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Re: Getting 10psi Boost on a NA engine...
Because of the pressure difference. The waves will want to move from an area of high pressure to an area of lower pressure. The exhaust gases wouldnt be able to force there way back into the intake tract because there would be a positive pressure build up of air waves in the intake runners. That positive pressure would force its way through the now open valves at the speed of sound giving you your "boost" effect.
It's weird, because we are learning about this kind of stuff with regards to sound waves in my phycial agents class...so I am starting to actually understand this a little better I think.
Think of it as your engine is one big air pump. It has areas of low air pressure and high air pressure. Most street cars have a volumetric efficiency of somewhere in around 70%...in order to make this happen, you have to increase the volumetric efficiency to over 100%. This means that you have to somehow get more air into the engine, without using some sort of FI. To do this, you would tune your intake runners for resonation. (think about how people tune musical instruments to resonate off a certain sound) Now, if you design your intake manifold to increase the velocity of the air coming in, as well as designing it to resonate the air in the intake runners you can up that volumetric efficiency. But, heres the thing. You can only bring soo much air into an engine at one time being NA, so inorder to get that increase in air pressure, you are going to have to do something with the air that is already coming in. Thats where the resonation tuning comes into play. As you are essentially tuning the intake runners so that when "X" amount of air enters the engine at "Y" speed, it bounces around in the intake runners and off of the closed valve a couple of times amplifying itself. (Think of how waves in the water grow in size when they collide with each other) When this amplfied wave returns to the valve (thats now open) you now have an extremely high pressure air wave, that is now forcing its way to get to that lower pressured area (the cylinder). On a normal engine, the air is not forced down into the cylinder when that valve opens, the engine merely sucks in what it needs to run, as it functions like an air pump/vaccum. By creating that wave, you are FORCING that air into that cylinder when the valve opens. That force happens because of the size of the air wave produced by the resonance, and because of the larger pressure variance now.
I hope that explains it maybe a little better...remember that this "Boost" is only for a very narrow rpm band, and will actually cause the car to loose torque when not in that power band. So city driving might be a little more sluggish...but when you get on it and you're in that rpm range...should make for quite a nice little pull...
Originally posted by 3.4grapeofwrath
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Because of the pressure difference. The waves will want to move from an area of high pressure to an area of lower pressure. The exhaust gases wouldnt be able to force there way back into the intake tract because there would be a positive pressure build up of air waves in the intake runners. That positive pressure would force its way through the now open valves at the speed of sound giving you your "boost" effect.
It's weird, because we are learning about this kind of stuff with regards to sound waves in my phycial agents class...so I am starting to actually understand this a little better I think.
Think of it as your engine is one big air pump. It has areas of low air pressure and high air pressure. Most street cars have a volumetric efficiency of somewhere in around 70%...in order to make this happen, you have to increase the volumetric efficiency to over 100%. This means that you have to somehow get more air into the engine, without using some sort of FI. To do this, you would tune your intake runners for resonation. (think about how people tune musical instruments to resonate off a certain sound) Now, if you design your intake manifold to increase the velocity of the air coming in, as well as designing it to resonate the air in the intake runners you can up that volumetric efficiency. But, heres the thing. You can only bring soo much air into an engine at one time being NA, so inorder to get that increase in air pressure, you are going to have to do something with the air that is already coming in. Thats where the resonation tuning comes into play. As you are essentially tuning the intake runners so that when "X" amount of air enters the engine at "Y" speed, it bounces around in the intake runners and off of the closed valve a couple of times amplifying itself. (Think of how waves in the water grow in size when they collide with each other) When this amplfied wave returns to the valve (thats now open) you now have an extremely high pressure air wave, that is now forcing its way to get to that lower pressured area (the cylinder). On a normal engine, the air is not forced down into the cylinder when that valve opens, the engine merely sucks in what it needs to run, as it functions like an air pump/vaccum. By creating that wave, you are FORCING that air into that cylinder when the valve opens. That force happens because of the size of the air wave produced by the resonance, and because of the larger pressure variance now.
I hope that explains it maybe a little better...remember that this "Boost" is only for a very narrow rpm band, and will actually cause the car to loose torque when not in that power band. So city driving might be a little more sluggish...but when you get on it and you're in that rpm range...should make for quite a nice little pull...
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