I usually tune for performance and sound....smoke is something that can be inconsistent depending on weather conditions and ambient temperature....Some days you wont see much smoke at all, other you will see a thick trail of smoke.... As a rule the exhaust note doesn't lie, if the engine is out of tune it will sound out of tune, if a engine is tuned correctly it will sound like it is tuned correctly........A properly tuned engine has certain performance characteristics that Ialso look for. Same applies to an improperly tuned engine.........Now of course when your racing at a indoor event, and even outdoor for that matter it can be very difficult to to hear your own engine run...which can make it a little difficult to tune by sound.........This is why I feel it pays to take time with a new engine away from the track, so you can learn its tuning characteristics in a environment where you can hear it exclusively.....learning to tune a new engine at the track is definitely much more challenging then learning to tune it on its own away from the noise of other engines....