This may sound crazy but my buddies 12 valve does it, but you have to be on a street without street lights to see it. He is running a 10 plate, 370's and lazer cut delivery valves. It is a dull orange flame that shoots out about 4" from the end of the tail pipe.
We found this by driving my truck beside his, and he powering past me. We were listening for a popping sound we thought was coming from the exhaust. Instead we (I) see the flame as he rolls into it at about 35 mph. It is truly incredible, and he has a 4" exhaust and you can see a orangeish glow amongst the excessive smoke. What makes it easier to see is that he has a 4X4 with 35's. This puts the exhaust at a very good level to see whan it is beside my 2 wd.
I know it sounds crazy but you can see it if you are on a dark road.