Radiator and engine bay aero

Thanks for the dedicated aero discussion.  Good stuff.

I'd like to ask about a little different aspect of aero - radiators and cooling.  I'm swapping a 2.0 EcoBoost engine into a 1973 TVR M-series, and I'm currently working on mounting and ducting for the radiator and intercooler.

Here's roughly what I'm working with:

And the radiator by itself:

Ultimately I'll be shrouding the whole front end and sealing off the nose to the ducting.  The M-series is actually pretty amenable to this sort of ducting.

Questions (I'm a bullet-point guy - sorry in advance):

1. Should I duct tightly to the intercooler, then neck that ducting out to meet the radiator?  Or should I just do one big radiator-sized duct and have the intercooler inside that?

2. What about ducting on the back side?  I could pretty readily duct downward to the bottom of the car, in front of the engine.  Would this do anything?  Or would that have to be in conjunction with some flat-paneling on the bottom?

3.  Will an oil cooler behind the radiator get any reasonable air flow, or should I try to mount it up front somewhere?

Thanks!

Anecdotally I have heard that most folks spend way too much time thinking about ducting air to the front of the cooler and way too little time ducting air away behind the cooler. 

Best approach is to just build something and test it, use a magnehelic gauge (sensitive pressure gauge, tests differential pressure, cheap on ebay - I just bought one less than $20) to measure pressure on both sides of the cooler. Higher pressure differential means better flow through the cooler. 0 pressure differential means 0 airflow. 

It's all about the pressure differential. High pressure on both sides of the heat exchangers gets you very little.

Air is lazy. If it can go around something, it will. Hanging your IC out in the breeze will not work as well as encasing it in ducting.

Pusher fans are less efficient than pullers, but sometimes packaging is not your friend.

In reply to Keith Tanner :

The pusher fans are what's available.  Things get tight right behind the radiator.

Yeah, that's pretty clear from the picture. You do what you have to do.

Keith, would you say that ducting tight to the intercooler, then spreading to match the radiator would be the way to go?

Ducting tight to the intercooler and then flaring out to the radiator only works if theres enough air coming in through the tightest part. I would thing a good bell mouth necking down to the smaller and bigger for the radiator would have a venturri effect.

But thats me....

Concepts:

Here's a side view.  All the cooling air first goes thru the intercooler.  The ducting expands to match the radiator - both in width and height.  The oil cooler is smushed up against the radiator to get some air flowing thru there.

Top view:

Assume gaps will be sealed with an appropriate foam object / rubber edge trim.  Assume the front end meets up reasonably closely with the grill opening.

Thoughts?

I'm not strong enough on my theory to say if you'll get a venturi effect, but if you don't duct the intercooler you won't get air through it. The air will bypass the intercooler otherwise.

I'd be tempted to put that oil cooler somewhere if you have room. It's going to see air that's been preheated by both the IC and the radiator, so its efficiency will be pretty poor.

Can you use a duct the size suitable for radiator with a smaller duct inside of it dedicated to the intercooler? Then air in the dedicated intercooler duct wouldn't pass around the intercooler and the radiator will have mixed air cooler than if all of it's air came through intercooler. Someone with more math skills than I have could calculate the duct sizes necessary.

I'd put the oil cooler out in front of the other stuff.

Edit: I'll add that in the nice colored pics above it appears you're trying to make the air inlet at the front of the duct the same size as the radiator. You should be able to make a system where the duct entrance is smaller than the radiator size. Fans would cool radiator when stopped or going slow and air pressure difference (front/back of radiator) at speed would allow enough air for intercooler and radiator cooling. If you get it right the fans shouldn't be needed at steady highway speeds.

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TVR Scott said:

Concepts:

Here's a side view.  All the cooling air first goes thru the intercooler.  The ducting expands to match the radiator - both in width and height.  The oil cooler is smushed up against the radiator to get some air flowing thru there.

Top view:

Assume gaps will be sealed with an appropriate foam object / rubber edge trim.  Assume the front end meets up reasonably closely with the grill opening.

Thoughts?

So, the first thing to keep in mind is the subsonic conservation of mass relationship of:  A1*V1 = A2*V2

so, in your current design, you are accelerating the flow into the intercooler, which is actually a bad thing.

 The other thing to keep in mind is, (again for sub-sonic flows) that exit pressure controls the flow through the system.  This is part of why “puller fans” are better than “pusher fans”.  Another way to think about it is you can have a single inlet area cover a wide speed range if you have the exit area in a sufficiently low pressure area.

IIRC, there’s A general rule of thumb is you want you inlet to be 30-50% the size of your radiator.

Considering the space you have between them longitudinally (I.e. front to back), I’d be tempted to suggest that you drop the intercooler slightly, and angle the top back, and then duct it separately from the radiator... using the top of the intercooler duct as the floor for the radiator duct.  Then you’d exit the intercooler flow out the bottom, and then do the same for the radiator further back.  But, I don’t know if that is feasible with the TVR’s front body work?

edit to add a quick sketch of the suggestion above...

All good info, thanks.

I had thought about doing what NOT A TA  is suggesting with the small intake inside the large one.  I hadn't thought about having a totally separate inlet and outlet for the intercooler, like sleepyhead is suggesting.  I'm going to have to think a bit more on packaging.

As far as hood space goes, the frame shown in the drawing is about as low as I want to go.

The hood picks up roughly there and is a little higher than the spare tire shown.  I probably do have room to totally separate the flow.

Good info on the inlet size.  I'll keep that 30-50% in mind as I move forward.

I was talking with a friend this morning who did a bunch of FSAE stuff in college, and he said the rule of thumb there was to slow the flow down into the heat exchanger.  So small opening, expanding to larger.  Basically what you all are saying.

Thanks!

I assume you want to keep the spare there. If so-can you throw a space saver in there and move the rad up or down 6" and throw the intercooler below or above it? Makes ducting simple, shortens intercooler piping, centralizes mass, etc..

In reply to TVR Scott :

I’m a bit behind on your thread, so I’m going to go back and read it.

off-hand, though, is this going to be a “weekend cruiser” build; or will it see competition, and if so: autoX or track?

sleepyhead said:

In reply to TVR Scott :

I’m a bit behind on your thread, so I’m going to go back and read it.

off-hand, though, is this going to be a “weekend cruiser” build; or will it see competition, and if so: autoX or track?

Use will be Auto-X, neighborhood driver, mountain cruiser.  Probably no track time, since I don't want to risk rolling it.

Ultimately I'd like to figure out an A/C system for it, which will contribute to the heat load a bit.

Alright, so I’ve read through your thread...

and one thing seems glossed over is the new radiator.  Was that sized by Wizard Cooling based on the volume of the Focus radiator?  I’d guess it was 1/3 the height of the one the EB usually uses... but maybe it’s 3x as deep to make up for that?

I think, in the end, you’re going to want to expend some effort to make the fender vents as functional as possible.  If you add AC, i’d consider putting the condenser around the pax frame rail, and between the fender-liner and the battery box... feed it from the pax N.A.C.A. Duct in the hood and out that fender vent.

If you weren’t going to add A/C, I’d wonder about sticking the intercooler somewhere around there and feed it from a duct from the front and then out the fender vent.  Although, the exit for that is probably too small for the full flow of the intercooler.  And this suggestion is definitely one of those “think outside the box”, just to better understand the constraints system, ideas.

A little less “outside the box” is to put the intercooler behind the spare tire, but rotate it so the flow is “up to down”.  Then you’d want to build a duct for it into the hood that goes up and over the tire.  This is one of the few cases where you’d probably want to start with an inlet area around 75% to 100% the size as the IC, then constrict it a bit in area over the tire before expanding to match the IC.  This is one place where a Venturi could be helpful, since it would allow the flow to overcome the drag of the distance of the duct, and the 100-120deg of turning it would have to do.  In the scenario you might move the radiator forward a little bit, and then you’d probably want to build a duct that combines the exit of the IC and the radiator and pushes it out the bottom of the car in front of the oil pan, but turned so that it’s pointed “back” and not “down”.  (I’ll see if I can mangle up what that would look like later).

A final thought is similar to what I proposed originally.  With the IC moved forward a little bit, and probably with the spare tire moved back, if possible.  The I’d suggest, since you’ve already got to fix the ‘bonnet’ to frame attachment some, that you build in a IC exit ahead of the attachment rod.  Unfortunately, that would mean hacking the bonnet some, which I reckon you’re not too keen about?

I realize these probably all seem a bit convoluted... but I’m concerned about ducting the intercooler inside the duct to the radiator with the fans in front of the radiator... which means you can’t get a good “seal” between the IC and the radiator... which i think would cause problems, and probably will lead to a dead zone of air in between them.

Also, I find frenchyd’s comment about ‘ducts after the radiator being unimportant, because the air is turbulent’... interesting?  I mean, it’s not like the air outside the car before it gets to the duct isn’t turbulent... that’s why we put the duct there... to smooth the flow and encourage it to do what we want it to do.  That works well for exhaust flows and inlet flows, imho.  And some of the exhaust flows I’ve described most likely need that help to do what we want it to do.

standard caveats:  imho; seek a second opinion, I’ll defer to stafford’s expertise; ymmv; choose your own risk, etc etc etc

 Sleepy, what I Know about Ducting It Is to Move Air from where it is available to where it Isn't.

       What I am Saying here Includes 'Ram Air' Effects,

    If You Have an Opening say it's 1000 CFM Capable, carb or ducting,

  To a Radiator , Once the open area is filled with air no more than 1000 cfm can flow through it, the radiater in the line of flow also makes it Back up and 'Stack up' around the opening, and Turbulance Further distuerbing Intake, IF you could build an exausting duct into a low pressure area That Could Help But would need to be the size of the Radiiator itself. best to just let it out.

I Don't care how big of a scoop you put over a carb, Only the amount of CFM can flow through the engine that Equals Cubic inch X rpm,  This was a big Argument when Nascar went too Smaller carbs,  Like a GMC Blower Air Drops in to a Carb or Blower, From Atmosphereic Pressure Not being Sucked in, So Scooped Air only flows what the restriction allow's

so Frenchyd's right

In reply to sleepyhead :

Couple quick responses before I go further in detail.

The new radiator replicates the stock one in size and position.  The material has been upgraded to aluminum and the triple fans replace just an engine-mounted fan.

Size-wise it is a little less than half the height of a ST radiator - about 8" vs 18", but it's three times thicker at 3".  Width is the same at 26".

I hadn't really thought about using the NACA duct for cooling air, though it might be a good spot for engine air.  Would need an appropriate heat shield.

BTW, the spare shown in the concept above is already a compact 20" OD x 5" wide.  The stock spare is 24" x 8" and dominates the space.  I like the idea of keeping the spare, but if packaging wins then it'll get deleted.  I think that right now the compact will be a good compromise.

I'm going to work on some more 3d modeling, and I'll post more later.

Thanks!

Here's another version with the intercooler up high, and a separate duct for the radiator down low.

In width, the intercooler duct would be only 18" wide, and the radiator opening could also use some of the space around the ends.  Unless the packaging on that was terrible.

This also maximizes the mounted height on the spare tire.  I moved it up about 1-3/4 from where it was before.

Thoughts?