The only way to do it on newer cars is to run a dedicated line to the end of the exhaust and have a spark wired to the dash. there are kits out there that can turn the sparks off in the engine and have the unburned fuel run down the exhuast but those only work if you dont have cats and o2 sensors.

Im goin to do it on my truck...i have dual exhaust and im gonna have a big flame so when some ricer tailgates me i can melt there front end...haha

 

It's not street legal in the least in Jersey, dunno about your states.

 

I doubt have an uncontrolable flame thrower on ure vehicle is legal anywhere!

 

Here's a site that has them! My dad had his '57 Chevy setup with flames. Should look pretty cool pn a truck, besides what better joy them melting a ricers ground effects package as you go around him....

http://www.gotflames.net/

 

Here's another one from autoloc
http://autoloc.com/products/flame.lasso

...says it will shoot up to 20' That'll get the unsuspecting pedestrian walking on the sidewalk all the way from the left lane Would that make me a pyro?