boostedrotor89

I am making a cold air box for my 89 TII, so thats fine and dandy. But i got to thinking and i was remembering from 7th grade science class that dead air is a pretty good insulator. So that made me think. If i make my box out of sheet aluminum and then i give it about 1/4 to 1/2 inch space, and then put another layer on would this keep my temps down? Just looking for some other peoples thoughts, thanks

classicauto

iTrader: (3)

Well I believe you've gotten a little off base. VACCUM is a great insulator because the space between molecules in a vaccum is much greater then open air, thus its that much more difficult for heat to jump from molecule to molecule. Evidenced by you traveler's coffee mug.

And really there wouldn't be much more difference between a cold air bow with two layers + a vaccum space in between compared to a regular one. The biggest factor in a cold air box is the location of the filter as far as what temp of air its ingesting. Meaning - is it in a fresh stream of outside air? or just getting engine bay air that is has been insulated by a thin layer of material?

But its an interestingthought - good luck on the box.

jouslee

hmm.. interesting concept

Goofy

Air is also an excellent thermal (and electrical) insulator, but classicauto is correct in saying the major factor is air source, not necessarily box temperature.

The benefit of using a better thermal barrier (air or vacuum gap) would be reduced heatsoak, which should affect the output temperature mostly at low air intake volume, when the air goes slowly enough that the intake box warms the air.

Real-world data would be appreciated if you intend to go this direction, hopefully with a control/compare value as well.

boostedrotor89

unfortunatly I like my windshield washing capabilities so i am trying to steer away from that route. but that is the only location that i heard of for getting cool air to the filters in 2nd gens(besides vented headlight covers, which im not too sure about). I realize with crazy hot turbo sitting not to far from the intake i should use anything i can get to keep that heat from the turbo away from the intake.

I am keeping the tube that brings air to the stock airbox over the shroud in my designs too. So there will be some fresh air coming in.

So you dont think this would be worth my time then?

classicauto

iTrader: (3)

the box will be worth your time......but as far as a vaccm insulated ones, thats a little too much IMHO.

But - don't forget that you can get a headlight washer bottle out of another FC ( unless you already have one) They mount on the left side, you can plumb the lines to your squirterand BAM you've got some realestate for sucking up nice cool air.....so if the w/s washers werea major factor preventing that end of the box then there is a solution.

classicauto

iTrader: (3)

the box will be worth your time......but as far as a vaccm insulated ones, thats a little too much IMHO.

But - don't forget that you can get a headlight washer bottle out of another FC ( unless you already have one) They mount on the left side under the headlight, you can plumb the lines to your w/s washer squirters and BAM you've got some realestate for sucking up nice cool air.....so if the w/s washers werea major factor preventing that end of the box then there is a solution.

boostedrotor89

what models came with the headlight washer?

Goofy

https://www.rx7club.com/2nd-generation-specific-1986-1992-17/cone-filter-vs-stock-box-temperature-flow-544699/

Some good air box info there.

boostedrotor89

Yeah, i've been reading on that one. Some really interesting stuff. This is what really sparked my thinking into this. The idea of keeping the hot turbo air from the intake sounded fine, but i guess i should focus more on getting the air into it

rotarygod

iTrader: (1)

The idea is very sound. It is used in building construction.

royaltrex7

what if you did that set up and added a second space that would be cooled by something like dry ice?

boostedrotor89

haha i would rather not have to get out of my car every 30 mins to go refil the ice for optimum performance

royaltrex7

i would have said a/c but who uses that any more

evelhalo

theres gotta be some way to condense/ cool the air, electric a/c condensor? Air compressor? would an eletric fan (i.e. electric supercharger) cool the air at all, maybe help tp suck in fresh air at low power/speeds.

theres a cool hood 5one5 is making with a vent above the turbo, but the front vent wont fit with the tmic, but its an idea, maybe you could cut a vent above your turbo, with a lip to suck out the hot air??

beyond refilling some ice all the time lol or gas cooling (are there any non explosive compressed gas that could cool the air) like nitrous theres no real small/mobile cooling systems are there?

fcdrifter13

Wow I havnt said the same thing in countless threads, but instead of air you fill the space with great stuff, and yet it was deemed a bad idea for some reason, and I was harrassed for being an idiot through PMs. You guys need to make up your minds.

rotarygod

iTrader: (1)

You weren't the idiot. Half of the people that responded to you were. Remember there's only 1 way to do things.

cdaleracer669

iTrader: (1)

i dont think a box with some extra space between is a bad idea for a DRAGSTRIP car. fill it with crushed dried ice or ice water to keep the box cool, and route cold air to the filter and you know it wont be sucking hot air....only practical to use at the dragstrip tho, which MOST NA's arent fast enough anyway, and a turbo car would have an intercooler and you would be icing that down anyhow....

evelhalo

would it be better to have air, gas, vacuum, or heat insulation around the CAB??

Boostmaniac

Man, I think your idea rocks and is definitely worth a test. You might be on to something. Keep us posted.

evelhalo

or how about a 12v air compressor hooked up to a vortex tube??
with adequate heat sheilding that would provie air somwhere between -50 an -20 degrees into the CAB

Goofy

lol @ halo.
Vacuum would be technically best, though an inert like argon, like they use in windows, would probably be my second choice.

You'd also want to use a high-heat, thermally insulating, low specific heat thermal barrier. I'm sure there's an appropriate plastic out there, though I don't know of any offhand.

The specific heat problem is the part that hurts ceramic cold air boxes. However, a sandwich of thermal reflective material then ceramic barrier then gas/vacuum gap then thermally insulating plastic should work out really well.

Any true thermal engineering guys out there willing to put forth any info?

-Goofy

boostedrotor89

Yeah, anybody out there that really knows it this idea is worth a damn?

classicauto

iTrader: (3)

Im no thermal engineer, but the rule applies that you can't get something for nothing.....or at the least - you only get a little for a little.

Meaning - what gains do POSSIBLY percive a vaccum insulated air box packed in ice will get? 2hp? 7hp? And how much time and money will go into that (sky high guesstimate) of 7 hp?

Is it a good idea? yeah, its a neat thought. Is it a breakthrough or somethi that has NEVER been researched or thought about before? probably not. Is it worthwhile to test? yes. Will it make an extreme difference when compared to a normal cold air box? no. - dispute that answer if you like but its bascially like comparing the engine bay temps of a car with ceramic coated manifolds to one that has the same manifolds but they are also wrapped. The difference is hardly measurable.

ericgrau

iTrader: (1)

This looks like a job for... (toy soldier blows trumpet) a UC Berkeley mechanical engineering student.


COLD AIR BOX INSULATION
Air is a great insulator. Air moves heat through convection (fluid motion), not conduction (still fluid or object, moving heat). So if you can stop the air from moving, you'll be in pretty good shape already. A cold air box made of sheet aluminum should do just fine. If you're still concerned, put a little fiberglass insulation around it. But what's more important is to seal it off really well from the air under your hood to stop convection. I've seen pics of some nice looking cold air boxes with rubber seals that push into the hood above them.


AIR CONDITIONED INTAKE?
I calculated earlier that an ideal cold air intake would yield 8HP on a stock N/A. A forum member revealed that real cold air intakes get about 7HP. Not bad considering I had no idea what kind of power a real cold intake yielded. According to my calcs, every 1 degree fahrenheit yields an 0.2% boost in horsepower (so you get even more HP on, for example, a tricked out turbo).

Let's see what kind of A/C we need. A rotary displaces 1.3L every revolution. So at 6500rpm we have 1.3L x 6500rpm /(60s/m) = 140.8L/s (290cfm) of air to cool.
140.8L/s * 1m^3/(1000L)*0.8kg/m^3 * 1000J/kg*C = 112.64(J/s)/C = 112.64W/C (214 Btu/hr*F)

I'm guessing you could get about 20F out of a common A/C, which means you need 214*20 = 4280Btu/hr. What a coincidence, that's just what a common window A/C produces. But wait, you can't get 20F and max Btus; it's usually either-or. So let's say 15F and 3200Btu/hr, to be more reasonable. That gives you a 3% boost in power, or a little over 4HP on an N/A. Power consumption on these things is about 500W, or 2/3HP. So you're left with about 3.5HP. But wait, adding that 50 pound window A/C is the same as losing 2.5HP. So you're left with a 1HP gain. Not to mention another 45A on your alternator. What if you don't want to use R134a or freon? What if you want to use something colder? I've calculated that out before, and the power consumption gets pretty ridiculous.

It makes sense. After all, an A/C works with a compressor. Why not just compress air instead and pump that into your engine? (i.e., use a turbocharger). Still, I think a tank of compressed air might work in short bursts. At 3000psi a 2L tank can hold 200L of gas, enough to last you 1.4s. But the air will be freezing cold. I don't remember how cold, but assuming -30F you'd get a 20% boost in horsepower. For 1.4 seconds you could also boost horsepower by up to 360% with pure compressed oxygen, but I'm certain your engine would blow up first... in a spectacular explosion. And if you're going to do all that, why not go with nitrous?




For those of you that fell asleep. An A/C consumes almost as much horsepower to run than it gives. And since it runs using a compressor, why not put a turbo in instead? A bottle of compressed air lasts a couple seconds and increases HP by 20%, but then why not go nitrous? Read above blurb on cold air box and stick with that.

Disclaimer: this is all theory, not practice. Reality may be a little different, but at least it gives you an idea... unless I screwed up a calculation.