WHY DO SOME MOTORCYCLES PRODUCE MASSIVE EXHAUST FLAMES OR POP?
Is it good? Does it hurt the bike? And why don’t MotoGP or race bikes produce these size flames often?
For starters we need 3 things to produce big exhaust flames OR a lot of popping on deceleration, unburnt fuel, heat and oxygen. While in the days of yesteryear the ‘fuel tune’ lean or rich and an unrestricted / open exhausts were the main factors, today there is more at play.
It’s ironic but one of the biggest factors in producing big flames on modern bikes is actually part of the motorcycles ‘anti-pollution’ systems. Yep! The Air Induction System or AIS (also called SAI and PAIR systems) is a system that channels fresh air from the airbox into the exhaust system. The idea is the fresh or cleaner air will result in ‘cleaner’ emissions. Truth is it’s just a masking agent but whateves let’s not go there.
The thing is, the fun police designed these AIS systems to be used in conjunction with a catalytic convertor (or CAT) in your exhaust. The CAT is a dense honeycomb section in your exhaust that breaks up the unburnt mixture, traps some of it, restricts the flow stopping or at least massively reducing the chance of the unburnt fuel igniting in your exhaust.
Of course hoons being hoons (responsibility of course) either remove the CAT or replace the exhaust with either an aftermarket link pipe or full system. While the main reason we do this is for performance and to allow the poor motorcycle to breathe, we now we have a recipe for sick flames bro! You see the unburnt fuel, ‘fresh’ oxygen from the AIS and an unrestricted exhaust is going to light up and explode as soon as that exhaust builds up enough heat, simple. This is amplified on a dyno because of the extreme exhaust heat produced at constant full noise. This is how we can produce sick videos 😊
As we said, the AIS only works on deceleration thus why this only happens on decel.
The reason we don’t see these flames so much in racing is because the bikes have no AIS systems and production race bikes like Superbikes have them blocked off. Thus the amount of oxygen in the exhaust is greatly reduced. They can still blow flames but won’t be anywhere near as much.
There are a few reasons to block off the AIS system on a track or race bike. Firstly the fresh air on decel masking emissions can make it harder to tune the bike. However an experienced tuner will be able to work around this, just don’t run an auto tuner with the AIS connected 😉. Other reasons include it can be too distracting. You should have stealth focus when racing and constant popping and carrying on can be a pain in the backside. Also you may burn your mate behind you (assuming you have mates that is). Another factor is race bikes are always in the high RPM range, the exhaust gets really hot leading to frequent and large explosions. Over time that will start to damage your exhaust system and cost you $$ (the thing most racers don’t have spare). On a road bike it won’t be such a problem.
So other than the potential long-term exhaust damage, this isn’t going to hurt your motorbike, especially a road bike. When it comes to tuning, for track bikes we always block off the AIS. For road bike we give the customer the option…. And yes most of the time the request is ‘flames please!’ 😊
In this particular case below, we think the customer may change his mind once he has burnt through enough rear indicators 😊
We hope you enjoyed this info and remember; motorbikes are awesome.