OT An interest in hemi engines stirred me, and I found this site

http://auto.howstuffworks.com/hemi1.htm

which gave as the advantage of the hemi that 2 valves could be placed
opposite each other, instead of next to each other, and thus could be
made bigger, for more power.

I had assumed that the advantage was with fewer corners, etc. in the
combustion chamber, there was less chance of power-losing knocking.

OTOH, now it occurs to me that if the combustion chamber is domed, it
might be bigger than one with a flat top, leading to a lower
compression ratio and less power.

So why are hemi engines powerful?


BTW The last time I posted off-topic, a couple nervous Nellys thought
it was spam. It's not.

"mm" wrote in message
...
OT An interest in hemi engines stirred me, and I found this site

http://auto.howstuffworks.com/hemi1.htm

which gave as the advantage of the hemi that 2 valves could be placed
opposite each other, instead of next to each other, and thus could be
made bigger, for more power.

I had assumed that the advantage was with fewer corners, etc. in the
combustion chamber, there was less chance of power-losing knocking.

OTOH, now it occurs to me that if the combustion chamber is domed, it
might be bigger than one with a flat top, leading to a lower
compression ratio and less power.

So why are hemi engines powerful?

The hemi design was great in it's time pre-OHC. Other designs are as good or
even better. What makes them so popular to day is their reputation and
advertising hype. The pentroof allows four valves per cylinder. That have
been many other types of head designs that just never had the advertising
catch that the hemi achieved.

mm wrote:
OT An interest in hemi engines stirred me, and I found this site

http://auto.howstuffworks.com/hemi1.htm

which gave as the advantage of the hemi that 2 valves could be placed
opposite each other, instead of next to each other, and thus could be
made bigger, for more power.

I had assumed that the advantage was with fewer corners, etc. in the
combustion chamber, there was less chance of power-losing knocking.

OTOH, now it occurs to me that if the combustion chamber is domed, it
might be bigger than one with a flat top, leading to a lower
compression ratio and less power.

So why are hemi engines powerful?


The pistons are domed to match the head

see
http://www.streetrodderweb.com/tech/.../photo_09.html

mm wrote:
OT An interest in hemi engines stirred me, and I found this site

http://auto.howstuffworks.com/hemi1.htm

which gave as the advantage of the hemi that 2 valves could be placed
opposite each other, instead of next to each other, and thus could be
made bigger, for more power.

I had assumed that the advantage was with fewer corners, etc. in the
combustion chamber, there was less chance of power-losing knocking.

OTOH, now it occurs to me that if the combustion chamber is domed, it
might be bigger than one with a flat top, leading to a lower
compression ratio and less power.

So why are hemi engines powerful?


BTW The last time I posted off-topic, a couple nervous Nellys thought
it was spam. It's not.

You're assuming that a typical hemi uses a flat top piston - they don't.
Most have a domed shape piston and you are correct, the chamber shape
allows a higher compression ratio on the same gas.

nate

--
replace "roosters" with "cox" to reply.
http://members.cox.net/njnagel

todays hemi gets the air in and out of the engine more efficiently.
todays gasoline hemi engines in production vehicles dont get horsepower
by high compression ratios like in the 1960's , we just dont have the
pump gas for it. todays engines get more power thru volumetric
efficiency .getting the air in and out in a better way,many with hemi
combustion chamber, and of course computer controlls on the engine. most
of todays engines use exhuast manifolds that are made like the headers
racers use, to increase volumetric efficiency.

----------------------------------------------------------------
http://www.minibite.com/america/malone.htm

On Sat, 24 Jan 2009 22:40:58 -0700, Reed wrote:

mm wrote:
OT An interest in hemi engines stirred me, and I found this site

http://auto.howstuffworks.com/hemi1.htm

which gave as the advantage of the hemi that 2 valves could be placed
opposite each other, instead of next to each other, and thus could be
made bigger, for more power.

I had assumed that the advantage was with fewer corners, etc. in the
combustion chamber, there was less chance of power-losing knocking.

OTOH, now it occurs to me that if the combustion chamber is domed, it
might be bigger than one with a flat top, leading to a lower
compression ratio and less power.

So why are hemi engines powerful?


The pistons are domed to match the head

see
http://www.streetrodderweb.com/tech/.../photo_09.html

I should have thought of that. I guess I'll never make it as an
engine designer. That's a shame too, because I'm 62 now and looking
for a new career.

Thanks. And to you too Nate.

On Sun, 25 Jan 2009 10:32:15 -0500, wrote:

todays hemi gets the air in and out of the engine more efficiently.
todays gasoline hemi engines in production vehicles dont get horsepower
by high compression ratios like in the 1960's , we just dont have the
pump gas for it. todays engines get more power thru volumetric
efficiency getting the air in and out in a better way,

I guess this couldn't be true, becaus high mpg cars don't have
especially high compression ratios, but I've always thought:::

Related to your last quoted line above: Unless this means a leaner
mixture, and I don't think it does, doesn't this lower mileage, to
burn more air and the accompanying gas?

Besides power, I've always thought that a high compression ratio means
getting the most out of the gas. That every portion of its expansion
applies power to the wheels of the car.

Doesn't that seem reasonable, and how come it must not be true?


many with hemi
combustion chamber, and of course computer controlls on the engine. most
of todays engines use exhuast manifolds that are made like the headers
racers use, to increase volumetric efficiency.

----------------------------------------------------------------
http://www.minibite.com/america/malone.htm

GAS ENGINE HEMIS IN THE 60'S-70'S COULD HAVE 12:1
COMPRESSION RATIOS. TODAYS GAS CAR/ TRUCKS WITH HEMISPHERICAL
COMBUSTION CHAMBERS ONLY RUN ABOUT 8:1 COMPRESSION RATION.. IT TAKES
RACING FUEL TO BURN IN A 12:1 ENGINE OR THE ENGINE WONT HARDLEY RUN..

----------------------------------------------------------------
http://www.minibite.com/america/malone.htm

mm wrote:
....
Besides power, I've always thought that a high compression ratio means
getting the most out of the gas. That every portion of its expansion
applies power to the wheels of the car.

Doesn't that seem reasonable, and how come it must not be true?
....

Efficiency and power are competing design features -- the hemi initially
was designed for a higher power output per unit volume (remember when
NASCAR really was "stock" car and the 60s muscle cars?). The higher
efficiencies to produce better mileage are optimizing other parameters.

Not that all was totally bad w/ some consideration -- my '69 Charger w/
the 383 (not hemi) and the 4-bbl split-bowl Holley would average 18+ mpg
at interstate+ speed. Around town where it was start 'n stop it only
might do 10-12, though, but it surely got off the entrance ramp into
traffic in a heartbeat! Dang, wish I had kept that puppy. Saw
an auction on eBay the other day for about 20X what I paid new off the
showroom floor...

--

On Mon, 26 Jan 2009 08:32:46 -0500, against all advice, something
compelled , to say:

GAS ENGINE HEMIS IN THE 60'S-70'S COULD HAVE 12:1
COMPRESSION RATIOS. TODAYS GAS CAR/ TRUCKS WITH HEMISPHERICAL
COMBUSTION CHAMBERS ONLY RUN ABOUT 8:1 COMPRESSION RATION.. IT TAKES
RACING FUEL TO BURN IN A 12:1 ENGINE OR THE ENGINE WONT HARDLEY RUN..


My Audi runs at 11.25:1 on 92 pump gas.


--

Real men don't text.

On Mon, 26 Jan 2009 07:35:36 -0800, Steve Daniels
wrote:

On Mon, 26 Jan 2009 08:32:46 -0500, against all advice, something
compelled , to say:

GAS ENGINE HEMIS IN THE 60'S-70'S COULD HAVE 12:1
COMPRESSION RATIOS. TODAYS GAS CAR/ TRUCKS WITH HEMISPHERICAL
COMBUSTION CHAMBERS ONLY RUN ABOUT 8:1 COMPRESSION RATION.. IT TAKES
RACING FUEL TO BURN IN A 12:1 ENGINE OR THE ENGINE WONT HARDLEY RUN..

My Audi runs at 11.25:1 on 92 pump gas.

Without any knocking ever? I too thought that would be hard. Is
there a trick?

Real men don't text.

I agree with that. Just look at the girl who does 30,000 a month (or
whateer the number was) and the one behind her who did 20,000.
Teen-age girls. Who wants to be one of those. (Other than Norminn
maybe, but we were talking aobut "real men".

wrote in :

On Mon, 26 Jan 2009 09:17:21 -0600, dpb wrote:

mm wrote:
...
Besides power, I've always thought that a high compression ratio means
getting the most out of the gas. That every portion of its expansion
applies power to the wheels of the car.

Doesn't that seem reasonable, and how come it must not be true?
...

Efficiency and power are competing design features

Not true. Any time you raise the horsepower generated per cubic inch,
you increase fuel efficiency.

not necessarily.

You get more power from a given volume
of fuel. Take a 2 lire engine, and add a turbocharger to it. Both
available power AND fuel efficiency benefit. You are getting more
power out of the same size engine from a given amount of fuel.



no,because you have to increase the fuel delivered when using a turbo or
supercharger. They effectively increase -displacement-,meaning they
compresss a larger charge of fuel/air mixture.(equalling a larger motor)
The more air you cram in,the more fuel you have to add to keep the proper
combustion ratio.

--
Jim Yanik
jyanik
at
kua.net

In article , wrote:
On Mon, 26 Jan 2009 09:17:21 -0600, dpb wrote:

mm wrote:
...
Besides power, I've always thought that a high compression ratio means
getting the most out of the gas. That every portion of its expansion
applies power to the wheels of the car.

Doesn't that seem reasonable, and how come it must not be true?
...

Efficiency and power are competing design features

Not true. Any time you raise the horsepower generated per cubic inch,
you increase fuel efficiency. You get more power from a given volume
of fuel. Take a 2 lire engine, and add a turbocharger to it. Both
available power AND fuel efficiency benefit. You are getting more
power out of the same size engine from a given amount of fuel.

A turbocharger achieves more power per unit engine volume by
cramming more air (to be used with more fuel) in the same volume.

Superchargers do the same thing but are powered in a different manner.

Both achieve an increase in power and decrease fuel economy slightly.

However, if 2 cars have equal power and one has a turbocharger and the
other has a bigger engine, then the car with the turbo could possibly get
better city fuel economy by weighing less.

- Don Klipstein )

In article , wrote:
On 26 Jan 2009 17:59:30 GMT, Jim Yanik wrote:

wrote in :

On Mon, 26 Jan 2009 09:17:21 -0600, dpb wrote:

mm wrote:
...
Besides power, I've always thought that a high compression ratio means
getting the most out of the gas. That every portion of its expansion
applies power to the wheels of the car.

Doesn't that seem reasonable, and how come it must not be true?
...

Efficiency and power are competing design features

Not true. Any time you raise the horsepower generated per cubic inch,
you increase fuel efficiency.

not necessarily.

You get more power from a given volume
of fuel. Take a 2 lire engine, and add a turbocharger to it. Both
available power AND fuel efficiency benefit. You are getting more
power out of the same size engine from a given amount of fuel.



no,because you have to increase the fuel delivered when using a turbo or
supercharger. They effectively increase -displacement-,meaning they
compresss a larger charge of fuel/air mixture.(equalling a larger motor)
The more air you cram in,the more fuel you have to add to keep the proper
combustion ratio.

Really? So the engine will only run at full throttle?

A turbo will ALLOW you to cram more fuel in, but that is not a
requirement. At less than full throttle, you will be getting more
power per volume of fuel used. A lower throttle setting will get you
as much power as a higher throttle setting on a normally aspirated
version of the same engine.

Due to cramming more air and fuel into the engine. If you only cram in
more air and not more fuel, all you accomplish is a leaner mixture.

- Don Klipstein )

In article , mm wrote:
On Mon, 26 Jan 2009 07:35:36 -0800, Steve Daniels
wrote:

On Mon, 26 Jan 2009 08:32:46 -0500, against all advice, something
compelled , to say:

GAS ENGINE HEMIS IN THE 60'S-70'S COULD HAVE 12:1
COMPRESSION RATIOS. TODAYS GAS CAR/ TRUCKS WITH HEMISPHERICAL
COMBUSTION CHAMBERS ONLY RUN ABOUT 8:1 COMPRESSION RATION.. IT TAKES
RACING FUEL TO BURN IN A 12:1 ENGINE OR THE ENGINE WONT HARDLEY RUN..

My Audi runs at 11.25:1 on 92 pump gas.

Without any knocking ever? I too thought that would be hard. Is
there a trick?

Sounds fairly reasonable to me. My 1995 Oldsmobile Delta 88 LSS has the
"3800 series II" engine. My owner's manual says the compresiion ratio is
9.4:1 and specifies 87 octane gasoline.

- Don Klipstein )

Hemi engines can incorporate larger valves than other combustion chamber
shapes. This means that they breathe better and have a higher volumetric
efficiency (a measure of how much air (and hence fuel) the engine can
swallow).

Because of the hemi shape the distance from the spark plug tip to the
furthermost point in the combustion chamber is shorter in a hemi, than
in any other chamber shape of the same volume. What this means
practically is the hemi engine can carry more power without knocking
than other combustion chamber shape.

HTH,

EJ in NJ

mm wrote:
OT An interest in hemi engines stirred me, and I found this site

http://auto.howstuffworks.com/hemi1.htm

which gave as the advantage of the hemi that 2 valves could be placed
opposite each other, instead of next to each other, and thus could be
made bigger, for more power.

I had assumed that the advantage was with fewer corners, etc. in the
combustion chamber, there was less chance of power-losing knocking.

OTOH, now it occurs to me that if the combustion chamber is domed, it
might be bigger than one with a flat top, leading to a lower
compression ratio and less power.

So why are hemi engines powerful?


BTW The last time I posted off-topic, a couple nervous Nellys thought
it was spam. It's not.

On the contrary, Turbocharging increases fuel efficiency, whereas
supercharging always decreases it.

EJ in NJ

Don Klipstein wrote:
In article , wrote:
On Mon, 26 Jan 2009 09:17:21 -0600, dpb wrote:

mm wrote:
...
Besides power, I've always thought that a high compression ratio means
getting the most out of the gas. That every portion of its expansion
applies power to the wheels of the car.

Doesn't that seem reasonable, and how come it must not be true?
...

Efficiency and power are competing design features
Not true. Any time you raise the horsepower generated per cubic inch,
you increase fuel efficiency. You get more power from a given volume
of fuel. Take a 2 lire engine, and add a turbocharger to it. Both
available power AND fuel efficiency benefit. You are getting more
power out of the same size engine from a given amount of fuel.

A turbocharger achieves more power per unit engine volume by
cramming more air (to be used with more fuel) in the same volume.

Superchargers do the same thing but are powered in a different manner.

Both achieve an increase in power and decrease fuel economy slightly.

However, if 2 cars have equal power and one has a turbocharger and the
other has a bigger engine, then the car with the turbo could possibly get
better city fuel economy by weighing less.

- Don Klipstein )

wrote in :

On 26 Jan 2009 17:59:30 GMT, Jim Yanik wrote:

wrote in
m:

On Mon, 26 Jan 2009 09:17:21 -0600, dpb wrote:

mm wrote:
...
Besides power, I've always thought that a high compression ratio
means getting the most out of the gas. That every portion of its
expansion applies power to the wheels of the car.

Doesn't that seem reasonable, and how come it must not be true?
...

Efficiency and power are competing design features

Not true. Any time you raise the horsepower generated per cubic
inch, you increase fuel efficiency.

not necessarily.

You get more power from a given volume
of fuel. Take a 2 lire engine, and add a turbocharger to it. Both
available power AND fuel efficiency benefit. You are getting more
power out of the same size engine from a given amount of fuel.



no,because you have to increase the fuel delivered when using a turbo
or supercharger. They effectively increase -displacement-,meaning they
compress a larger charge of fuel/air mixture.(equalling a larger
motor) The more air you cram in,the more fuel you have to add to keep
the proper combustion ratio.

Really? So the engine will only run at full throttle?

A turbo will ALLOW you to cram more fuel in, but that is not a
requirement.

Yes,it is.
ever hear of stoichiometric ratio?
that's the proper mixture of air and fuel,for best combustion.
you must maintain the proper air:fuel ratio.
If you cram in more air,you have to inject more fuel,or go lean and burn
pistons.

At less than full throttle, you will be getting more
power per volume of fuel used.

sorry,it doesn't work that way.

A lower throttle setting will get you
as much power as a higher throttle setting on a normally aspirated
version of the same engine.

Still by using MORE fuel.


--
Jim Yanik
jyanik
at
kua.net

(Don Klipstein) wrote in
:

In article ,
wrote:
On 26 Jan 2009 17:59:30 GMT, Jim Yanik wrote:

wrote in
:

On Mon, 26 Jan 2009 09:17:21 -0600, dpb wrote:

mm wrote:
...
Besides power, I've always thought that a high compression ratio
means getting the most out of the gas. That every portion of its
expansion applies power to the wheels of the car.

Doesn't that seem reasonable, and how come it must not be true?
...

Efficiency and power are competing design features

Not true. Any time you raise the horsepower generated per cubic
inch, you increase fuel efficiency.

not necessarily.

You get more power from a given volume
of fuel. Take a 2 lire engine, and add a turbocharger to it. Both
available power AND fuel efficiency benefit. You are getting more
power out of the same size engine from a given amount of fuel.



no,because you have to increase the fuel delivered when using a turbo
or supercharger. They effectively increase -displacement-,meaning
they compresss a larger charge of fuel/air mixture.(equalling a
larger motor) The more air you cram in,the more fuel you have to add
to keep the proper combustion ratio.

Really? So the engine will only run at full throttle?

A turbo will ALLOW you to cram more fuel in, but that is not a
requirement. At less than full throttle, you will be getting more
power per volume of fuel used. A lower throttle setting will get you
as much power as a higher throttle setting on a normally aspirated
version of the same engine.

Due to cramming more air and fuel into the engine. If you only cram
in
more air and not more fuel, all you accomplish is a leaner mixture.

- Don Klipstein )


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

From http://en.wikipedia.org/wiki/Turbocharging;

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
jyanik
at
kua.net

(Don Klipstein) wrote in
:

In article , mm wrote:
On Mon, 26 Jan 2009 07:35:36 -0800, Steve Daniels
wrote:

On Mon, 26 Jan 2009 08:32:46 -0500, against all advice, something
compelled , to say:

GAS ENGINE HEMIS IN THE 60'S-70'S COULD HAVE 12:1
COMPRESSION RATIOS. TODAYS GAS CAR/ TRUCKS WITH HEMISPHERICAL
COMBUSTION CHAMBERS ONLY RUN ABOUT 8:1 COMPRESSION RATION.. IT
TAKES RACING FUEL TO BURN IN A 12:1 ENGINE OR THE ENGINE WONT
HARDLEY RUN..

My Audi runs at 11.25:1 on 92 pump gas.

Without any knocking ever? I too thought that would be hard. Is
there a trick?

Sounds fairly reasonable to me. My 1995 Oldsmobile Delta 88 LSS has
the
"3800 series II" engine. My owner's manual says the compresiion ratio
is 9.4:1 and specifies 87 octane gasoline.

- Don Klipstein )


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.

--
Jim Yanik
jyanik
at
kua.net

Jim Yanik wrote:
wrote in :

On 26 Jan 2009 17:59:30 GMT, Jim Yanik wrote:

wrote in
:

On Mon, 26 Jan 2009 09:17:21 -0600, dpb wrote:

mm wrote:
...
Besides power, I've always thought that a high compression ratio
means getting the most out of the gas. That every portion of its
expansion applies power to the wheels of the car.

Doesn't that seem reasonable, and how come it must not be true?
...

Efficiency and power are competing design features
Not true. Any time you raise the horsepower generated per cubic
inch, you increase fuel efficiency.
not necessarily.

You get more power from a given volume
of fuel. Take a 2 lire engine, and add a turbocharger to it. Both
available power AND fuel efficiency benefit. You are getting more
power out of the same size engine from a given amount of fuel.


no,because you have to increase the fuel delivered when using a turbo
or supercharger. They effectively increase -displacement-,meaning they
compress a larger charge of fuel/air mixture.(equalling a larger
motor) The more air you cram in,the more fuel you have to add to keep
the proper combustion ratio.
Really? So the engine will only run at full throttle?

A turbo will ALLOW you to cram more fuel in, but that is not a
requirement.

Yes,it is.
ever hear of stoichiometric ratio?
that's the proper mixture of air and fuel,for best combustion.
you must maintain the proper air:fuel ratio.
If you cram in more air,you have to inject more fuel,or go lean and burn
pistons.

At less than full throttle, you will be getting more
power per volume of fuel used.

sorry,it doesn't work that way.

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
--
replace "roosters" with "cox" to reply.
http://members.cox.net/njnagel

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 Willson wrote:
On the contrary, Turbocharging increases fuel efficiency, whereas
supercharging always decreases it.

EJ in NJ

Don Klipstein wrote:
In article ,
wrote:
On Mon, 26 Jan 2009 09:17:21 -0600, dpb wrote:

mm wrote:
...
Besides power, I've always thought that a high compression ratio means
getting the most out of the gas. That every portion of its expansion
applies power to the wheels of the car.

Doesn't that seem reasonable, and how come it must not be true?
...

Efficiency and power are competing design features
Not true. Any time you raise the horsepower generated per cubic inch,
you increase fuel efficiency. You get more power from a given volume
of fuel. Take a 2 lire engine, and add a turbocharger to it. Both
available power AND fuel efficiency benefit. You are getting more
power out of the same size engine from a given amount of fuel.

A turbocharger achieves more power per unit engine volume by
cramming more air (to be used with more fuel) in the same volume.

Superchargers do the same thing but are powered in a different manner.

Both achieve an increase in power and decrease fuel economy slightly.

However, if 2 cars have equal power and one has a turbocharger and
the other has a bigger engine, then the car with the turbo could
possibly get better city fuel economy by weighing less.

- Don Klipstein )


--
replace "roosters" with "cox" to reply.
http://members.cox.net/njnagel

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 in NJ

wrote:
On Mon, 26 Jan 2009 09:17:21 -0600, dpb wrote:

mm wrote:
...
Besides power, I've always thought that a high compression ratio means
getting the most out of the gas. That every portion of its expansion
applies power to the wheels of the car.

Doesn't that seem reasonable, and how come it must not be true?
...

Efficiency and power are competing design features

Not true. Any time you raise the horsepower generated per cubic inch,
you increase fuel efficiency. You get more power from a given volume
of fuel. Take a 2 lire engine, and add a turbocharger to it. Both
available power AND fuel efficiency benefit. You are getting more
power out of the same size engine from a given amount of fuel.

Don Klipstein wrote:
In article , mm wrote:
On Mon, 26 Jan 2009 07:35:36 -0800, Steve Daniels
wrote:

On Mon, 26 Jan 2009 08:32:46 -0500, against all advice, something
compelled , to say:

GAS ENGINE HEMIS IN THE 60'S-70'S COULD HAVE 12:1
COMPRESSION RATIOS. TODAYS GAS CAR/ TRUCKS WITH HEMISPHERICAL
COMBUSTION CHAMBERS ONLY RUN ABOUT 8:1 COMPRESSION RATION.. IT TAKES
RACING FUEL TO BURN IN A 12:1 ENGINE OR THE ENGINE WONT HARDLEY RUN..
My Audi runs at 11.25:1 on 92 pump gas.
Without any knocking ever? I too thought that would be hard. Is
there a trick?

Sounds fairly reasonable to me. My 1995 Oldsmobile Delta 88 LSS has the
"3800 series II" engine. My owner's manual says the compresiion ratio is
9.4:1 and specifies 87 octane gasoline.

- Don Klipstein )

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

--
replace "roosters" with "cox" to reply.
http://members.cox.net/njnagel

In article , Nate Nagel wrote:
Jim Yanik wrote:
wrote in :

On 26 Jan 2009 17:59:30 GMT, Jim Yanik wrote:

wrote in
:

On Mon, 26 Jan 2009 09:17:21 -0600, dpb wrote:

mm wrote:
...
Besides power, I've always thought that a high compression ratio
means getting the most out of the gas. That every portion of its
expansion applies power to the wheels of the car.

Doesn't that seem reasonable, and how come it must not be true?
...

Efficiency and power are competing design features
Not true. Any time you raise the horsepower generated per cubic
inch, you increase fuel efficiency.
not necessarily.

You get more power from a given volume
of fuel. Take a 2 lire engine, and add a turbocharger to it. Both
available power AND fuel efficiency benefit. You are getting more
power out of the same size engine from a given amount of fuel.


no,because you have to increase the fuel delivered when using a turbo
or supercharger. They effectively increase -displacement-,meaning they
compress a larger charge of fuel/air mixture.(equalling a larger
motor) The more air you cram in,the more fuel you have to add to keep
the proper combustion ratio.
Really? So the engine will only run at full throttle?

A turbo will ALLOW you to cram more fuel in, but that is not a
requirement.

Yes,it is.
ever hear of stoichiometric ratio?
that's the proper mixture of air and fuel,for best combustion.
you must maintain the proper air:fuel ratio.
If you cram in more air,you have to inject more fuel,or go lean and burn
pistons.

At less than full throttle, you will be getting more
power per volume of fuel used.

sorry,it doesn't work that way.

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.

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 )

In article , Ernie
Willson wrote in part:

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.

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

- Don Klipstein )

(Don Klipstein) wrote in
:

In article , Ernie
Willson wrote in part:

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.

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

- Don Klipstein )

From http://en.wikipedia.org/wiki/Turbocharging;

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.

--
Jim Yanik
jyanik
at
kua.net

On Mon, 26 Jan 2009 18:17:18 -0500, Nate Nagel
wrote:

Don Klipstein wrote:
In article , mm wrote:
On Mon, 26 Jan 2009 07:35:36 -0800, Steve Daniels
wrote:

On Mon, 26 Jan 2009 08:32:46 -0500, against all advice, something
compelled , to say:

GAS ENGINE HEMIS IN THE 60'S-70'S COULD HAVE 12:1
COMPRESSION RATIOS. TODAYS GAS CAR/ TRUCKS WITH HEMISPHERICAL
COMBUSTION CHAMBERS ONLY RUN ABOUT 8:1 COMPRESSION RATION.. IT TAKES
RACING FUEL TO BURN IN A 12:1 ENGINE OR THE ENGINE WONT HARDLEY RUN..
My Audi runs at 11.25:1 on 92 pump gas.
Without any knocking ever? I too thought that would be hard. Is
there a trick?

Sounds fairly reasonable to me. My 1995 Oldsmobile Delta 88 LSS has the
"3800 series II" engine. My owner's manual says the compresiion ratio is
9.4:1 and specifies 87 octane gasoline.

- Don Klipstein )

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

Thanks, you guys.

In article , Jim Yanik wrote:
(Don Klipstein) wrote in
:

In article , Ernie
Willson wrote in part:

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.

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

- Don Klipstein )

From http://en.wikipedia.org/wiki/Turbocharging;

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.

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 )

Who said Nate is right?

EJ in NJ

Don Klipstein wrote:
In article , Ernie
Willson wrote in part:

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.

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

- Don Klipstein )

On Jan 26, 10:50 pm, Jim Yanik wrote:
turbocharging uses the wasted energy of the hot exhaust to compress the
intake charge,while supercharging is a parasitic drag all the time.

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.

(Don Klipstein) wrote in
:

In article , Jim Yanik
wrote:
(Don Klipstein) wrote in
:

In article , Ernie
Willson wrote in part:

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.

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

- Don Klipstein )

From http://en.wikipedia.org/wiki/Turbocharging;

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.

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.

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.

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 )


I think we agree,then.

--
Jim Yanik
jyanik
at
kua.net

In article , Jim Yanik wrote:
(Don Klipstein) wrote in
:

In article , Jim Yanik
wrote:
(Don Klipstein) wrote in
:

In article , Ernie
Willson wrote in part:

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.

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

- Don Klipstein )

From http://en.wikipedia.org/wiki/Turbocharging;

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.

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.

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 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.

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.

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 )

I think we agree, then.

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

Best Regards,

- Don Klipstein )

Larry Fishel wrote:
On Jan 26, 10:50 pm, Jim Yanik wrote:
turbocharging uses the wasted energy of the hot exhaust to compress the
intake charge,while supercharging is a parasitic drag all the time.

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.

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

--
replace "roosters" with "cox" to reply.
http://members.cox.net/njnagel

http://www.amazon.com/Internal-Combu.../dp/007028637X

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 Willson wrote:
Who said Nate is right?

EJ in NJ

Don Klipstein wrote:
In article , Ernie
Willson wrote in part:

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.

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

- Don Klipstein )


--
replace "roosters" with "cox" to reply.
http://members.cox.net/njnagel