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MG MGF Technical - Cold Weather Question

As the temperature drops........ well we all want cold air going in to our engines don't we? Cold air is more dense, and so holds more oxygen so the logic goes.

So, at this time of year, can we expect to get more BHP from our engines?

Always wanted to know.

Cheers guys and Merry Christmas
Gary
Gary

Simple answer is yes, your engine will perform better in cold weather, but don't expect a huge difference LOL.
Steve White

okay ;-) so what's the difference between living in Cairo and somewhere in Greenland?

anwsers in BHP please.
Gary

>>> so what's the difference between living in Cairo and somewhere in Greenland <<<

If you lived in Ciro your igloo would melt at 35BHP (approx)
I have a question, why dont you use the EU standard of Kw?
Cecil Kimber

some things will always sound better in BHP, just like some things are still quoted in inches (!) But really, I wouldn't know what Kw means. My electric fan heater gives out 3Kw, so how many BHP is that?
Gary

1kW ~ 1.341bhp
or
1bhp ~ 0.746kW

So a 3kW heater equates to about 4bhp!
Steve Madden

Hi,

This is all so confusing. Doesn't a fan heater give out 3kw an hour? And doesn't bhp come all at once? Surely the K series gives out more power than 30 fan heaters?

I suppose somebody is going to say it all depends on what power means.

Oh yes, if your engine gives out more power in cold weather then it will need more power to push the colder (and more dense) air) aside, won't it?

Regards, Kes.
Kes

Density increases as temperature drops - approx. 3.3 deg C will see a change of around 1% in density and perhaps 1% increase in bhp. However, production engine intake temperatures are regulated to about 80-85 deg C for maximum all round efficiency, and are not therefore the same as ambient temperatures.

Paul
Paul

Don't forget that that car will sap more power as well - for the lights and the heater.

Talking of BHP & Kw... what about PS?
1PS ~ 0.97BHP

Ralph
Ralph

Kes,
Power is the rate of transferring energy.
1 kilowatt = 1000 joules of energy transferred per second. So, no - a fan heater does not give out 3kw in an hour but does transfer 3kWh (1080000J) of energy in that time.

Cecil,
the kiloWATT, the NEWTONmetre and the JOULE are obviously unBritish. ;)
Steve Madden

oops... dropped a nought there: 10800000J

bliddy nasty font thingies send you cross-eyed.
Steve Madden

>> I have a question, why dont you use the EU standard of Kw? <<

Oddly, MG-Rover use the German standard of Ps.

I believe it is to make the cars sound like they have more power as the Ps scale has slightly small graduations resulting in a bigger number for a given output. It's basically a marketing tool, and the difference between the Ps scale and the bhp scale is small enough to not matter too much to the lay person.

In the UK the traditional measure is Brake Horse Power (bhp), when the 'man in the street' discusses engine power they use (and think in) bhp. This is because, despite the fact that we in the UK are a Metric country, 90% of the population still thinks in Imperial. Ask any Joe on the street in the UK how far away something is and you're bound to get a response in Inches, Feet, Yards or Miles - we may be Metric as a country, but we're all Imperial as people.

Using the conversion figures given above, here's how a TF 135 stakcs up...

1Ps ~ 0.97bhp
1kW ~ 1.341bhp or 1bhp ~ 0.746kW

Ps - bhp - kW
135 - 131 - 98

Hmmm, if you were trying to sell a performance car, which scale would you use? The one that the UK public understand, the one that is the EU standard, or the one that is close to, but slightly above the one the UK public understands and gives the highest figure?

:-)

SF

Notes:

1 bhp is 550 foot pounds per second.
1 PS is 75 kilogram metres per second.
1 kilowatt is 1000 Newton metres per second.

To convert from: To: Multiply by:
BHP : PS : 1.01387
BHP : Ft : Lbs/second 550
BHP : Watts : 745.7
PS : Kg M/second : 75
PS : Ft Lbs/second : 542.476
PS : Watts : 735.5
Kilowatts : BHP : 1.341
Kilowatts : PS : 1.360
Lb Ft : Nm : 1.356

From this website:
>> http://www.pumaracing.co.uk/power1.htm <<

Scarlet Fever

>So, no - a fan heater does not give out 3kw in an hour
>but does transfer 3kWh of energy in that time.

But shirly the two statements are equivilent, I think you mean:
So, no - a fan heater does not give out 3kw of heat in an hour but does use 3kWh of energy in that time, that energy turns into magnetic, heat, movement of air and a little light.
Will Munns

No, the two statements are not equivalent.
Kes' statement suggested that 3kW is the power given out in an hour. We do not define power that way. This is a wrong statement. You can put your red pen away.

And don't call me Shirley. ;)
Steve Madden

But the energy has to go somewhere, so (ah here come the assumptions) assuming the heater has been given time to heat itself up before you start the watch (so it's now a steady state) all the energy going in has to come out somehow.

Power = energy per unit time, which every way you cut it
Will Munns

Bliddy Heck, Will!
Kes wrote "Doesn't a fan heater give out 3kw an hour?" (Apologies to Kes for dragging this on.)
Kes' fan heater has a power of 3kW. Since time is already implicit in the definition (P=E/t) and the unit (1W = 1J/s), any further mention of time is unnecessary and irrelevant in the context of describing its power. If Kes had written "Doesn't a fan heater give out 3kw a second?" or "Doesn't a fan heater give out 3kw a day?" the statement would have been just as meaningless. But we might talk about Kes' fan "giving out" 3kWh (rearranging P=E/t to E=Pxt) of energy in an hour and, in that context, the time is relevant.
A 100W light bulb has a power of 100W no matter how long you leave it on but how much energy it transforms/transfers/changes/gives out (and therefore the amount you owe the leccy company) depends on how long you leave it on.
This is not just semantics but how we define Power and Energy - terms which most people see as interchangeable but which are not.

Phew. Didn't want or expect to get into an argument there, Will. Have a good Christmas. ;D

Steve Madden

SF,
Good post there.
My 143bhp VVC has just been uprated to 147Ps. It feels faster already. ;)

And apologies to Gary for giving his fan-heater to Kes.
Steve Madden

Ahh, I see what you're saying - sorry.

Will Munns

Hi,

Look, it's not my bloody fan. It was only an attempt at light-hearted whimsy.

What I want to know is how much energy do I waste running around after my daughter switching off lights and televisions, turning off taps, closing doors, and throwing cats out.

Cheers, Kes.
Kes

About half a mini mars bar
Will Munns

Kes
Hmmm... interesting dilemma there: is it worth getting off the sofa to do those things if the amount of energy saved by switching off the lights and TV is less than the amount expended? Given that the leccy bills have rocketed this year, I'd guess that it's worth the effort and you can still have enough left over to buy yourself a few Mars Bars to replace the energy loss.
How much do you weigh, how high are your stairs, how much time do you spend per day per activity, how fat is your cat and how far do you throw it?
Of course, I will be assuming a spherical hairless cat on a parabolic trajectory in a vacuum for the purposes of my calculations...

Will,
No probs. I'll save my trolling for the yanks on Flame Wars in future.
Steve Madden

Steve, some other things to add to the calculation is that any muscle generated in the above excercise will hve to be fed, and muscle uses more energy just sitting there than flab does.

Also you have to figure how much longer you may live by getting the regular excercise, and how much energy it will take to sustain you for all those extra years.

very little calculation required to see running round switching off the lights is bad for the enviroment
Will Munns

>>okay ;-) so what's the difference between living in Cairo and somewhere in Greenland?

anwsers in BHP please. <<

Depends on the temperature difference Gary, but assuming a difference of up to 40C, then the difference in developed power could be as much as 10bhp... ;o)
Rob Bell

Cheers Rob

So how much would you assume the temperature difference is in this country between our hot Summers and our cold Winters - 30C? That should be something noticeable in our beloved cars, and surely the bigger the engine, the more the difference. Anyone have any experiences of this?

Gary
Gary

I have a feeling that more of the difference is in low/mid range power/torque Gary - although we could see about 5 bhp difference in peak power depending on how you've got your air intake system set up.
Rob Bell

This thread was discussed between 20/12/2004 and 22/12/2004

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