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Best angle for intercooler ducting?

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Since this is an airflow question, I put it here, but if it's better suited elsewhere, feel free to move it, moderators. Anywho, it's regarding an intercooler that is slant mounted (we'll just say 60-degrees for simplicity's sake). I'm going to fab up some ducting/scooping to it and was wondering what the best angle for the bottom edge would be: parallel to the ground/airflow, or, parallel to the intercooler itself. I'm thinking in the 2nd case, it would better guide the air into the intercooler fins. Would this be a correct assessment?

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IMO, there isn't a good reason to angle an IC on a S30. After the air gets through the IC, if it can, it has to go through the radiator. It would be easier for the air to continue in the same direction. If the air doesn't get through the IC easily it could restrict the radiator airflow some, possibly causing it to run warm at speed. I over think the radiator as I'm in Az.

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On my 280ZX the IC is mounted vertically in front of the radiator with diffuser style ducting welded to it. The converging angle of the ducting is ~12 degrees which means that the duct opening is smaller than the IC.

 

According to the aero research I did if there is too much air ducted in then the air becomes turbulent and so reluctant to pass through the IC or radiator core, less air flowing straight will pass through the core more readily.

 

Thats the theory, in practice it all seems to work fine on my car.

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more space between the IC and radiator will cause turbulence, which will cause loss in air velocity and thus will inadequate cooling.

 

If you "really must" angle it, for whatever reason, angle the IC and radiator together.

 

I don't recommend it, unless you are already heavily modifying the frame.

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There isn't a best angle then. Air come in the front and goes through the IC.

 

I agree. Only reason why you would angle the IC is to lessen the amount of high pressure air that gets built up at speed. As far as efficiency goes, the normal mounting is the most efficient. The front is just a pocket for air and ruins the drag coefficient :P.

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As quoted in the HP book "Aerodynamics" authored by Forbes Aird (from pages 42 and 43):

 

Front-Mounted Cooler ...so it is obviously desirable to use as little as possible of both. To take best advantage of a small core area, however, demands passing a large mass of air through it. At the same time, to minimize the disturbance to external aerodynamics, it is advantageous to admit the cooling air through the smallest possible hole. Considered together, these factors favor a small inlet area followed by gradually expanding diffuser ahead of the core, to convert a small, high velocity stream into high pressure flow over the larger area of the core.

If the internal walls of this diffuser diverge too slowly, it will wind up longer than necessary. Not only is this inconvenient from the point of view of packaging, there will also be a penalty in friction drag because of the extra length. On the other hand, there is a limit to how rapidly the duct can expand without flow separation occurring. The optimum seems to be a duct that is about as long as the core is high, and an inlet area anywhere from one half to one sixth of the core area, depending on the design speed.

 

I bolded the text where it comes closest to answering your question but I put the rest in there to help explain everything. An example would be if you had an IC that was 10"H X 24"W your duct needs to be 10" long and the opening of the duct (at one sixth size) would be 1 3/4"H X 4"W or as large as (at one half size) 5"H X 12"W which would probably be better for what you want. In my interpretation of what is said the angle of the IC does not matter as long as the inlet hole for the ducting is centered in front of the IC and the ratio that is used in the example above is followed.

 

As a side note I know from personal experience that if you run ducting like what you are asking about you will get absolutely no airflow when stopped (by that I mean any breeze or air movement that is naturally occurring) which can lead to heat soaking when sitting still (unless you decide to put a fan behind the IC to pull air through when needed).

 

Dragonfly

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Clarification, I have not read any threads within the Aerodynamics section. However, when designing the air intake and IC for my 83 280zxt, the copied photos below that came from my MsPs showed what I suggested to James, the engine builder. There is an electric auxiliary fan between the slanted IC and the radiator. I believe that adding an air dam and air channeling to the radiator would assist air movement and lessen air turbulence. The auxiliary fan is needed during the summer time; not so much now (AR).

restoringtakeadeepbreathtitle.jpg

john

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As quoted in the HP book "Aerodynamics" authored by Forbes Aird (from pages 42 and 43):

 

 

 

I bolded the text where it comes closest to answering your question but I put the rest in there to help explain everything. An example would be if you had an IC that was 10"H X 24"W your duct needs to be 10" long and the opening of the duct (at one sixth size) would be 1 3/4"H X 4"W or as large as (at one half size) 5"H X 12"W which would probably be better for what you want. In my interpretation of what is said the angle of the IC does not matter as long as the inlet hole for the ducting is centered in front of the IC and the ratio that is used in the example above is followed.

 

Excellent post, but I have to correct your mathematics; its an easy slip-up, and I had to triple check myself to make sure you were wrong and I was right.

 

A core 10"x24" has an area of 240 sq inches. You would therefore be looking for an opening with an area around 40-120 square inches, which would vary from 4"x10" to say, 8"x15". 5x12=60 sq inches, 1 3/4x4=7 square inches!!!

 

You forgot squaring :)

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Excellent post, but I have to correct your mathematics; its an easy slip-up, and I had to triple check myself to make sure you were wrong and I was right.

 

A core 10"x24" has an area of 240 sq inches. You would therefore be looking for an opening with an area around 40-120 square inches, which would vary from 4"x10" to say, 8"x15". 5x12=60 sq inches, 1 3/4x4=7 square inches!!!

 

You forgot squaring :)

 

Ha ha good catch, I started to square it but thought to myself "nah your just making it more complicated". Most people I know tell me that I make things much to complicated for people to understand so I tend to now try to simplify things as much as I can.

 

Dragonfly

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Ha ha good catch, I started to square it but thought to myself "nah your just making it more complicated". Most people I know tell me that I make things much to complicated for people to understand so I tend to now try to simplify things as much as I can.

 

Dragonfly

 

I hear you; same here.

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