lowpro

A while ago I installed a cold air intake by cutting a hole where the rad overflow is mounted and connecting 3" pvc from the intake to the grill under the bumper. Is water getting sucked into the engine when it rains? Im wondering if I have to put a screen on it. Also, I've heard that ram air dos'nt work until 170mph but it must help a bit above hwy speed shouldnt it?

Scalliwag

Without seeing the setup it is hard to say if you are getting water in. This would better be described as a cold air intake though. There are ways to deflect water from getting into a setup like this. That would be different with each setup and impossible to make a suggestion without some pictures. You need some sort of screen in front of it to keep leaves and other debris out.

KiyoKix

I'd also like to see some pics. By the way here's how ram air works (very basic). At 60mph the pressure is equivalent to 1psi, and then at 100 it's 2psi. So yes it does work and no you don't have to do 170 to do it

Gearhead

iTrader: (1)

Kiyokix, I don't think you can assume that. It depends on location of the inlet, size, and ducting. I hardly think you are gonna get 1psi at 60mph. I could be wrong.
Don.

Scalliwag

You are right. There are a lot of factors on this. A straight 5" duct going directly into the induction system is going to push more air at lower speed than a smaller duct with a lot of bends in it. I would not speculate the numbers, but one thing that is for sure is there would be a significant difference.

KiyoKix

That's why I said very basic, it's true that the position of the inlet matters the world. But a good system will give you those results. I forgot where the information came from but I've been studying that type of thing for sometime now and I know it came from a very reputable source.

lowpro

Right now the inlet is resting on the thick round bar behind the grill in front of the radiator. It could be lower but I'm going to add a 4"x6" inlet to make sure nothing is in its way. I attatched the other end of the pvc using a 3" rubber pvc connector with clamps to the stock intake with a gasket so the 3" connector would fit. Their is a flow restriction because of the size difference but it's not a big deal. The car feels faster, especially because its October and even if air isnt getting rammed into the engine, It's most likely going in at near the same rate the engine is sucking it in. It only costs 10-$15 so its easily worth it. Ill get pics soon.

Scalliwag

The reason it feels stronger is because you are getting cooler air into the system. That is why you hear people talk about cold air systems. The colder the air the higher the oxygen concentration. The higher oxygen concentration makes a lot of difference.

Detriuch

iTrader: (1)

ahi i doubt its sucking water unless its siting for a while. need a pic though man

lowpro

Thanks, I'll try to get a pic within the next few days.

purple82

Actually, the cross sectional area of the inlet air doesn't have anything to do with the pressure built at the front of the air inlet. It's simply the amount of pressure created by bringing air speed to a stop relative to the car speed. Using Bernoulli's equation for incompressible flow, the pressure created by bringing air to the same relative speed as the car is 1/2*density*(velocity^2) where the velocity is the speed of the car. If the car is moving at 60mph at sea level, the pressure built up at the inlet of an exposed air duct (or anything else directly facing the front of the car) is 0.06psi. Insignifiant compared to the vacuum created in the intake plenum. Notice that the pressure increases with the square of the speed so every time the speed doubles, the pressure buildup quadrouples.

The AMOUNT of air that enters the duct depends on the inlet area of the duct as well as the pressure (or vacuum) in the duct.

The bigger benefit of a Ram air system is the lowering of the temperature of the inlet air. The density of an ideal gas (air within the temperatures here behave as an ideal more or less) decreases linearly with temperature. If the engine bay inlet air is at 95C but the air ouside the car is at 70C, the difference is about 7% on absolute scale, meaning the inlet air to the plenum is 7% more dense. This is a real improvement in inlet air density that can be used by the engine.

Scalliwag

That would be the scientific explanation of my previous post

Gearhead

iTrader: (1)

Purple, just out of curiosity, can you use the incompressable flow equation for air, which is compressable?
Thanks,
Don.

purple82

Air doesn't act very compressible until it's speeds are much higher or there is a large pressure change.

schexy1

If the flow capacity of the duct work exceeds the draw of the engine and the inlet size is larger than the duct size, positive pressure can be achived at the intake ports. The amount will depend on restrictions (bends and filter). A local motorcycle racing team claimed to achive 4psi at 140mph on a 86 ZX6 by modifying the ducts.

Scalliwag

Like Purple said, "Air doesn't act very compressible until it's speeds are much higher or there is a large pressure change." The "boost" effect from the increase in air pressure is minimal even at higher speed and does not do you any good until you are getting pretty close tp the end of the track.
But the effect of the cooler air is immediate and maintained throughout the entire run. People notice that their cars are running better and in their mind they are thinking "man this forced air is the ****!" not realizing that the difference is being caused by the air temperature.

purple82

At 140mph, the ram air system has added .33psi at sea level to the inlet of the intake system. I don't know what the nominal pressure is in an intake plenum, but I would still guess this isn't doing much for power.

What schexy1 is talking about is the conservation of mass within the duct. Conservation of mass and incompressible flow dictate that the mass flow rate of any fluid flowing through a duct must remain constant. The equation here is:

(mass flow)=(density)*(velocity)*(area)

You can increase the velocity of the air flowing through the intake duct by having a large area at the intake inlet and gradually making it smaller as it reaches the ports.

Lets say the area at the inlet is double the area at the ports. At the port, you've doubled the speed of the air coming into the inlet. If you use the dynamic portion of the bernoulli equation again (1/2*density*(velocity^2)), you have quadroupled the pressure by doubling the velocity.

There are lots of frictional losses in automotive intake systems so the actual gains will probably be 15-25% lower in velocity.

Scalliwag

Here is the way I equate it that is somewhat relative but only to give an idea of what is going on. If you had a bucket with a hole in the bottom and you tried to pour water in a bucket at a faster rate than the hole allowed the bucket would overfill and the faster you added water would not really matter. That would be a naturally aspirated bucket.
But if you put a lid on the bucket with a fitting to attach the hose to, the higher you turned up the water pressure the faster it will go through the hole. This would be "turbo bucket"( or supercharger bucket")!
I know a lot of the principles here are different but I think it may help to grasp the concept a little easier. The air will take the path of the least resistance. Once the duct has reach full volume any excess air diverts around it.

schexy1

the motorcycle is just an example to say that positive pressure can be achieved with ram air. Is it practicle or benificial? It is not benificial where we want it (low end). Because the ZX6 already had a ram air intake the 60' and 1/8 mile times didn't change much. the bike did see a significant change in 1/4 mile time and was able to incresse top spped by about 15mph. As far as practical goes. The ZX6 had intakes that looked simular to the one on a V-max, only 3 or 4 times as large. On a car the intake would probably have to be about 4' x 8'.

I am not saying any of you guys are wrong, most of the cars with ram air intakes only benifit from the cold air. I'm just saying that it can make a difference if a system could be built the right way (which would make the car undriveable)

purple82

So are you saying they had ram air on the bike, added a larger inlet and saw an improvement? This isn't the ram air helping as much as it's the change in flow area increasing flow momentum.

schexy1

I am saying that the stock intake system (called ram air) equated to a cold air system (which most of the cars actually have), because there was no positive pressure at the intake valve. By modifying the size and redirecting the path positive pressure was achived, proving that ram air can provide significant boost.

purple82

Again, it's the change in area that increased pressure, not the ram air. You'd get the benefit at any road speed.