PixelHarmony

I guess when different companies factor in this problem, it's what'll make the intkaes perform differently. Also why one should NOT buy a ripoff intake system

howstuffworks.com
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The intake system on a four-stroke car engine has one main goal, to get as much air-fuel mixture into the cylinder as possible. One way to help the intake is by tuning the lengths of the pipes.

When the intake valve is open on the engine, air is being sucked into the engine, so the air in the intake runner is moving rapidly toward the cylinder. When the intake valve closes suddenly, this air slams to a stop and stacks up on itself, forming an area of high pressure. This high-pressure wave makes its way up the intake runner away from the cylinder. When it reaches the end of the intake runner, where the runner connects to the intake manifold, the pressure wave bounces back down the intake runner.

If the intake runner is just the right length, that pressure wave will arrive back at the intake valve just as it opens for the next cycle. This extra pressure helps cram more air-fuel mix into the cylinder -- effectively acting like a turbocharger.

The problem with this technique is that it only provides a benefit in a fairly narrow speed range. The pressure wave travels at the speed of sound (which depends on the density of the air) down the intake runner. The speed will vary a little bit depending on the temperature of the air and the speed it is moving, but a good guess for the speed of sound would be 1,300 feet per second (fps). Let's try to get an idea how long the intake runner would have to be to take advantage of this effect.

Let's say the engine is running at 5,000 rpm. The intake valve opens once every two revolutions (720 degrees), but let's say they stay open for 250 degrees. That means that there are 470 degrees between when the intake valve closes and when it opens again. At 5,000 rpm it will take the engine 0.012 seconds to turn one revolution, and 470 degrees is about 1.31 revolutions, so it takes 0.0156 seconds between when the valve closes and when it opens again. At 1,300 fps multiplied by 0.0156 seconds, the pressure wave would travel about 20 feet. But, since must go up the intake runner and then come back, the intake runner would only have to be half this length or about 10 feet.

Two things become apparent after doing this calculation:

The tuning of the intake runner will only have an effect in a fairly narrow RPM range. If we redo the calculation at 3,000 rpm, the length calculated would be completely different.
Ten feet is too long. You can't fit pipes that long under the hood of a car very easily.


There is not too much that can be done about the first problem. A tuned intake has its main benefit in a very narrow speed range. But there is a way to shorten the intake runners and still get some benefit from the pressure wave. If we shorten the intake runner length by a factor of four, making it 2.5 feet, the pressure wave will travel up and down the pipe four times before the intake valve opens again. But it still arrives at the valve at the right time.

There are a lot of intricacies and tricks to intake systems. For instance, it is beneficial to have the intake air moving as fast as possible into the cylinders. This increases the turbulence and mixes the fuel with the air better. One way to increase the air velocity is to use a smaller diameter intake runner. Since roughly the same volume of air enters the cylinder each cycle, if you pump that air through a smaller diameter pipe it will have to go faster.

The downside to using smaller diameter intake runners is that at high engine speeds when lots of air is going through the pipes, the restriction from the smaller diameter may inhibit airflow. So for the large airflows at higher speeds it is better to have large diameter pipes. Some carmakers attempt to get the best of both worlds by using dual intake runners for each cylinder -- one with a small diameter and one with a large diameter. They use a butterfly valve to close off the large diameter runner at lower engine speeds where the narrow runner can help performance. Then the valve opens up at higher engine speeds to reduce the intake restriction, increasing the top end power output.

iamhomin

Interesting.

Which makes me wonder, do we even need an intake or the factory intake?

I ran a good 8 months without the factory intake or the aftermarket I currently have installed, and there wasn't much a difference.

xizor

too tired to read carefully, but aren't they talking about the intake manifold and not the intake itself? And I believe we do have a dual chamber intake manifold that changes at RPMs like the article suggests. if i'm just crazy tonight

JTso

iTrader: (2)

I think the article is talking about the intake manifold and the runners going to the cylinder head and not the "intake tube" that connects to the airbox.

The TSX doesn't have dual runners like the AE86, Prelude or Integra.

xizor

here's an article that explains how its done on the K20A (DC5R/CL7) . I assumed it carried over to all the k-series

link from TOV

Stokeless_TSX

Wow....complex you think??? haha

JTso

iTrader: (2)

The K20A does have the similar effect as the dual runners, perhaps a better design. But our TSX doesn't have it. Remember the Hondata gasket install? There isn't any rotary valve like the K20A.

Here is the dual runner design on a Intergra GSR. The butterfly is controlled by vacuum.

RMATIC09

Didnt know a car could run without an intake!

JTso

iTrader: (2)

Btw, the rotary valve system is not implemented on the RSX-S model.

RSX- Type S intake manifold



Standard RSX intake manifold with rotary valve



TSX intake manifold

xizor

interesting, so why would they take it off the K24 and K20A2, the 2 best engines they have after the K20A, but keep it on the base RSX K20A3?

And does that mean the new 2005 RSX-S w/ the K20A intake manifold now has the rotary system?

vwong

I haven't finished reading the entire article from TOV, but in the introduction of that article, it's talking about the Honda Stream and the K20A that it's talking about is the lower output version of the K20A. It says the K20A puts out 154ps. So I'm assuming that this is the same motor as the base RSX.