Stoopid Turbo Question

[mrapocalypse]

OK - So I'm a V8 type person, but I was wondering, if you bolt a turbo onto any engine and it's job is to suck more air into the engine, doesn't that make the engine use more fuel? or is there something I'm missing here.... and why then are there not more pretol engines turbo charged?

And what's better, a turbo or a supercharger, or are they the same results with different technique.

Here begineth the lesson!!!

[BigJon]

There are no stupid questions, only stupid people.... heh heh LOL

The short answer is yes and no.

Any form of forced induction (turbo or super charging) is used to artificially increase the volumetric efficiency of an engine. That is, to get more air (and fuel) into the engine to give a higher power output for a given size.

If you run any engine "on boost" it will use more fuel than "off boost". Generally speaking you can't just hang a turbo or supercharger off a stock engine andexpect it to hang together, there is a bit more to it than that.

As far as which is better, there is no easy answer to that question. Turbochargers use waste exhaust gas to generate the boost, so it is in effect 'free' power. A supercharger is belt driven off the engine, therefore uses some power to create the boost. There is a net gain because you create more power than you use.

[abaddonxi]

Have a look at this, Wikipedia article (http://en.wikipedia.org/wiki/Turbocharger), or this from Exploroz. (http://www.exploroz.com/vehicle/servicing/forcedinduction.asp)

Cheers
Simon

[mrapocalypse]

Oh!

So a turbo is more efficient than a supercharger. So how come they still supercharge cars, especially Rangeys and Mercs?

[abaddonxi]

I think a supercharger works all through the rev range. Sorry tdi turbo only kicks in at about 2000 revs. If you want turbos that work across rev range you have to get into variable vanes or two turbos, or other complicated stuff.

Cheers
Simon

[BigJon]

Just saying that a turbo is more efficient than a supercharger isn't really accurate.

New vehicle manufacturers and aftermarket suppliers have many problems to work around with either installation.

These include marketing, heat issues (turbo chargers get VERY hot), packaging (what will fit in the space), required outputs (as mentioned, superchargers work off idle, turbo chargers need to spool up), etc.

[mrapocalypse]

So what about this, I saw a performance guy the other day who sells Blow Off valves. He reckons that they work well because the back pressure on decelleration doesn't slow the turbo down. So each time you change gears your turbo is on max boost.

[BigJon]

Yep, what is the question?

[Tusker]

Superchargers were popular in the 1920s & 1930s with the more expensine machinery. Mercedes & I think Bentleys had them on a clutch - floor the pedal & the clutch would engage - bit like a modern kickdown.

But manufacturers like GM figured thay could get the same fuel/air volume, same horsepower by simply fitting bigger & bigger engines. No excess parts, no warranty issues, lesser thermal loads, longer engine life.

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

Can't speak for Mercedes, but I know that Aston Martin fitted the twin Eaton superchargers to their V8 purely for throttle response reasons. No lag. The greater fuel economy that could be had with a turbo setup won't worry the average new Aston buyer!

Regards
Max P

[camel_landy]

<div class='quotetop'>QUOTE(mrapocalypse &#064; May 18 2006, 11&#58;06 AM) Quoted post</div><div class='quotemain'>
Oh&#33;

So a turbo is more efficient than a supercharger. So how come they still supercharge cars, especially Rangeys and Mercs?
[/b][/quote]

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. https://www.aulro.com/afvb/

I&#39;ve seen plenty of big, turbo charged cars, in ditches just after the corner onto fast roads.... https://www.aulro.com/afvb/

HTH

M

<div class='quotetop'>QUOTE(Tusker &#064; May 18 2006, 02&#58;34 PM) Quoted post</div><div class='quotemain'>
But manufacturers like GM figured thay could get the same fuel/air volume, same horsepower by simply fitting bigger & bigger engines. No excess parts, no warranty issues, lesser thermal loads, longer engine life.
[/b][/quote]

Ahhhh yes.... "There&#39;s no replacement for displacement", from our friend Mr. Shelby. https://www.aulro.com/afvb/

[Hellspawn]

<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.

[/b][/quote]

<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. https://www.aulro.com/afvb/

I&#39;ve seen plenty of big, turbo charged cars, in ditches just after the corner onto fast roads.... https://www.aulro.com/afvb/

HTH

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

<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>

[JDNSW]

<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. https://www.aulro.com/afvb/

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

HTH

M
Ahhhh yes.... "There&#39;s no replacement for displacement", from our friend Mr. Shelby. https://www.aulro.com/afvb/
[/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