Cold air OR Hot air

[b3nje]

Morning,

Just having a heated discussion at work and i'd like to say i know a fair bit about cars but me and my boss have different views on engines and cold air and hot air.

Basically i say that cars run better off cold air, its denser and works better with the conbustion system. Obviously it doesn't start as well as it would with warm air but that wasn't the talk point.

He says that no matter whether its hot or cold air the car will run the same. ECU's and blah blah blah all change fuel and air mixtures etc to make the car run at its best constantly and how that old fords sed to have a stupid air feed system that took air from the manifold because it was hot air and supposedly good for the car.

I'm not admitting i'm right or wrong but if someone could shine some light on this and maybe give me some advantages and disadvantages of it been a cold morning or a hot morning

Personally my car always seemed nippier on a cold morning rather than a hot day but could of been my imagination!

Thanks!

 

[Pep]

from what i know you are right, colder air is denser and therefore more combustible, hence why open induction kits are said to lose power, but cold air fed kits gain power?

 

[Chris_H]

Cold air is denser thus more O2 molecules per given capacity of air than hot air. So this will make more power as theres more air to mix with fuel, which more will be injected to match the increased density of air.

However!

for those interested in hot vapouyr engines which use HOT inlet air to make more power by good old Smokey Yunick heres a link

http://www.schou.dk/hvce/?mode=2

but basically for a normal car, colder denser air means more power.

 

[b3nje]

"As the fuel burns, combustion gases rise inducing rotation of the asymmetrical arms in an anti clockwise direction. Fresh air is drawn in from the bottom – it will be pre-heated by the asymmetrical arms as it enters the combustion chamber"

Is the ECU's job not to add/remove fuel/air depending on the situation. If a cold day the car will add more fuel or less fuel? So logically should the car would always run the same?

"Continuous combustion of fuel produces a stream of hot rising gases whose energy can be converted into rotation which is conveyed to the axle. Again if the products of combustion are used to preheat incoming air, energy losses are minimised and a conversion efficiency of heat into mechanical energy of over 80% should be possible."

 

[John D]

Your right.

Your boss is a plank. Has he actually driven a car in hot weather? surely he'd feel the difference in power

 

[b3nje]

lol, whats funny is hes worked in fleet management for 7years so deals with cars and problems everyday...he is still googling it and looking for more info !

 

[DebV6]

I always find that mine feels faster when it's colder.

 

[Dubai182]

Get the tool on here and we can give him a roasting. Cold air is has more density which provides more O2 as already stated. Its simple science really.

 

[b3nje]

But then what about diesels. Diesels obviously work differently to petrols as they don't ignite the fuel with a spark plug, they compress the mixture to ignite. So it has to make the air hotter. Obviously taking freezing cold air is denser so there is more air the compress BUT its cold and a diesel engine needs to make it hot by compressing it?

I still think cold air is more efficient even for a diesel engine as it comes down to the denisty and that there is more air there for when the compression takes places?

Hope i'm not giving you headache yet but i'd rather know 100% than try and argue with false statements

 

[DynamiqueDebz]

I dont know all the technical reasons like the other guys on here, but I do know most cars (including mine) run loads better when its cold. The only advantage to running it in warm weather as far as I can make out is, I get slightly more mpg when the weather is hot. I presume this is because the car runs on more fumes during warmer weather. I could be wrong though. lol

 

[Steve2004]

I don't know about diesels but petrols certainly seem to produce extra power when the air temperature is lower.

 

[b3nje]

When the air around is warmer the ECU reduces the amount of fuel to the mixture hence more MPG. Correct if i'm wrong

 

[philmots]

Yeah your correct mate. i'm pretty sure someone asked this question in that new technical section in evo magazine a few months back and got a really good answer for his question... maybe should try dig it out if you keep them?

 

[DynamiqueDebz]

Another thing I have just thought about; dont cars have cold air feeds to pull in the cold air to make them run better? (again don't know the technical reasons behind this). Surely cars wouldn't have these if they run better on hot air? Am I just grabbing at straws here?

 

[b3nje]

Well...obviously a engine needs air to run so an air feed or something that will allow air flow into the engine is a key to the design of the car.

You will find on some cars such as a 1.2 16v MK2 PH2 clio the "cold" air feed was attached to the airbox and the other end was pointing at the manifold so basically just drawin in extremly hot air. Hence people adding aftermarket air feeds and getting better performance.

I had the problem with add a cold air feed and aftermarket air filter but ended up getting too much air and the car was running a bit lean but then again the ECU should sort that out, should it not?

 

[philmots]

ECU only sorts it out so much, if you make big changes to air feeds etc thats when you need a remap

 

[DynamiqueDebz]

Well Hubby says his car has a direct cold air feed straight from the front of the car through the grille, it doesnt go anywhere near the manifold. His car is totally standard (apart from the wheels). He has a Megane Coupe 2ltr 16V.

 

[b3nje]

Where is the air feed on a standard 172? Does it not bend form the airbox to the middle of the engine bay?

 

[Alex_225]

Simple fact is that colder air is more dense, more dense means more Oxygen to burn, better combustion and therefore the engine responds better to cold air.
Otherwise, why would people and manufacturers go to lengths to get cold air from the front of the car rather than just sticking the air filter any old place???

Ask your boss what he thinkgs the purpose of an INTERCOOLER is on a turbo'd car???????

 

[Chris_H]

this was covered at the top in my reply! lol

Diesels, diesels run lean all the time, theres no throttle plate. The engine speed and power is altered by how much fuel is injected.

Its basically the same as a petrol engine as you need oxygen for it to burn, cold air means more O2 molecule per given capacity means a better burn, more power.

 

[b3nje]

Already done so

I said why would people want to spray nitrous oxide on there intercoolers OR cold water if the car is going to run better on warm air. he's hushed down about it now !

 

[Alex_225]

Wind him up and tell him that all the tuning guys are going on about 'Interwarmers' for their turbos!!

 

[Wilkeh]

ive also had this aguement and there is a big aticle somewhere that does say it will run the same. I disagree. Why else would they but fridge units on cars when running roading them?

 

[alexbleubolt]

i like engines

 

[GordonD]

So if cold air is so great, why don't cars ONLY have a cold air feed? Why do they have a cold air feed that only opens under high throttle, and the rest of the time they suck warm air?

 

[DynamiqueDebz]

So if cold air is so great, why don't cars ONLY have a cold air feed? Why do they have a cold air feed that only opens under high throttle, and the rest of the time they suck warm air?

I'm guessing because under heavy throttle they get warmer so need more cold air to stop them overheating and give them more power?

 

[b3nje]

good one ^ but very simple answer from me, not sure if its right but under high throttle the engine needs more fuel and more air mixture to turn the engine faster thus making more power. As the conversation has been saying cold air is denser so blah blah blah more power so it seems like a good time to use cold air?

Running from warm air will result in more mpg will it not as you will not have to use as much fuel?

 

[GordonD]

good one ^ but very simple answer from me, not sure if its right but under high throttle the engine needs more fuel and more air mixture to turn the engine faster thus making more power. As the conversation has been saying cold air is denser so blah blah blah more power so it seems like a good time to use cold air?

Running from warm air will result in more mpg will it not as you will not have to use as much fuel?

Liquid fuel doesn't burn. It has to be vaporised to burn. The lower the fuel temperature is and the colder the air you're trying to mix it with is the harder it is to vaporise the fuel, so you uneven mixture and incomplete burning of the fuel in the combustion chamber, higher emissions, and poorer fuel consumption. So in the engine operating conditions where those things are important, cold starting, meeting emission regulations and getting best fuel consumption you have the engine suck warm enough air that you get good fuel atomisation. And in the engine conditions where you want maximum power you just give it a rich mixture and suck cold dense air.

Petrol engines want to run lean to get the best fuel economy, and rich to get the best power. You and I want an engine that's reasonably economical when we're not caning it, and produces the maximum amount of power when we do. The manufacturer puts the warm air intake in to pass emission laws and maximise the mpg figure they can claim.

Diesels always run lean. A fleet operator with diesels doesn't care if his engines produce every last bhp they're capable of, he cares what fuel consumption he gets out of them. That's what important to him. He doesn't want stuff like cold air intakes.

 

[b3nje]

thanks GordonD, explanis it a bit easier to me but yeah thats sort of the jist of things that i thought!

 

[Chris_H]

hot air feed pipes are generally fitted to carbed cars and SPi engines.

Carbs need them to prevent carb icing and also so the mixtrure doesn't comndense on the inlet tract.

SPI cars need it so the mixture doesn't condense only.

MPI engines have no need for it as the fuel is injected onto the back of the inlet valve/port floor to atomoise it, or into the cylinder itself directly (GDI)