Thread: Stoopid Turbo Question

<div class='quotetop'>QUOTE(Tusker &#064; May 18 2006, 02&#58;34 PM) Quoted post</div><div class='quotemain'>


I&#39;m intrigued why they&#39;re back too. Why on earth did GMH fit a supercharger to the commondoor 3.8? Beats me.

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<span style="color:#3366FF">Superchargers never went away.

GMH did the superV6 I believe for sales, as with everything these days. Why else would GM design a commodore coupe and refer to it as a Monaro ? Commodore and Monaro, they have always been so not related and sales proved that.

Turbos never left the scene either, have always been healthy in the modified scene and are now an epidemic in the modern manufacturers market. </span>


<div class='quotetop'>QUOTE(camel_landy &#064; May 18 2006, 05&#58;48 PM) Quoted post</div><div class='quotemain'>
Yeeeessss.... Part of it is down to the people who drive them & where they drive them.

A supercharger works off the crank on the engine and so therefore is constantly being driven. The turbo charger is being driven by the exhaust gasses. The upshot of this is that there is usually a delay before a turbo charger will kick in (known as turbo lag) where as a super charger is immediate.

Modern turbos are getting better but in the old days this &#39;delay&#39; was a common cause of accidents in big, rear wheel drive cars.... Basically, the <inexperienced> driver would floor it from idle and wonder why their big turbocharged car wasn&#39;t doing anything. They would then keep their foot planted on the floor, at which point the turbo starts to kick in... and "KICK" it would. Usually ending up with the back end kicking out.

I&#39;ve seen plenty of big, turbo charged cars, in ditches just after the corner onto fast roads....

HTH

M
Ahhhh yes.... "There&#39;s no replacement for displacement", from our friend Mr. Shelby.
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<span style="color:#3366FF">Wouldn&#39;t be limited to turbo motors, most automatic transmissions will "gear hunt" midcorner when pushed hard resulting in the <experienced> driver performing a quite spectacular "drift".

For short straight lines there is a "replacement", comes in a blue bottle.</span>

<div class='quotetop'>QUOTE(camel_landy &#064; May 18 2006, 05&#58;48 PM) Quoted post</div><div class='quotemain'>
Yeeeessss.... Part of it is down to the people who drive them & where they drive them.

A supercharger works off the crank on the engine and so therefore is constantly being driven. The turbo charger is being driven by the exhaust gasses. The upshot of this is that there is usually a delay before a turbo charger will kick in (known as turbo lag) where as a super charger is immediate.

Modern turbos are getting better but in the old days this &#39;delay&#39; was a common cause of accidents in big, rear wheel drive cars.... Basically, the <inexperienced> driver would floor it from idle and wonder why their big turbocharged car wasn&#39;t doing anything. They would then keep their foot planted on the floor, at which point the turbo starts to kick in... and "KICK" it would. Usually ending up with the back end kicking out.

I&#39;ve seen plenty of big, turbo charged cars, in ditches just after the corner onto fast roads.... [img]style_emoticons/<#EMO_DIR#>/rolleyes.gif[/img]

HTH

M
Ahhhh yes.... "There&#39;s no replacement for displacement", from our friend Mr. Shelby.
[/b][/quote]

As with any design feature there are compromises all round. The turbo-supercharger or turbocharger is generally a much simpler installation at least from the mechanical point of view, and is more efficient in that the power to drive it is derived from waste heat - but at the expense of back pressure, so the overall increase in efficiency is less than you would think compared to a mechanical drive. Because of the close proximity of the compressor to the turbine, a bigger intercooler is required, and more boost is usually needed to make up for the convoluted exhaust and intake piping needed to plumb the whole setup.

The big advantages of a crankshaft driven supercharger is that the plumbing is a lot simpler and more direct, and the available boost is proportional to crankshaft speed not power, which means better throttle response. The mechanical drive of the turbocharger can present serious problems, especially if a centrifugal compressor is used due to the high speed and momentum of the impeller(don&#39;t think anyone does today), and noise both from the compressor and the drive are real problems. I suspect that gear driven superchargers are a lot more expensive than turbochargers today.

Of course the question is why supercharge anyway? Basically, it makes it possible to have a lighter and smaller engine for the same power and torque. There is the additional advantage with modern engine control systems of having variable compression ratio (The effective compression ratio is the boost multiplied by the geometrical compression ratio) to help fine tune emissions and in the case of petrol engines to allow it to operate always at the highest practical compression ratio for the conditions and fuel, hence having maximum efficiency and power. Whether it is worth the cost and complexity may well be another question - certainly historically it has not been except in specialist cars, but especially for diesels, turbochargers have been accepted as normal for at least the last twenty-five years.

John