Cold air inlet

[LostMy65]

Originally Posted by joedoh

people who talk about hot air in an engine compartment usually arent really clear on what that means, they have heard some explanations that make sense and then repeat them. What people are usually referring to is the pressure/volume/temperature chart that says that colder air is denser at the same pressure, and since we know engines run better with denser air (been to the mountains and seen a decrease in performance? been in cold weather and seen an increase in performance? but dont confuse barometric pressure for anything said below, that is a system pressure change that has more effect than the temperature change) they think the "colder" air outside the engine compartment will be significantly denser than the air inside the engine compartment. the problem with this theory is the effect of temperature on density vs the effect of pressure change on density.

since the air pressure is exactly the same inside the engine compartment and outside it, the density change has to be based only on temperature difference. it takes a HUGE amount of temperature change to affect density the same as even a very small increase in pressure. we also know this is true because even small amounts of boost (3-5 psi, a 25-50% increase in pressure at sea level) from turbos or superchargers affect the power of an engine dramatically. thats what forced induction does, changes the density of air in the cylinder by increasing the pressure. you get a higher effective compression ratio.

engine compartments seem like they should be extremely hot places, after all when you pop the hood after driving it sure feels hot in there. but with the engine fan turning, and especially once you are moving, the engine compartment air is only slightly hotter than the outside air, and there is no pressure change inside vs outside, so the density change of an intake outside the engine compartment vs inside is very very very small. I would be lying if I said it wasnt any change at all, because it is there, but it is very small. Couple that with the fact that internal cylinder temperatures are very high, and the inefficiency of heat transfer by convection, especially with smooth metal surfaces like a cylinder, means the slightly cooler charge will be affected more by the lump capacitance (storage capability of heat in a large dense chunk of metal) of the hot cylinder components than it could possibly affect the cylinder to cool it off.

that's very technical, think about getting a pan very very hot and pouring water into it, unless you pour in at high gpm, the pan will convert the water to steam instantly, raising the water temperature quickly without lowering the pan temperature at all. Its an even simpler concept to imagine as running your air conditioning in a truck that has been sitting in direct sunlight for hours and hours. It takes a long time, usually longer than your drive home, to cool off those interior components that are very hot, even though air conditioning air is sometimes 90 degrees cooler than the surface temps. That is lump capacitance, and convection, explained simply.

most of the improvement people feel with an intake tube is the restriction reduction and flow improvement. and the sound, that really makes it seem like you are thrashing around at 10/10ths.

cold has its place for intake cooling, forced induction motors benefit greatly from cooling that intake charge, because the pressure change of the turbo or supercharger heats up the air a lot (see a PVT chart!), an intercooler will cool it back down slightly, but an intercooler is not usually used for density increasing reasons, but because really hot air at really high pressures can cause fuel to detonate (see "how a diesel works"), sometimes before it should (see "knock" or "playing a really expensive percussion instrument")


sorry for the book. worry less about cold air and more about improving flow as some guys have said. Keep your headlights mounted where they belong. You will see a small benefit if you slug along in 2mph traffic and have the intake routed outside, because the lower speed wont bring fresh cool air into the engine compartment.

Thanks for this post.
It makes total sense.

[Snailed]

I disagree with nearly everything in that giant post. I would advise anyone reading it to do A LOT more research before taking that post for fact. It's a mishmash of concepts not being correctly applied to what actually happens in the real world. It is NOT scientific at all even though lots of scientific terms are thrown around. Reader beware.

[Jmageee902004]

Not to start any debates, but interesting/educational subject matter here. Snailed id like to hear more than just you disagree, about the subject.

[joedoh]

Originally Posted by Snailed

I disagree with nearly everything in that giant post. I would advise anyone reading it to do A LOT more research before taking that post for fact. It's a mishmash of concepts not being correctly applied to what actually happens in the real world. It is NOT scientific at all even though lots of scientific terms are thrown around. Reader beware.

master degreed engineer here, worked in lumped capacitance for environmental control systems in aerospace.

but I say that not to give absolute creedence, only to tell you I do know the scientific terms and their applications. I agree to do your own research, my other engineer friends debated this pretty lively and we figured the gain at 100 degrees difference in inlet temp was something less than 1%, multiplied by the efficiency of the gasoline engine of course, which is around 65%, so 0.65% gain, thats almost 2 hp on a 300hp engine!

['63GENIII]

Damn Joe... ya just killed like three of my ideas in one post. LOL! All kidding aside though, thanks for that explanation (in terms I can understand) Especially the capacitance part. Looks like I'm scrapping the cold air intake idea for a intercooled turbo 396! HAHA
Posted via Mobile Device

[LostMy65]

I was thinking it wouldn't be too difficult to channel to the carburetor the air that enters these two large openings.


Posted via Mobile Device

[likaroc13]

Originally Posted by Jmageee902004

Not to start any debates, but interesting/educational subject matter here. Snailed id like to hear more than just you disagree, about the subject.

He had a lot more to say but edited it. Maybe thought it was too controversial? I know because I was/am subscribed to the thread, so I saw what he originally posted via email notification. No harm in a civil discussion though!

[LostMy65]

The funny thing is his original post made sense too.
Posted via Mobile Device

[kieth]

FYI, JUST TO SAY THIS IS A GOOD CONCEPT AND IT DOES WORK. WHAT IS ACTUALLY GOING ON BESIDES THE COOLER AIR IS THAT AT THE BASE OF THE WINDSHIELD THERE IS A HIGH PRESSURE AREA THAT DEVELOPS AS SPEED INCREASES. WHEN A AIR INTAKE IS ADDED TO THIS AREA (A 1989 FREIGHTLINER FLD12064ST OVER THE ROAD TRACTOR ) USED THIS PRINCIPLE TO REMOVE EXTERNAL AIR CLEANERS FOR THE TRUCKS AND THEN USED THE HIGH PRESSURE AIR TO HELP CLEAN UP THE AIR FLOW AND PROVIDE AIR TO THE ENGINE. SO THIS DOES 3 THINGS, PROVIDES MORE AIR TO THE INTAKE, PROVIDES COOLER AIR TO THE INTAKE, AND HELPS REDUCE THE TURBULANCE OF THE AIR AROUND THE TRUCK. GOOD IDEA.

KIETH

[kieth]

GM probably used the same type of wind tunnel research before they designed the cowl induction hood on the chevelles, if you will note the intake is at the back of the hood to take advantage of the high pressue area in front of the windshield. JMO Kieth

[LostMy65]

The part I keep trying to figure out with these exterior scoops and cowls, is how do you keep the rain water out?
Posted via Mobile Device

[61K10]

I was waiting for that to come up---------

[joedoh]

Particle separators, the air can change directions faster than dust or rain, so an aero device is put in the airstream that collects the particles and does not restrict airflow (much). Turboprop aircraft engines use two, one for rain and particulate, and another that can be opened when in ice.

You can see the air dam and drain tubes on a cowl induction chevelle
Posted via Mobile Device

[mr andrerson]

in a recent classic trucks issue they had an article on running a cold air intake through the inside headlight holes through the inner fender and over to the carb.

[theastronaut]

Originally Posted by LostMy65

I was thinking it wouldn't be too difficult to channel to the carburetor the air that enters these two large openings.


Posted via Mobile Device

Exactly what I'm planning on doing.

[LostMy65]

Here's another idea.
Found it in another thread.

[LostMy65]

Some pics from another thread:

[LostMy65]

Originally Posted by joedoh

people who talk about hot air in an engine compartment usually arent really clear on what that means, they have heard some explanations that make sense and then repeat them. What people are usually referring to is the pressure/volume/temperature chart that says that colder air is denser at the same pressure, and since we know engines run better with denser air (been to the mountains and seen a decrease in performance? been in cold weather and seen an increase in performance? but dont confuse barometric pressure for anything said below, that is a system pressure change that has more effect than the temperature change) they think the "colder" air outside the engine compartment will be significantly denser than the air inside the engine compartment. the problem with this theory is the effect of temperature on density vs the effect of pressure change on density.

since the air pressure is exactly the same inside the engine compartment and outside it, the density change has to be based only on temperature difference. it takes a HUGE amount of temperature change to affect density the same as even a very small increase in pressure. we also know this is true because even small amounts of boost (3-5 psi, a 25-50% increase in pressure at sea level) from turbos or superchargers affect the power of an engine dramatically. thats what forced induction does, changes the density of air in the cylinder by increasing the pressure. you get a higher effective compression ratio.

engine compartments seem like they should be extremely hot places, after all when you pop the hood after driving it sure feels hot in there. but with the engine fan turning, and especially once you are moving, the engine compartment air is only slightly hotter than the outside air, and there is no pressure change inside vs outside, so the density change of an intake outside the engine compartment vs inside is very very very small. I would be lying if I said it wasnt any change at all, because it is there, but it is very small. Couple that with the fact that internal cylinder temperatures are very high, and the inefficiency of heat transfer by convection, especially with smooth metal surfaces like a cylinder, means the slightly cooler charge will be affected more by the lump capacitance (storage capability of heat in a large dense chunk of metal) of the hot cylinder components than it could possibly affect the cylinder to cool it off.

that's very technical, think about getting a pan very very hot and pouring water into it, unless you pour in at high gpm, the pan will convert the water to steam instantly, raising the water temperature quickly without lowering the pan temperature at all. Its an even simpler concept to imagine as running your air conditioning in a truck that has been sitting in direct sunlight for hours and hours. It takes a long time, usually longer than your drive home, to cool off those interior components that are very hot, even though air conditioning air is sometimes 90 degrees cooler than the surface temps. That is lump capacitance, and convection, explained simply.

most of the improvement people feel with an intake tube is the restriction reduction and flow improvement. and the sound, that really makes it seem like you are thrashing around at 10/10ths.

cold has its place for intake cooling, forced induction motors benefit greatly from cooling that intake charge, because the pressure change of the turbo or supercharger heats up the air a lot (see a PVT chart!), an intercooler will cool it back down slightly, but an intercooler is not usually used for density increasing reasons, but because really hot air at really high pressures can cause fuel to detonate (see "how a diesel works"), sometimes before it should (see "knock" or "playing a really expensive percussion instrument")


sorry for the book. worry less about cold air and more about improving flow as some guys have said. Keep your headlights mounted where they belong. You will see a small benefit if you slug along in 2mph traffic and have the intake routed outside, because the lower speed wont bring fresh cool air into the engine compartment.

I forgot about this post.
Makes good sense.

[Steeveedee]

If one takes the ambient air in without disrupting the stock inlet one can (usually) see a benefit. I had an '05 Toyota Corolla that I added a cold air intake to. It took air in through the hole where a driving light would be. The original inlet for the duct to the filter box was between the battery and the radiator. Kind of a dead space, and possibly the hottest place under the hood. I ran 2" ABS with a "Y" pipe that takes 3 inputs and has one output, sort of like a "scoop". The stock setup was in place, but cooler air could push out of there when the ram air effect overcame its input. There is a circular part of the duct to the air filter box that was accessible from the bottom; that's where I fed the cold air in. I gained about 1% in mileage, and it cost me about $13 in parts. 1% doesn't look like a lot, but I put 220k+ miles on it. That's 2.2k miles less fuel; at $3 a gallon and 35 MPG, that's 63 gallons, for a savings of $189. It did have a bit better performance, especially on really hot days. Nothing to write home about, though.

Buick had a set-up in '68 that was OTC at the dealership. It fed in from a hole in the firewall into the back of the air cleaner, so it didn't block the snorkel. It was verified to give ~ .1 second reduction in 1/4 mile ET by several users.

I wouldn't mind doing that on my truck, except for the secondary roar. It would be louder than the exhaust!