Timing can have an effect on what comes out the exhaust pipe, or in this case stack, but usually it's the fuel mixture that plays a big part of the "fireworks" display. Lean mixes tend to heat up a manifold, stack, or header to where it would glow. Rich mixes add the "Burzamatic" effect. Depending on how much load the engine is under, and the fuel she's quenchin', unburned fuel coming out a super hot exhaust manifold or header can be an awesome site. I ran a Pro Dragster many years ago, and depending on how much fuel we put to her, at the 1000 foot mark all 8 candles were lit in the evening hours! Steve B.