Cold Weather = More Horsepower but how much more ?

[Rodge]

As we know, colder temp's gives extra horsepower and this is especially so in forced induction engines, but how much more power ?, has anyone done dyno tests on this ?.

So late last night I was out in my SC FPV and it got down to 4 degrees celcius on the temperature guage and I decided to give it a bit of a go to see how she goes in the colder temps and OMG what a difference
I know with colder temps the tyres are colder too so there was less traction but the bloody thing was almost uncontrollable at full throttle This got me wondering how much extra power is there at say 4 degress compared to 24 degrees celcius ?
Thoughts ?

[pottery beige]

colder dense air will always make more power Rodge..

dunno if any tuners have done the 4am comparisons.. to me there may be a difference to a car parked on a dyno and a car actually moving through the cold air..

there must be a bum dyno kw to rwkw calc on the internetz somewheres..

[EVLKNEVL]

I voted 20-30, using my Boss 260 as reference. They are particularly sensitive to ambient air temp, even feel (dare I say it) torquey in cold weather.

[Rodge]

Originally Posted by EVLKNEVL

I voted 20-30, using my Boss 260 as reference. They are particularly sensitive to ambient air temp, even feel (dare I say it) torquey in cold weather.

Yeap, that was pretty much the reading from my slightly oversized and well used bum-o-metre too
and yes, we'll let you get away with the word torquey

[jpd80]

Sticky tyres, near freezing weather, a tank full of 98..... what's not to like...

[Rodge]

Originally Posted by jpd80

Sticky tyres, near freezing weather, a tank full of 98..... what's not to like...

yeah, I'm using 95 over winter to try and tame it down a bit.

[zx10]

I don't know the exact mathematics of it, but someone did tell me years ago that my WRX would act like it was producing more boost at lower temps. Hard for me to explain (cause I really don't understand it) but he said that 12 PSI at 30c was very different to 12 PSI at 10c. The lower temp would have a higher pressure after the turbo had done its thing.

Would love someone to correct me or explain it for me lol

[Sioso]

I used to drive an '01 WRX with a bigger turbo and frount mount and cold mornings (around 0c) the difference was huge, I would estimate 15-20 kw @ all 4 wheels.

[GTP534]

Took mine for its regular Saturday drive yesterday after having the 6/4 Brembos fitted.

Tyres felt a bit lumpy for a few kms or so; guess that's the result of sitting on a cold garage floor for a week!

They do like the colder air. Went to the station this morning to get my weekly ticket. Coming back on the motorway I entered slowly and let the traffic move ahead. Then, just slipped it across to Performance mode and hit it at about 80kmh. Gee's, it just sucked the cold air in and in an instant it was flying. This ZF is so smooth at wide open throttle.

Love it!

Can't answer your question Rodge about the number of kW, but I remember an old saying, "I don't count 'em, I just enjoy them!"

[FPV GTHO]

Depends what temp you normally compare it to but on a 300rwkw+ car it's probably substantial. I remember part of the drama with FPV/HSV over the DIN/ECE power standards was only 5 degrees difference difference during testing.

[Rodge]

Originally Posted by GTP534

Took mine for its regular Saturday drive yesterday after having the 6/4 Brembos fitted.

Tyres felt a bit lumpy for a few kms or so; guess that's the result of sitting on a cold garage floor for a week!

They do like the colder air. Went to the station this morning to get my weekly ticket. Coming back on the motorway I entered slowly and let the traffic move ahead. Then, just slipped it across to Performance mode and hit it at about 80kmh. Gee's, it just sucked the cold air in and in an instant it was flying. This ZF is so smooth at wide open throttle.

Love it!

Can't answer your question Rodge about the number of kW, but I remember an old saying, "I don't count 'em, I just enjoy them!"

You're on to it mate but all the same it would be interesting to know. The way my car lit the tyres up on kickdown at 60 k.p.h. on a dry road in a straight line, really has me wondering.

Same in my former F6 which I once had out in freezing conditions, (not sure if the temp guage goes to minus) but anyway it was reading zero degrees at midnight one night and I opened her up and honestly wopndered if I was driving a Ferrari

Might have a wee dig on the net and see if I can find some anecdotal evidence on raw numbers.

[flappist]

Originally Posted by zx10

I don't know the exact mathematics of it, but someone did tell me years ago that my WRX would act like it was producing more boost at lower temps. Hard for me to explain (cause I really don't understand it) but he said that 12 PSI at 30c was very different to 12 PSI at 10c. The lower temp would have a higher pressure after the turbo had done its thing.

Would love someone to correct me or explain it for me lol

General gas equation:

P*V = R*M*T

where:
P = pressure
V= volume
R = gas constant
M = moles (amount of gas molecules)
T = temp

So if P and V are constant then the only way T can be lower is if M is higher.

More M = more to burn = more energy = zoom.......

N.B. the gas constant is only to allow all the others to have units we understand i.e. R is different if pressure is PSI, V is In3 and T in deg F than if P is in Bar, V is mm3 and T in deg K.

[Rodge]

^^ So how does that formula work for a forced induction Ford FPV making say 300 rwkw's at 24 degrees, how much more at 4 degrees ?

[ratter]

some of it comes down to whether it is tuned in closed or open loop boost control

[chevypower]

Depending on how cold, there's also a negative effect on performance with a lower efficiency of the engine because of higher fluid viscosity. Not usually a concern with Australian climate though.

[MITCHAY]

Originally Posted by zx10

I don't know the exact mathematics of it, but someone did tell me years ago that my WRX would act like it was producing more boost at lower temps. Hard for me to explain (cause I really don't understand it) but he said that 12 PSI at 30c was very different to 12 PSI at 10c. The lower temp would have a higher pressure after the turbo had done its thing.

Would love someone to correct me or explain it for me lol

I tend to get boost spikes when its cold in my WRX. Definitely goes harder.

[Outbackjack]

Dont under estimate the P (pressure) in any calculation. Tests done at sea level will be very different at altitude... That is, the higher you get, like driving over a mountain range, the less power your engine will produce. Regardless of the cooler air. Turbo's and super chargers minimise these affects.

[Cuyper]

You typically drop a couple of tenths on a 1/8th mile as the temp goes from day to night. However humidity level is where you set your pb's

[Work Horse]

Originally Posted by Rodge

^^ So how does that formula work for a forced induction Ford FPV making say 300 rwkw's at 24 degrees, how much more at 4 degrees ?

About 20kw at the engine. But this assumes elevation, altimeter setting and relative humidity remain the same.

http://wahiduddin.net/calc/calc_hp.htm

[MattSAU2XR8]

A few formulas I think I recall from high school:

PV = nRT where P is pressure, V is volume, n is number of gas molecules in a given space, R is a constant, and T is temperature in Kelvin (Celcius plus 273)

This could be rearranged and simplified to show the relationship between the number of gas molecules (including oxygen) in a given space (i.e. inlet tract) as follows:

n = (constant) X pressure
temperature in Kelvin

Rearranging further you can get the difference in n (number of gas molcules) at different temperatures by doing:

Percent change in n = 100 X T1 (Celcius + 273)/ T2 (Celcius + 273)

So on a five degree day vs a 30 degree day you could expect about a 9 % increase in power based on temperature alone

On top of this in a tropical climate (eg. Brisbane as compared to Melbourne) then quite often there is more water vapour in the air which will displace all the other gasses. Also the warmer the air the more water it can hold. I think I recall correctly that lung air is about 6 % water molecules and fully saturated at 37 degrees C, and so probably slightly cooler air at 30 degrees would be saturated at about 4 %.

So a 'dry' day as opposed to a very humid day might be worth another 4 % increase in power. Although I'd be happy to be corrected on this by someone with better maths.

Finally, the cooler and dryer air described above will probably change the fuel:oxygen ratio at wide open throttle if the car is running open loop. I'm not sure about newer cars but my AU XR8 runs closed loop at part throttle opening and open loop at full throttle. So if it is programmed to run rich at WOT then a bit of extra oxygen could make a bigger difference by correcting the fuel:oxygen ratio as well.

So all up now there is up to 9% from more air, up to 4% from less water vapour displacing O2 from the air on 'dry' days, and some unknown gain from correcting a rich fuel:oxygen ratio, which I'll assume is at least 3 %

So if you had a 300 odd KW FPV then an extra 16+ % power would be nearly 48 kw extra which would explain the extra mumbo pretty well. Although its more likely its making 252 kw on a warm day and 300 kw at night - I can't see many car makers doing their 'claimed power' figures on hot days :-)

[Lotte]

Found this handy little calculator. Don't know how accurate it is (I'd have to sit down and plug out the maths in excel to compare), but you can get the info you need off the weather sites and then multiply your standard HP by the relative percentage.

http://wahiduddin.net/calc/calc_hp_dp.htm

[LyleXR8]

ill up the numbers a bit here, here in winter can get down to -2 or so, summer up to 47 degrees, definite power difference in both my XR8 and SS!
up the numbers a bit our trucks at work are 2650 hp, summertime when its 60 odd degrees down the bottom of our pit, they'll drag out 220 tons in first gear, this time of year when its single figures they'll pull 260 ton 2nd gear humming along. the more power your making the more hp you will lose via temp changes,

[shyun]

Originally Posted by MattSAU2XR8

A few formulas I think I recall from high school:

PV = nRT where P is pressure, V is volume, n is number of gas molecules in a given space, R is a constant, and T is temperature in Kelvin (Celcius plus 273)

This could be rearranged and simplified to show the relationship between the number of gas molecules (including oxygen) in a given space (i.e. inlet tract) as follows:

n = (constant) X pressure
temperature in Kelvin

Rearranging further you can get the difference in n (number of gas molcules) at different temperatures by doing:

Percent change in n = 100 X T1 (Celcius + 273)/ T2 (Celcius + 273)

So on a five degree day vs a 30 degree day you could expect about a 9 % increase in power based on temperature alone

On top of this in a tropical climate (eg. Brisbane as compared to Melbourne) then quite often there is more water vapour in the air which will displace all the other gasses. Also the warmer the air the more water it can hold. I think I recall correctly that lung air is about 6 % water molecules and fully saturated at 37 degrees C, and so probably slightly cooler air at 30 degrees would be saturated at about 4 %.

So a 'dry' day as opposed to a very humid day might be worth another 4 % increase in power. Although I'd be happy to be corrected on this by someone with better maths.

Finally, the cooler and dryer air described above will probably change the fuel:oxygen ratio at wide open throttle if the car is running open loop. I'm not sure about newer cars but my AU XR8 runs closed loop at part throttle opening and open loop at full throttle. So if it is programmed to run rich at WOT then a bit of extra oxygen could make a bigger difference by correcting the fuel:oxygen ratio as well.

So all up now there is up to 9% from more air, up to 4% from less water vapour displacing O2 from the air on 'dry' days, and some unknown gain from correcting a rich fuel:oxygen ratio, which I'll assume is at least 3 %

So if you had a 300 odd KW FPV then an extra 16+ % power would be nearly 48 kw extra which would explain the extra mumbo pretty well. Although its more likely its making 252 kw on a warm day and 300 kw at night - I can't see many car makers doing their 'claimed power' figures on hot days :-)

Don't forget this is only for the air at the start of the cars intake system. The temperature difference of the air inside the combustion chamber won't be as much as this. based on some ECU corrections against temperature ive seen it would be about 4-5%difference between 5-30.

The way you're meant to correct power readings on a dyno is using a correction factor which compensates for different atmospheric pressure and temperature.

[TyLeR3397]

http://en.wikipedia.org/wiki/Density_of_air

30 degree day 1.1644kg·m−3

Average 20 degree day 1.2041kg·m−3

0 degree night 1.2922kg·m−3

Say a 300hp engine is tuned and tested @ 20 degrees

300/1.2041 = 249.15
249.15 x 1.1164 (30deg) = 278.15hp
249.15 x 1.2922 (0deg) = 321.95hp

[Kevxr8Leexr6]

Didn't vote cause I don't know be honest. but when first starting your car in the morning the ecu reads cold and ups timing and fuel and feels aggressive till at operating temp then it retards . similar to them fake chips used between the maf sensor (inline resistor telling ecu cold)until it reads others an readjusts. so there is some merit to cold air im thinkin.

[Rodge]

WOW thanks guys, some really interesting formula's and information.
Looks like my bum-o-metre might not be far off 20-30 extra rwkw's for a 312 rwkw car but there was so much extra power and less traction at 4 degrees that it was wheel-spinning so bad I couldn't get enought traction on a dry road in a straight line to wind it out to max revs and feel the max difference, so it could easily have been more.

[ratter]

Originally Posted by Kevxr8Leexr6

Didn't vote cause I don't know be honest. but when first starting your car in the morning the ecu reads cold and ups timing and fuel and feels aggressive till at operating temp then it retards . similar to them fake chips used between the maf sensor (inline resistor telling ecu cold)until it reads others an readjusts. so there is some merit to cold air im thinkin.

actually the ford ecu removes spark to help get the cat up to temp quickly,

[Kevxr8Leexr6]

Originally Posted by ratter

actually the ford ecu removes spark to help get the cat up to temp quickly,

Thanks for that, didn't know that be honest. so when a cats cold im guessin by the logic it cant convert gasses. love learning .

Need a 47 yo apprentice Ratter. lol.

[PHATXR8]

The F6E seems to be noticeably more athletic when the air temp is <10 degrees Celsius, and even sharper down around zero.

But the wife's turbo territory doesn't seem to be any noticeably different.

[Rodge]

F6's really, really HONK when its zero I reckon there was more difference in my F6 than the SC wolf but it also works the other way and there's more heat soak over 30 degrees in a turbo F6 than I notice in my SC GT-P. I guess the F6's intercooler is more effective when its really cold.

Part of the other reason I guess could be the turbo pressure is higher in turbo's than superchargers stock for stock their releative prssure is 13 v 8 p.s.i. and as intake air is compressed its heats up so if its really really cold and compressed more stands to reason the coldness would benifet the car running the higher boost pressure I suppose.