Stock airbox + curiosity= interesting conclusions *update*
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Stock airbox + curiosity= interesting conclusions *update* Ive fooled around with several intakes and allways seem to go back to the stock setup. I wondered why that big box is so special and why it does what it does so well. I turned it over and examined it from all sides and probed the inner tube as well. I also did some crude flow testing with a shop vac.
The first question i had was why was the whole box so large when there is really only a reletively short tube inside that doesnt take up near the space that the box occupies. By probing the inside with a flex wire it is a straight shot through the box except for the curved area for the inlte an outlet. You can also see near each bend on the inside a half inch hole filled with some white stuff. The rest of the tube goes straight through without any further indentations or impediments as far as I could tell.
I hooked up a shop vac to one inlet to gauge the "pull" and how quickly it sucked by placing my hand over the other end. I covered the intake hole and and then put the suction on the other end. It was an instantanious pull, not like there were baffles and crap that it had to make it's way around. I felt no delay at all. Something interesting happened when I placed my hand over the other end with the vacume on. It was still sucking. Closer examination showed 5 small holes, presumably drain holes, on the bottom of the box. I dont think this box needs drainholes. I went ahead and taped over them and tested again and placing my hand over the inlet felt a strong suction this time. Since the locations of the holes are near the engine and transmission i will assume that there is hot air being drawn into the box through those holes. However small the amount may be, I assume that eliminating all but the cooler air behind the battery will somehow benefit the performance since plugging them eliminates any warm air from getting in.
As for the shape of the box. You basically have a tube that is surrounded by a large box. The box around the tube is not hollow. I figure there is a large amount of insulation and sound deadening material filling the void around the tube. This allows the incoming air to stay cool surrounded by so much material. The material also absorbs the intake noise keeping the sound of the incoming air quiet. Theres nothing fancy going on inside the box. It's not twisting and turning in all directions and is not impeeded by having to go around baffels either. Its a plasctic tube surrounded by a large mass of insullating material. To have made the box smaller would have allowed the air to be a few degrees warmer. Why not use all the space within that area of the engine bay and keep the air cooler was what the engineers were thinking.
I think plugging the small holes will have a positive effect on performance as well. I tried to find an internal diagram of the airbox and could not find one. I would have liked to cut it open for better examination but that would have ruined it. Final thoughts: There is nothing restrictive about the stock airbox and thats probably why other intakes cannot outperform it within the entire powerband. We get good low end and good topend balance. Other intakes just move the power around and it usually suffers somewhere. Our boxes are the best compromise.
*update*
Covering the holes resulted in a loss of performance. I decided to open it up and see once and for all whats inside. The airbox is in fact completley hollow, like a chocolate Easter Bunny!!! the intake tube floats in the middle. There are 2 small tubes (1/2 inch) that branch off the main tube just after the bends. They are about 4 inches long and just hang open in the open box. This must be for equilizing pressure or something. my conclusion is that what we have is really a cold air intake made out of plastic. What these secondary tubes are doing is beyond me, but apparently something important. The box itself must create a vacume around the main tube because if the intake is pulling air then once the air aorund it is evacuated theres nothing left for these secondary tubes to pull.
The first question i had was why was the whole box so large when there is really only a reletively short tube inside that doesnt take up near the space that the box occupies. By probing the inside with a flex wire it is a straight shot through the box except for the curved area for the inlte an outlet. You can also see near each bend on the inside a half inch hole filled with some white stuff. The rest of the tube goes straight through without any further indentations or impediments as far as I could tell.
I hooked up a shop vac to one inlet to gauge the "pull" and how quickly it sucked by placing my hand over the other end. I covered the intake hole and and then put the suction on the other end. It was an instantanious pull, not like there were baffles and crap that it had to make it's way around. I felt no delay at all. Something interesting happened when I placed my hand over the other end with the vacume on. It was still sucking. Closer examination showed 5 small holes, presumably drain holes, on the bottom of the box. I dont think this box needs drainholes. I went ahead and taped over them and tested again and placing my hand over the inlet felt a strong suction this time. Since the locations of the holes are near the engine and transmission i will assume that there is hot air being drawn into the box through those holes. However small the amount may be, I assume that eliminating all but the cooler air behind the battery will somehow benefit the performance since plugging them eliminates any warm air from getting in.
As for the shape of the box. You basically have a tube that is surrounded by a large box. The box around the tube is not hollow. I figure there is a large amount of insulation and sound deadening material filling the void around the tube. This allows the incoming air to stay cool surrounded by so much material. The material also absorbs the intake noise keeping the sound of the incoming air quiet. Theres nothing fancy going on inside the box. It's not twisting and turning in all directions and is not impeeded by having to go around baffels either. Its a plasctic tube surrounded by a large mass of insullating material. To have made the box smaller would have allowed the air to be a few degrees warmer. Why not use all the space within that area of the engine bay and keep the air cooler was what the engineers were thinking.
I think plugging the small holes will have a positive effect on performance as well. I tried to find an internal diagram of the airbox and could not find one. I would have liked to cut it open for better examination but that would have ruined it. Final thoughts: There is nothing restrictive about the stock airbox and thats probably why other intakes cannot outperform it within the entire powerband. We get good low end and good topend balance. Other intakes just move the power around and it usually suffers somewhere. Our boxes are the best compromise.
*update*
Covering the holes resulted in a loss of performance. I decided to open it up and see once and for all whats inside. The airbox is in fact completley hollow, like a chocolate Easter Bunny!!! the intake tube floats in the middle. There are 2 small tubes (1/2 inch) that branch off the main tube just after the bends. They are about 4 inches long and just hang open in the open box. This must be for equilizing pressure or something. my conclusion is that what we have is really a cold air intake made out of plastic. What these secondary tubes are doing is beyond me, but apparently something important. The box itself must create a vacume around the main tube because if the intake is pulling air then once the air aorund it is evacuated theres nothing left for these secondary tubes to pull.
Last edited by flqu05; May 21, 2005 at 03:39 PM.
The one and only....
Joined: May 2004
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Rep Power: 0 That is very interesting! I recently put my stock intake back on and I found that low through mid rpms is a lot stronger than my Injen SRI but the top speed is a lot slower, but then again I do not need to go that fast ya know? 
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