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Old 11-15-2010, 04:46 PM   #21 (permalink)
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supercharged engines have horrible bsfc
Computing BSFC for Supercharged Engines - Moderated Discussion Areas

I don't like seeing them "greenwashed".

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Old 11-15-2010, 09:31 PM   #22 (permalink)
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...how many TURBO-charged WWII fighter aircraft were there compared to SUPER-charged WWII fighter aircraft? Uh, one, the P-38 Lightning!

...(with all due respect to the Hallmark Cards™ slogan):

"...when you absolutely NEED maximum HP, use SUPER-charging."
"...when you absolutely NEED maximum FE, use TURBO-charging."

...is brown-washing better than green-washing?

Last edited by gone-ot; 11-16-2010 at 11:40 PM.. Reason: per Mustang Dave's reminder, added P-38 Lightning
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Old 11-15-2010, 09:51 PM   #23 (permalink)
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For some reason turbos seem to help efficiency on diesels, but make it worse on gassers as compared to normally aspirated. I haven't quite thought that one through yet.

Even the Rutan Voyager that flew nonstop around the world was normally aspirated. It also was essentially true multi displacement, with a 200 in back running for the whole flight and a 240 up front to help w/takeoff and initial flight. I haven't seen any cars try the multi-IC approach yet.
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Old 11-15-2010, 09:52 PM   #24 (permalink)
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Quote:
Originally Posted by Old Tele man View Post
...how many TURBO-charged WWII fighter aircraft were there compared to SUPER-charged WWII fighter aircraft? Uh, none!

...(with all due respect to the Hallmark Cards™ slogan):

"...when you absolutely NEED maximum HP, use SUPER-charging."
"...when you absolutely NEED maximum FE, use TURBO-charging."

...is brown-washing better than green-washing?
Uh, the B17 had exhaust driven trubosuperchargers. The P51 had two stage supercharging in the Packard built Merlin engine copy that ws originally on the Spitfire and many other Brit planes.

But it was not a fighter. I think some of the radial engine planes were turboed, but the mettalurgy was the weak point in turbocharging until after the war.

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Old 11-16-2010, 03:36 AM   #25 (permalink)
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And neither turbo or supercharging is done for efficiency is the point I am trying to make here, not even in planes where enabling higher altitude and power to weight could possibly be a contributing factor. Normally aspirated is still the aspiration of choice for economy.
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Old 11-16-2010, 08:58 AM   #26 (permalink)
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At 30,000 feet with 40 below ambient temperatures turbocharging and supercharging were essential when you consider atmospheric pressure is 50% of sea level pressure at 18k feet. Even in cars when the elevation gets above 6k feet the power loss is significant.

Ford apparently does not agree with the assumption that there is no place for supercharging in an economy car.

Counterpoint:

The most efficient diesel engines at just over 50% do not use supercharging. Instead they utilize a 3 to 1 stroke to bore ratio, with a 3 foot bore and a 9 foot stroke, running at about 100 RPM to minimize the losses due to reciprocation of their massive pistons and rods. The sctoch yoke between the piston and rod eliminates side loads on the piston.

Personally I like the idea of electric supercharging especially when it is designed to allow air flow to not have to pass through the supercharger. The energy to run the supercharger can be supplied by regenerative braking.

Combined with start stop and DFCO in an engine of about 50% of the normal displacement and you can get better mileage, just like the Edison car in the X prize.

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Old 11-16-2010, 12:52 PM   #27 (permalink)
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the vlc is a curious example, I wonder if they added a turbo only to make the performance metrics. I'm guessing it has an efficiency penalty over a slower acceleration curve, dunno though.
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Old 11-16-2010, 07:32 PM   #28 (permalink)
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Question

The Story of Turboing a Hybrid Prius - Part 5

Anyone want to rebut Julian?

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Old 11-16-2010, 07:51 PM   #29 (permalink)
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The only way I could see forced induction helping is if it is coupled with downsizing the engine displacement, and/ or giving the transmission a very long legged overdrive. A mild boost designed to kick in at low rpms would allow lugging in lower gears and being able to stay in overdrive in more situations.

IIRC the new Corvettes are supercharged, but with a 1:0.50 overdrive gear ratio (it may be even higher, can't find the info) it could achieve ridiculously high fuel economy for a v-8 performance car. A friend told me his buddy could reliably get 30 mpg from his Corvette 6 speed when cruising.

One example is this quote from Ford:
Quote:

EcoBoost uses gasoline turbocharged direct-injection technology for up to 20 percent better fuel economy, 15 percent fewer CO2 emissions and superior driving performance versus larger displacement engines
I'd been reading about OEMs using turbos to increase economy while minimizing performance losses, and this is one example.

Another quote worthy of consideration is this one from the above article.

Quote:
“Compared with the current cost of diesel and hybrid technologies, customers in North America can expect to recoup their initial investment in a 4-cylinder EcoBoost engine through fuel savings in approximately 30 months. A diesel in North America will take an average of seven and one-half years, while the cost of a hybrid will take nearly 12 years to recoup – given equivalent miles driven per year and fuel costs,” he said
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Quote:
Originally Posted by jamesqf View Post
I think you missed the point I was trying to make, which is that it's not rational to do either speed or fuel economy mods for economic reasons. You do it as a form of recreation, for the fun and for the challenge.
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Old 11-16-2010, 07:53 PM   #30 (permalink)
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Quote:
Originally Posted by dcb View Post
the vlc is a curious example, I wonder if they added a turbo only to make the performance metrics. I'm guessing it has an efficiency penalty over a slower acceleration curve, dunno though.
I think it was a 250 cc bike engine. Considering the weight of the vlc and the performance requirements, a turbo was the only solution. Of course the durability would probably be pitiful.

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