any of you seen this site? what a riot.

[Russianblue]

http://www.turbominivan.com/index.html

Incidentally, I found it googling turbocharging 101...because I didn't see a sticky or anything here that would give me the basics of how a turbo works. I was just curious.

[Matt]

A turbo charger works by converting the "wasted" energy in exhaust gasses into mechanical energy to drive an air compressor. The goal is to get more air into the engine, since power is a function of the amount of air involved in combustion.

the turbo has two different impellers, connected by a shaft, kind of like a small wagon axle or something. Exhaust gasses spin one of the wheels, causing the other wheel to spin. The other wheel compresses the intake air charge, so that you have positive manifold pressure or "boost", i.e. air is forced into the combustion chambers under pressure instead of due to the vacuum effect of the intake stroke of the piston.

the downsides of turbo charging include
- incredible heat. there is a conductive link between exhaust air and intake air through the body of the turbo charger. also, compressing air heats air. heat is the enemy of efficient and safe engine operation, which is why aftercooling (a big radiator between the turbo and the intake plenum) is required to run high levels of boost

- turbo lag. the exhaust must be flowing a certain volume/velocity before the turbo will actually start compressing effectively. the time period between you "stepping on it" and the power coming on due to boost is the "turbo lag". Not really a "downside", just a "its different" w.r.t. an N/A car.

the "bible" of turbo charging is a book called "Maximum Boost" by Corky Bell. I recommend picking it up.

[M635CSi]

A turbo charger works by converting the "wasted" energy in exhaust gasses into mechanical energy to drive an air compressor.

Oh, I don't believe turbochargers run off "wasted" energy in the exhaust gasses any more than I believe superchargers run off "wasted" energy in the crankshaft...

Both turbochargers and supercharges increase power. Both turbochargers and superchargers increase load on the engine in order to increase power.

To confirm this:

1) Put a turbocharged E28 on a dyno and plot the hp curve to redline. While you're doing this, also graph intake air temp, cfm and air pressure at 500RPM increments.

2) Remove the turbocharger and exhaust manifold and replace with a tuned exhaust header sized correctly for the engine and connected to the same exhaust system.

3) Using the temp, cfm and pressure graphs derived from 1) above, allow for an external air supply to the engine providing air flow matching the temp, cfm and pressure as reflected in the work product of 1) (above).

4) Put the E28 back on the dyno and again plot the hp to redline being careful to supply the engine an external intake air supply with the same temp, volume and pressure characteristics as the engine in number 1) above.

5) Superimpose the graphs of 1) and 4) above. If the area under the curve on the graph in number 4) is greater than the graph in number 1), that increased area is the amount of load the turbocharger placed on the engine.

If the area under the curves is the same in 1) and 4) above, then and in that event, the “turbo charger works by converting the "wasted" energy in exhaust gasses into mechanical energy to drive an air compressor"

I'm betting the area under the curve will increase when a turbocharger isn't using the "wasted" energy in the exhaust gasses...

IMHO

[Matt]

The word wasted appearned in quotes for a reason.

Your message, while nice, has added nothing to a basic description of turbocharging. However, I eagerly await the results of your experiment.

[M635CSi]

The word wasted appearned in quotes for a reason.

Your message, while nice, has added nothing to a basic description of turbocharging. However, I eagerly await the results of your experiment.

[Tjn182]

you don't believe that it's wasted energy?

The heat, the push, the energy just comes out your tailpipe otherwise. Instead - it will propel the turbines on your turbocharger to force air into the car. So... yes... it's using wasted energy.


oh and www.howstuffworks.com has stuff on turbochargers

[pdx 528e]

you don't believe that it's wasted energy?

The heat, the push, the energy just comes out your tailpipe otherwise. Instead - it will propel the turbines on your turbocharger to force air into the car. So... yes... it's using wasted energy.


oh and www.howstuffworks.com has stuff on turbochargers

Yes, but it also then restricts the exhaust making more work for the engine as it has to push the gasses through the turbo. So while some of the energy would have been wasted, its also using non wasted energy, like an investment. Give up a few hp to create many more.

[Shawn D.]

Apparently, there is a bit of confusion about the terms "waste heat" and "waste energy." "Waste heat" is indeed a form of "waste energy," but not necessarily vice-versa. Besides heat, the "waste energy" of exhaust also contains momentum and pressure.

[M635CSi]

Apparently, there is a bit of confusion about the terms "waste heat" and "waste energy." "Waste heat" is indeed a form of "waste energy," but not necessarily vice-versa. Besides heat, the "waste energy" of exhaust also contains momentum and pressure.

I think the term "waste heat" and "waste energy" are more discriptive and lend themselves to less minunderstanding.

The point that I would like to make clear, is that turbocharging increases parasitic loss over natural aspiration.

[Matt]

The point that I would like to make clear, is that turbocharging increases parasitic loss over natural aspiration.

Ok, but to what extent? I think most people would assert that the loss is minimal, especially compared to a supercharger of any design.

So are you talking 1% loss? 10%? 50%?

[M635CSi]

The point that I would like to make clear, is that turbocharging increases parasitic loss over natural aspiration.

Ok, but to what extent? I think most people would assert that the loss is minimal, especially compared to a supercharger of any design.

So are you talking 1% loss? 10%? 50%?

Most people are wrong most of the time, or so the saying goes. So because "most people would assert..." doesn't mean a whole lot.

If we say it takes 300 cfm of additional intake air to boost the M30 engine from 200 bhp @ 5,700 RPM to 400 bhp @ 5,700 RPM, and to get that additional 300 cfm of intake air into the engine we need 15 psi (over atmospheric) of pressure at the intake port, then we can determine the energy required to pump 300 cfm at the required pressure of 15psi.

From the standpoint of parasitic loss, it makes no difference if the energy to pump that air comes from the exhaust, or if the energy to pump that air come from the crankshaft; 1 horsepower is 1 horsepower.

This isn’t to say there is no difference between a turbocharger and another form of supercharger, of coarse there are many.

[Rich in WI]

http://auto.howstuffworks.com/turbo.htm

Turbos get their drive force from two sources:
1) Exhaust moving through the system
2) Expanding exhaust gases

Parasitic losses would be more associated with #1, and less with #2. The expanding exhaust gases are the waste heat/energy that we're talking about. A supercharger does not capture this waste heat. It is 100% parasitic.

Rich in WI

[DMNaskale]

From the standpoint of parasitic loss, it makes no difference if the energy to pump that air comes from the exhaust, or if the energy to pump that air come from the crankshaft; 1 horsepower is 1 horsepower.

If you are trying to say that a turbocharger and a supercharger present the same drag on an engine for the same output, I don't see it. Due to design differences you can't even directly compare two turbocharged engines for HP losses to driving the compressor, much less crank driven to exhaust driven. Not to mention the compressors will be different in terms of efficiency, thus affecting HP production. To generalize that a supercharger is more of a drag on an engine than a turbocharger is accurate, however, because all the power put into driving a supercharger is power that would have otherwise been driving the wheels. A significant part of the energy used to drive a turbocharger would have been lost out the tailpipe anyway.

[M635CSi]

http://auto.howstuffworks.com/turbo.htm

Turbos get their drive force from two sources:
1) Exhaust moving through the system
2) Expanding exhaust gases

Parasitic losses would be more associated with #1, and less with #2. The expanding exhaust gases are the waste heat/energy that we're talking about. A supercharger does not capture this waste heat. It is 100% parasitic.

Rich in WI

Actually both a supercharger and a turbochargers are 100% parasitic...

[M635CSi]

From the standpoint of parasitic loss, it makes no difference if the energy to pump that air comes from the exhaust, or if the energy to pump that air come from the crankshaft; 1 horsepower is 1 horsepower.

If you are trying to say that a turbocharger and a supercharger present the same drag on an engine for the same output, I don't see it. Due to design differences you can't even directly compare two turbocharged engines for HP losses to driving the compressor, much less crank driven to exhaust driven. Not to mention the compressors will be different in terms of efficiency, thus affecting HP production. To generalize that a supercharger is more of a drag on an engine than a turbocharger is accurate, however, because all the power put into driving a supercharger is power that would have otherwise been driving the wheels. A significant part of the energy used to drive a turbocharger would have been lost out the tailpipe anyway.

This isn't that complicated. We're talking about the energy required to pump air, nothing more, nothing less.

Pumping air takes horsepower. An air pump (turbocharger/supercharger) doesn't know if it's being turned by a turbo shaft or a crankshaft. For a given volume of air, it takes the same energy to move that air.

There are of course many other factors that come into play, but the constant is the energy required to pump air. Whether a turbocharger or supercharger is superior for a given application is a question of the individual fact pattern.

[DMNaskale]

We're talking about the energy required to pump air, nothing more, nothing less.

Pumping air takes horsepower. An air pump (turbocharger/supercharger) doesn't know if it's being turned by a turbo shaft or a crankshaft. For a given volume of air, it takes the same energy to move that air.

I think you are trying to prove a point by dwelling on the semantics and ignoring the practical details of the application. The energy required to pump a given amount of air is largely irrelevant to the issue. How much of that energy is derived from a source that would otherwise be turning the wheels is the core of the matter.

[Boru]

You have to take into consideration that you are using machines to pump this air and no machine is 100% efficient... some are more efficient at executing a task than others.
Assume that the compressor of the belt driven, centifugal supercharger is equal in all respects to the compressor of the turbocharger.
The supercharger requires a pulley, belt, and oil bath gear box.
The turbo requires a turbine with its shaft running in a plain bearing or ball bearings.
It requires more Hp to turn all the bits of the belt driven supercharger than is lost through exhaust restriction in the turbine of the turbocharger.
More stuff to move with more drag for the same end result of manifold pressure.

[M635CSi]

We're talking about the energy required to pump air, nothing more, nothing less.

Pumping air takes horsepower. An air pump (turbocharger/supercharger) doesn't know if it's being turned by a turbo shaft or a crankshaft. For a given volume of air, it takes the same energy to move that air.

How much of that energy is derived from a source that would otherwise be turning the wheels is the core of the matter.

I would have to say 100%

If you're asking whether the parasitic loss of a supercharger is higher than a turbocharger I would agree that it generally is.

[M635CSi]

You have to take into consideration that you are using machines to pump this air and no machine is 100% efficient... some are more efficient at executing a task than others.
Assume that the compressor of the belt driven, centifugal supercharger is equal in all respects to the compressor of the turbocharger.
The supercharger requires a pulley, belt, and oil bath gear box.
The turbo requires a turbine with its shaft running in a plain bearing or ball bearings.
It requires more Hp to turn all the bits of the belt driven supercharger than is lost through exhaust restriction in the turbine of the turbocharger.
More stuff to move with more drag for the same end result of manifold pressure.

I think that's a pretty fair analogy.

[Bonapartist]

I'm sure one of those vans is actually fairly awesome for a domestic, 7 passenger vehicle. If I came across one at an absurdly good price...

[j9fd3s]

We're talking about the energy required to pump air, nothing more, nothing less.

Pumping air takes horsepower. An air pump (turbocharger/supercharger) doesn't know if it's being turned by a turbo shaft or a crankshaft. For a given volume of air, it takes the same energy to move that air.

How much of that energy is derived from a source that would otherwise be turning the wheels is the core of the matter.

I would have to say 100%

If you're asking whether the parasitic loss of a supercharger is higher than a turbocharger I would agree that it generally is.

on a gasoline piston engine roughly 30% of the engergy content goes to propelling the wheels, 30% goes into the cooling system and about 30% goes out the exhaust.

to be simple the superchager takes its power from the crank, and the turbo takes its power from the heat energy in the exhaust, which otherwise is "wasted" as heat and noise.

also it is possible to size a turbo so that there is a tuned effect like a header, and have backpressure in the exhaust less than the boost pressure in the intake...

and granted setups like these are the ones (like the 80's f1 cars) that make HUGE hp numbers, not "normal" street cars

mike

[M635CSi]

We're talking about the energy required to pump air, nothing more, nothing less.

Pumping air takes horsepower. An air pump (turbocharger/supercharger) doesn't know if it's being turned by a turbo shaft or a crankshaft. For a given volume of air, it takes the same energy to move that air.

How much of that energy is derived from a source that would otherwise be turning the wheels is the core of the matter.

I would have to say 100%

If you're asking whether the parasitic loss of a supercharger is higher than a turbocharger I would agree that it generally is.

on a gasoline piston engine roughly 30% of the engergy content goes to propelling the wheels, 30% goes into the cooling system and about 30% goes out the exhaust.

to be simple the superchager takes its power from the crank, and the turbo takes its power from the heat energy in the exhaust, which otherwise is "wasted" as heat and noise.

also it is possible to size a turbo so that there is a tuned effect like a header, and have backpressure in the exhaust less than the boost pressure in the intake...

and granted setups like these are the ones (like the 80's f1 cars) that make HUGE hp numbers, not "normal" street cars

mike

Mike, thanks for the post, one of the things I like most about mye28.com is that it makes me think!

Even though I'm in the minority, I'm not buying the simplicity that "the superchager takes its power from the crank, and the turbo takes its power from the heat energy in the exhaust, which otherwise is "wasted" as heat and noise"

Although I agree that "30% of the chemical energy of fuel is converted into useful work; 40% is removed as heat by cooling water and another 30% is lost with exhaust gases", I don’t accept the argument that existing waste energy in the exhaust gases result in significant increases in power output. Turbochargers increase exhaust waste energy to drive the turbocharger.

What can’t be gotten away from is that cylinder pressure drives both the crankshaft driven supercharger (via piston pressure) and the turbocharger via exhaust pressure.

Also, both the “crankshaft driven" supercharger and the “exhaust driven” turbocharger increase crankshaft loading as a result of increased cylinder pressure. So while the supercharger is directly coupled to the crankshaft to drive its compressor, the turbocharger is indirectly coupled to the crankshaft to drive its compressor.

At least that’s the way I look at it.

[j9fd3s]

yeah the energy does ultimately come from the same source.

this is one of those situations where statements like "always" and "superior" dont work. especially on a street car.

on a street car giving up 10-15hp more to drive the crank driven supercharger isnt a big deal as long as the car always feels (and sometimes is) fast, right?

mike