kapusta

There is a simple experiment that you can do to fully understand how intake and exhaust modifications work. Go ahead and run as fast as you can for a min or two (or run up/down the stairs for a min/two) until you start huffing and puffing. Once you're there you will notice two things:

1) Your mouth is partially closed on both intake and exhaust of air from your lungs. If you try to open it further on either one you will have a harder time breathing ("you will lose power"). Same if you try to close it down further on either one you will also have a harder time breathing ("you will lose power").
2) On the intake cycle, your mouth is open slightly larger than on the exhaust cycle.

Both of those points allow you to be most efficient - to maximize the air flow to "allow your lungs to make the most amount of power" by matching the piping (mouth opening) size to your lung air capacity. So why is there a specific optimal mouth opening size? Simple - As you increase the mouth opening size from optimal you get a reduction in air velocity and that loss is larger than the gain from reducing the opening restriction. Similarly as you decrease the mouth opening size from optimal you get a loss in air capacity due to the increased restriction that is larger than any gain you get from increased air velocity.

An engine is just an air pump, just like your lungs. So based on displacement there is an optimal size for both - intake and exhaust piping. With intake being slightly larger. This is true for the entire intake and exhaust train - including not only piping but also engine valves where on 2 or 4 valves per cylinder the intake valves are larger than the exhaust ones and on 3 or 5 valves per cylinder the number of intake valves is larger than the number of exhaust valves.

Now go ahead and find two dust/painter's masks. Put both of them on. By now you're probably well rested, so go ahead and run some more until you start huffing and puffing again. Now you will notice two new things:

1) The masks or restrictions make you breathe harder and you "loose power."
2) There is still an optimal size that your mouth takes on both intake and exhaust but now it is larger than before. As before, the intake opening is slightly larger than exhaust opening - this hasn't changed.

Now go ahead and take one of the masks off. You will notice that you breathe easier and that you "gain power." At the same time your mouth opening get's slightly smaller than with two masks, but larger than without any.

So what can we deduce from that? Restrictions do make you lose power. As you remove/lessen restrictions you will need to decrease your piping size to keep making optimum amount of power.

All cars have the following 3 restrictions in place:

1) Air filter on the intake
2) Cat on the exhaust
3) Sound deadening on the exhaust

All sports/sporty cars including BMW cars have their piping tuned to make the maximum amount of power given those 3 restrictions. There is no rocket science there. All it takes is a simple computer model to figure out the optimal piping sizes given the known restrictions. You will not be able to gain any power with only pipe diameter changes and you're guaranteed to lose power if you do!

To gain any power you will need to lessen or remove one or more of those restrictions and then tune the piping for the new "restriction model." This is why simply replacing the stock air filter with an aftermarket one will not give you more power. (although it may make you save money by cleaning it rather than replacing it in the future) To gain the most power on the intake you would need a less restrictive usually conically shaped intake along with slightly *smaller* piping. On the exhaust, the first thing that you usually tackle is the sound deadening restriction. Most people that tune their cars like a louder exhaust which usually means a less restrictive sound deadening. Now because people perceive that "larger piping" means more power, the tuners usually restrict the piping inside the muffler - out of sight - in order to tune the less restrictive system to get the equivalent of a *smaller* diameter piping and most power along with it. The tuners that don't do this will give you less power than you started with!

I hope this isn't too confusing.

ShadeZeRO

Holy crap, that's a hell of a 1st post lol.

IT'S NOT EVEN A QUESTION!

rkhettry23

Nice Read, did you really write that? I feel like I've heard that analogy before haha regardless nice post!

NobleForums

For what its worth, opening your mouth all the way closes top of the the oral pharynx (opening in the back of your mouth near the opening of your throat) a bit. Since that opening is the limiting factor (not the mouth), that's why your mouth is only partly open. If that area didn't close, then there would be no loss from opening your mouth all the way.

kapusta

You don't need to open your mouth all the way. It's enough to open it slightly more without affecting the pharynx to notice a difference.

kapusta

Yes I did really write it.

I've been a fan, but never owned a BMW. I started my love affair with german cars by acquiring a used Golf as my first car. This was followed by a new 99 Audi A4, which I still drive, but after 10 years I'm slowly looing for a replacement. I'm currently looing at E60 CPOs as potential contenders.

I do love to tinker with everything, including cars, and whaterver I tinker with I like to understand it to its fullest.

sleeper50

thanks for sharing. So it makes sense to get a CAI upgrades at the same time as a free flow exhaust. that makes sense to me!

cheers,

miguex

+1000