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Geirskogul posted:Doesn't flywheel inertia have something to do with it? Unless I'm way off here, that shouldn't change the fact that no matter how hard you try, you can't generate more than 1 atmosphere of pressure difference by just pulling a vacuum.
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Jan 28, 2015 20:24
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I misunderstood initially. That makes sense now.
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Jan 28, 2015 20:27
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Wouldn't be the first time I've seen a stock location panel filter fold in on itself on a turbo subaru.
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Jan 28, 2015 20:30
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IOwnCalculus posted:Unless I'm way off here, that shouldn't change the fact that no matter how hard you try, you can't generate more than 1 atmosphere of pressure difference by just pulling a vacuum. 14.7 psi across that size filter is a lot of force, though. It's about 6"x10". 6 in. * 10 in. * 14.7 pounds/in.^2 = roughly 882 pounds of force on a flimsy little paper and rubber filter. Pneumatics can be a hell of a thing. Of course, a straight atmospheric-to-vacuum pressure drop isn't likely to happen - but even 1 measly psi of difference is still 60 pounds. It's evenly distributed across the face of the filter, but it's still enough that if there's some tiny weak point where an assembler didn't put on just the right amount of glue, it'll find it and eventually do unpleasant things.
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Jan 28, 2015 20:50
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IOwnCalculus posted:Unless I'm way off here, that shouldn't change the fact that no matter how hard you try, you can't generate more than 1 atmosphere of pressure difference by just pulling a vacuum. It's not just about the pressure. The sheer VOLUME of air a large diesel is able to magically turn into vacuum, through a comparatively tiny intake tract is what really does the damage.
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Jan 28, 2015 22:08
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Also 'fish stories' Listen at the end him explaining "it sucked it right out of my hand". However upon review of the tape its clear he just panicked, ran and dropped it. https://www.youtube.com/watch?v=8M1o2rpO_JY
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Jan 28, 2015 22:32
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Slavvy posted:It's not just about the pressure. The sheer VOLUME of air a large diesel is able to magically turn into vacuum, through a comparatively tiny intake tract is what really does the damage. That doesn't change the pressure differential limits placed by the relatively low pressure atmosphere. Slap a phone book on there solidly and it won't get pulled in. Hell, lots of corrugated cardboard has a burst strength above 14.7 psi.
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Jan 28, 2015 22:46
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EightBit posted:Hell, lots of corrugated cardboard has a burst strength above 14.7 psi.
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Jan 28, 2015 23:12
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Fire Storm posted:More like horrible welding failures. Saw this in a magazine, I think Home Machinist: Could be a variety of things, probably multiple concurrent fuckups like using a non-ferritic rod at too high a temperature.
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Jan 28, 2015 23:25
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streetlamp posted:Also 'fish stories' The title of this video should actually be "I wonder why they stopped using this truck 30 years ago".
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Jan 28, 2015 23:44
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EightBit posted:That doesn't change the pressure differential limits placed by the relatively low pressure atmosphere. Slap a phone book on there solidly and it won't get pulled in. Hell, lots of corrugated cardboard has a burst strength above 14.7 psi. So lets say you're right and a flush placed phonebook can't get sucked into the intake of a semi. What happens instead? Does the 600hp truck engine just stall?
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Jan 29, 2015 00:28
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That would be the goal, yes. If it can't get any oxygen to allow the fuel to combust in the cylinders, it's going to make exactly 0hp.
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Jan 29, 2015 00:30
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This is something I really want to test empirically. I have the feeling that you're right in a theoretical sense but finding a practical way of instantly blocking the intake without whatever object you're using getting destroyed piecemeal or getting partially sucked in at an awkward angle would be nigh-impossible in the timespan you have between a runaway beginning and the engine blowing up.
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Jan 29, 2015 00:33
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Slavvy posted:This is something I really want to test empirically. The technique works. This is a 4-53T which is pretty small and two-stroke so I don't think it'll be pulling as hard as a modern diesel would, but he still stopped the thing with what looked like a shingle and his hand. A phone book or similar would have done a much better job. https://www.youtube.com/watch?v=3NRaqgab0_w&t=80s wolrah fucked around with this message at 00:43 on Jan 29, 2015 |
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Jan 29, 2015 00:40
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Slavvy posted:So lets say you're right and a flush placed phonebook can't get sucked into the intake of a semi. What happens instead? Does the 600hp truck engine just stall? It starts sucking the people in through the phone. First Adams, then Allen, then Anderson...
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Jan 29, 2015 00:57
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Slavvy posted:This is something I really want to test empirically. Not saying a piece of cardboard or a phone book would work, but air intake shutoff valves are a thing.
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Jan 29, 2015 02:44
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Nidhg00670000 posted:Not saying a piece of cardboard or a phone book would work, but air intake shutoff valves are a thing. Oh yeah I know, I'm meaning in terms of nearby object into intake.
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Jan 29, 2015 03:03
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Friend of mine borrowed his then father-in-laws Chevy Van 6,2 D. It came with a piece of plywood, about 40x40 cm. To turn off the engine, you removed the hood (inside the cabin, as it is on those), removed the air cleaner and then plopped down the plywood, thus killing the engine. IIRC the plywood plate had some kind of hole in it that fit over some part of the intake that wasn't flat, meaning if you lost that particular plate you couldn't turn it off...
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Jan 29, 2015 03:24
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Fart Pipe posted:The title of this video should actually be "I wonder why they stopped using this truck 30 years ago". Actually it probably didn't do that 30 years ago. Engines with mechanical unit injectors (each injector is its own HP fuel pump, driven by a cam lobe and pushrod of its own) have a rack that runs the length of the engine that controls fuel delivery per injection at each injector, and is attatched to the governor. When your foot asks for some action, the governor pushes the rack out and you get, rather predictably, more fuel. Then when the engine reaches the desired speed the governor's flyweights retract and pull the rack back down. Remember that it doesn't take much fuel to maintain a higher idle speed (and in fact much less fuel per injection, since there's more injections for a given time period at a faster engine speed), it's changing that speed that takes a bunch of fuel because of inertia. So what happens if the rack has been sitting a while (or was assembled incorrectly, which is where Detroits got most of their reputation for runaways in the first place) is it gets sticky. And it'll tend to stick at a higher delivery rate because it spends less time at the higher rates during normal operation. So when you get a stuck rack at a high rate, your fuel delivery is now controlled by engine speed alone, and because it's throwing the max fuel per injection into the cylinders that's already going up rapidly. The only limit becomes the amount of fuel you can move through a 3/8" fuel line with that 14.7 psi potential maximum pressure differential. Or the ability of the engine to withstand operation at ~10k RPM 
Turbo Fondant fucked around with this message at 05:01 on Jan 29, 2015 |
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Jan 29, 2015 03:35
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Remember also that the engine isn't sucking in air with 600hp. In, say, a turbo engine, the compressor's basically doing all the work, and those only take a small amount of energy to drive, say 15-20 horsepower (extracted from the exhaust, not the engine output, but you get the point). Even on a big Top Fuel motor with a supercharger that has about 500HP powering it, it still cannot create a pressure differential more than atmospheric (14.7psi) to perfect vacuum (0 psi). Multiply that by the area of a filter/phone book/whatever, that gives you the absolute maximum force it can possibly experience, and NOTHING can exceed that. Engine size/intake diameter have nothing to do with it (vacuum is literally Nothing, how can how have flow restriction on Nothing?) Now if that engine was powering a compressor and filling a sealed room with outside air, so that the pressure differential from room to intake vacuum was greater, then you might have a point.
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Jan 29, 2015 03:37
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Fucknag posted:Remember also that the engine isn't sucking in air with 600hp. In, say, a turbo engine, the compressor's basically doing all the work, and those only take a small amount of energy to drive, say 15-20 horsepower (extracted from the exhaust, not the engine output, but you get the point). Even on a big Top Fuel motor with a supercharger that has about 500HP powering it, it still cannot create a pressure differential more than atmospheric (14.7psi) to perfect vacuum (0 psi). Multiply that by the area of a filter/phone book/whatever, that gives you the absolute maximum force it can possibly experience, and NOTHING can exceed that. From an abstract perspective, isn't that the whole point of boost pressure aside from cramming more O2 into each and every stroke? Delivering air to the engines faster cause now you can have a higher than 15 PSI pressure difference and therefore higher flow rates or am I off base?
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Jan 29, 2015 04:46
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QuiteEasilyDone posted:From an abstract perspective, isn't that the whole point of boost pressure aside from cramming more O2 into each and every stroke? Delivering air to the engines faster cause now you can have a higher than 15 PSI pressure difference and therefore higher flow rates or am I off base? A turbo making 45lbs of boost on the compressed side of the compressor turbine is still pulling vacuum from the intake side. It only has the difference between atmosphere and 0 psi to work with. Additional pressure on the engine side comes from more air being pulled through and crammed into the intake manifold, not from vacuum below 0 psi. There is literally never more than ~14.7psi of pressure difference between atmosphere and the compressor side of the air filter. Lots and lots and lots of airflow != pressure.  Wind is like 0.5 psi max but there are millions of CFM of movement in a gust.
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Jan 29, 2015 04:58
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QuiteEasilyDone posted:From an abstract perspective, isn't that the whole point of boost pressure aside from cramming more O2 into each and every stroke? Delivering air to the engines faster cause now you can have a higher than 15 PSI pressure difference and therefore higher flow rates or am I off base? Yeah, and if the the filter was on the compressor outlet, that would be a different story. However, I can pretty much guarantee there's not a car in the world set up like that.
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Jan 29, 2015 05:09
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sofullofhate posted:A turbo making 45lbs of boost on the compressed side of the compressor turbine is still pulling vacuum from the intake side. It only has the difference between atmosphere and 0 psi to work with. I was commenting more on the mechanics of having the added pressure, it would be absolutely stupid to have a filter AFTER any mechanical component on the engine
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Jan 29, 2015 05:26
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Fucknag posted:Engine size/intake diameter have nothing to do with it Intake inlet size has everything to do with the total force being applied to an object blocking the intake inlet. Let's stop using the phone book analogy and use an air filter as an example. Let's say the air filter is 6"x8". There are now 48" square inches of air filter. Now let's say the air filter lets through 300 CFM max. If theoretical intake were to draw 600CFM, you have roughly half efficiency. So we are at 7.35PSI on the draw side of the filter, and 14.7PSI on the atmospheric side. There is a total of ~350lbs now trying to suck down that air filter to equalize that 7.35lbs of differential. There is a reason those things are corrugated/reinforced like they are, both to provide strength, and to maximize surface area to pull air through. The differential just needs to be able to overcome the object's strength (phone book no; cereal box/plastic bag/rag/etc Yes..
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Jan 29, 2015 05:33
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Dannywilson posted:Intake inlet size has everything to do with the total force being applied to an object blocking the intake inlet. Let's stop using the phone book analogy and use an air filter as an example. Let's say the air filter is 6"x8". There are now 48" square inches of air filter. Now let's say the air filter lets through 300 CFM max. If theoretical intake were to draw 600CFM, you have roughly half efficiency. So we are at 7.35PSI on the draw side of the filter, and 14.7PSI on the atmospheric side. There is a total of ~350lbs now trying to suck down that air filter to equalize that 7.35lbs of differential. There is a reason those things are corrugated/reinforced like they are, both to provide strength, and to maximize surface area to pull air through. The differential just needs to be able to overcome the object's strength (phone book no; cereal box/plastic bag/rag/etc Yes.. Sorry, I meant the size of the charge pipe, not the area of the filter itself.
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Jan 29, 2015 05:42
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Fucknag posted:Engine size/intake diameter have nothing to do with it (vacuum is literally Nothing, how can how have flow restriction on Nothing?) My boss had an ancient holden with a 3 speed traumatic. It had a vacuum valve thingy for kickdowns. I remember that a common modification to them was to make the (very tiny) hole in the valve port larger, either by drilling or buying an aftermarket valve. I don't understand how a bigger hole would change the behaviour of the transmission (and it most certainly did!) if there's nothing to restrict.
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Jan 29, 2015 05:51
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Slavvy posted:My boss had an ancient holden with a 3 speed traumatic. It had a vacuum valve thingy for kickdowns. I remember that a common modification to them was to make the (very tiny) hole in the valve port larger, either by drilling or buying an aftermarket valve. I don't understand how a bigger hole would change the behaviour of the transmission (and it most certainly did!) if there's nothing to restrict. My Ford's 44 year old C4 has a vacuum line attached for shift points. At atmospheric, it will never shift up (I haven't tried the extent of this), but as vacuum (RPM) increases it activates each shift circuit. It redlines at about 6k, but with "proper" vacuum it shifts at about 2.5k. If I wanted to raise the shift points, I could decrease the amount of vacuum it's getting by introducing a pinhole, thus getting it to shift father into each gear (higher rpm per gear).
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Jan 29, 2015 06:03
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Yeah but you're reducing the vacuum in that scenario. In my boss' car the diameter of the restricter on the vacuum line itself was made bigger. The amount of vacuum the engine punched out was the same, it was just 'flowing' through a larger hole.
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Jan 29, 2015 06:11
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Slavvy posted:Yeah but you're reducing the vacuum in that scenario. In my boss' car the diameter of the restricter on the vacuum line itself was made bigger. The amount of vacuum the engine punched out was the same, it was just 'flowing' through a larger hole. I'd imagine it allows for a faster slew rate. The engine only makes so much vacuum, but it's acting on a bunch of different things. Power brakes, vacuum advance, kick down, actually pulling the air into the cylinders. By widening the orifice it seems like you'd be able to change the absolute pressure on the transmission side of the orifice faster. Maybe? I'm not great with physics.
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Jan 29, 2015 06:18
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If he hole is small enough and the pressure difference great enough you could create a choked flow scenario which would delay how long it will take before the transmission sees a significant pressure change. Putting Ina larger orifice would remove he choke condition and make it repairs faster.
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Jan 29, 2015 06:30
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But why? What flow? Vacuum, as stated above, doesn't 'flow' so changing the size of the hole shouldn't make a difference. It's emptyness, it doesn't care how big the hole is. Changing the size of the atmospheric air entry hole on the other side of the diaphragm would certainly make a difference, as would changing the area of the diaphragm itself.
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Jan 29, 2015 07:17
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Dannywilson posted:My Ford's 44 year old C4 has a vacuum line attached for shift points. At atmospheric, it will never shift up (I haven't tried the extent of this), The C6 in my 1980 Ford would upshift eventually with the vacuum line disconnected, but it would only upshift right at redline. And it shifted hard. I eventually wound up disconnecting the vacuum line and shifting it manually for the last year or so I had it, because it slipped really bad on the 2 -> 3 shift otherwise.
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Jan 29, 2015 07:34
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Slavvy posted:But why? What flow? Vacuum, as stated above, doesn't 'flow' so changing the size of the hole shouldn't make a difference. It's emptyness, it doesn't care how big the hole is. Changing the size of the atmospheric air entry hole on the other side of the diaphragm would certainly make a difference, as would changing the area of the diaphragm itself. Because when you change throttle position, your manifold vacuum changes dramatically. Going from atmospheric pressure (WOT) to 10 inches of mercury (half throttle) is going to require that some air move through that orifice. The size of the orifice will govern how fast that can happen.
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Jan 29, 2015 07:37
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Slavvy posted:But why? What flow? Vacuum, as stated above, doesn't 'flow' so changing the size of the hole shouldn't make a difference. It's emptyness, it doesn't care how big the hole is. Changing the size of the atmospheric air entry hole on the other side of the diaphragm would certainly make a difference, as would changing the area of the diaphragm itself. Raluek posted:Because when you change throttle position, your manifold vacuum changes dramatically. Going from atmospheric pressure (WOT) to 10 inches of mercury (half throttle) is going to require that some air move through that orifice. The size of the orifice will govern how fast that can happen. This, basically. There is still some air in there, and as pressure in the manifold changes, there's a small flow as pressure equalizes. Larger hole == faster equalization.
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Jan 29, 2015 07:43
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Talking of run away diesel motors, I work in the underground coal industry and all our underground diesel vehicles are fitted with pneumatic operated 'strangler' valves which is simply a spring loaded flap that is hooked to an e-stop that will choke the engine in a heart beat.  Sometimes it causes engine damage too as it's been known to suck water back through the exhaust from the wet scrubbers we run (we don't want raw exhaust going into a potentially explosive atmosphere) . Anyway the reason we run these is because some years ago, a transport was driven into an underground area with high methane present the machine was shutdown however the diesel engine failed to shut down due to the 'right' amount of methane present in the atmosphere and kept on chugging away and thus a very loving dangerous situation occurred. After that it became part of the mining regs to have stranglers fitted : )
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Jan 29, 2015 08:47
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Runaway diesels are the best when they're running on their own lube oil. Some can run backwards, too! The LDS-465 in a deuce and a half will very happily stall, and then start back up, running backwards, if you're not Johnny-on-the-spot clutching in when you start to roll backwards. Everything works fine, running backwards. Except the oil pump. That doesn't turn. 
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Jan 29, 2015 13:09
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The first sign of that happening is usually the lack of exhaust from the stack, exhaust coming out the intake, and the fact that you have five reverse gears and only one forward. Very strange. I've not done it to mine, but I've heard of it. apparently the LDS-465 / LDT-465 runs so little injection advance/retard that it injects basically at TDC, making this possible. E: the oil pump does turn... just backwards. So it pumps the oil away from the bearings and back into the sump. REALLY NOT GOOD.
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Jan 29, 2015 13:56
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I had to choke out my two stroke YDS3 one time. Luckily it was on the stand at the time and the carbs were exposed so I just used my arm to block off the carbs. The sound was terrifying 
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Jan 29, 2015 14:32
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wolrah posted:The technique works. This is a 4-53T which is pretty small and two-stroke so I don't think it'll be pulling as hard as a modern diesel would, but he still stopped the thing with what looked like a shingle and his hand. A phone book or similar would have done a much better job. related vid: https://www.youtube.com/watch?v=b6WDwsdH_A0 @2:30 is the best. lack of fire extinguishers and a crowd of spectators ready to catch the flaming car as it rolls back down the hillclimb at them. @3:40 is just 
GnarlyCharlie4u fucked around with this message at 14:44 on Jan 29, 2015 |
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Jan 29, 2015 14:41
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