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Re: Generally yeah right, but my point is.... Posted by Larry West [Email]  (#1140)  [Profile/Gallery]
(more from Larry West) on Tue, 30 Dec 2008 12:30:45
In Reply to: Generally yeah right, but my point is...., Kurt, Tue, 30 Dec 2008 07:30:27 Members do not see ads below this line. - Help Keep This Site Online - Signup |
The compensation feature you're talking about has nothing to do with air temperature. T7 has a feature where the engine will produce rated horsepower from sea level to 10,000 or so feet, something not all turbos do.
All engines lose power as the air density gets lower. Non T7 Saab turbos continue to produce the same amount of **boost** as the air gets thinner, but not the same amount of horsepower.
Don't confuse boost with manifold pressure. Boost is the amount of pressure above ambient pressure. So a motor that produces 10 PSI of boost will have an absolute manifold pressure of about 25 PSI at sea level, and about 20 psi at 10,000 feet, so you have lost 5 PSI (or 20%) of your manifold pressure, and a corresponding amount of horsepower.
The T7, instead of referencing the boost limit to the ambient pressure, references it to absolute pressure. So a T7 equipped Viggen or Aero or any other FPT Saab will make (or try to make) its top absolute manifold pressure as much as it can, and to any altitude that it can. So, a T7 equpiied Aero that has a max manifold pressure of 25 PSI (just for arguments sake) at sea level will also make 25 PSI of manifold pressure at 10,000 feet altitude, and perhaps higher, up to the limit of how much air you have to compress (it falls off if the air gets too thin). And, if you do the math, that means that yes, it IS making more boost up higher (15 PSI vs 10). And it'll make your 200-odd horsepower all the way up the Rockies.
The T7 is a very sophisticated system that will allow you a lot of boost when conditions are right, and take it away if you're in danger of blowing up your motor. If I saw a marked decrease in power in warmer weather (there will always be some disparity), I'd be much more inclined to look for why I'm getting less power in warmer weather than why it makes more in cool weather.
_______________________________________ Current: 2002 9-5 Aero Kombi Cosmic Blue 2000 9-5 SE sedan, Imola Red 1990 900S Rose Quartz, Auto Past: 1999 9-5 LPT Combi 1999 9-5 LPT sedan 2002 9-5 Arc 1990 900 5-speed 1986 900 turbo Convertible 1991 9000 turbo 1980 99 GLi 1986 900 turbo 1986 900 S 1991 900 turbo 1984 900 turbo 1976 99 GL
, Tue, 30 Dec 2008 06:46:04, Tue, 30 Dec 2008 12:30:45 <-- Viewing This Message
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