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Alex Rodriguez wrote: > In article .com>, > says... > > >I thought a supercharger was demand based, i.e. not running at light > >throttle openings > > No, that more accurately describes a turbocharger. Until you get enough > exhaust gas flow, it is basically doing nothing. To get more exhaust gas > flow, you need to step on the throtle some more. > > ----------------- > Alex I didn't think superchargers were running full time, but were brought into use by a clutch. |
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> I didn't think superchargers were running full time, but were brought > into use by a clutch. Not necessarily. |
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Alex Rodriguez wrote:
> In article .com>, > says... > > >>I thought a supercharger was demand based, i.e. not running at light >>throttle openings > > > No, that more accurately describes a turbocharger. Until you get enough > exhaust gas flow, it is basically doing nothing. To get more exhaust gas > flow, you need to step on the throtle some more. > > ----------------- > Alex > Centrifugal gear driven superchargers also had very little boost at low rpm. Positive displacement ones such as Roots and the GMC style gave boost at all rpm. There were also some engine driven chargers that had a complicated drive mechanism that did respond to throttle position in terms of speed of charger. These were for street machines. I think there was a clutch that either kicked in, or speeded up the blower speed on higher throttle openings. |
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Don Stauffer wrote: > Alex Rodriguez wrote: > > In article .com>, > > says... > > > > > >>I thought a supercharger was demand based, i.e. not running at light > >>throttle openings > > > > > > No, that more accurately describes a turbocharger. Until you get enough > > exhaust gas flow, it is basically doing nothing. To get more exhaust gas > > flow, you need to step on the throtle some more. > > > > ----------------- > > Alex > > > Centrifugal gear driven superchargers also had very little boost at low > rpm. Positive displacement ones such as Roots and the GMC style gave > boost at all rpm. > > There were also some engine driven chargers that had a complicated drive > mechanism that did respond to throttle position in terms of speed of > charger. These were for street machines. I think there was a clutch > that either kicked in, or speeded up the blower speed on higher throttle > openings. The old centrifugal McCullochs (later Paxton) used a variable ratio drive pulley. http://www.vs57.com/ nate |
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Alex Rodriguez wrote: > In article .com>, > says... > > >I didn't think superchargers were running full time, but were brought > >into use by a clutch. > > It is possible to do it that way, Mel Gibson's car in 'Mad Max' comes to mind, > but most do not have a clutch. They are 'on' all the time. I call bull**** on that one, wasn't the "mad max" blower a GMC x-71 or similar? That would be a positive displacement (Rootes) type blower, if the drive were disengaged the engine wouldn't run at all unless some kind of bypass were provided. Looks cool as heck on film though nate |
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"N8N" > wrote in message oups.com... > I call bull**** on that one, wasn't the "mad max" blower a GMC x-71 or > similar? That would be a positive displacement (Rootes) type blower, > if the drive were disengaged the engine wouldn't run at all unless some > kind of bypass were provided. > > Looks cool as heck on film though > > nate I think you are right, Nate. It was a GMC type, with Hollywood drive. |
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In article >,
Alex Rodriguez > wrote: >In article .com>, says... > >>I didn't think superchargers were running full time, but were brought >>into use by a clutch. > >It is possible to do it that way, Mel Gibson's car in 'Mad Max' comes to mind, >but most do not have a clutch. They are 'on' all the time. Useless trivia: Robbie Coltrane (Haggrid in the Harry Potter films) is a gearhead. He made a documentary out of buying a 1949 (?) Cadillac in California and driving it across the US to the port of New York to ship it to his home in the UK. He also hosted an interesting miniseries called Robbie Coltrane's planes and automobiles. Each episode looked at a breakthrough in motive systems. The ones that I can recall are the gas turbine, the diesel engine, the two stroke engine, the V8, and the supercharger. The episode on the supercharger looked at automotive racing in the 1920's and aeroengines of WWII. Both of these situations involved competition between the british and the germans. Daimler-Benz introduced supercharging to auto racing with an on-demand system that only began supplying boost near WOT. A british racer (whose name eludes me) got tired of being smoked for a couple of races and convinced his sponsor to pay for mounting a paxton blower on his bentley. The engine was not built up to take the strain of the boost, so he did not finish the next race. Score one for british pride, anyways, as the germans had to keep running their supercharger to keep up, and their engine failed first, allowing a normally aspirated bentley to take the win. People say that all a supercharger does is cram more fuel/air mixture into the cylinder, but that is a very simplistic and inaccurate description, as it leaves important stuff out. What it does it make the engine behave like a larger displacement engine, with a higher ratio. So a 2 litre engine with an 8:1 compression ration, and 7 psi of boost, will behave as a 3 litre engine with a 12:1 compression ratio. Unfortunately, the similarity ends at top dead center. The 2 litre supercharged engine only expands the air charge by a factor of 8, not 12, so it is as if the exhaust valve of the larger, higher compression engine opened after the piston had only gone two thirds of the downward stroke. This explains why supercharging reduces the efficiency of an engine, as it increases the power. Turbocharging is more efficient than an accessory driven super charger, because it uses the power that is expelled out of the exhaust (by effectively openning the valve before BDC) to drive the compressor. |
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