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HappyAndy
HappyAndy Dork
2/17/12 2:06 p.m.

I know the short answer is because RaceCar! The slightly longer answer is that it has to do with fuel and/or ignition tuning.

I remember reading an article about the "bang bang" engine tuning used on WRC cars in the 80s and 90s to keep big turbos spooled up when off the throttle. I kind of grasp how that works and why it would spit magnificent fire balls out the pipes, I'm fairly sure that that engine tuning strategy is not in wide spread use these days, but I've seen lots of race cars still spitting fire balls even some with N/A engines doing it too.

What aspect of race engine tunning causes this, and if one were using megasquirt or having a custom chip made, for a 4cyl turbo with no muffler and a couple of resonators, how could they duplicate it, you know, for novelty purposes only.

Feel free to add hotlinked pics of all sorts of cars spitting flames. I would add a few myself but I haven't figured out how to do it with an android yet.

Gearheadotaku
Gearheadotaku SuperDork
2/17/12 2:12 p.m.

basically excess fuel burning off in the exhaust system when the throttle is closed rapidly.

pilotbraden
pilotbraden Dork
2/17/12 2:17 p.m.

Rich mixture with short and or low restriction exhaust.

nderwater
nderwater SuperDork
2/17/12 2:23 p.m.

because racecar.

Strike_Zero
Strike_Zero Dork
2/17/12 2:28 p.m.

Keith
Keith SuperDork
2/17/12 2:32 p.m.

Modern WRC cars still use anti-lag. You can see the exhaust tips of the Fords glowing constantly.

I have my Locost set up to blow flames on the overrun - I simply don't cut the fuel on a closed throttle in the engine management. There's no good reason for it other than I like the flames.

MG Bryan
MG Bryan Dork
2/17/12 2:34 p.m.
Keith wrote: Modern WRC cars still use anti-lag. You can see the exhaust tips of the Fords glowing constantly. I have my Locost set up to blow flames on the overrun - I simply don't cut the fuel on a closed throttle in the engine management. There's no good reason for it other than I like the flames.

Which is a berkeleying excellent reason...

HappyAndy
HappyAndy Dork
2/17/12 2:35 p.m.
MG Bryan wrote:
Keith wrote: Modern WRC cars still use anti-lag. You can see the exhaust tips of the Fords glowing constantly. I have my Locost set up to blow flames on the overrun - I simply don't cut the fuel on a closed throttle in the engine management. There's no good reason for it other than I like the flames.

Which is a berkeleying excellent reason...

That's my point exactly!

MadScientistMatt
MadScientistMatt SuperDork
2/17/12 2:36 p.m.

There are two common ways you can end up with a tune that makes a car spit flames. One is a rev limiter that cuts the ignition but leaves the fuel on. The other is if too much fuel is added at high RPM, low load cells in the fuel table - this results in a backfire when you lift off the throttle.

e_pie
e_pie Reader
2/17/12 2:52 p.m.

I want to know what makes some cars burble/pop/crack when you let off the throttle at high RPMs.

That noise + flames = racecar.

Keith
Keith SuperDork
2/17/12 3:44 p.m.

That noise is the same as flames, but smaller.

I was once bedding a set of Carbotechs on the Locost at night. Turns out the pads would throw a big stream of flaming sparks when they got hot. So I'd accelerate up to 60 mph or so and nail the brakes. Big streamers of sparks off the open front wheels as the exhaust banged and blew flames right below my elbow. It was AWESOME.

DaveEstey
DaveEstey Dork
2/17/12 3:51 p.m.

My cat-less Miata pops on the overrun but I NEED MOAR FLAMES.

mistanfo
mistanfo SuperDork
2/17/12 3:54 p.m.

Side dump pipe might shorten things enough for flames.

92CelicaHalfTrac
92CelicaHalfTrac SuperDork
2/17/12 3:55 p.m.
mistanfo wrote: Side dump pipe might shorten things enough for flames.

Yeah.... maybe.

mad_machine
mad_machine SuperDork
2/17/12 4:02 p.m.

my old type4 powered superbeetle would spit flame on acceleration and pop and blow fireballs when the throttle was rapidly closed. It was probably a combination of dual carbs and aggressive timing and the fact that the exhaust system might have been 2 feet in length at most

ditchdigger
ditchdigger Dork
2/17/12 5:06 p.m.
Keith wrote: Modern WRC cars still use anti-lag. You can see the exhaust tips of the Fords glowing constantly. I have my Locost set up to blow flames on the overrun - I simply don't cut the fuel on a closed throttle in the engine management. There's no good reason for it other than I like the flames.

Hmmm. I think I know which switch to turn off in tunerstudio this weekend

DrBoost
DrBoost SuperDork
2/17/12 5:07 p.m.

That is socially irresponsible. I'm going to report you to the nearest tree-hugger......then I'm going to make flames come out of my wife's (minivan) tail-pipe.

iceracer
iceracer SuperDork
2/17/12 5:42 p.m.

Now that NASCAR has go to FI. I wonder if we will still see the flames like on the carb;d cars .

JohnyHachi6
JohnyHachi6 Reader
2/17/12 6:07 p.m.

It's also not unusual on RPM-MAP based ecus in race applications for the lowest MAP bins to be set at the max vacuum that you can pull while opening the throttle quickly. When you quickly close the throttle quickly at high-load, high-rpm, you can often get the MAP to dip below that value and it will cause a rich condition that produces popping and flames. You can tune it out by spreading out your MAP bins, but it will lower the resolution of your fuel tables in the normal operating range and hence isn't usually done in race applications.

Armitage
Armitage Reader
2/17/12 6:17 p.m.
MadScientistMatt wrote: There are two common ways you can end up with a tune that makes a car spit flames. One is a rev limiter that cuts the ignition but leaves the fuel on. The other is if too much fuel is added at high RPM, low load cells in the fuel table - this results in a backfire when you lift off the throttle.

The third is to drive something rotary-powered :)

Tom_Spangler
Tom_Spangler Reader
2/17/12 6:24 p.m.
nderwater wrote: because racecar.

And... I have new desktop wallpaper. Thank you.

11110000
11110000 Reader
2/17/12 6:44 p.m.

My Volvo does it.

MAF engine management + Turbo boost + TurboXS RFL BOV dumping to atmosphere + 3" side-dump exhaust = Fireball at throttle drop.

'For novelty purposes only.'

92CelicaHalfTrac
92CelicaHalfTrac SuperDork
2/17/12 6:47 p.m.
11110000 wrote: My Volvo does it. MAF engine management + Turbo boost + TurboXS RFL BOV dumping to atmosphere + 3" side-dump exhaust = Fireball at throttle drop. 'For novelty purposes only.'

What's your record so far? I've gotten a good 6-8 feet out of mine.

novaderrik
novaderrik SuperDork
2/17/12 9:11 p.m.
11110000 wrote: My Volvo does it. MAF engine management + Turbo boost + TurboXS RFL BOV dumping to atmosphere + 3" side-dump exhaust = Fireball at throttle drop. 'For novelty purposes only.'

this was my cousin's recipe for an awesome fireball..

1973 Monte Carlo- qty 1

small exhaust pipes with1/4" holes drilled every 6" or so.- qty 2

take the 1973 Monte Carlo up to about 45mph in first gear.. shut off ignition, making sure the leave the car in gear.. furiously pump the gas pedal about 10 times in about 5 seconds.. turn ignition switch back on..

following this recipe will result in flames about 10 feet long out the back of the car, and may result in a pair of blowed up mufflers..

dyintorace
dyintorace SuperDork
2/17/12 9:13 p.m.

Rotary engines seem to be especially capable of fireballs. I love them.

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