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22 degrees F - like a needle in the arm

I haven't yet convinced myself to put her to bed for winter....so I roared off to work this morning at 0-dark-30 with ambient temps resting at 22 degrees. I do believe that may be the record low for my 930.

For those of you who reside in hot/humid locations where anything less than 45 degrees warrants FEMA intervention, unfortunately you won't be able to relate to this. But let me tell you, until you've tasted cold dense air you don't know what a kick in the pants these old CIS cars can be.

Some Google-search provided the following: Air at 22 degrees is 10% more dense than air at 70 degrees....at atmospheric pressure. Now boost her up to 1.0 bar and that extra density becomes extra HP. 10% more HP...??? If I were an automomotive engineer I could answer that, but my butt dyno says at least that.

Who really cares. The fact is that boost is quicker, lag is less, and performance overall is simply awesome. She was just happily barking at me as I ran her through the gears. The only problem is that it was way-dark outside, so I had to keep her under triple digits.

One final note: My idle was hanging up at around 1500 when stopping after 20 miles. Seems my AAR would need a different calibration at these cold temps. Oh...and even though my foot well blowers suck (winter project to fix them) the cabin was comfortable enough.
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Mark H. 1987 930, GP White, Wevo shifter, Borla exhaust, stock everything else. The result of a massive Pelicanite good will fire recovery effort. Truely an open book, ready for the slippery slopes to modification.

Last edited by mark houghton; 11-05-2011 at 02:28 PM..
Old 11-05-2011, 02:25 PM
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Mark last winter I saw 34* inlet air temps on my datalogger running down the highway.... The car was loving it
Old 11-05-2011, 02:42 PM
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44 * f

Had mine out today also. Twisted her sideways in a S curve, and took a couple 180's to straighten her out. Luckily I didn't leave the road. Car loves this weather, but you have to remember you don't have the traction without the warm tires/road.
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Old 11-05-2011, 03:14 PM
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Quote:
Originally Posted by drmatera View Post
Mark last winter I saw 34* inlet air temps on my datalogger running down the highway.... The car was loving it
..around december 10 last year I'd guess. Coldest december on record here last year.
Old 11-05-2011, 03:28 PM
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I have been taking out the car on these brisk mornings also. Yeah, it seems faster.
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Old 11-05-2011, 03:37 PM
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I drive mine every single day, and have for the past 4 years....

Yep cold, crisp days are a blast, but with 2 1/2 inches of ground clearance, mine becomes a snow plow if the white s**t falls.

The coldest I have driven mine, was when the thermometer at my house read 17 degrees!

Mark
Old 11-05-2011, 05:21 PM
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Quote:
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I drive mine every single day, and have for the past 4 years....

Yep cold, crisp days are a blast, but with 2 1/2 inches of ground clearance, mine becomes a snow plow if the white s**t falls.

The coldest I have driven mine, was when the thermometer at my house read 17 degrees!

Mark
Ok Mark, you've thrown the gauntlet. I vow to beat your 17 degrees (I hope, before the snow falls). I drive mine probably 70% of the time except in winter, and today was the coldest morning yet this fall. But I don't do Porsche-snow (I have an exceedingly long and boring story of a trip to Chicago many moons ago in late January driving my ol' 72 Targa...took 5 days 'cause of snow/ice/weather, etc. My 930 flat refuses to go there).
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Old 11-05-2011, 06:20 PM
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The colder temps definitely help - getting down to around zero C (32 f) in the mornings now and the car is certainly more responsive. My idle is also a little faster, and even on warm starts it will idle around 1,000 - 1,200 rpm whereas in the summer it starts and idles at about 800 rpm. I guess the AAR just never cools enough to raise the idle in the summer, but once we get into single digit temps (in celsius) maybe it never gets warm enough to lower the idle? I've tried squeezing the pipe between the IC and the AAR though and it doesn't drop the idle so maybe something else is raising the idle?

I don't have a built in AFR gauge but it would be interesting to see how the colder temps affect AFRs - have you noticed it running any leaner?

Once I get heat exchangers these lower temperatures will be much more enjoyable
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Old 11-06-2011, 05:11 AM
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Makes me wish I had heat!
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Old 11-06-2011, 07:04 AM
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The colder temps definitely help - getting down to around zero C (32 f) in the mornings now and the car is certainly more responsive. My idle is also a little faster, and even on warm starts it will idle around 1,000 - 1,200 rpm whereas in the summer it starts and idles at about 800 rpm. I guess the AAR just never cools enough to raise the idle in the summer, but once we get into single digit temps (in celsius) maybe it never gets warm enough to lower the idle? I've tried squeezing the pipe between the IC and the AAR though and it doesn't drop the idle so maybe something else is raising the idle?

I don't have a built in AFR gauge but it would be interesting to see how the colder temps affect AFRs - have you noticed it running any leaner?

Once I get heat exchangers these lower temperatures will be much more enjoyable
My AFR's were about .2 higher. No big surprise. My AAR is working fine I think (just for kicks, I checked the voltage to it as well as the resistance of the heating element...and pinching the hose brought the idle back to 950).
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Old 11-06-2011, 10:07 AM
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Living here in the Minnesota tundra has at least one benefit. Come the many frozen days of autumn and early winter every turbocharged engine out there in River City becomes an unpredictable monster. I once owned a Volvo turbo wagon that could lay rubber in every gear and damn near got me killed and/or arrested several times spooling up at 20F. I'm almost afraid of what will happen with my 930 when it returns from Arizona next year, but it's the kind of fear I love.
Old 11-06-2011, 10:33 AM
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With my Carrera 3.2/turbo in ~30 degree temps, my old worn 285 Potenzas didn't have much of a chance in 4th gear! It was a hand full. Haven't got ant cold temps lately.
Old 11-06-2011, 10:59 AM
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When to florida to visit my mother last week. Came home last night.. woke up this morning it was about 30F.. Man she was an animal. I run16lb of boost with meth injection, I could not keep the wheels from braking loose. I was running leaner and I was also getting about 1lb more boost also..
Old 11-06-2011, 12:22 PM
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Not trying to be a wiseazz, just throwing in some data.

The most important factor when considering performance is for sure temperature.

When we consider performance we consider density altitude, which is a product of pressure and temperature and pressure.

I will use ISA units:
Standard sealevel pressure is 1013.25 hPa (29.92 Inch)
Standard temp is 15C at sea level.

At 18000feet the pressure is down to half that a sea level.

The standard lapse rate (temp drop per increase in altitude) is 2C per 1000 feet.

When we calculate density altitude ( ie to figure out the current environmental effects on performance) we first need to figure out pressure altitude. Pressure altitude changes by approximately 30 feet per hPa change. At high pressure we have increased performance.

To finally figure out density altitude (DA) we need to consider temp. A change of 1C changes the DA by 120 feet.
Though this is not linear. This is close enough.

Rho is the term referred to as density. When relating this to the temp and press effects. And knowing in ISA we have only 50% at 18000 feet, we can begin to figure out the effect on our engines on a given day.

Let's say we have a hot southern summer at 40C then take the car up north to -10C. This change is 50C which is a change of 6000 feet, which is about a conservative increase in performance of about 15%

I only consider temp in this example since it has Gita way bigger impact. Furthermore press changes are not that big, relatively speaking, even in extreme weather, where we don't drive our cars anyways.

It is important to note that a significant temp decrease does not just bring I creased performance, but it also requires us to adjust our fuel, AFR.

Disclaimer. This is posted on iPhone, so no review of the post. I hope it makes sense.
Old 11-06-2011, 12:47 PM
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Jsveb;

Like I said earlier, if I were an automotive engineer I would expound further. But, sadly, I'm not, so I'll take what you've posted as an experts assessment and will have to spend some time digesting it. Cold(er) is good, no doubt.
Your comment here distills it all down:
Let's say we have a hot southern summer at 40C then take the car up north to -10C. This change is 50C which is a change of 6000 feet, which is about a conservative increase in performance of about 15%
....which just confirms that my10% performance increase guess (just a wild ass guess) wasn't that far off afterall.

I just got back from the local car wash, and had to goose her a bit to break into the traffic. Oops....gave everyone a show as she went sideways. What fun!!!!
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Old 11-06-2011, 01:49 PM
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Jsveb - not sure if you're a pilot as well (I am) but it seems you've nicely described the effect of temperature and pressure on engine performance. I've not taken the time (nor do I have the inclination!) to determine the real effect on our engines, but my butt dyno (and others too it seems) confirms that there is a significant change in performance that our "other" cars do not benefit from. Presumably that's because modern sophisticated engine management systems are able to optimise performance for a wider range of conditions which our prehistoric CIS systems cannot do, which makes it that much more noticeable.

.2 difference in AFRs - interesting. I wonder at what temps we need to get concerned about going too lean, assuming we're still thrashing our cars when it gets really cold?
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Old 11-06-2011, 04:30 PM
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I don't need science to know that the colder the temps, the higher the tq/hp.
Old 11-06-2011, 04:41 PM
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Mark---

I concur. Cold temps are great!!! I also had a problem while back with the AAR-Sticking over 1200rpms...Just took it out one day and cleaned it, and took my time..(with a beer on the side) After that, all was good..

The weird thing this weekend--temps were in high 40's-low 50's -sunny--practically no wind.. I was hitting 1bar--with no problem with the targa-top off(hmmm)..Haven't seen this before with a stock intercooler..My fuel settings and the cold air made a perfect combination.

Just be careful with cold tires...

Walt
Old 11-07-2011, 04:24 AM
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Have you guys been to dragtimes.com ? They have a listing of all the tracks and record weather conditions every hour. You can use their calculator to figure out the density altitude at any given time. Last Friday night at my track the DA was 688 ft. On really cold dry nights it's dropped below theoretical sea level.... What they refer to in drag racing as "mine shaft" conditions
Old 11-07-2011, 02:30 PM
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Ice on the track last sunday @ Cayuga. The motor loved it but the Toyos not so much. I mowed some frosty grass in the morning.
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Old 11-07-2011, 05:51 PM
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