v-mounted intercooler

[KTem]

Heya,

I'm building a Mazda RX7 FD right now. It's going to get modified a bit; I'm going for an "RX7 biturbo" (a small stock turbo plus a bigger one). Now I heard the 13b engine gets pretty hot, so it needs an efficient intercooling system. That made me think of putting a mk4 supra intercooler in it, and mount it in a way like this;



V-mount. Pardon me for the "brilliant" drawing... According to a RotaryExtreme.com, this is the most efficient intercooler setup you can dream of. The intercooler and the radiator would both get a sufficient amount of cool air, without the one blocking the other's airflow.

However, I'm having doubts. How would the intercooler get cold air? I mean, the biggest surface the intercooler has will not be cooled by driving wind when the car is moving. Would't I need a hood scoop, like this?



The cold air gets to the intercooler through the scoop.

Sooo, am I right? Do I need to make a hood scoop in order to make the v-mount "work"?

dang, I hope not...

Thanks, Koen

[hirofkd]

I think intercooler's hot air exits from the top of the hood, i.e, the air hits the bottom face of the intercooler.

ADDED:
I'm not familiar with automotive aerodynamics in detail, but in aerospace engineering, the air that travels over a curved surface (like engine hood) is accelerated, and the faster the air travels, the lower the pressure gets. I don't know how strong the effect is, but I think it should create a certain degree of suction and pulls air out of the intercooler.

ADDED2:
http://www2.mech.kth.se/courses/5C1211/extlec04.htm
Okay, I've found a picture so I can explain this better. Look at the analysis on the Volvo. It shows the stream velocity and pressure gradient. The coefficient of pressure (Cp) is negative around the front end of the hood(blue and cyan regions). If you make a hole around there, the air will be sucked out of the engine room (assuming that the Cp value in the engine room is positive). Also, look at the side, just behind the front wheel, the velocity is fast (red), and the Cp is negative. That's why cars like RE Amemiya's RX-7 racer has a huge opening there, so the hot air from the engine room can escape effectively.

Here's an animated sequence of airflow around a car. The page doesn't say what the colors of the ball indicate, but I'm almost certain it's the velocity, and in this one, red is slow and blue is fast.
http://www.tecplot.com/showcase/gall...imation/50.asp

[freakray]

Have a look at the WRC...the 2001-2002 Subaru is a great example of what Hiro is referring to.

[redstang423]

Well don't take it too literal because you'll never have the "most efficient" setup for anything that you could dream of, because you'd really need to have the surroundings of the system at absolute zero to get the most efficient as efficient as possible. obviously thats not possible. With any system in automobiles that involves airflow, there are going to be trade offs. In this case, the more "unobstructed" airflow you get to the intercooler/radiator while your moving, the better they will perform, but you'll face more aerodynamic drag on the car. You'll throw lots of eddy currents and junk into the engine bay as well, so its difficult to say whats "best."

Basically what it comes down to, do it however you want!

[yelo]

hiro is right, the air goes out the hood scoop.

you'll have to build some sheet metal on both side of your set-up so the air goes trought the rad. and inter-cooler (not around it)

yelo

[KTem]

Thank you all.

So, if I understand correctly, the hot air exits the intercooler through the hood scoop. The airflow around the hood creates a suction that sucks the hot air out of the intercooler. So a v-mounted intercooler without a hood scoop would have little use, as the hot air stays within the intercooler. Am I correct?

[yelo]

it's almost that

the air goes out trought the hole in the hood but i don't think it's suck out like you say

the air is forcedinto the front of the car and split between the rad. and the i/c, that's why you have to shroud the space around so the air goes trought and not around your assembly.

hope you understand better now, Yelo

[KTem]

Hiro: thanks for all your effort to explain me! This is really helpful. So, the green dots indicate that the air is moving fast, so the pressure gets lower. Because of that suction occurs, which helps the intercooler to get rid of the hot air, if I understand correctly? (I'm not much of a physicologist )

Yelo: thanks for pointing that out, you're right. The v - mount setup wouldn't be that efficient if the air goes around the IC and radiator, so I need to build some cover...
Are you sure the air isn't sucked out?