ENGINE BASICS

On Jun 9, 8:35*pm, "Tom Wait"
wrote:

I'm going to go out on a limb here Bob and say that the RATE of valve
opening and closing is a function of RPM and cam lobe contour only. Mass of
the valve train would primarily affect the max RPM attainable without
destructive valve float.
-------------------------------------------------------------------------------------------------------

Dear Tom,

Not a problem. There's plenty of room on the limb for the two of us.
(See my error as caught by Charlie.)

With regard to the rate at which the valve opens, what I'm trying to
say is that a valve train having greater mass will open more slowly
than a valve train having less mass. The assumption here is that all
else -- including the factor you've mentioned -- are equal.

The object here was ways to increase Volumetric Efficiency, for which
the rate at which the cylinder fills is a critical factor. According
to Taylor (or possibly Litton) the shape of the combustion chamber,
especially with regard to the shrouding of the intake valve, AND the
mass of the valve train components, are the only ways of improving VE
without going to super-charging.

I can see where you're coming from with regard to RPM but as you must
know, VE falls as rpm increases. The idea behind lighter valve train
components is to allow more time for charging the cylinder at a given
RPM. For the purpose of this exercise, RPM is fixed.

So put away the saw -- there's plenty of room for the two of us on
this branch :-)

In a more serious vein, I apologize for stating my explanation so
poorly.

-R.S.Hoover

Going back to some hot rodding roots,I believe V.E. was increased
in the late '60's-70's thru the use of a specially designed double
cone affair placed in the collector pipe of a tuned exhaust
system,which created a stronger vacuum effect , creating stronger
scavenging of exhaust, and to some extent , helping draw more fuel/air
mix into the cylinder.

I believe that Ballenger Headers had the "pickle" located in the
collector of 4 tube equal length headers and there was also the
"coanda" effect which is specifically what I think you were speaking of.
It was used experimentally in a truly weird exhaust setup in the early
days by of one of the major racing teams back in the mid 60s, but my
memory is a bit foggy for specifics that far back, such as who or on
what car, sorry.


cmyr wrote:
Going back to some hot rodding roots,I believe V.E. was increased
in the late '60's-70's thru the use of a specially designed double
cone affair placed in the collector pipe of a tuned exhaust
system,which created a stronger vacuum effect , creating stronger
scavenging of exhaust, and to some extent , helping draw more fuel/air
mix into the cylinder.

On Jun 11, 11:32�am, George wrote:
I believe that Ballenger Headers had the "pickle" located in the
collector of 4 tube equal length headers and there was also the
"coanda" effect which is specifically what I think you were speaking of.
� It was used experimentally in a truly weird exhaust setup in the early
days by of one of the major racing teams back in the mid 60s, but my
memory is a bit foggy for specifics that far back, such as who or on
what car, sorry.



cmyr wrote:
� �Going back to some hot rodding roots,I believe V.E. was increased
in the late '60's-70's thru the use of a specially designed double
cone affair placed in the collector pipe of a tuned exhaust
system,which created a stronger vacuum effect , creating stronger
scavenging of exhaust, and to some extent , helping draw more fuel/air
mix into the cylinder.- Hide quoted text -

- Show quoted text -

You remembered the word I couldn't put my finger on........coanda

"cmyr" wrote in message
...
On Jun 11, 11:32?am, George wrote:
I believe that Ballenger Headers had the "pickle" located in the
collector of 4 tube equal length headers and there was also the
"coanda" effect which is specifically what I think you were speaking of.
? It was used experimentally in a truly weird exhaust setup in the early
days by of one of the major racing teams back in the mid 60s, but my
memory is a bit foggy for specifics that far back, such as who or on
what car, sorry.



cmyr wrote:
? ?Going back to some hot rodding roots,I believe V.E. was increased
in the late '60's-70's thru the use of a specially designed double
cone affair placed in the collector pipe of a tuned exhaust
system,which created a stronger vacuum effect , creating stronger
scavenging of exhaust, and to some extent , helping draw more fuel/air
mix into the cylinder.- Hide quoted text -

- Show quoted text -

You remembered the word I couldn't put my finger on........coanda

---------------------------------------------------------------------------------------------------------

Back in the 70s or so, there was a three cylinder two stroke radial, with
all three cylinders in a common crank case - that used the exhaust system
exclusively for scavenging the engine. There was no intake draft without it.

It was featured on an ultralight one year at OSH.

"cmyr" wrote in message
...
Going back to some hot rodding roots,I believe V.E. was increased
in the late '60's-70's thru the use of a specially designed double
cone affair placed in the collector pipe of a tuned exhaust
system,which created a stronger vacuum effect , creating stronger
scavenging of exhaust, and to some extent , helping draw more fuel/air
mix into the cylinder.

There have been a number of things that improved VE: Generally, higher
compression ratios help especially at higher RPM, roller tappets seem to
withstand much faster ramp angles and can stay open further during the open
part of the valve cycles, and anti-reversion cones in the exhaust are said
to work very well in the mid-range of RPM for any given four cycle engine.
In addition, intake and exhaust port shapes play a major role; as do other
aspects of head ad piston crown design.

In a nut-shell, there has been a lot of progress over the past three
quarters of a century, and the only place that I can think of in which
aircraft engines have led the way has been in the area that we used to call
"blue printing" in which the ports are more carefully caste, machined, and
finished to closely match the design drawings for the engine. Today, every
late model engine that I have seen is done that way at the factory; but
forty years ago, automotive engines were really crude.

Peter

On Thu, 11 Jun 2009 07:40:10 -0700 (PDT), cmyr
wrote:

Going back to some hot rodding roots,I believe V.E. was increased
in the late '60's-70's thru the use of a specially designed double
cone affair placed in the collector pipe of a tuned exhaust
system,which created a stronger vacuum effect , creating stronger
scavenging of exhaust, and to some extent , helping draw more fuel/air
mix into the cylinder.

The anti reversion cone was a dirty fix for a crappy header design.
Better than a manifold, but not as good as a proper "tuned" header.

On Jun 11, 8:06�pm, wrote:
On Thu, 11 Jun 2009 07:40:10 -0700 (PDT), cmyr

wrote:
� Going back to some hot rodding roots,I believe V.E. was increased
in the late '60's-70's thru the use of a specially designed double
cone affair placed in the collector pipe of a tuned exhaust
system,which created a stronger vacuum effect , creating stronger
scavenging of exhaust, and to some extent , helping draw more fuel/air
mix into the cylinder.

The anti reversion cone was a dirty fix for a crappy header design.
Better than a manifold, but not as good as a proper "tuned" header.

As I recall, this system was on the cover of Hot Rod magazine, on a
high end test vehicle,and was "scientifically" researched. In this
instance the reference to a crappy header design would be wrong.

"cmyr" wrote in message
...
On Jun 11, 8:06?pm, wrote:
On Thu, 11 Jun 2009 07:40:10 -0700 (PDT), cmyr

wrote:
? Going back to some hot rodding roots,I believe V.E. was increased
in the late '60's-70's thru the use of a specially designed double
cone affair placed in the collector pipe of a tuned exhaust
system,which created a stronger vacuum effect , creating stronger
scavenging of exhaust, and to some extent , helping draw more fuel/air
mix into the cylinder.

The anti reversion cone was a dirty fix for a crappy header design.
Better than a manifold, but not as good as a proper "tuned" header.

As I recall, this system was on the cover of Hot Rod magazine, on a
high end test vehicle,and was "scientifically" researched. In this
instance the reference to a crappy header design would be wrong.

All the previous 6 or7 posters have come up with methods of increasing VE
w/o superchargers. I want to add 4 or more valves per cylinder which would
probably increase the mass of the valve train. Certainly the complexity. I
don't see how a massive rocker arm or longer fatter pushrod could decrease
VE. Certainly a larger valve head would increase mass but would also
increase VE. A thicker valve stem would increase mass and decrease VE but I
think only marginally. I think the only way more mass would decrease VE
would be if the push rods were rubber.
Tom

Tom Wait wrote:
"cmyr" wrote in message
...
On Jun 11, 8:06?pm, wrote:
On Thu, 11 Jun 2009 07:40:10 -0700 (PDT), cmyr

wrote:
? Going back to some hot rodding roots,I believe V.E. was increased
in the late '60's-70's thru the use of a specially designed double
cone affair placed in the collector pipe of a tuned exhaust
system,which created a stronger vacuum effect , creating stronger
scavenging of exhaust, and to some extent , helping draw more fuel/air
mix into the cylinder.
The anti reversion cone was a dirty fix for a crappy header design.
Better than a manifold, but not as good as a proper "tuned" header.

As I recall, this system was on the cover of Hot Rod magazine, on a
high end test vehicle,and was "scientifically" researched. In this
instance the reference to a crappy header design would be wrong.

All the previous 6 or7 posters have come up with methods of increasing VE
w/o superchargers. I want to add 4 or more valves per cylinder which would
probably increase the mass of the valve train. Certainly the complexity. I
don't see how a massive rocker arm or longer fatter pushrod could decrease
VE. Certainly a larger valve head would increase mass but would also
increase VE. A thicker valve stem would increase mass and decrease VE but I
think only marginally. I think the only way more mass would decrease VE
would be if the push rods were rubber.
Tom

The British made some WWII engines with rotating cylinder sleeves that
had in and out ports cut into them - rotary valves! No poppets. Good
performance, but burned oil and left conspicuous smoke trails, not a
good thing for a warbird to do.

That's what I remember from an engine class, unless I'm hallucinating again.