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Old 11-25-2013, 01:02 AM
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Altitude question for math freaks

Well, here goes a question for the math gurus... ;)

If I ran 17.7 at 8500 feet above sea level and outside air temperature was 22C°, then what time I would doing with a same setup at sea level (or maybe, at 700feet) with same OAT???


Thanks in advance for who can give me the most precise answer
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Old 11-25-2013, 01:53 AM
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Re: Altitude question for math freaks

What's your trap speed, and where the crap is there a track at 8500ft??
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Old 11-25-2013, 02:02 AM
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Re: Altitude question for math freaks

Anyway, at sea level that'd be just under 15.8. I'm sure in your googlin' around you probably found all the NHRA charts that didn't give you any info for any location above 6000ft elevation. If you didn't come across that, well;

NHRA altitude correction factors

I just saw the patterned change for altitude factor, measured it with your 8500 elevation, and completed the equation to get that answer. 70-75 degrees is a pretty optimal temp for automotive competition.


Multiply your trap speed at that elevation by 1.1151 and you should get the ~mph you'd run at sea level.
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Old 11-25-2013, 07:52 AM
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Re: Altitude question for math freaks

Ok... so how does altitude and temperature matter how long it takes to get from point a to b?

I need to know. When my boss says I'm late I can tell him altitude and temperature boss...
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Old 11-25-2013, 09:40 AM
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Re: Altitude question for math freaks

thanks for feedback people
a 8500 track is located in Arequipa, Peru

using wallaceracing calculators Iīm calculating my time is between 15.5 and 15.7
not bad for F22A

thatīs the track
look at the freaking mountains around )))
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Old 11-25-2013, 10:42 AM
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Re: Altitude question for math freaks

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Originally Posted by bykfixer View Post
Ok... so how does altitude and temperature matter how long it takes to get from point a to b?

I need to know. When my boss says I'm late I can tell him altitude and temperature boss...
Altitude = the air is less dense ("thinner"). Less dense air = less power, and I'm sure you can figure out the rest

You need to watch the Top Gear episode where they try taking 3 4x4's over some mountain in South America 3 miles in the air (15,000ft up). Not only were they complaining that they're trucks only had a fraction of the power, but eventually they got to the point where simply breathing normally was so exhausting that they didn't make it over the top, and had to turn around and go around the mountain.
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Old 11-25-2013, 01:30 PM
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Re: Altitude question for math freaks

If you wanted to take in all aspects, you would have to calculate the weight of your car at 8500 ft above sea level, because things tend to weigh less at higher altitudes.

Air is less dense resulting in an AFR that is lower, causing your engine to run lean.

Temperature won't play too big of a role, as long as the car is warmed up.

All in all I have no idea, it would be a long and tedious calculation.


Source: Physics Major
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Old 11-25-2013, 01:46 PM
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Re: Altitude question for math freaks

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Originally Posted by aqprider View Post
thanks for feedback people
a 8500 track is located in Arequipa, Peru

thatīs the track
look at the freaking mountains around )))
Hah no wonder ya'll are taking out the headlights in front of your air filters haha. Cool stuff.
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Old 11-25-2013, 02:09 PM
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Re: Altitude question for math freaks

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Originally Posted by twokexlv6coupe View Post
Altitude = the air is less dense ("thinner"). Less dense air = less power, and I'm sure you can figure out the rest

You need to watch the Top Gear episode where they try taking 3 4x4's over some mountain in South America 3 miles in the air (15,000ft up). Not only were they complaining that they're trucks only had a fraction of the power, but eventually they got to the point where simply breathing normally was so exhausting that they didn't make it over the top, and had to turn around and go around the mountain.

Thanks!

By the time I explain that to my boss, I'll either be fired, or promoted to head of public relations
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Old 11-25-2013, 09:29 PM
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Re: Altitude question for math freaks

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Originally Posted by Garurumon View Post
If you wanted to take in all aspects, you would have to calculate the weight of your car at 8500 ft above sea level, because things tend to weigh less at higher altitudes.

Air is less dense resulting in an AFR that is lower, causing your engine to run lean.

Temperature won't play too big of a role, as long as the car is warmed up.

All in all I have no idea, it would be a long and tedious calculation.

Source: Physics Major
A physics major who hasn't taken thermodynamics yet. The difference in gravity between sea level is measurable if you're using instrumentation borrowed from NASA, but irrelevant for a ton-and-a-half car plus tenth-of-a-ton driver!

On the other hand, temperature makes a big difference. Every gearhead should be able to play with Boyle's Law (aka, the Ideal Gas Law), which says Pressure * Volume is proportional to Temperature (PV=nRT; n and R are constants). Right away, you can see that cold air takes up less space (V~T/P), so you can push more air-fuel mixture into the combustion chamber. Maximum torque (and from there, power) is a function of maximum pressure in the combustion chamber, and since P~T/V, which is why we light the mixture on fire...and the largest change in T produces the largest change in P (for equal V).

The OP did ask for the math.... :)
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Old 11-25-2013, 11:23 PM
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Re: Altitude question for math freaks

Quote:
You need to watch the Top Gear episode where they try taking 3 4x4's over some mountain in South America 3 miles in the air (15,000ft up). Not only were they complaining that they're trucks only had a fraction of the power, but eventually they got to the point where simply breathing normally was so exhausting that they didn't make it over the top, and had to turn around and go around the mountain.
well, I work as a guide in the Colca canyon region, so I make it every week. We have to pass 16118 feet level while going from Arequipa to Chivay ))

all tourist vans we use are turbodiesel powered. Also I went hrough that altitude in my lude. It loses about 50% of power, but a mileage is sweet))))) and yes, you can feel all symptoms of altitude sickness: dizziness, head ache, nausea, gases. And if you run few meters itīs like you ran 100 meters

Quote:
Air is less dense resulting in an AFR that is lower, causing your engine to run lean.
maybe Iīm wrong, but donīt map sensor can manage it properly?
it stills negative pressure in the IM...

Quote:
Hah no wonder ya'll are taking out the headlights in front of your air filters haha. Cool stuff.
itīs because weīre in the middle of a freakinīhighland desert (Atacama). Air temp is not SO high, but the sun is too strong, so temp under the hood rises easily to 150 - 160 F° under the black hood, with engine running thing gets even worst, so while racing during the daytime - itīs vital for us to have a filter outside the hood. That day I forgot an air hose, so I couldnīt put a filter out, and just took out a headlight
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Old 11-26-2013, 10:11 PM
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Re: Altitude question for math freaks

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Originally Posted by aqprider View Post
And if you run few meters itīs like you ran 100 meters
No joke -- I remember cross-country skiing in Colorado at 7500 feet, and feeling like my lungs were bleeding afterwards.

Quote:
maybe Iīm wrong, but donīt map sensor can manage it properly?
it stills negative pressure in the IM...
Yes. That's the beauty of computer-controlled fuel systems. In the bad old days of carburetors, you'd have to change the jets or risk leaning out the engine (then change 'em back when you came down), but the ECU will read the lower air pressure and compensate. If for some reason it runs down to its lower limit, the knock sensor would retard timing if detonation became a problem.

Quote:
itīs because weīre in the middle of a freakinīhighland desert (Atacama). Air temp is not SO high, but the sun is too strong, so temp under the hood rises easily to 150 - 160 F° under the black hood, with engine running thing gets even worst, so while racing during the daytime - itīs vital for us to have a filter outside the hood. That day I forgot an air hose, so I couldnīt put a filter out, and just took out a headlight
The stock intake is a cold-air setup -- it draws from the right front wheel well. If you're plumbed into that and insulate the intake duct, you should be in good shape for intake temperature.
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Old 11-26-2013, 10:48 PM
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Re: Altitude question for math freaks

yes temperature is very important thats why most nhra racing is done early morning or going into the evening when it is coldest.... the colder the air going into the engine the more power you are able to make
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Old 11-26-2013, 10:52 PM
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Re: Altitude question for math freaks

and dude how awesome is that... you are racing in the atacama desert i didn't even know they did that there
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Old 11-27-2013, 01:57 AM
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Re: Altitude question for math freaks

Quote:
cross-country skiing in Colorado at 7500 feet, and feeling like my lungs were bleeding afterwards.
))
then imagine, Iīm living here at 8.500. Every day. Walking. Exercising. Having sex ))
when I was younger I used to train in track cycling sprint. And actually after a 25 second run you feel you gonna puke your lungs out...

But nothing compares to walk up a step hill with 20kg downhill bicycle on your back at 15000 a.s.l.

Quote:
If for some reason it runs down to its lower limit, the knock sensor would retard timing if detonation became a problem.
My engine is non-VTEC F22, and doesnīt have knock sensor...
however, due to low air pressure at that altitude, the enginesī tendency to detonation is lower than at sea level

Quote:
The stock intake is a cold-air setup -- it draws from the right front wheel well. If you're plumbed into that and insulate the intake duct, you should be in good shape for intake temperature.
yes, but itīs necessary to take in account the extreme solar radiation in the desert at high altitude. The under hood space goes VERY hot (even worst if you have a black car like mine) in question of 15 minutes. So we DO need some fresh air entering freely into engine bay. Iīm looking forward to make some space moving my battery to the trunk and also moving my coolant expansion reservoir in order to make some space for a bit more efficient cai. And oh, Iīll make a heat insulation box. Hot air - bad air for an engine!

Quote:
the colder the air going into the engine the more power you are able to make
when we race illegaly (in my dreams, of course, īcause itīs a bad bad thing ) at night, when the OAT in the desert falls below the 10C° and there are no sun, the performance difference is SO noticeable
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Old 11-27-2013, 06:57 PM
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Re: Altitude question for math freaks

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A physics major who hasn't taken thermodynamics yet. The difference in gravity between sea level is measurable if you're using instrumentation borrowed from NASA, but irrelevant for a ton-and-a-half car plus tenth-of-a-ton driver!

On the other hand, temperature makes a big difference. Every gearhead should be able to play with Boyle's Law (aka, the Ideal Gas Law), which says Pressure * Volume is proportional to Temperature (PV=nRT; n and R are constants). Right away, you can see that cold air takes up less space (V~T/P), so you can push more air-fuel mixture into the combustion chamber. Maximum torque (and from there, power) is a function of maximum pressure in the combustion chamber, and since P~T/V, which is why we light the mixture on fire...and the largest change in T produces the largest change in P (for equal V).

The OP did ask for the math.... :)
I was refering to the difference in a couple of degrees... say 295 to 297 kelvin. The error is less that a percent... besides, OP stated that the temperature did not change, so it will not play a large role.

You seem to be confusing things. Look at the ideal gas law. Decreasing the temperature of the air will decrease the pressure*volume. I'm borrowing this example, but if you go from 293K to 313K, the pressure*volume will increase by |1-(313/293)|=6.8%. That is like having 1 litre of air become 1.068 litres of air if pressure is constant. Even a 20 degree increase will only have an increase of this small, so if the difference was a couple of degrees it would be pointless to calculate the difference because it would be less than a percent. Do you see what I am saying now?
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Old 11-27-2013, 06:59 PM
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Re: Altitude question for math freaks

Also while we are on the temperature discussion, here are some people who actually TESTED cold air intakes.



And they found MINIMAL power increases. On a Dyno.
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Old 11-27-2013, 11:34 PM
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Re: Altitude question for math freaks

I guess itīs not a best idea to test CAI eficience in turbo INTERCOOLER car which is considered one of the most reliable and good-performing cars on the market...
))
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Old 11-28-2013, 01:58 PM
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Re: Altitude question for math freaks

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Decreasing the temperature of the air will decrease the pressure*volume. I'm borrowing this example, but if you go from 293K to 313K, the pressure*volume will increase by |1-(313/293)|=6.8%. That is like having 1 litre of air become 1.068 litres of air if pressure is constant.
You're only looking at it in one dimension. Torque is proportional to the change in temperature produced by combustion in the momentarily fixed volume of the combustion chamber...that produces a corresponding change in pressure, translated to mechanical work by moving the piston. If you can get 6.8% more fuel-air mixture into the combustion chamber, you'll theoretically get 6.8% more torque.

Take into account underhood temperatures -- a major factor if drawing air from the engine compartment, a bit less if just considering heat soak through an uninsulated intake duct -- and the temperature difference can be double your 20-degree difference. Control that by pulling air from outside the car and by insulating the intake duct, and you've doubled your gain.

In practice, thermal inefficiency trims some of that off, but depending on where you started from, you're still looking at about a 10% gain in torque (at the crankshaft) by drawing outside air and insulating the duct. Power ~ Torque*engine speed, so figure a roughly corresponding increase in power as well. Mechanical losses suck some of that away by the time it reaches the wheels, but 5-8% at the wheels isn't unrealistic. Now I know racers who'd sell their children for a 5% increase in power, so it's not as inconsequential as it sounds. :)

Because 4th and 5th gen Preludes already draw outside air, they don't benefit as much, which is why you'll find lots of comments elsewhere that CAIs don't make much of a difference, although there's a little to gain by changing the stock airbox for something more efficient and by insulating the duct. We generally advise against short-ram intakes, because they're pulling hot air from the engine compartment...there's a potential loss.
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Old 11-28-2013, 05:25 PM
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Re: Altitude question for math freaks

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Originally Posted by Jamie View Post
You're only looking at it in one dimension. Torque is proportional to the change in temperature produced by combustion in the momentarily fixed volume of the combustion chamber...that produces a corresponding change in pressure, translated to mechanical work by moving the piston. If you can get 6.8% more fuel-air mixture into the combustion chamber, you'll theoretically get 6.8% more torque.

Take into account underhood temperatures -- a major factor if drawing air from the engine compartment, a bit less if just considering heat soak through an uninsulated intake duct -- and the temperature difference can be double your 20-degree difference. Control that by pulling air from outside the car and by insulating the intake duct, and you've doubled your gain.

In practice, thermal inefficiency trims some of that off, but depending on where you started from, you're still looking at about a 10% gain in torque (at the crankshaft) by drawing outside air and insulating the duct. Power ~ Torque*engine speed, so figure a roughly corresponding increase in power as well. Mechanical losses suck some of that away by the time it reaches the wheels, but 5-8% at the wheels isn't unrealistic. Now I know racers who'd sell their children for a 5% increase in power, so it's not as inconsequential as it sounds. :)

Because 4th and 5th gen Preludes already draw outside air, they don't benefit as much, which is why you'll find lots of comments elsewhere that CAIs don't make much of a difference, although there's a little to gain by changing the stock airbox for something more efficient and by insulating the duct. We generally advise against short-ram intakes, because they're pulling hot air from the engine compartment...there's a potential loss.
Yeah, I wasn't arguing with you, just reinstating my point lol, because it was very vague. And that video is exactly the same case for Preludes, seeing as our stock air boxes are already drawing outside air. I guess I was generalizing that a ~5% would be insignificant.

Definitely good info Jamie!
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Old 11-28-2013, 05:27 PM
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Re: Altitude question for math freaks

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Originally Posted by aqprider View Post
I guess itīs not a best idea to test CAI eficience in turbo INTERCOOLER car which is considered one of the most reliable and good-performing cars on the market...
))
The car being turboed and intercooled has no effect on the air going into your engine...
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Old 11-29-2013, 05:33 PM
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Re: Altitude question for math freaks

IMHO, it has, īcause the turbo firstly heats up the air, then the intercooler colds it down

so there are two more factors affecting the final temperature of the air going into IM

then CAI would not provide any gain there

they should test it with any low performance car with restrictive intake for see the real difference
after all, thermodynamics laws are there, and there are no way to disobey those laws: cold air is denser then hot air, so cold air WILL give more power īcause it will allow burn more fuel
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Old 11-29-2013, 06:47 PM
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Re: Altitude question for math freaks

Sigh. This doesn't apply because the Prelude doesn't have a restrictive intake... The air will still have to be cooled by the intercooler and heated by the turbo regardless, so none of this really applies at all to the situation.

Back on track, the Prelude's intake pretty much is a cold air intake. It already draws air from the footwells.
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Old 11-30-2013, 01:10 AM
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Re: Altitude question for math freaks

weīre off-toping now, īcause my question just was answered...

but... regarding to previous post - I must accept that preludes have good intake system stock, but itīs not a CAI, itīs NSCAI - in other words - Not So Cold Air Intake
measure temperature below my black hood after a car being exposed to a sun with engine working after 30 minutes, and measure it OUTSIDE the engine bay. Sure, there are two diferente values...

Then, when I ran my lude with headlight pulled out, my metal intake pipe is cold after one hour of driving

when I had a headlight on itīs place - it wasnīt cold.
so...
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Old 11-30-2013, 10:27 AM
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Re: Altitude question for math freaks

Quote:
Originally Posted by aqprider View Post
but... regarding to previous post - I must accept that preludes have good intake system stock, but itīs not a CAI, itīs NSCAI - in other words - Not So Cold Air Intake
measure temperature below my black hood after a car being exposed to a sun with engine working after 30 minutes, and measure it OUTSIDE the engine bay. Sure, there are two diferente values...

Then, when I ran my lude with headlight pulled out, my metal intake pipe is cold after one hour of driving

when I had a headlight on itīs place - it wasnīt cold.
so...
Sounds like you're introducing cool air under the hood...that helps avoid heat soaking through the intake duct, but otherwise has nothing to do with what's flowing inside the duct, unless you've modified it to draw from inside the engine compartment, as with a short-ram intake. Insulate your duct (especially if it's metal), you'll get the same result -- cool air into the intake. Just make sure you use something fire resistant for the insulation.
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Old 11-30-2013, 11:20 AM
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Re: Altitude question for math freaks

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Originally Posted by Garurumon View Post
The car being turboed and intercooled has no effect on the air going into your engine...

Quite possibly one of the DUMBEST things I've ever heard, ever.
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But you need that scoop on the hood. Is it true that they're big enough to fit your lunch box and all your camera gear in it?
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Old 11-30-2013, 01:29 PM
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Re: Altitude question for math freaks

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Quite possibly one of the DUMBEST things I've ever heard, ever.
Yeah, I forgot how a turbo works for a moment, too drunk to taste this chicken
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Old 11-30-2013, 02:51 PM
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Re: Altitude question for math freaks

hahaha ))
Iīm glad this thread is the happy one now ))

Quote:
Just make sure you use something fire resistant for the insulation.
what material can you recommend? I thought about construction foam... Itīs fire safe?
asbesthum?
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Old 11-30-2013, 02:51 PM
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Re: Altitude question for math freaks

moders, please delete, I double posted accidently, Iīm sorry
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Old 11-30-2013, 06:34 PM
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Re: Altitude question for math freaks

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...construction foam... Itīs fire safe?
That could work. Any fiberglass insulation in a sleeve will do well. Makes it a bit bulky, but it'll keep the duct cool!
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