Well upon taking apart my engine today for some cools mods i decided to cut the stock throttle body to supercharger inlet tube at its most restrictive point. After a few mesurements I figured out that the area of that part of the tube is about half the area of the stock throttle body.

So my question is, how can a larger throttle body increase to power of the car is the bottle nech is not the TB, but the tube right after it?

I'm going to make one out of aluminum tubing to get rid of this god aweful thing. If anybody had made a new one post up some pics.

PS: i know about M7s air gain thing, i just don't like the idea of pulling in air from directly behind the radiator.

 

How small is the stock tube? and if you get the alta cai the optional hose is what your looking for right? you might want to see if you can just buy that



Or is there another hose your talking about?

 

I'm talking about the plastic pipe after the throttle body. it goes from the TB to the supercharger inlet.

 

Good info. What were the measurements that you got?

 

My measurement was taken four inches away from the supercharger inlet. The port has an upsidedown L shape to it.

I'm picking up materials tomorrow to finish my turbo setup that i'm putting together, and while i'm getting that i'm going to pick up some alum stock so i can start to make a new pipe.

 

The benefit is that, assuming air can flow nicely into the larger TB and through the tube, it will gain velocity roughly proportional to the change in the cross area of the SC duct. If the cross sectional area is cut in half, the air moves roughly twice as fast. It's the same idea as a "velocity stack." The faster the air moves through a given cross-sectional area, the more mass you flow, and the more air will pass through the valves per unit time. The faster the air, the theory goes, the more power.

 

OK, i see what you're saying. I have a question though. Have you ever seen the inside of the SC inlet tube? It is far from being a velocity stack. Not only that, but it is so deformed and not straight that it HAS to hurt the volume and velocity of the air traveling though this peice.

If what you're saying at trully be applied to this inlet tube, then i'll make a new tube that is made of 1" pipe. It'll act as a velocity stack right? Botum line, i think a straight 2.5" or 62mm ID pipe would work MUCH better that the stock peice.
In fact, i want to try this so badly that i've already started to make a new peice. I just finished making the part that holds the gasket for the SC inlet. tomorrow i'll make a merge for this peice to a 2.5" ID alum pipe. I'll then snake that pipe towards the original location of the TB.

I think i'm going to test the vacume at the SC inlet with the stock tube and the new one too, so i have some hard facts.

 

You're basically re-inventing the AGS, which is a worthwhile mod given some recent but as yet unreleased data [it's coming soon!] data. Even the stock tube DOES give a functional velocity increase- the only limiting factor to velocity is how smooth you make the flow path.

Anyways, before mocking up a design, you must remember that you're gonna need to drill holes to add all of the lines that intersect the stock tube. You're also gonna need to mold a new SC-mating interface. The SC mating surface is NOT circular. Overall, the project is not gonna be easy, especially considering you must measure to make sure your tube fits! Test fit with the radiator and fan assembly replaced BEFORE you get too far. It's close, from personal experience .

 

Already finished with the peice that connects to the SC The ID of one side is 2.5 (roughly) and the ID of the other side is 2.25 (roughly). I cut a 1/2 inch strip of 1/4" alum that was just over a foot long then bent it around pipes (2.5" and 2.25") to get the shape i needed.

 

Cool . Now, make sure the holes you tap are _smooth_ on the inside. If they aren't, they'll impede laminar, smooth flow. You could lose hp if they aren't flush.

Please post a picture, if you can!

 

Not sure I buy into this velocity stack idea. If the cross sectional area is cut in half, sure the average velocity of the flow would double, but the mass flow rate wouldn't change. No air mass flow increase, no more power. But, even this description is optimistic. As the flow velocity increases, viscous losses increase proportionally to the shear rate (at least for a Newtonian fluid in laminar flow, which is a reasonable assumption for the flow in the SC tube, although admittedly I haven't tried to calculate a Reynolds number). Therefore, if the flow area were cut in half, in actuality the flow velocity would increase somewhat less than 2x, and therefore mass flow would be reduced.

Great idea on the new SC tube, BTW. Don't bother with any "velocity stack" flow restriction, though. Make the flow area as large as possible!

 

I'm waiting for a friend to come over with a digi camera.I port heads and what not all the time so everything will be smooth. i'll raduis the entry to the bypass valve and to the vac lines.

 

I intend to keep everything at 2.5" ID

 

Agreed on making the area as large as possible. The wider the intake tube, the more volume of air you can flow per unit surface area. The wider the cross-section, the less resistance there is along the tube, hence the "faster" the air will travel. People always imagine flowing water through a narrow hose versus through a wider hose.

Therefore, I must respectfully disagree about the velocity stack bringing no benefit. I'm positive you'll agree:
When the path area decreases, the air velocity WILL increase [not perfectly, but nonetheless]. Also, you'll likely agree that the cam lobes keep the valves open for a set and predictable amount of time. The faster the air flows through them, the more air you're passing in.

Now, I'll agree that the air mass does not change in a given tube during the acceleration (air is not created ). BUT, there is a functional increase in the amount of air that can pass through when you widen the intake end, because of the reduction in resistance in the larger tube. So, when you widen the intake end, you take more air in, and when you take more air in and the area of the path narrows, you get a net gain in air velocity.

The path keeps narrowing down, all the way down to our tiny intake valves. The velocity increases quite a bit, especially after the supercharger.

 

Increasing velocity doesnt mean that pressure (density) remains constant. You're not necessarily gaining power with velocity.

I'm FAR from an intake runner design expert but I'm pretty sure that cross sectional area isnt where its at, especially when dealing with turns. You want the short turn wider because the air naturally wants to follow the shortest path. You'll have a higher velocity around the inside turn and the air slows down as the turn get wider.
Bigger duct means the larger surface area of creates more friction.

Its not simple and not always intuitive (atleast to me). Bigger isnt always better.....yeah i said it.

 

perv . Bigger tube does mean more surface area, but cross section area=1/2*pi*r^2 whereas tube surface area=2*pi*r, so for a two-fold increase in radius, you get a 2-fold increase in tube surface area, but a FOUR-fold increase in cross-section area. Hence, less tube surface area per unit cross section area/air volume. Right? :smile:

Put another way, it is much harder to drink through a thin straw.

As far as density, density will only change with temperature as it passes through a simple tube, I do believe. Increase the temp, decrease the density. But, since temp would not appreciably change if you swap tubes, it's a non-factor, I think...

 

Bernoulli's Principle says otherwise!

 

In this case the supercharger is the glass and this tube is the straw. I'm going to datalog boost levels before and after to see if there is any change with this mod.

Remember that there are two air pumps here, the more you get to the first one, the more gets to the next one. :smile:

 

You are quite right about that, we should ideally consider Bernoulli's Principle, but I didn't/don't believe that the sorts of velocities we will see before the SC will make a significant change in the air pressure in the tube in question. If anything, I would expect the pressure to increase due to the resistance to flow as you approach the SC. The flow will oscillate as the impellar turns, thus creating a certain back pressure...

Anyways, though, I was trying to keep it sort of simple, and I'm pretty sure that the density won't change too much. If it does decrease, then that will be at the product of creating even higher velocities per given decrease in tube size, since, if pressure fell and the number of particles remained the same, volume would have to increase.

 

I do agree that when the flow gets to the valves, which open a fixed amount determined by the cam, that a higher flow velocity should = greater mass flow. However, the SC tube is so far upstream from the valves that any change in velocity there will be inconsequential. For example, even if the flow were to speed up thru the SC tube, it can't penetrate thru the vanes of the SC, so the inertia of the gasses upstream of the SC will be wasted as heat.

 

If this were true, the twincharge kits would not see the extra boost created by the turbo... . I'm pretty sure that some extra inertia CAN add to the boost. Otherwise, people wouldn't see increased manifold pressures with the Alta intake [or the HAI, AGS]...

 

Think of the system. The faster the air is before the SC, the more air will cram into the SC when the vanes are open to flow. More velocity upstream of the SC is essentially like having a minor boost increase, like ingsoc said.

 

this is ain't quite right:
"The faster the air moves through a given cross-sectional area, the more mass you flow, and the more air will pass through the valves per unit time. The faster the air, the theory goes, the more power"
the first assumption in tracking flow is that that mass is conserved; it may bunch-up, but you can't get more out than what came in. One advantage I can see to higher velocity is if you have a carburettor. another is to maintain momentum right in the intake ports to aid cylinder filling.
the second assumption for flow analysis is that the total flow is a function of summing all the restrictions and pumps. Starting at the intake end, air can more easily enter your system if the entry is shaped like a velocity stack, which has the function of coupling the infinitely large exterior area gradually (over the length of the stack) down to the intake tube size.

 

The faster air moves through A GIVEN [the same] area, barring any difference in pressure, the more air [mass] you flow [per unit time].

 

i think your conclusion was:"The faster the air, the theory goes, the more power." By constricting parts of the system, in order to conserve mass, flow has to speed up, so yes, in that constricted arera, there is more density (and less volume), but no new mass is being developed.

my point is that velocity is irrelevant to the the total mass flowing and it is the mass that develops the power, assuming you can get it into the cylinders.