Science behind 'Colder air = More Power'

[Coupe-R]

Yeh, hot air expands and rises, so less oxygen in a given "cube". I wonder how much the ecu actually would compensate, if at all, with cold vs hot air.. O2 sensors are for pussies anyway :p, just tune it correctly without and be done with it

UHHHH in a honda thats like one of the biggest factors affecting fuel apart from the raw fuel maps it self.

IAT=Intake Air Temperature sensor
There is a table in the ecu for IAT vs fuel (OBD0 has this also in BRE)

it matters a shit load to tune this correctly, especially with big injectors, if you have this wrong. Winter comes around and boom goes your car, not enough fuel added at that temp. (depends how you set up the base map tho)

This is also the reason why people running big injectors with VAFC2 have a dam rich cold start, they can't change offsets for cold coolant temps, and cold air temps, cold starts etc which=more fuel delivered

You've been living in nissan world too long
The airflow sensor has the temp conversion in the sensor already, and then the zone the ecu reads on a nissan ECU is determined by "TP" theoretical pulse width) This is measured from the air flow voltage, the Crank angle sensor, RPM, cylinders ect into a forumla the ECU calculates all the time so it knows which zone to read off at the specified RPM.

nissans have a complicated system because they are air flow, but do not require a IAT vs fuel talbe as such, because the air flow metre compensates for this.

[WhiteRice]

While we're on this subject, I've got a couple of questions that I've never been able to figure out

1. Why the hell does anyone ever use atmospheric BOVs? All the hard work of your turbo is let off into the engine bay. Surely it's preferable to have all that nice, cold, dense air go straight back into your intake? Unless you're a real putz and you only care about the noise, in which case you deserve to be pulled over (puts on flame suit)

2. Why are A/A intercoolers always shiny? Their job is to dissipate heat, and silver is about the worst colour for that. I would have thought that matt black would be better
Doesn't look as cool though

[Lycanthrope]

I'm no expert but I'll hazard a guess at those;

1. Because the whole point of a BOV is to reduce pressure in the intake when the throttle is closed, and stop pressure being forced back into the turbo wheel, slowing it down rapidly (often accompanied by a "flutter" sound) and putting excess wear/strain on it. You can get BOVs that recirculate the air back before the compressor wheel (if that's what you meant), so the air just keeps circulating through the turbo until the throttle is opened again, but I'm not sure what the benefit of that would be, other than to eliminate the BOV noise that most people like anyway. (Some countries have restrictions on unmuffled atmospheric BOVs).

2. The same reason a heatsink is always bare metal/shiny - the heat is transferred from the fins to the air passing through, and any coating/paint would just make another layer the heat has to pass through, making it less efficient. The colour of something relating to heat, to me only really applies when you're thinking about the sun or some external source of heat - black absorbs the sun's rays, silver reflects so doesn't heat up as much, etc.

My theories, experts feel free to correct me.

[Kiwi XTR2]

Originally Posted by grandell

Nitrous oxide + nitromethane ftw! they're running that on some of the drag cars in the states...


hmmm, got off topic? sorry

Ortho-Dinitrotoluene

Stand well back . . .

. . . further . . .

. . . further . . .

. . . further . . .

[Horny_Devil]

Originally Posted by WhiteRice

While we're on this subject, I've got a couple of questions that I've never been able to figure out

1. Why the hell does anyone ever use atmospheric BOVs? All the hard work of your turbo is let off into the engine bay. Surely it's preferable to have all that nice, cold, dense air go straight back into your intake? Unless you're a real putz and you only care about the noise, in which case you deserve to be pulled over (puts on flame suit)

2. Why are A/A intercoolers always shiny? Their job is to dissipate heat, and silver is about the worst colour for that. I would have thought that matt black would be better
Doesn't look as cool though

1. more piping is needed and looks like ass under the bonnet

2. its all to do with heat transfer, ali is a good conductor so thats y the are made from that + it doesnt hurt that they are light aswell, add anything to the outside and u reduce the heat transfuring properties.

black absorbs heat better than any other colour, stand outside on a hot day in a Black T-shirt and then in a White one.

[doo0T!doo0T!]

Also air heats up when it's compressed, it's also been drawn in through a very hot turbocharger too so the air temp in the intake pipe after the turbo is probably 100degrees celsius + when being driven hard and after the intercooler maybe 70 degrees.
So if you are plumbing the hot air back into the turbo again your only going to add to the heat.

[WhiteRice]

Ok. Thanks for the response.
Couple of points for consideration - regarding the compression of air from the turbo - yes it heats the air up as it is compressed, but then when it is released back into the intake (pre-compressor) it will cool again as it expands, so net temperature change is zero, assuming negligable temperature loss in the plumbing. However, if you placed your BOV post-intercooler (do you do this? I don't know), then you'd get cooled, dense air released back into your intake pre-compressor, which would either expand and cool to well below ambient, or remain relatively compressed. In either case, you'd get benefit from giving the intercooler a chance to cool down.

Regarding the heat sink issue - everyone uses shiny heat sinks, so presumably it's all for the best...
Heat is transferred by radiation, convection and conduction. Convection is not really an issue with heat sinks. Presumably most heat transfer occurs through conduction - hot metal transfers heat to surrounding air, and yes, you would want a good conductor. Black paint is probably a worse heat conductor than aluminium, but how about anodised alu?
The colour black is generally regarded as the most effective colour for heat transfer by radiation. Sure, it gets hot quickly on a sunny day, but that's as an absorbing surface. If the black surface is hotter than the surroundings, e.g. intercooler, it will radiate heat faster than a shiny surface, thus shedding the heat.
So I guess my question becomes - is there a sufficient aspect of heat radiation to justify having a dark heatsink, or is heat transfer almost invariably by conduction?

[Horny_Devil]

Originally Posted by WhiteRice

Ok. Thanks for the response.
Couple of points for consideration - regarding the compression of air from the turbo - yes it heats the air up as it is compressed, but then when it is released back into the intake (pre-compressor) it will cool again as it expands, so net temperature change is zero, assuming negligable temperature loss in the plumbing. However, if you placed your BOV post-intercooler (do you do this? I don't know), then you'd get cooled, dense air released back into your intake pre-compressor, which would either expand and cool to well below ambient, or remain relatively compressed. In either case, you'd get benefit from giving the intercooler a chance to cool down.

yes the air will expand again when it has been released back into the intake of the turbo, but just wont cool down anywhere near to what its tmpertaure was before it was compressed. cause all it will do is shed its heat into the surrounding air making it warmer, ie convection. so yea it will loose some heat but in doing so it has expand and heat up the surrounding air.

BOV's are normally placed close to the throttle body, and yes the intake air there will be colder but it still wont be the same as the outside air. and to this, have a look at a turboed hondas engine bay, do u really want a 2in pipe going from one side of the bay to the other (dependant on turbo orientation).

how would the air get below ambient? with out u having to put more energy into it? newtons law the time fram just isnt quick enough and the pressures were talking about are just too low

Originally Posted by WhiteRice

Regarding the heat sink issue - everyone uses shiny heat sinks, so presumably it's all for the best...
Heat is transferred by radiation, convection and conduction. Convection is not really an issue with heat sinks. Presumably most heat transfer occurs through conduction - hot metal transfers heat to surrounding air, and yes, you would want a good conductor. Black paint is probably a worse heat conductor than aluminium, but how about anodised alu?
The colour black is generally regarded as the most effective colour for heat transfer by radiation. Sure, it gets hot quickly on a sunny day, but that's as an absorbing surface. If the black surface is hotter than the surroundings, e.g. intercooler, it will radiate heat faster than a shiny surface, thus shedding the heat.
So I guess my question becomes - is there a sufficient aspect of heat radiation to justify having a dark heatsink, or is heat transfer almost invariably by conduction?

again putting a coating on the metal is going to reduce its effiecncy, in a few different ways, 1 being smaller gaps in the fins for air to go through, 2 being that the paint/anidisation might not have the same transfer properties of the material of the intercooler.

what uve said may hold true for a stationary car but for a moving car it just really have to much of an affect

[Colza]

It has been shown that both painting and anodizing reduce the efficiency of an intercooler. Sorry, I dont have the article on hand.

As for the recirc BOV, thats actualy an interesting point.

The problem is your charge air temperature is increasing for several reasons, partly from compression, and also from heatsoak through the turbocharger.

If it was only heating due to compression then when you cooled it with the intercooler, and then decompressed it you should get colder than ambient. You have a refrigeration cycle (thought not a very good one).

Whether the cooling you get from this is greater than the heating from the heat soak i do not know. It would be an interesting experiment

[doo0T!doo0T!]

Originally Posted by Colza

As for the recirc BOV, thats actualy an interesting point.

The problem is your charge air temperature is increasing for several reasons, partly from compression, and also from heatsoak through the turbocharger.

If it was only heating due to compression then when you cooled it with the intercooler, and then decompressed it you should get colder than ambient. You have a refrigeration cycle (thought not a very good one).

Whether the cooling you get from this is greater than the heating from the heat soak i do not know. It would be an interesting experiment

I also thought it was an interesting thought but as Horney has already pretty much said, when you decompress, it only cools down because heat energy is given off, this is usually taken up by the surrounding atmosphere but if you are decompressing straight back into the turbo intake it's only going to loose the heat energy back into air which is about to be fed into the turbo anyway so there is no net loss in temperature except the small amount that soaks thought he walls of the plumb-back pipe.

It would be an interesting experiment but I seriously doubt that the cooling effect could ever be more than the heat soak from the turbo, at Taupo my hot side was hot enough to melt heatwrap into glass beads after 4 laps so we're talking 1000 degrees plus! sure there is water cooling between the hot and cold sides but it's cast iron and we know how well that conducts.

[Coupe-R]

at Taupo my hot side was hot enough to melt heatwrap into glass beads after 4 laps so we're talking 1000 degrees plus! sure there is water cooling between the hot and cold sides but it's cast iron and we know how well that conducts.

Somethings not right there!!!!
Either it was crappy wrap, or the ignition timing is way retarded and your EGT is through the roof!!

On a mates RB25DET 270kw drift car, the whole exhaust housing is wrapped and it don't melt at all.

[Mike1234]

*Fights off science nerds*

Haha, Some good info here guys, chur

[racerdad1]

damn....for sum reason reading that felt like i was back at skool haha...a kool skool thow lmao

[tarmac-]

Originally Posted by Coupe-R

UHHHH in a honda thats like one of the biggest factors affecting fuel apart from the raw fuel maps it self.

IAT=Intake Air Temperature sensor
There is a table in the ecu for IAT vs fuel (OBD0 has this also in BRE)

it matters a shit load to tune this correctly, especially with big injectors, if you have this wrong. Winter comes around and boom goes your car, not enough fuel added at that temp. (depends how you set up the base map tho)

This is also the reason why people running big injectors with VAFC2 have a dam rich cold start, they can't change offsets for cold coolant temps, and cold air temps, cold starts etc which=more fuel delivered

You've been living in nissan world too long
The airflow sensor has the temp conversion in the sensor already, and then the zone the ecu reads on a nissan ECU is determined by "TP" theoretical pulse width) This is measured from the air flow voltage, the Crank angle sensor, RPM, cylinders ect into a forumla the ECU calculates all the time so it knows which zone to read off at the specified RPM.

nissans have a complicated system because they are air flow, but do not require a IAT vs fuel talbe as such, because the air flow metre compensates for this.

Yeah, was joking hence the :p

[Coupe-R]

I saw the ;P for "oxy sensors are pussies".

but a question saying "I wonder how much the ecu compensates for cold/hot anyways"

Oh well i missed the sarcasm

[doo0T!doo0T!]

Originally Posted by Coupe-R

Somethings not right there!!!!
Either it was crappy wrap, or the ignition timing is way retarded and your EGT is through the roof!!

On a mates RB25DET 270kw drift car, the whole exhaust housing is wrapped and it don't melt at all.

I have an exhaust temp gauge which goes to 1200 but to be honest I wasn't watching it on the track. Normal spirited driving it usually sits around 700-750.
Probably looked something like this at the time.


As a rough guide I have been told 800 degrees is cherry red in visible daylight, 900 is yellow, bright yellow white is about 1000
I've found out glass wool becomes malleable at 550 degrees and fully liquid at anywhere up to 1500 degrees so to form beads it must have been right up around 1000 degrees!
Cast iron melts at 1200 so any higher and things would be starting to go pair shaped.
Where the header cracked and the flame was blasting out, if you looked closely you could see where lip of the steel had been bent out around the crack in the direction of the gas-flow where it had got hot enough to actually melt and go soft. Once it had cooled the metal was partly crystalized.

It's a pretty damn small turbo and I'm pushing it right to it's limits to be getting 160wkw with only 8.3:1 compression on a ZC!

off topic a bit but cool story...
At my old work there was a full carbon fibre bodied Porsche 956 Lemans car and the engineer I was working with had led the team that had hand built it, it was an incredible machine (and no I dont have pics, my old hard drive died)
When it was on the dyno the titanium exhausts were so hot you could see the pulses of flame and standing waves through the exhaust, they were so hot they were see-through!!
They had to build brackets to hold up the turbos because the headers were getting so hot they were drooping. At one stage you could see the relection off the heat reflective lining in the engine bay through the headers.
In one of the dump pipes straight off the turbo you could see a bright white helix through the tubing which was glowing inside, it was apparently where an exhaust wheel in the turbo had been spat out and as it shot down the exhaust pipe and out the end it had rifled the inside of the exhaust pipe, the flame catching on the tiny gouges inside the tube was lighting up bright white and you could see it through the outside of the pipe.

i hate to think what sort of temps that thing was producing. It was around the 700hp mark.

[Coupe-R]

Where the header cracked and the flame was blasting out, if you looked closely you could see where lip of the steel had been bent out around the crack in the direction of the gas-flow where it had got hot enough to actually melt and go soft. Once it had cooled the metal was partly crystalized

My GOD, that is EGT is HOT.

Trust me heaps of it is in the igniton timing, not just the fact it's making big power.

I'm amazed at the heat of that porsche also!!!!! Not good!
Again, im not sold on the fact cause it was 700HP it was making the exhaust metal so hot it was see through and all 700HP turbo cars do this?
(I believe you but I'm saying there was probably a solution to the problem, to much ignition retard heating up the exhaust like CRAZY!!)
thats why people use EGT gauges, to check if they are too hot, if so they increase the timing a bit.

However I don't have experience in turbo tuning and 700HP cars, so maybe thats just how hot they run?

Amazing stuff anyways
Would love to see some of the stuff you see, sounds like you have an interesting job

[doo0T!doo0T!]

^different job now, I used to work for NZsupercars building the HulmeF1, not really sure whats going on with it these days but I hear they have the mule "Bear2" almost ready to run. And yeah it was pretty cool alright, got to see a lot of cool stuff but the Porsche was by far the best! I've tried to find it on the net but it's pretty covert, whoever owns it now must want it on the down-low, I know it was insured for over 3 million so he's probably not keen to whore it around.

Back then the Hulme was going to be BMW M5 v8 powered and there was a brand new crate motor sitting on the shop floor which arrived from Germany in individual pieces and had to be assembled bit by bit as the parcels arrived :LOL:
There was also a 6 speed sequential quaife transaxel box, AP Racing 6-pot brakes the size of Texas, Motec & Dash, recaro kevlar buckets from the Carerra GT (which at the time was still conceptual) and the wheels of pure sex, 20 x 13 rear and 19 x 10 front custom built single nut knock on centres cnc'd from billet blocks. splurge.

Oh yeah and an 800hp Mitsibushi GTO which was built for a rich guy who wanted to do the Gumball rally, it looked totally stock, full interior, rudey poos maroon paint job, even stock rims. Underneath the skin though it was a monster, ran on race fuel only, Motec computer and the brakes were off a Ferrari!!
It was not your average GTO thats for damn sure

I so hope they get it up and running, apparently now they are using the latest corvette engine and box which is kind of more appropriate since Denny's CanAm cars were originally chevy powered and the first car is an open top rather than a hard top.

Heres a pic of the model....

[grandell]

sticky?

yes i am