Barwick

I've done some calculating and I've come up with what should be ideal dimensions for a FMIC for a 13B.

It looks like 28" wide by 6.5" tall by 2.5" thick allows for enough CFM (630 CFM) to flow exactly enough air at 14.7 lbs boost at 8000 RPM on a 13B (630 CFM) at 85% VE. It's about 20 or 30 CFM short of 20 lbs boost at 85% VE though (but who the heck runs that on the street?).

How'd I come up with this:

With 28" x 2.5" available for the charge face, that leaves 70 sq-in charge face. Now, a little more than half (about 45%) of the charge face is available for flow (remember you have chambers for ambient air to flow through, *plus* you have the walls of all those chambers, *plus* you have the turbulators).

So you're left with 31.5 sq-in available for charge air. For every sq-in of charge air, *about* 20 CFM can reasonably flow through there without hitting too much restriction.

That leaves you with 630 CFM available flow through the intercooler before you start hitting too much restriction and causing pressure drop.

Now, why 2.5" and not 3"?

With 3", you can flow enough CFM to support 760 CFM before hitting restriction, which is 20 lbs boost at 8200 RPM. That's a *LOT* of boost and a *LOT* of RPM for a street driven car that you want to last.

So, would 3" help, yeah, it'd help a bit, but 2.5" is suficient to keep the ambient air flow as high as possible while maintaining enough area for the charge air to flow through.

Now, why 28" x 6.5"? This allows for 6600 CFM to flow at the ambient side of the intercooler (again take 45% for the available space (I'm not sure if you do this for the ambient side, but I'll do it to be safe)) and you're left with a 4.7:1 ratio of ambient air to charge (hot) air, still more than sufficient I believe. (10.4:1 if you don't take 45%). Having it only 6.5" allows it to fit and leave space for the radiator to flow air, and also not have the charge air have to run through miles of pipe to get through the intercooler (6.5" is WAY less than the 10" or 12" other intercoolers have), the longer the chamber, the more restrictive it is.

$150FC

not really any room for a 28" core. with endtanks that will be close to three feet.

rzograbian

how about a greddy 3 row for a single?

RETed

Where are you getting all these ludicrous formulae from???



-Ted

Barwick

Endtanks aren't going on the left and right side, that'd be utterly ridiculous to try to shove all that air through 28" of intercooler. The end tanks go on the top and bottom.

The formulas are from:
1) A book on turbo setups by Corky Bell
2) Common sense (ambient flow = 60 mph * x sq-ft * 5280 ft/mi... you get the idea)..

Barwick

You want all the formulas?

Download MathGV and I'll post my graphs for calculating different CFM on the engine at different boost levels and such...

http://home.comcast.net/~mdeminico/turbocalcs/index.htm

j9fd3s

iTrader: (3)

its like 27" frame rail to frame rail (unless you put it way up front), there's room for about 11" tall. the fc might be one app where the available space dictates the size of the ic

Barwick

man I wish my TurboII was here already, I'd be measuring it right now...

SPOautos

So your going to have the end tanks on the top and bottom with the rows going up and down?

STEPHEN

RETed

How do you compensate for thicker cores, different internal fin designs, airflow vector to fin direction, etc.?

Doesn't the book also tell you that you can run 1/4th the duct area to IC core area, right?



-Ted

Carl Byck

I will be running a 26x10x3 core, it is 33.5 end to end. I can fit a 12" high, but that will interfere with the airflow to my top oil cooler, and the top third of my radiator. tho only obstruction that cannot be removed in the front of the car is the Round ~2" tube(subframe?) everything else can be removed, and the IC fit without too much Drama. I am using the Billet TB elbow off Ebay, and a Spearco Boost coolers IC as described above. for me the greddy is too tall, and too narrow.

Carl Byck

another, this is actually the fmic from my 97 supra, but it is roughly the same size. The one I will be using is 2" wider, and an inch taller. as far as "utterly ridiculous, ther are ~200 Supra guys making 750+ RWHP with ICs this big, and larger(4" thick).So much for that theory. Yes a vertical bar and plate would be best, but it would have to be two smaller ICs welded together as nobody make one that big. there was a guy, Kieth Ta that made one to use with his TWIN T66 Setup . Carl
WEENIES

Barwick

It's assuming the charge air ducts are equal length to the ambient air ducts.

And for thicker cores to calculate the charge air area:

Core width * Core Thickness * .45
(28" * 2.5" *.45 in this case)
If you have the same core but 3" thick:
28" * 3" * .45

Barwick

That's what's going to happen, the guy who bought my FD could afford to buy it because he got into making custom piping, intercoolers, manifolds, and other such things.

He uses blackstone cores (silver core intercoolers) for better heat transfer (silver is a better conductor of heat than aluminum even), and it's surprisingly cheap. He makes them custom, and they end up being very cheap for a full setup.

I'm going to be the "tester" for this FMIC setup (once we get it designed) and hopefully if all looks good, he'll offer them on the site here as a vendor.

SPOautos

I think what RETed is saying is only 25-30% of the overall face of your IC actually flows air. Your going to loose 1/2 of it just in the charge air rows, then all the ambient air rows are about 1/2 metal for the fins. The actual passage ways for the ambient air to go thru are only about 25-30% of the over all face size of the core.

If I wanted to know how much ambient air could go thru it I'd get the sq inches of the face which is 28x6.5 I think you said (core only). Thats 182sq inches for your face, then multiply that time .25-.3 and you get 45.5-54.6 sq inches of passageway for ambient air to actually pass thru.

STEPHEN

Barwick

I don't think it'd be *that* low (25-30%). Half would go away instantly because of the charge air rows, and take away another ten percent *maybe* for the turbulators and walls of the ducting.

I suppose it wouldn't hurt to do a 28" x 8", or even 10" (but then it's getting to be HUGE IMHO.

I could even go to 3" thick, but you're getting into diminishing returns because by the time the air is in the back of the core, it's already pretty friggin' warm and doesn't do a whole heck of a lot. Plus that longer path for it to flow through just makes more restriction for the ambient airflow.

(oh and I meant to say in my previous post, charge air ducts are equal *width* compared to the ambient air ducts)

$150FC

i just bought (another) intercooler, the core is 21x12x3. measures 28" endtank to endtank.

should fit perfectly when i move the radiator back ~4 inches.

I don't suppose any of this math includes pressure drop, does it?

Why must our magic intercooler be 28" long and 6.5" tall? Couldn't it be, for instance, 15"x12"?

SPOautos

If I had the choice between going with a larger foot print versus making it thicker I'd go with the larger footprint...that way you'll flow more ambient air. The more ambient air you have going thru the core the more heat you can absorb.

Especially if you feel like your IC is already going to efficiently flow enough cfm for your hp goals.

Really if it were me though, I'd get the biggest damn thing you can fit (biggest overall footprint and thickness). Its not going to cost much extra now but when you out grow it, going to to spend all the money all over again.

STEPHEN

$150FC

this coming from the guy who's not happy trapping 125mph

but, is there not a limit to size? If it's too big, won't that hamper the response and power of the car?

Barwick

it doesn't matter *how* tall it is (actually taller makes more restriction for the charge air).

By the way I'm talking when the charge air runs from top to bottom.

If you have a 15" x 3" intercooler, that's 45sq-in of area available times 45% (mentioned why above) = about 20.25 sq-in actually available for flow. That'll flow about 410 CFM before becoming restrictive due to the lack of somewhere for it to flow through.

It doesn't *have* to be 28", it's just what worked with the numbers I have. I think 28" might be too wide to run on an FC unmodified, so it might change to 26" or 24" with 3" thickness. That would flow 650ish CFM.

Like I said, check the graphs I've got.

Start with the Core Thickness graph, look up your width on the Y scale, go up the 2" or 3" line (whichever thickness you have) then look where that falls on the X axis to get your available charge area (I know it's backwards, but you get the idea...)

Then go to the Intercooler_sqIN graph, and look up the 45% available line going up the y-axis using your determined charge area from the previous step and look on the x-axis to determine the approximate CFM that will flow.

I probably just confused you because I confused myself. If you got some questions, I'll try to clarify later.

suganuma

I have a bad feeling this might be a stupid question that I just say "oh ya" to the answer....BUT....what is the ratio or how is it determined how much HP can be "run" with intercooler X. I see a lot of intercoolers rated with a HP number rather than a cfm number. Wouldn't how much HP you could make from a certain CFM of air differ from engine to engine b/c of differing efficiency? There has to be some sort of "standard" conditions or guidelines I would think.

TIA,

Nic

Barwick

yeah, there's no "horsepower" number that an intercooler can effectively flow, it's a dumb thing to do. The closesst we can come is estimating the CFM.

And you do that by determining the size of the charge air face (if the endtank covers over an area of 20" wide (or long) by 3" deep, then you have 60" for the charge air. Now take that and multiply it by .45 (an estimate of how much space is taken by the ambient passageways and metal walls of the tubes). That leaves you with 27sq-in of charge air face available for flow. 27sq-in of charge face with an average intercooler flows ____ CFM (look it up on a graph, the graphs I've seen for an intercooler with average turbulators (the fins inside the charge air tubes) it flows about 20 CFM for every sq-in of charge area.

RETed

It's just a waste of time in my book...
Most people who are thinking FMIC have already going with a big turbo upgrade or will be doing it very soon.
There is limitations up front to what you can fit, and this is basically your limitation.  RUN THE BIGGEST THING YOU CAN FIT UP FRONT.  Trying to calculate what's "best" ends up being a mathematical exercise.



-Ted

Barwick

Yeah but the guys running those 24" wide intercoolers with the tanks on the left and right are just completely screwing themselves over.

SPOautos

I dont see why, to me it seems like it would cool better with the end tanks on the left and right. If the charge air has to go thru 24" of distance to get to the other side its going to be inside the core 4x longer than if it were only going across 8" of core. Seems like the longer the charge stays inside the core the more time there is for the IC to absorb heat from the charge....there for cooling it better

STEPHEN