intercoolers--all info!!!

[anglin]

Forgive me for getting this thread back on topic. Took the Rapido intercooler out of my racer this evening to start fitting the RS bumper to the front of the car. The Rapido IC interferes with the lower section of the RS bumper and I don't think I'll be trimming a genuine Cosworth bumper to clear the IC.

The Rapido IC is bar and plate and the core measures 12" wide, 7" tall and 3.5" deep. The core has 0.25" gaps between the plates and the plates are .25" wide. The external fin density is about 11 fins per inch. The core and endtank assembly (nothing else) weighs 10 lbs. The tubing from the turbo outlet elbow to inlet side of the intercooler is 33" and the tubing from the oulet side of the intercooler to the throttle body is 48" (that's 6.75 feet!!!). The tubing is 2.25" OD. The endtanks are cast.

Let me put this in a more concise format.

core type:
bar and plate

core dimensions (not including endtanks):
width: 12"
height: 7"
thickness: 3.5"
wetted area (w*h) = 84 in²

plate or tube dimensions:
gap between plate/tube: 0.25"
width of plate/tube: 0.25"

fin density: approximately 11 fins per inch

tubing/plumbing info:
inlet length: 33"
outlet length: 48"
OD: 2.25"

weight: 10 lbs

other details:
end tanks are cast

Edit: formula for surface area changed from wxh to w*h for the sake of clarity.

[anglin]

I have a Pace Products RS500 style intercooler laying around, so I decided to measure that one too while I was at it. (Connie's out of town this weekend, so it leaves me with quite a load of free time on my hands.)

core type:
tube and fin

core dimensions (not including endtanks):
width: 21.5"
height: 16"
thickness: 1.5"
wetted area (w*h) = 344 in²

plate or tube dimensions:
gap between plate/tube: 0.3125" (5/16")
width of plate/tube: 0.1875" (3/16")

fin density: approximately 9 fins per inch

tubing/plumbing info: N/A

weight: 9.5 lbs

other details:
inlet and outlet tubes on IC core ar 3" OD, but the manufacturer has 2.5" OD inlet and outlets available.

Edit: formula for surface area changed from wxh to w*h for the sake of clarity.

[Ray]

I'm going to question the validity of the 'wetted area' measurement (do you do wetted perimeter for streams, too? just curious).


If you just look at length x width you dont get the real deal:
Surface Area : Volume, AKA SA:V

without looking at the SA:V you might assume the following -
Since a large object has more total surface area, (let's say, an elephant) that it is more efficient at cooling off (ie, can lose heat more rapidly) than something smaller (a mouse).

IE, just because the tube and fin has more wetted area, we may neglect to note the greater depth of the other IC, which is also bar and plate (dont they lose less pressure?) - among other characteristics, such as total amount of heat available to be shed, which one can assume is somehow proportional to the total SA:V ratio that the air passing thru the core meets. (plus fins for shedding heat)

This is a post just started after i started my first cup of coffee - if it doesn't make sense, ... well i'm sorry.

[anglin]

Ray, you bring up some decent points about wetted area, pressure drop and fin density. Just for clarity for those who aren't necessarily understanding the term wetted area, it describes the surface area that the air "sees" as it approaches the intercooler. I guess it could also be described as the surface area of the intercooler that you see when you are looking at the front of it.

I'm oversimplifying the the important features that make an intercooler work well by only mentioning the wetted area, but wetted area is one of the more important dimensions for the thermal efficiency (or more generically, performance) of the intercooler. The rate of heat transfer that takes place across a heat exchanger like this is related to the difference in temperatures of the hot and cold substances. The relationship is logarithmic, and I believe the specific term is "log mean temperature difference." The bottom line is that the larger the difference between hot and cold substances, the faster the heat transfers between them.

Numerical example: If the hot substance is 500° and the cold substance is 50°, heat transfer happens very quickly. If the hot substance is 60° and the cold substance is 50°, heat transfer happens much more slowly. If the hot substance is 51° and the cold substance is 50°, the rate of heat transfer is very close to zero.

I guess I should try to put this in terms that matter to us. As hot air passes through the intercooler, from the "hot" side to the "cold" side, it transfers heat quickly (the rate of heat transfer is higher) at first since it is much hotter than the cooling air coming across the intercooler. Since it is cooler by the time it is about to exit the intercooler heat transfers less quickly (the rate of heat transfer is lower). Same with the cooling air as it passes through the intercooler. As it warm up it doesn't take the heat away from the intercooler as quickly. So, a larger wetted area has more area for the ambient air to act upon.

Admittedly, my head isn't completely in the game this morning discussing this subject. If you have any questions I'll try to discuss them later.

[Ray]

That being said (rate of heat loss) would also be proportional to fin length... such that


somethign like this

|||||||||||||||||||||

would be better overal than something like this

===========
===========

even tho the total wetted area might be the same.

[turbofan]

read the intercooler link i've got posted on the main page. that will explain a ton about internal finning.

and yes, wetted area is one of the biggest considerations. many people will say "the thickness of the core is just as important!" while the thickness does matter, it's a very quickly diminished benefit. the first 2 inches of core will do most of the cooling, but as you get into 3 and 4 inch deep cores, the back portions of the core do less and less because the air has already taken the heat.

i've done a lot of research on this, and it seems to me like there is only one reason to go tube and fin: to allow more flow externally through the core to reach a radiator or whatever behind the intercooler, in which case i'd say find a way to go bar and plate anyway. i believe it is THAT MUCH better.

ray, i don't understand what you're saying with that last bit there.

[lazerscort]

so let me ask this since i really dont know much about intercoolers
is the rapido cooler any good? is it worth the money?
im completely new to the turbo setups so im trying to take it slow in the beginning

[anglin]

is the rapido cooler any good? is it worth the money?

Good question. I purchased my Rapido IC in December 1994. I don't think Modern Performance had marketed their IC yet, but RS Consultants may have. The RS Consultants IC was very similar to the RS Cosworth setup, with a short IC stacked above a short radiator. Required a Cosworth grille (out of my league then) in addition to it's $1400+ price tag. I was still two years away from joining IMON, my resources were very limited - more evidence of the dark days prior to internet access. (Yes, kiddies, there was a time when this HUGE amount of information wasn't right at your finger tips; and people wonder why I get annoyed when someone asks "how much is 25 mm in inches?" )

Anyway, the Rapido certainly improves power over stock. Rapido claims a 140° F temperature drop through the core. My car is faster with it than without (but put on a 3" exhaust first). The Rapido IC is certainly better at rejecting heat than the TCIC based on placement alone (Oh, snap! I went there!).

The Rapido IC has something going for it that very few intercoolers for the XR can claim - it bolts on without removing anything. You do have to drill a hole in the turbo inlet casting for the bypass valve (BPV) to dump to. It lets you keep your A/C and everything else. The BPV mine came with was a little tiny thing at 0.75". I upgraded it to a real BPV years ago (Bosch 110).

For the cost it doesn't give massive performance gains. The issue is that just about every other intercooler on the planet for the XR is just that - an intercooler; no plumbing, no BPV/BOV, no mounting brackets. You have to fabricate everything yourself (or pay somebody to do it for you). You could spend more for a custom setup or less, depending on what you do. A RS500 core like the Forge or the Pace will run you about $550 to get it to North America. That's just the core. Plumbing will be $35 to $200 depending on the amount of silicone you use, steel or aluminum tube, clamps, etc. Then your BPV/BOV could be $5 or $200 (junkyard Bosch or monster Tial). Then you may have to buy a different radiator if you want the plumbing over the top of it. That could run $75 to $500. Or, you could go with a TCIC or SCIC and mount and plumb it for cheap. Lots of options, but you have to fabricate or pay someone to do it for you.

Would I buy the Rapido now? No. I have fabrication and mechanical skills, local resources for welding and anodizing, and the internet. Additionally, my car is headed to the local road course for track adventures. For someone who doesn't have much in the way of mechanical skill, doesn't want/need huge performance, wants to keep A/C, doesn't want to hack the car, or whatever, the Rapido IC might be exactly what the doctor ordered.

The Rapido IC will:

- give performance gain
- let you keep your A/C
- not require you do buy anything else to install it

I think it's a good option for those who aren't going for max power. The IC has been into the 13s on at least one car and into the low 14s on mine. The Pace RS500 IC I have should help me well into the 13s with ease. Like a lot of things with our cars, whether or not the Rapido IC is good for you is based on a lot of factors. Figure out where you want to be, how much you have to spend and what your skills and resources are. If you made it this far into the post, the last sentence will help you with more than just the IC selection process.

Good luck!

[lazerscort]

wow thanks
that was more than i was expecting but it was very helpful
so the rapido so far is the only one that comes with all the piping
and since im pertty new at the turbo game and dont have alot of resources for fabrication and only atleast for the next year jsut want at max do 20 psi and keep it simple and easily driveable

[MerkXRTurbo]

The modern performance one comes with all the piping, but it is WAY overpriced, and is in a crappy location. The whole thing is just jury rigged, especially where it goes next to the A/C compressor they just smashed the pipe to get it to clear.

All things aside, I pass several drainage ditches on my way to work that I'd much rather throw money into than buy a modern performance product.

[Ray]

ray, i don't understand what you're saying with that last bit there.

what i'm saying is that given the total wetted area being equal, it's better to have more short runners than fewer longer ones.

[John Brennan]

Forgive me for getting this thread back on topic. .

With all due respect, I believe the name of this topic is "Intercoolers-- all info." If the issue of IC placement and its efficacy as a result are not on that topic, I don't understand. If an ancillary discussion of whether or not the mass of an IC has an effect on vehicle dynamics ( I would posit that it is NOT significant) is helped by amplifying on that topic and providing examples or analogies to more completely illustrate it is not on topic, I don't understand. Thank you.

[anglin]

With all due respect, I believe the name of this topic is "Intercoolers-- all info."

Dooood, just giving you guys crap. I was enjoying the heck out of the discussion. Isn't there a "just giving you crap" emoticon somewhere? I guess I should learn better to draw the line between my humor and anything I supply resembling data. I was particularly proud of my later comment referencing your IC placement discussion; "Oh, snap! I went there!"

And just to make sure we stay on topic:

intercooler = good

<insert "just giving you crap" emoticon here>

[turbofan]

BTW, thanks for the info anglin. i'll update the main post with that info soon. anyone have good pics of the rapido intercooler, like where it installs or just a pic of the kit itself?

[John Brennan]

Ha! I'm so "molded!" Well, I did need a vacation, so I took one-- feel much better now!