Hang on tight!!!!!!!!!!!!!

[Grant]

Blimey, I had forgotten how the Turbo goes from fast to "ROCKETSHIP" once the weather gets cold and dense. I have to say at this moment in time the old 996TT is a bit of a beast, you have to hang onto the steering wheel to stop being sucked out through the back window!!
Are fellow Turbo owners (of all types) feeling the same noticable step up in grunt?
I wonder what the rough real world BHP difference is between a hot day & a freezing one in something like a TT, are we getting a real chunky gain or is it just subjectively "feeling faster".
Any one any idea's?

 

[lee fulford]

It's kind of strange but I've only had my TT about 3 months and I remember my first impressions......."Wow this old sausage is seriously fast"

I'm use to fast cars but this thing was relentless.

I've since fitted a Tubi-style to make it more audiable. Even so it's funny how you get use to the performance at which point it doesn't appear so incredibly fast so maybe it's the noise that gives this effect.

Stonking car but I don't notice any real difference in the cold and damp......but then it seems faster or slower one day to the next anyway, depends on the mood I guess.

cold damp air is proven to give more power in the main.

 

[Guest]

I'm not sure about how much faster it actually is.
It does seem to run better and the performance comes with less apparent effort.
Plus the speedo has even more trouble than normal with keeping up.

I was thinking last night and this morning that the exhaust sounded louder as well.

At 0 deg C, the air is about 9% more dense than at 25 deg C.
All things being equal, then you should be getting 9% more air molecules into the cylinder, which if you get 9% more fuel should give 9% more power.
However, I'm not sure if it all scales linearly or not.
Your peak boost pressure will be unchanged of course, since the valve will open.

Given that I reckon the exhaust is louder, then I think there may really be a bit more power on tap.
9% would be 37.8bhp for a regular TT, or 40.5bhp for a X50.

However, it depends on what temperature they use for the quoted figures.
If 450 comes at 20 deg C, which is a good average European temperature, I could be getting 481.5 at 0 deg C. Admin got 476 a while ago on a rolling road, so perhaps the temperature does make a difference.

Perhaps a rolling road session is needed in January and July to confirm it.

At the top end (not an issue in the UK) the air is 9% more dense, which will require more power to puch it out of the way. So the top end may be dented by a few miles an hour.

BTW - if you keep the seat back upright, then you don't need to hang on to the steering wheel as much. []

 

[tallmat]

Even if I don't fully understand Stuart's immaculate scientific analysis (though when I worked for a team running a 962 at Le Mans, the best lap times were at night when the temperature dropped), I'll vouch for one thing - the car seems to fly in this current chill....

BTW, anyone watch 5th gear? Thought the item on merits of Optimax and BP Premium Unleaded was good. Basically we should use higher octane juice for max output.

 

[Guest]

I checked this morning to see if the accleration was more than usual.
At between -5 and -4 deg C, it is definately accelerating faster than normal.
I can't check whether the top speed is affected.

I thought about is some more last night, to see whether there might be a flaw in my thinking yesterday, since 9% seems a lot of gain.
But if the air flow meter is measuring the mass of air, and not the volume of air, and fuelling accordingly, then there really should be more grunt on tap.
I don't know how accurate the air flow metering is though.

I also confirm it goes quicker when it is damp, but since this is also when it is misty or foggy, it is not the best time to be using the additional power.

However, if you are getting more power, you should also be getting worse fuel economy, since you don't get something for nothing.
Since most of the driving is not a foot-to-the-floor affair, the affect is quite small. It is hard to say on this score. Although the throttle opening does seem to less at the moment (i.e. I seem to press the pedal less far for the same effect, but it could be my imagination).

 

[Rotorhead]

The ambient temperature, and denser air, makes a huge difference to the take off performance of piston engined light aircraft. There are some small grass strips where you wouldn't want to attempt a heavily laden take off in mid-summer but, in this weather, even without a head wind, but aided by a harder runway surface, the aircraft will climb like a lift.

In fact, these are near perfect flying conditions - unless you are heading into low sun.

Fuel consumption is usually higher in denser air, as the air/fuel mixture needs to be set richer. At higher altitude the air is thinner, even though it may be colder, so the mixture runs leaner.

 

[vitesse]

I seen some "non sequors" but is someone attempting to take off in their Porsche because the weather is colder.Do gliders fly better in hot air;piston engined planes better in cold or denser air or is our 964 just too slow?

 

[garyw]

I was cruising the M6 toll road only the other night thinking the same. I also realised why I don't use the car to commute...to damn easy to lose my licence []
But I had a bigger smile than most when I arrived on site []

garyw

 

[sniper]

Agree this time of year is superb for the porker. Have also had turbo charged cars since I was eighteen[] and the cars definately have more grunt the colder it gets. 9% seems reasonable.

 

[gaxor]

Boost guage hit 1.1 bar this morning

 

[lee fulford]

What happens when you turn off the traction and give it plenty of welly?

Not had the space or the balls to do yet. I suspect it's not like a Skyline where you can put your feet up on the dash and have a chill? Is it reasonably straight line or does the back still try and overtake?

 

[Guest]

In the wet:
If the front wheels are not straight, then you will spin the rears and go round in a circle, doughnut style.
If the fronts are straight, the rears will spin, some power (30%+) will go to the front, and you will mostly go in a stright line.

In the dry:
If the fronts are straight, you will quickly go in a straight line. If you dump the clutch you may be able to smoke the rears, but there is really too much traction.
If the fronts are not straight - not quite sure, I presume some large diameter doughnut is possible. You may just spin the inside rear but still go around with just a bit of understeer.

I have not conducted exhaustive testing, so am prepared to be corrected.

 

[lee fulford]

Thanks Stuart, I'll experiment one wet day when I have an empty airfield....I've had the back end twitch occasionally when on boost in 2nd and the car sometimes twitches too.....[]

I've noticed that I don't ordinarily get the same boost in the damp air. Is that because the engine doesn't need it to achieve maximum power?

 

[Guest]

I think the boost just has a pressure limit, i.e. once you get to the maximum the valve will open to stop it going any higher. It is under the control of the engines processor.
I don't know if there is any way it can tell how much power you are getting and decide you have reached the power limit. I think not.

Why the maximum seems to vary I am not sure.
I can't think of any obvious explanation.