Turbocharging — one more reason to like autumn
Many folks like autumn for things such as football (North American style), crisp weather and colorful foliage. Saab owners have at least one other reason — turbocharging. Especially when intercooled.
Here in North America, autumn weather is upon us. Just in time, too, since the autumnal equinox is just over a week behind us. Here in Nashville, Tennessee, the autumn can be very unpredictable — Halloween can be as hot and sticky as any June day, or it may require a jacket worthy of December. As of this writing at the beginning of October, we are just a touch above the average temperatures of 80 deg F (27 deg C) and 50 deg F (10 deg C) for highs and lows, respectively.
With the air noticably cooler, thoughts of the rites of autumn come to fore. Here in the American South, football is such a strong tradition that people quite literally plan their weekends around “game time“. For the record, our Tennessee Titans are 4-0, having beaten two of the better teams in the league already and they sit atop the AFC power rankings on ESPN.com. (Jeff, the Ravens are up this weekend — not a chance.) Even more surprising, my Vanderbilt Commodores, the perenial Southeastern Conference doormat, are also 4-0 and ranked 19th in the country. To all of you outside the U.S., here’s how unusual this is: Vandy’s last winning football season was in 1982. I do love football season, and this season is going especially well for me.
But, for we Saabisti, fall brings another little boost (pun intended): a few extra horsepower. Driving the 9-5 on this chilly, clear morning just after sunrise I noticed the difference immediately. The car more effortlessly accelerates from a stop, and there is noticeable amount of additional pull after each shift. As I’ve written in these pages before, the 900 “boosts like mad” in this kind of weather. With the 9-5 the feeling is much more subtle; I’ve always chalked that up to the fact that it’s a low-pressure turbochager set up rather than the “full”-pressure turbo on the 900. It likely also indicates some design refinements. In any event, fall and spring are always great for a smile-on-your-face drive on the long way home. Which is precisely what I took early today after shuttling my ten-year-old son to school.
All cars, but especially those equipped with turbochargers, make more horsepower when the air is cooler and drier. It’s all basic physics, but it makes a substantial difference in your “bottom line” horsepower because this gain comes for free — there are no additional parasitic loads to be paid, no tempermental modifications to fuss with and no fancy fuel to buy. Just more air and better cooling. That’s all that it takes.
(In my case especially, I guess that you could say that really I don’t get any real gains in power as much as I cease losing power to hot weather conditions. Tomato, tomahto. It feels like a gain to me after a long, hot summer, so let me enjoy it.)
How does this work? I’m glad that you asked, because I was going to tell you anyway. It’s actually very simple: cooler air is more dense and therefore contains more oxygen per unit volume. More oxygen available to the combustion process means more fuel can burn and thus more horsepower is produced with each ignition cycle. After all, this is the whole concept behind turbocharging, right? Use exhuast gases to compress air to allow the engine to consume more oxygen thus increasing output and efficiency.
For an intercooled turbocharged car (both of my Saabs are intercooled), the cooler ambient air has an additional benefit: the intercooler cools the compressed inlet air to a lower temperature. The idea behind the intercooler is that at constant pressure the inlet air will be more dense, thus rendering the turbocharger more effective. Due to the heat rise associated with air compression, an intercooler has a substantial impact on turbocharger effectiveness. With cooler ambient temperatures comes lower intercooling temperatures that increase the boost the turbocharger is able to deliver. It works. Believe me, it works.
So, to all of you out there lamenting the shorter days and the approaching winter, I say, “Rejoice!” Go have a drive in your Saab. You’ll be glad that you did!
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Where can I find a full-size version of that thumbnail pic you used for this post with the Saab engine with exhaust manifold glowing orange-hot? Was that pic colorized or somehow enhanced? I can’t believe the metal can get THAT hot without melting.
That pic is from the Saab 900 Engineering Manual. I have the real thing somewhere.
Also, I have two non-turbo Saabs. For me, winter just means water pooled in the floor boards of the 900.
OH YEAH! We are getting our first rain of the season and the fall air is crisp (by Northern California standards) and the SAAB is smiling when it draws in that air!
Hmm.. Funny thing… I hit 245 kph during one night in May at the autobahn (oh, how many people have I bored to tears with this story now? MANY!), but when I went the other direction it was early evening… Not quite so fast then… A slight temperature difference perhaps?
I guess a retry is in order! hahahaha! (there is always an excuse if you need one, right?)
We have plenty of cold air here now, but no decent roads to take advantage of that. (today we might see 10.5 degrees Celcius, but it will soon cool down again)
Grip:
Mag-X is right, it’s from the engineering manual. I don’t know if it exists anywhere that we can access in any larger size.
As far as the color, some metals will melt at that temperature. Based upon this reference
the exhaust and turbo look to be 1200 deg C. This temperature is the beginning of the melt range for cast iron which has a relatively low melting point. I believe that the exhaust is a high-carbon steel alloy (alloyed with manganese?) which has a higher melting point.
Oops, forgot that even though the full size is on the server, the image shown on the article is very small.
Here is the original.
Thanks for explaining this! I’m new to Saab and to a turbo engine (as of April this year, I have an 08 9-3 with the 2.0 engine). I really thought I was crazy the other morning, when it finally cooled down here in San Diego and the temperature was in the 60s and there was a nice ocean breeze coming in. I was driving to work and I felt that kind of additionally pull after shifting (i have a manual transmission). Now I know it is not just that I love the car, it is actually giving me some extra power when I accelerate!
eggs: thanks for the bigger pic. It amazes me the exhaust system can be that hot but not burn-up the engine. They need some seriously effective cooling and oil circulation if they get the engine that hot. I imagine that’s what my engine’s been looking like lately in the hot weather here!
too bad i cant use my turbo, always a stupid scraping noise whenever i get into boost, saabusa claims its normal.
Oooooh, the joys of a Saab. That turbo acting like a slingshot as you approach 2000-odd rpm headed toward a speeding ticket before you realise how fast you are really going. The 2003 sales campaign for the 03 93SS featured a smiling cartoon character. Thats me - every time that turbo kicks it. The nice thing is that its free power as you dont even have to plant your foot thru the firewall to get such performance!
I have quite a short commute so I always let the engine idle for a minute or two before I shut her off. Gotta look after my baby, ya know!
Just thought of something, how about this for a tag line.
The (insert year) Saab (insert model) Turbo - one hit and your addicted!
Possibly controversial in some markets but it would get attention!
zippy: sure, and you can have the newly-reunited Cheech & Chong be the pitch-men!
I thought I read recently that you no longer have to idle the car before shutting-off for turbo safety. See this page under “Oil and Water Plumbing” (or search the page for the term “heat soak”). This page is from Garrett’s website, and I don’t think newer Saabs use Garrett turbos anymore (aren’t they now Mitsubishi?).
My ‘85 900T (and I believe my long-gone 1981 900T) has a sticker on the driver’s sun visor advising the owner to allow 30 seconds of idle time before shutting-down the engine, but I don’t remember reading this or seeing a sticker anywhere advising the same procedure in our (now-gone) 2001 9-3 nor our new 2005 9-5 Arc SportWagon.
The earlier Classic 900s had the oil cooled turbos; hence idling was mandatory so that the oil would not be “cooked.”. Newer models have oil and coolant lines to the turbo so idling is not needed after a drive. For me, I let it idle nonetheless.
Woo woo! Vanderbilt beat Auburn for the first time since 1955 to go 5-0 for the first time since 1943! 3-0 in the SEC for only the second time in history! (Makes sense when you note that Alabama was our first game for over 50 seasons in a row.)
We were close.
I think that’s gonna be the tagline for this season.
Eggs: Thank’s for the turbo information. Thank’s for a positive, fun post regarding
Saab. Very fun to read. I will be pumped for the am ride to work. TOP DOWN, HEATED SEATS ON !
Extra idling before driving off or after stopping is bad for the car and the environment (idling = o mpg). Actually driving with a light foot (low load) for a few minutes at start-up and a few seconds before shutting off is all a modern engine needs. Plus oil changes. And yes, I recall too that current SAAB gasoline turbo units are Mitsubishi. (I’m not sure about the diesels–the motor itself is from Fiat.)
B
My 86 9000 turbo has the idle down instructions on the driver’s side sunvisor, water-cooled turbo or not, I always let the car idle for about a minute, and I usually make the last few minutes of my trip much easier, though still at $4 a gallon for 93, I’ve had a lighter right foot, but its hard to resist!
Maybe it is just placebo, but… This morning… 20 degrees Celcius in my parking facility… 2 degrees outside…
My engine usually feels a bit placid in the lower rpms, but this cold morning it felt distinctly more present. Unfortunately I was caught up in the rush hour, so I could not go faster than 80 kph. The idiots put up a big 60 kph sign (when wet — but people treat it as a real speed limit) near a sharp turn, so everybody slows down there, even though that turn is perfectly navigable at 100 kph (wet or not). Do not ask how I know.
But in any case… Am I supposed to notice anything in the lower rpms? Does the turbo kick in earlier now?
I am still a bit n00b with my 9-3. I have passed 15000 km, but most of that was driven this summer… Now I must soon change to winter tires. I should probably find myself some snow-filled paths in the forrest as well…
(My dad received some complaints from his neighbour last year, so not there)