What causes the fire to come out of the exhaust that was depicted in the racing scene from this movie? And how does nitrous work? Is it delivered into the air intake or fuel injection?

1. Back in the middle 1960's I had an autocross car with a Ford V8-60 (135 cid flathead) midget racing motor in it (and Austin-Healy 3000 trans!), and I could get flames out of the sidepipes, even through glasspack mufflers, because the twin Stromberg carbs were set up a hair richer than they needed to be to work with the Isky full-race cam. I've also seen (at the same autocrosses) flames from the exhaust of aftermarket-exhaust-equipped early Porsche 911's, which also came from the factory set up very rich in their Webers (these same cars regularly burned holes in pistons from high-speed pre-ignition in the 1968 models, partly, I believe, because the new air quality regulations required them to be leaned out). I suspect that movie technicians make sure that their cars are set up way over rich if they want flames, but most race cars used to be set up very rich in the low speed circuits of the carbs in order to have the excess fuel cool the piston tops on overrun (braking for corners, etc.).

2. Nitrous Oxide serves only to provide more oxygen for the combustion process, so it is useless without some means of adding extra fuel, too. Early hot rod nitrous systems consisted of an extra FUEL injection nozzle, often fitted to an unused vacuum port on carburated American V8's, along with another nozzle to inject the nitrous, both controlled by some sort of electric on-off control from the dash, but I'm not really up-to-date on what they're doing on fuel injected cars of more recent vintage. I've been more interested in the propane injected VW diesel hot rods running on the Autobahns.

I have heard of cars being run rich and then installing an extra spark plug and coil in the exhaust tip. This could ignite the mixture and send out flames. Nitrous adds extra power by injecting nitrous oxide into the intake adding oxygen to the mix. There is also an additional gas jet to keep the mixture from going too lean. This jet could also be used to create the rich mixture for the flames out the exhaust.

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Currently
1991 Mazda Miata 174000
1991 Subaru 189,000 Winter beater

got rid of:
1984 VW Vanagon 195,000
1976 350SE Euro 185,000 KM
1973 280SE 4.5 (boy do I regret that)
1980 280SE European W126 4 speed manual (miss it)
1989 BMW 735iL 119000 (good riddance)

Just saw this while doing a search, had to mention a VW LT28 diesel a friend of mine had which used to blow a flame out the exhaust while on the motorway.

Usual response when I tell people of it "a diesel??"

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306D 1975 (camper) - rusting away
W116 450 SEL 1975 - sold
W114 long wheelbase ambulance, 3 litre diesel 1974

VW Golf 1 convertable - midlife crisis item
VW T4 van - support vehicle

The fuel mix must be very potent to ignite with all of the exhaust fumes in it. the only time i could get fire out of a muffler is if the engine missed and unburned fuel was vented into a hot enhaust sysyem. but in that case there was no burnt fuel exhaust combined with it. if my chemistry is correct, mixing a pure gas (fuel/air) with an impurity (exhaust) denatures the pure mix and changes its properties (ie wont burn). i sayits a hollywood effect, not a real-world effect

also, if theres flame in the exhaust, there will be flames in the compression stroke of a 4 stroke engine thus causing pre-ignition and stalling.

thus i argue that sustained flames in the exhaust is impossible in normal operation. i could be wrong.

its a product called "dragon fire" or something like that originated in japan. it has a small fuel by pass and spark plug at the end of the muffler. upon a hit of a switch extra fuel will go out the exaust and ignite. i suppose they mix certain stuff to make it different color.

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198? 300D ???K - Future DD
1989 300TE 285K - traded in '12
1984 300SD 186K - Sold in 08
1978 300SD 330K - Died in 05

There are all kinds of flames from the exhaust, as has been mentioned!

You can get it "honestly" like on race cars where the engine is set up rich enough on the low load fuel control (carb or FI) so that there's enough unburned fuel in the exhaust to ignite when it finds O2 in the atmosphere;
you can get it by cheating with kits that are offered now that give you a switch to push and it cuts out your ignition for a second and at the same time starts pulsing a spark plug in your exhaust tip;
or you can do it UP and inject your favorite witches brew (often involving kerosene & gas) into your exhaust just in front of the spark plug(s) you've got mounted out there! Then you can enter contests and shoot 30 foot flames!

I've seen Mercedes with flame from the exhaust, but for a different reason. If you take a Mercedes such as an early '70s 280SE 3.5 or something similar (early 350SL etc.) with D-jetronic injection that has spent most of its time doing short city trips, it will have considerable carbon build up in the rear muffler. If you then take that car on a fast (wide open throttle) highway run and suddenly lift off the throttle, it is possible that the carbon in the rear muffler (which is now very hot) will ignite. It ignites on the overun due to excess oxygen in the exhaust gasses because the D-jetronic shuts off the fuel on overun. Opening the throttle again will extinguish the fire. Flames are not common under these conditions but a trail of whitish smoke on a closed throttle is. Once again, opening the throttle stops the smoke.

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107.023: 350SLC, 3-speed auto, icon gold, parchment MBtex (sold 2012 after 29 years ownership).
107.026: 500SLC, 4-speed auto, thistle green, green velour.
124.090: 300TE, 4-speed auto, arctic white, cream-beige MBtex.
201.028: 190E 2.3 Sportline, 5-speed manual, arctic white, blue leather.
201.028: 190E 2.3, 4-speed auto, blue-black, grey MBtex.
201.034: 190E 2.3-16, 5-speed manual, blue-black, black leather.

The only fire I've seen coming out of the exhaust on any of my cars was the time the soot in the Volvo caught fire after I fixed the turbo.

Apearantly there was quite a bit of coked oil and soot in there from turbo seal leaks and bad performance (the EGR would stick open at full throttle, made an immense amount of smoke), and after pulling a long grade, it burned. Chunks the size of my thumb blew out from Louisville to Evansville on downgrades that night, quite spectacluar. I had to replace the exhaust soon after that.

The old 50's trick of blowing flames out the back was performed by a spark plug at the tailpipe and pulling the choke on a hot engine and flooring the throttle. The excess fuel burned in the atmosphere as much as in the pipe.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!