OT why ar hemis powerful?

[Jim Yanik]

[e-mail] (Don Klipstein) wrote in news: [e-mail]:

and that's when you burn pistons. Too lean,and it wil not ignite at all.

From

The objective of a turbocharger is the same as a supercharger; to improve upon the size-to-output efficiency of an engine by solving one of its cardinal limitations. A naturally aspirated automobile engine uses only the downward stroke of a piston to create an area of low pressure in order to draw air into the cylinder through the intake valves. Because the pressure in the atmosphere is no more than 1 bar (approximately 14.7 psi), there ultimately will be a limit to the pressure difference across the intake valves and thus the amount of airflow entering the combustion chamber. This ability to fill the cylinder with air is its volumetric efficiency. Because the turbocharger increases the pressure at the point where air is entering the cylinder, a greater mass of air (oxygen) will be forced in as the inlet manifold pressure increases. The additional oxygen makes it possible to add more fuel, increasing the power and torque output of the engine.

[Jim Yanik]

[e-mail] (Don Klipstein) wrote in news: [e-mail]:

often,the spark advance is retarded to prevent knocking. many modern engines have knock sensors that allow the engine electronics to alter spark timing to stop knock,and permit operation of lower octane fuels without damaging the engine,although at reduced power.

Today's Chrysler Hemi's are no comparison to the Hemi's that are so reknown.Today's hemi's have low compression ratios so owners do not have to spend more on high octane premium.

Racing fuel is 105 octane.

[Nate Nagel]

Not necessarily; the expansion ratio is better on a supercharged engine. It might actually get better economy than the NA engine, even after the losses from driving the supercharger.

nate

[Nate Nagel]

Turbocharging is simply a special subset of supercharging.

Supercharging: using a mechanical device to pressurize the air intake of an engine to the end of achieving more than 100% volumetric efficiency.

Turbosupercharging, often shortened to turbocharging: using an exhaust driven turbine to drive a supercharger.

nate

Ernie Wills> On the contrary, Turbocharging increases fuel efficiency, whereas

[Ernie Willson]

It is true that turbocharging will increase efficiency and power output. It is absolutely not true that anything that increases output per cubic inch will increase efficiency. Supercharging is an example. It always increases output and decreases efficiency. There are many other things that can cause the same effect. It depends on where the engine is operating on it's "performance map".

EJ > >

[Nate Nagel]

Aluminum heads, along with thoughtful chamber design, help a lot. I'm guessing that said 3800 has aluminum heads. I forget the CR on my 944, but I think it's over 10:1, and it runs happily on pump premium. That engine is *all* aluminum, however...

nate

[Don Klipstein]

My make, model and year of car (1995 Oldsmobile Delta 88 LSS) is available with 2 different 3.8 liter 6-cylinder engines - one supercharged, one not.

The naturally aspirated one has compression ratio of 9.4:1.

The supercharged one has compression ratio of 8.5:1.

- Don Klipstein ( [e-mail])

[Don Klipstein]

In article , Ernie Willson wrote in part:

How are the above all true if turbocharging is, as explained well by Nate, a kind of supercharging?

- Don Klipstein ( [e-mail])

[Jim Yanik]

[e-mail] (Don Klipstein) wrote in news: [e-mail]:

From

The objective of a turbocharger is the same as a supercharger; to improve upon the size-to-output efficiency of an engine by solving one of its cardinal limitations. A naturally aspirated automobile engine uses only the downward stroke of a piston to create an area of low pressure in order to draw air into the cylinder through the intake valves. Because the pressure in the atmosphere is no more than 1 bar (approximately 14.7 psi), there ultimately will be a limit to the pressure difference across the intake valves and thus the amount of airflow entering the combustion chamber. This ability to fill the cylinder with air is its volumetric efficiency. Because the turbocharger increases the pressure at the point where air is entering the cylinder, a greater mass of air (oxygen) will be forced in as the inlet manifold pressure increases. The additional oxygen makes it possible to add more fuel, increasing the power and torque output of the engine.

the "efficiency" gained is VOLUMETRIC efficiency. "size-to-output efficiency". meaning the motor acts like it is of much larger displacement.

turbocharging uses the wasted energy of the hot exhaust to compress the intake charge,while supercharging is a parasitic drag all the time.

[mm]

Thanks, you guys.

[Don Klipstein]

Adding a mechanical load to the exhaust flow would increase the pressure in the exhaust manifold. That means work done by the pistons other than turning the crankshaft. I hear even about so much as catalytic converters decreasing fuel economy by adding impedance to the exhaust flow.

The Wiki article does say that efficiency is better with a turbocharger than with a supercharger. However, I still expect both to reduce engine efficiency.

One item from the Wiki article, under "Advantages":

"Fuel Economy. Although adding a turbocharger itself does not save fuel, it will allow a vehicle to use a smaller engine while achieving power levels of a much larger engine, while attaining near normal fuel economy while off boost/cruising. This is because without boost, less fuel is used to create a proper air/fuel ratio."

- Don Klipstein ( [e-mail])

[Ernie Willson]

Who said Nate is right?

EJ > In article , Ernie

[Larry Fishel]

A turbocharger is also parasitic. It raises the exhaust pressure, thereby raising the pressure inside each cylinder during the exhaust stroke. Ain't nuthin' free...

There are two advantages to a turbocharger that I can think of. Fewer moving parts means less friction (basically one). It can run at higher speeds that make for more efficient compression.

If any given engine is more fuel efficient with the turbo engaged, it most likely is only because that engine was designed to run with a turbo and runs inefficiently without it.

But I could be full of it too.

[Jim Yanik]

[e-mail] (Don Klipstein) wrote in news: [e-mail]:

Agreed,but the mechanical load from a turbo is small compared to that of a supercharger(and HOT exhaust gas still contains a lot of energy). I don't believe the Wiki article was considering catalytics,which also are a exhaust restriction. One might have to resize their catalytic for a high boost turbo modification,or settle for less than maximum potential power gains.

I think we agree,then.

[Don Klipstein]

I will agree to "minimal" or similarly small detriment to efficiency with a turbocharger and much more significant detriment to efficiency with a supercharger powered from the crankshaft. I maintain disagreement that a turbocharger improves efficiency, other than fuel economy improvement achieved by allowing a smaller engine.

Maybe we majority do on turbocharging and related engine efficiency matters!

Best Regards,

- Don Klipstein ( [e-mail])

[Nate Nagel]

One slight advantage to the turbo is that you can run a much less restrictive exhaust because exhaust passed through a turbo makes less noise than exhaust coming straight out of a set of headers. Even straight pipes or just glasspacks can make a turbo engine quiet enough to avoid notice from the cops unless you really get on the loud pedal.

nate

[Nate Nagel]

I still have my copy, although it's undoubtedly outdated by now... (hard to sell textbooks for electives that only a handful of people take every year...)

Actually anyone reading this thread that really wants to understand this stuff and can bear to wade through lots of really engineer-y dryness might want to see if you can get your hands on a copy

nate

Ernie Wills> Who said Nate is right?