Spitting in supercharger intake in Mad Max Fury Road

Factual Questions
1

A guy I work with said he hated this movie. He said there was too much CGI BS in it. I explained to him that all the stunts were practical and little CGI was used. Still said it was a “stupid” movie. Asked why. He cited the scene where Max and the war boy were spitting into the intake in order to get the rig to go faster.

Spitting gasoline into the intake would just cause the engine to run rich, he said.

Makes sense. I said it’s just a movie and you should be able to suspend your disbelief for a moment.

He wasn’t moved.

I dug around a little online opinions vary.

Is something like this possible in the real world?

2

An internal combustion engine works by combining fuel (gasoline) with oxygen (from the air) and adding a spark to make it go kablooey. There is an ideal mix where you balance out the oxygen and the fuel so that you get the biggest bang inside the engine. If you have less fuel than this ideal mix then your engine runs lean, which means all of your fuel is used up and there is extra oxygen in the mix that isn’t doing anything. Too much fuel and the engine runs rich, and all of the fuel doesn’t burn. Balance it out just right and all of your oxygen and all of your fuel is used up and you get the best engine performance.

To make a more powerful engine, you need it to burn more fuel and oxygen. Adding more fuel is easy enough, but your air has a limitation. The amount of air that your engine can suck in depends on the air pressure.

This is where the supercharger comes in. By ramming the air into the engine, the supercharger allows more air into the combustion chamber, which means that you can put more fuel in (again, trying to maintain that ideal mix), and you get a bigger bang, which means more power. Or your engine just explodes if you didn’t design it to handle the bigger bang. But assuming you designed your engine to handle it, you get more power.

If your engine is running properly, then adding fuel into the supercharger is going to screw up the air/fuel mixture, and it’s also going to mean that there’s less air going into the supercharger (the fuel will displace some of the air). So your friend is right. It’s going to make the engine run rich and will make the performance worse, not better.

However, notice that I said “if your engine is running properly”. If the engine’s fuel/air mixture is screwed up because it’s not tuned properly or the fuel filter is all clogged up or some other reason, then the engine will be running lean and adding fuel will get it closer to that ideal mixture and it will run better. So you can technically get a boost, but it requires your engine to be kinda screwed up for it to happen.

Personally, I’d rate the idiot hanging from the front of the vehicle playing the guitar, the goofy pole acrobatics, the title character doing very little (this was more of a movie about Furiosa than Max), hugely underdeveloped characters throughout, and the piss-poor plot as worse than the fuel spitting idiocy. But that’s just my opinion.

So I agree with your friend on two points. First, the fuel spitting wouldn’t work, and second, it was a stupid movie.

3

Are the people in that movie mutants who spit gasoline instead of saliva? :confused:

4

The gasoline came from a can. The guy on the hood of the car (who amazingly wasn’t thrown off during all of the car’s maneuvering :rolleyes: ) sucked it out of the can and spit it into the engine.

Again, stupid movie.

5

Er, sort of. But not in the way they depict. In the past, some supercharged/turbocharged engines have used water injection. See, as you raise the pressure of air, you raise its temperature. The supercharger raises the air temperature, and after it forces the air-fuel mix into the cylinder, the temp of the air-fuel charge is raised even more by the piston compressing it. If it gets too high, the fuel can auto ignite which usually results in detonation (the entire air-fuel mix igniting at once, forming a shock wave which can quickly damage the engine.) injecting water into the intake stream cools it significantly as the water evaporates. The water takes no part in the combustion reaction; it just prevents detonation so you can increase the amount of boost pressure from the supercharger.
But in the real world, under sustained heavy load you need a continuous stream of water; spitting into the intake isn’t going to do shit.
And also in the real world, water injection has fallen into disuse in favor or air-to-air or air-to-water aftercooloers (usually called inter coolers.). They do the job of water injection without relying on a consumable material.

Edit: fun fact- the 1962 Oldsmobile Jetfire engine- one of the first mass produced turbocharged car engines- used water injection. Basically it drew windshield washer solvent into the intake under boost.

6

Oh, spitting gas into the intake. Never mind me.

7

Are we absolutely sure it was gasoline in the can? It could have been another liquid which enhanced the combustion process.

And as for being a stupid movie, both critics and majority of audience disagree with you. It got 97% fresh from critics on Rotten Tomatoes and 86% from audience.

8

I’d thought it was nitromethane or similar.

Great movie.

9

I didn’t care for the new movie either, thought it was cartoonishly stupid and over the top. And for all its claims to using mostly old-school practical effects instead of CGI, a great deal of it looked pretty CGI-fake to me.

Small comment regarding the original Mel Gibson Mad Max 2 (called The Road Warrior here in the US) and the use of superchargers: In the opening scene where Max is being chased and running low on fuel so he hits a button which turns off his supercharger. I’m pretty sure that would be impossible. Sure, you could fit an electromagnetic clutch to the pulley on one (like on AC compressors) but if the blower stopped turning like that it would restrict the air/fuel flow so much the engine would just stall.

10

…Only when they aren’t on the red carpet… :wink:

11

More than this, if you watch Fury Road closely you’ll notice that any vehicle with a supercharger has some sort of pull-lever on the shifter to engage/disengage the supercharger. It’s one of my favorite details in the movie; clearly superchargers work differently in the Mad Max universe, but they work consistently.

Anyone who’s ever watched a lap of a “Star in a Reasonably Priced Car” on Top Gear already knows that driving fast, if done right, actually looks really boring. Excessive shifting, throttle mashing, powersliding, sawing at the wheel… these all look great on film but just slow the car down, and anyone with some racing experience has to set aside this knowledge during any chase scene. Since the world of Mad Max is so well crafted, it’s exceptionally easy to suspend disbelief. Clutch-driven superchargers and spitting gas into intakes are badass visuals. Finely tuned fuel maps look like spreadsheets. I’ll take the former any day.

One thing to note, at one point one of the engines starts to overheat on the War Rig and the war boy (Nuk?) crawls into the engine bay to fix it. There’s a shot of him tightening a hose clamp. My friend pointed that out to me, with a sort of “that’s lame” expression, but I shot back that an overheating engine blowing off a coolant hose is a realistic scenario, and there’s not much you could expect someone to do to fix it at 50mph other than crank down a new hose clamp. So if OP’s friend wants some dull realism, it’s in there.

12

it could probably pull air through a free-wheeling Roots blower, but it would still be a significant restriction.

13

Huh? What? :eek: Did those people watch the same movie I did?

It’s not even a whole movie, just a three-hour chase scene.

14

Stupid does not cancel out wildly entertaining.

15

This. We had vacuum pumping systems with Roots boosters and they could freewheel. But I don’t think one on an engine would pass enough air to make it run normally.

Dennis

16

Alternate air passage with controllable door?? Bypass the supercharger you disconnected?

Any A&P mechanics older than I that remember the 3350 Turbo-Compound Engines with water injection? Direct into the cylinder?

Fuel air expands 7 to 1 in burning or something like that and water to steam is 9 to 1…

Slow turning big round aircraft engines are some different from F-1 race engines and back in the day… Also think old large ship engines… Also think old natural gas stationary pump engines that turned so slow the bearings were lubed with grease cups that were turned by hand…

Today, aircraft engines with turbo chargers not only have a waste gate to control the pressure, they have an alternate air source in case of a turbo problem.

Aircraft superchargers are mostly an integral part of the engine, not an add-on so they turn if the engine turns and they are mostly centrifugal in type.

IMO, if a person can’t suspend belief, Mad Max movies should be avoided at all costs.

You should see & hear me squirm & bitch about what movies do with aircraft reality…

17

I haven’t seen the movie, but I’ve heard nothing but good things about it. Also, read here under “critical reception” and "accolades. It seems to be an almost universally praised movie. And it won six academy awards (although those were for technical things.) I want to see it now to see why there is such a gulf between critical opinion and the dopers in this thread.

18

That’s more on the current Hollywood process than the film itself though. Some exec somewhere has decided that people did not want to see films starred by women. Another exec has decided that movies were supposed to be either sequels, reboots or franchises now. It is what it is.

And man, you did not get a raging post-apocalyptic nerdboner at the guy slamming on a flaming guitar in front of a truck that is a wall of amps on wheels and doubles as a giant moving Taiko drum set ? What the hell’s wrong with you ?! :smiley: Hell, I was stoked enough by the Doof Wagon as a pointless cool visual thing, but then the guitar even had a part in the action itself ! Rock your heart out, Chekov !

Sure, it’s silly - it’s also metäl as all getout. Ask the guys from Rammstein, they know ;). Which is pretty much all that Mad Max movies have ever been : gratuitously metäl funtimes. You sure don’t watch 'em for the thought provoking plot.

[QUOTE=dracoi]
It’s not even a whole movie, just a three-hour chase scene.
[/QUOTE]

You say that like it’s a bad thing :smiley:

19

Well, you won’t get a differing opinion from me. I thought it absolutely transcended the action-chase movie genre and was absolutely one of the best films of the year. It displayed imaginative and well-executed world building, exciting and novel visual effects, and nearly relentless pacing. Yes, the plot was paper-thin: but this wasn’t a movie about plot, it was an extended chase scene. It also happened to be one of the most pro-feminist action movies in a long time.

20

Mad Max is a mythological dude, Stories told in the Mad Max universe are the kind told around a campfire by survivors. Its a bit like How Raven put both the sun and moon in the sky (on 2 different occasions) and then Created the tides through a totally separate act. That Dont Make No Sense! but it is a good story.

They are supposed to have elements that are strange and not quite real.