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Date: Fri, 19 Nov 1999 23:15:00 -0800
From: Justin VanAbrahams <jvanabranopsamnet>
Subject: Re: Turbo vs. V6


wjgreernopsameja.com wrote: > > During the 1980s, turbos first came into common use on sports-oriented > cars in the US. My feeling is that they were used more as a marketing > tool than a real preformance tool, though. It seems sensible to say > that you should not turbocharge an engine that has not been optimized > in other ways first. For instance, I think a turbocharges 8-valve 4- > cylinder engine is a bad idea, but there were tons of those driving > around. Actually that is not entirely true... The tuning involved in making a good turbocharged engine is often diametrically opposed to the tuning involved in making a good naturally aspirated one. Compression ratios, block design, and cam profiles are often (if not always) very different between the two. For example, on a naturally aspirated car the easiest way to increase horsepower vs. another engine of the same displacement is to increase compression ratio; on a turbocharged engine you're relying on the additional cylinder pressure provided by the turbo to do that for you, so a base lower compression is highly advisible. In block design, a good way to increase cooling of the engine and (if I'm not mistaken) to simplify manufacturing process is to leave the block's deck open, allowing coolant to circulate more completely around the cylinders; on a turbocharged engine an open deck creates very obvious limitations to the amount of boost you can run since cylinder walls are reduced in thickness. And with respect to cam profiling (another good way to increase horsepower), the overlap of a non-turbo engine is exactly the opposite of what you'd want in a turbo. Also, while I'm thinking about it, exhaust tuning is very different as well - on a street-driven non-turbo car an engineer will usually rely upon a certain amount of backpressure in the system to increase the scavenging effect, whereas a turbocharged car doesn't rely on that virtually at all... With that in mind, taking a great naturally aspirated engine and turbo- charging it will often result in a very undrivable or unreliable engine. Why do you think all the rice racers out there are going around swapping cams, changing their engine timing, and dropping compression ratios so they can throw a turbo on? It's certainly not for their health! An 8-valve four cylinder actually makes a VERY good powerplant for turbocharging; actually, any 2v per cylinder engine can be quite good. You see, a 2v/cyl engine usually has breathing problems at higher RPMs, as engine breathing is limited greatly by the area of the intake valve(s). By adding a turbo, you can quite simply overcome many breathing problems by allowing the turbo to force air into the cylinders (putting more air past a smaller valve opening) rather than relying on tricky intake manifold designs or larger valves or a greater quantity of valves. It's a simple solution than many manufacturers (including Saab) latched onto early on - not perfect, but there's nothing wrong with it. A 2v/cyl design is simple, but not in any way inferior. GM does quite well with ancient pushrod V6 and V8 powerplants that make more power and getter better gas mileage than some of the latest DOHC engines *of smaller displacement*. Just look at the LT1 or LS1 engines and compare them to Ford's modular V8, such as in the Mustang. The Corvette/Camaro gets more horsepower and better mileage out of a larger engine, despite the "inferior" design of their engines. > For these and any number of other reasons, turbos developed a terrible > reliability reputation in this marketplace. In addition, insurers seem > to place a premium upon policies for turbocharged cars, even when the > power numbers are equivalent to a lower-premium non-turbo car. I think > I remember reading a review of a Saab 900 a few years back where the > guy said that he liked the car, but the insurance was higher than a > Mustang GT would have been for him. Most turbocharged cars got bad reputations for reliability for two reasons. The biggest perpetrators was Chrysler and Mitsubishi, who had no good engines to offer during most of the '80s, and made extra power by throwing a turbo on them. Unfortunately, the engines were not particularly well designed and were certainly never intended for turbocharging, and as a result grew even *more* unreliable when the turbo was slapped on. Other manufacturers, such as Lotus and even BMW, helped create bad reputations for turbocharged cars by being way too aggressive with their turbocharging programs and asking too much from too little. The result was either high maintenance or poor reliability, or both. > Saab has now made a total commitment to turbocharging, and you cannot > currently buy a new Saab without a turbo engine. Their warranty is > excellent at 5 years/50K miles, which must be a statement towards the > reliability of their current turbos. Personally I have always been a > Saab fan, but have never purchased one because of some reliability > concerns. At this point I can feel myself warming up though, and I > believe I will probably lease a 9-3 as soon as my current lease is up. Both Saab and Volvo have literally staked their names on the current level of their turbocharging technology. Saab has spent the last 20 years making sure their engines are bulletproof even when pushed, and quite honestly they've done an outstanding job. They've taken a previously expensive automotive technology and put it in the hands of the everyday person... In 1978, the only turbocharged cars you could buy were dedicated sports cars that carried an enormous price tag, but Saab managed to put that technology into a 4-door sedan (or 3-door hatchback!) and build a fun-to-drive, practical car around it. Saab does have (or has had, depending on how you look at it) some reliability issues, but I can absolutely assure you that you won't find a turbocharger behind those problems. > In the 1995 900, the V6 is definitely a General Motors engine. At 2.5L > (I think), it sounds like a reincarnation of the V6 they put in > countless midmarket cars through the years. I always thought it would > be odd to have a GM V6 in a Saab. The 2.5l V6 cannot be found on any other car currently or previously sold in the U.S. - it was an engine confined to Europe. I wish it had stayed there, or rather, been discontinued long ago. Among it's many faults (including its pathetic power to displacement ratio) it also requires frequent and expensive service to keep it running well (including 30k mile timing belt changes). There is a very specific reason Saab sold for only two years. The 3.0l V6 that followed it is actually, in all likelihood, a good engine. It's a goofy 54-degree V6, but seems to be fairly reliable and fairly well designed. I'm not sure about the turbo that Saab has thrown on it, but given all the work they've put into it, and it's previous track record in the mid-'90s 9000, I wouldn't be too terribly hesitant to rely on it. Still, Saab has built itself a reputation for making peppy, reliable, and responsive 4 cylinder turbocharged engines, and to my mind it seems somewhat sad to cripple a fun car with a sedate powerplant like the 'euro V6.' But that's me... I'm sure my parents would disagree... they like quiet and they don't drive like I do... so, I suppose, to each his (or her) own. -Justin

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