fuel use. Perhaps close, but it seems like you're going to still have more airflow through the engine-braked carb just because you have a greater difference in pressure between atmosphere and intake manifold. We're all just arguing black magic here anyway 
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Jul 20, 2016 18:15
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Can I ask a dumb question, then? How do you engine brake with an automatic? I've gathered with a manual you can just downshift (to a point). Mountains aren't really a thing here in Tennessee. I mean, not what you people on the frontier would call mountains, anyway.
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Jul 20, 2016 18:47
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You can downshift with an auto as well, it's just less effective. That's what the 2 and 3 under D are for.
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Jul 20, 2016 18:50
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QuarkMartial posted:Can I ask a dumb question, then? How do you engine brake with an automatic? I've gathered with a manual you can just downshift (to a point). You must not live in the eastern part of the state!
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Jul 20, 2016 18:54
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QuarkMartial posted:Can I ask a dumb question, then? How do you engine brake with an automatic? I've gathered with a manual you can just downshift (to a point). Depends entirely on the transmission/make/model/year. Many cars have an L, 2, or 3 position on the shifter below D/OD that will engage a sprag that allows torque in the other direction through the transmission, thus enabling engine braking.
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Jul 20, 2016 18:56
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The operation of most autos is such that its just going to upshift if you lift off heavy into the throttle so its never really going to be noticeable unless you force it to hold the gear you're in.
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Jul 20, 2016 18:58
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Even my 88 Oldsmobile had a non-OD, 2, and 1 setting. Essentially you chose max gear, preventing upshifts. I'm assuming technology hasn't moved backwards in 30 years
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Jul 20, 2016 20:11
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Slavvy posted:You can downshift with an auto as well, it's just less effective. That's what the 2 and 3 under D are for. I drove around for well over a year in a piece of poo poo Berreta that the entire brake system had failed on. All I had to slow and stop was the automatic transmission and the handbrake. That year improved my driving and my situational awareness like you would not loving believe.
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Jul 20, 2016 20:13
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You picked a fine time to desert me, piston skirt From a guy on one of the local jeep groups, he just finished doing the cylinder head, dropped the pan to replace it too and found this sitting in it. What a waste of time, time to look for a new motor.
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Jul 20, 2016 20:17
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kastein posted:You picked a fine time to desert me, piston skirt
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Jul 20, 2016 20:20
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Dude, they still run until there's just a connecting rod flapping around in the bore (and then continue to run until it hits something hard enough to pop the cylinder wall and breach the water jacket in the process... then they run for another few minutes at least) He said it still had pretty good compression, 130psi on all holes. Even though the skirt was broken off high enough up that you could see the oil control ring from below.
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Jul 20, 2016 20:25
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Structural oil control ring.
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Jul 20, 2016 20:57
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kastein posted:Dude, they still run until there's just a connecting rod flapping around in the bore That's basically the failure mode that my 2000 TJ's factory 4.0 had. Enough skirt broke off to eventually put a hole in the cylinder wall.
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Jul 20, 2016 21:52
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QuarkMartial posted:Can I ask a dumb question, then? How do you engine brake with an automatic? I've gathered with a manual you can just downshift (to a point). Modern autos are pretty drat sweet. Like tow/haul in the larger trucks will throw it a gear down and lock the torque converter essentially giving you manual trans like enginebraking. they'll do this alll the way down to first gear too.
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Jul 20, 2016 23:06
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What cars need is the ability to read your speed when in low gear, and when you release the brakes it maintains that speed as best it can with gear selection and engine braking. Seems like CVT's would be really good at it.
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Jul 20, 2016 23:35
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until you put an Alison 6 speed auto in a 15 tonne truck behind an anemic Hino Diesel and then load the fucker up to the gvm as a fire truck. That thing is absolutely AWFUL to drive- As soon as you lift your foot off the throttle with the exhaust brake on it will bang down a gear and punch the motor right up past the red line, with associated screaming beeper to tell you you done hosed up. Then theres the whole "Torque converter completely disengages from engine below 20kph under exhaust braking" bit, which is HILARIOUS fun when your coming down hill and it unlocks. Just what you want in a 4wd, 15 tonne truck that spends most of its life offroad! Im sure its completely unrelated, but its managed to smoke a set of brake shoes in 22,000kms.
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Jul 21, 2016 00:17
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xzzy posted:What cars need is the ability to read your speed when in low gear, and when you release the brakes it maintains that speed as best it can with gear selection and engine braking. Seems like CVT's would be really good at it. They are! Cruise control + CVT on my Lexus CT200h does exactly that. You lock it in at 60, and it maintains that up and down hills, engine braking as necessary. Love the hell out of that feature, it's something I always thought was missing from cruise control in the other cars I've owned.
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Jul 21, 2016 03:45
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Nuevo posted:They are! Cruise control + CVT on my Lexus CT200h does exactly that. You lock it in at 60, and it maintains that up and down hills, engine braking as necessary. That's actually pretty normal, everything I've driven will let off the gas if you get above the set cruise control limit. But I've never driven a car that will actually downshift to scrub off speed.
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Jul 21, 2016 05:09
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xzzy posted:That's actually pretty normal, everything I've driven will let off the gas if you get above the set cruise control limit. But I've never driven a car that will actually downshift to scrub off speed. The ford F-series trucks, and i would assume the dodges and chevies as well downshift to maintain cruise control speed.
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Jul 21, 2016 06:35
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Hondas have had something semi-similar for ages. If you tapped the brakes going downhill in my Integra, it immediately dropped from 4th to 3rd. And as you came to a stop, it would downshift slowly until it was back in 1st at about 5 mph. I don't remember how the cruise was tied into it, though. Probably not in any way, but that transmission's programming really had it shift a bit aggressively on hills - would hold gears longer before upshifting, downshifted quickly when you needed it to, engine braked a little, etc.
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Jul 21, 2016 07:49
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Nuevo posted:They are! Cruise control + CVT on my Lexus CT200h does exactly that. You lock it in at 60, and it maintains that up and down hills, engine braking as necessary. The toyota's hybrid drivetrain is more elegant than any of the usual CVT's IMO. Only a relative handful of moving parts, most of which are doing pretty low-stress jobs, but also super efficient, has modest packaging needs for the trans brick itself and is pretty low maintenance. When I see 'CVT' I think of a mechanical computer controlled doohicky with the moving cones or what have you and it seems wrong to lump it in with those.
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Jul 21, 2016 08:12
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Haha I drove a twenty year old fiesta a couple of weeks ago and it had a CVT. Confused the gently caress out of me " Wait, why isn't I shifting gears? Why is my speed going up but not the revs? What the gently caress is going on here?" Guest I only drove manuals and regular automatics before.
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Jul 21, 2016 11:41
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I had a rental Toyota hybrid a month ago, and it really messes with your head. "Come on you piece of poo poo, accelerate!" *looks down* "Oh, we're gong 120 already."
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Jul 21, 2016 12:29
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Ha! Yeah, having a car that gets to "optimal acceleration RPM" and just stays there takes some getting used to.
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Jul 21, 2016 13:21
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Wait, does it stay at acceleration rpm forever? Or does it move to "optimal cruise rpm" when you don't want to accelerate?
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Jul 21, 2016 13:36
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Data Graham posted:Wait, does it stay at acceleration rpm forever? Or does it move to "optimal cruise rpm" when you don't want to accelerate? The accelerator is even more disconnected from the drivetrain on a Prius than it is on a CVT automatic. That's because the Prius can mix in any proportion of electric drive depending on how much its got in the battery. On the Prius C, the engineers actually talked about how they made an effort to make the engine sound more like it was responding to the pedal than it did in earlier models in a SAE paper. The most batshit thing a Prius transmission does is how it implements overdrive. Prius enthusiasts (yes) call it "heretic mode" - Toyota calls it "power recirculation mode" - at highway speeds - the gas engine is spinning all the time. To make overdrive happen, one of the motor generators takes power off the output of the differential, and drives the other motor generator with that power together with the engine - which in effect slows the engine to a more efficient RPM. Seems kind of like a perpetual motion machine.
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Jul 21, 2016 13:52
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Well, not quite. It's just exchanging drivetrain losses for electrical losses
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Jul 21, 2016 14:01
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I do know the only way to engine brake on Nissan's xtronic CVT is to put it into 'sport' mode, or pressing the overdrive off at low speeds. It's pretty noticeable either way. Still though I've driven an 2012 altima and it eats so much more gas than a chipped and tuned manual BMW on the longer drives.
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Jul 21, 2016 19:42
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The transmission on my 2014 Ford Fusion will actually engine brake automatically if you're going down a hill and lightly apply the brakes. Freaked me out a bit the first time it happened.
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Jul 21, 2016 21:09
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Powershift posted:The ford F-series trucks, and i would assume the dodges and chevies as well downshift to maintain cruise control speed. Mazda's Skyactiv drivetrain will downshift to maintain speed going downhill. Surpised me when it did it at first.
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Jul 21, 2016 22:58
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