Why do professional race cars spark and flame as they brake into turns during the night portions of 24 hour races? In the days of carburetors, I can understand: at high rpm carburetors are too dumb to stop pouring in the fuel despite the throttle valve being closed. But a finely tuned modern fuel injection system? How does that much unburned fuel get into the exhaust system? I would like to do the same thing to my car. I am hoping that a few flames will keep those darned Porsches and Lamborghinis a little further off my butt as I enter turn 11 at Laguna Seca and they anticipate the inevitable point-by. I drive a 1991 318i sedan.
lol Brian! You better start running nitromethane. Ok, this is only a guess, but think about it - race engines aren't running (probably) 91 octane pump gas, and they're tuned for maximum horsepower. They'll be using the highest compression ratios and ignition advance they can get away with, and the tuning for max power is probably dumping as much fuel with the largest fuel injectors they can use or are allowed, balanced with whatever minimum fuel efficiency they'll think they need to win or whatever. Anyway, if you're observing that consistently things are lighting up when braking after being full throttle for whatever period of time, I suspect you're just seeing the obviously unburned fuel that's there after stepping off the gas and going to braking, igniting in a minimum-constriction uber-red-hot exhaust pipe. Even though fuel injectors probably cut off very, very quickly, there's probably some excess fuel when as much as possible is being pushed in (also probably being pumped by super-high-pressure fuel pumps). I may stand corrected by experienced race team engineers, tuners, engine builders and fuel-injection-system engineers. Without building a really, really expensive racing M42, if you want a flamethrower coming out the back, I think you'd have to design and build something along that line... I'm picturing some sort of igniter, fuel delivery system, and maybe a modified fuel injector, or some such, mounted near the exhaust tips. I can't wait for the pundits to start talking about how unsafe and inconsiderate it would be to expunge a jetstream of flaming fuel out the back of your vehicle to keep cars with 10x more horsepower behind you at bay, and how, really, melting the fascias of those tailgaters will place them at risk for lung cancer due to having to breathe the toxic fumes and smoke from the burning plastic because, well, they're forced to follow you that closely and couldn't possibly avoid being napalmed by keeping their distance, and how could you possibly make light of anyone needing chemotherapy, plastic surgery, and skin grafts from your recklessly endangering them with your homebuilt pyromania!
The old-school "lead-sled" guys used to do it with an extra spark plug in the exhaust pipe and a rich running engine. If you kludge one together, we expect video.....
open pipes... They also are running short tuned pipes right out of the heads or alternately right out of the headers. The part of the exhaust near the heads runs cherry red to almost white hot when the engine is performing. The closest you could probably get would to be to re-rout the exhaust to a header switch that would you allow to run open headers with the flick of a switch... highly illegal on the road. But be careful, if the system isn't tuned properly for open vs closed operation you can do a lot of damage to the exhaust valves in a very short time. I've run a small block chevy or 2 straight out of the exhaust ports... interesting sound and lovely blue-white flame shooting everywhere trying to set everything on fire. Not very recommended in most engine compartments. Chuck
Party Pooper. At this point, I'm thinking for a 318i there may not be a simple and practical solution. Oh well. I must conclude that fuel somehow passes unburned through the engine even in cars with modern fuel injection. A few years ago, I got to look at the BMW Formula 1 engine that is at the Deutsches Museum Verkehrszentrum in Munich. I was amazed how "rudimentary" the fuel injection was; basically just spritzers in each intake horn. Maybe they just pour in the gas and some comes out the other end.
You'll note I was only speculating about what might be said... Saaay.... if you DO get flames flying, don't use downward-pointing exhaust tips, you don't want to have to pay for repaving a racetrack!
Racing engines... Racing engines use a very "rich" mixture ( ie excess fuel) because of the high compression. This allows the excess fuel to be used as a coolant to keep the valves from burning up... when those hot rich exhaust gasses meet the air its like the afterburner of a jet. Chuck
That makes sense. I found instructions on the internet on how to convert the 318i to a mid-engine, like the Lamborghini is, so may try that instead. If you can't beat 'em, join 'em: http://www.youtube.com/watch?v=mF0kaHQ5oVM
