i agree some water will always get in the engine but why take the chance? as far as the air speed issue, me and a professor at college had a conversation about what would be the best way to cool the intake. he said to bring the air to the intake by forcing it (ram air) to increase pressure. if you have the intake very far away from the afm the pressure increases are far lower. he said build a heat shield to deflect radiation from the engine and pipe cool air from outside with a diffuser within the heat shield to increase pressure. if having your intake farther away was the best idea why don't high performance cars like vipers, porsches, ferrari's have intake setups like that

 

He's right, the inake should be close to the front of the car to pull in the coldest charge possible. Ram air is a VERY minor effect and can pretty much be ignored.

You're not, there's no need for the AFM to be up front too. The reason the AFM is upstream is to keep it cool and to make sure the air flow is measured at ambient intake temperatures. Along a plastic tube, you could place the AFM anywhere as long as it's not getting too warmed from the engine.

We went into a big discussion on RAM air here:

https://www.rx7club.com/showthread.p...&highlight=ram

 

sorry i wasn't talking about relocating the afm, just that the closer the filter is to the position of the afm the higher velocity air it is going to receive. the air slows after the filter and the closer the filter is to the afm the better. the closer the afm and filter are towards the intake manifold the better too. air being forced in though piping by outside air is much better than having your engine pulling in air from a filter 4 feet from the manifold. granted the gains aren't that much but hey every little bit helps.

 

As I said before, the relationship between the AFM and filter won't have an effect on flow losses.

 

it won't effect the flow but it will affect the flow speed. the air slows down after it passes through the filter. piping the air to a filter close to the afm which is close to the intake manifold will have an overall greater air flow velocity. if the air is moving 50mph before the filter and 20mph after the filter wouldn't you want the air moving the faster speed for longer? hence piping air to a filter attached to the afm close to the intake manifold.

 

Air at these (slow) speeds is considered incompressible. Hence, the speed of the air upstream of the filter is the same as downstream. The filter (and the afm) is a restriction that effects the airspeed in total.

 

i am not saying that the distance between the filter and afm is what slows the air. i am saying that after the impedence of the filter or afm, the air is slowed. the idea is to minimize the distance that slow air travels and maximize the distance that high velocity air is travels. that would mean shortening the distance between the impedences (filter and afm).

 

The air is INCOMPRESSIBLE, it's travelling at the same speed before AND after any restriction. Ask your professor friend to explain it to you.

 

i know what incompressible air is. and you need to actually think about what you are saying. you think that because the air is incompressible that there will be no loses to friction due to the restriction. does the equation x=Cd * Ab/A (Cd=coeffience of drag, Ab=cross sectional area facing into the airflow, A=area of airway) mean anything to you?

 

I've got a masters degree in mechanical engineering studying air flows. Trust me, you're not getting what I'm saying. So you need someone else to explain it to you.

 

so you are telling me that a person with a doctorate in mechanical engineering with a specification in fluid-thermal sciences is wrong?

 

No, I'm saying that you don't understand what he and I are telling you.

 

regardless of the air being incompressible the volume will decrease from the impedence

 

because the flow is being interrupted

 

No, volume is static, set by the intake tube and plenum dimensions. It can't change.

 

and those were his words

 

but not as much air is passing though the filter as opposed to a non-filtered system

 

If you print this out and show it to him, he can explain the principles of incompressible flow that I am talking about. I'm not trying to be a jerk, there are just some things that need to be understood at this point that I can't get across without some pictures and a couple of hours.

 

yeah that or i will just say f it, because it's not worth my time anymore. you think what you want and i know what i was told. the gains from what is being discussed is negligable and probably not worth all the discussion. but thanks always good to stimulate the mind during the summer.

 

For anyone interested, this web site shows some of the calculations for losses through a pipe.

http://www.engineeringtoolbox.com/21_459.html

Just to try to close things up here, you can see that the velocity through the pipe is set by the friction of the overall system but velocity does not change as you go further down the pipe. This is one of the effects of the incompressible flow assumption.

In this case, the friction is caused by the walls of the pipe, but it can also be caused by flow interferences like the flapper on the AFM or restrictions like the element of a filter.

 

that helps. some people are dumbasses and bs physics priniples to prove a gay point, but i believe you know what you are talking about. maybe my prof and i are just not on the same page as you are thinking.

 

Long Duck I have the Mariah NACA duct as well.
Could you give me some more info/details about what you did to make that.

 

who?

 

Isn't the velocity starting to get to the point where the incompressable fluid assumption starts to fall apart? I know for fact that further downstream past the butterfly valves that the incompressible fluid assumption falls apart. Heck, the whole purpose of the plenum is to take advantage of the pressure waves setup by the opening and closing ports. I seem to remember measuring the pressure drop across a filter once, albeit it was only a few millimeters mercury, thats still a pressure drop.

 

Flow has to be moving very fast before the equations for incompressibility stop working. It has to approach sonic velocities. I've modeled incompressible flow across valve openings with very good accuracy.

I'd be suprised if you didn't measure a pressure drop across a filter. Pressure is what forces flow. You're measuring static pressure though, not dynamic.